The phase diagram of copper - aluminum was constructed over the entire concentration range using thermal, metallographic, and x-ray analysis methods and is a complex diagram with intermediate phases. The state diagram of copper - aluminum (Fig. 1) is given on the basis of work carried out by various authors over a long period of time. The region of copper-based solid solutions (α-phase) extends to 9% (by mass) Al. With decreasing temperature, the solubility of aluminum in copper increases at temperatures of 1037; 900; 800; 700; 500 °C is 7.4; 7.8; 8.2; 8.8; 9.4% (by mass) Al, respectively. Phase a has an fcc lattice, similar to the lattice of pure copper, the period of which increases with increasing aluminum content and in the alloy with 10.5% (by mass) Al is 0.3657 nm.
Phase β is a solid solution based on the Cu 3 Al compound. In β-region alloys, depending on heat treatment and cooling conditions, two metastable intermediate phases can be observed: β" and β.
Phase γ 1 - a solid solution based on the Cu 3 Al 4 compound exists in the concentration range of 16.0...18.8% (by mass) Al and has a monoclinic lattice with 102 atoms in the unit cell. The α 2 phase has a lattice similar to that of the α phase.
In the region of up to 20% (by mass) Al, the liquidus of alloys consists of four branches of primary crystallization of the α, β, χ and χ 1 phases. At 1037 C, the eutectic α + β crystallizes with a eutectic point at 8.5% (by mass) Al. At temperatures of 1036 and 1022 °C, peritectic reactions Zh + β ↔χ and Zh + χ↔γ 1 occur. respectively. The χ phase exists in the temperature range 1036...936 °C. Phase β crystallizes from the melt along a curve with a maximum at a temperature of 1048 °C and corresponds to a concentration of 12.4% (by mass) Al. In the solid state, this region exhibits a series of eutectoid and peritectoid transformations. At 963 °C, the χ phase decomposes into β- and γ 1 -phases. The eutectoid point corresponds to 15.4% (by mass) Al. At 780 °C, the γ 1 phase decomposes according to a eutectoid reaction into β and γ 2 phases. At 873 °C, the γ-phase is formed by a peritectonic reaction. It is assumed that in the γ 2 phase a phase transformation occurs in the temperature range 400...700 °C with an aluminum content at the eutectoid point of 11.8...11.9% (by mass). In the concentration range of 9...16% (by mass) Al, the existence of another stable phase is assumed - χ or α 2, formed by the eutectoid reaction at 363 °C and the aluminum content at the eutectoid point is ∼11.2% (by mass). The concentration limits of the homogeneity region of this phase have not been established.
The authors, based on literature data on the thermodynamic properties of components and intermediate phases, as well as on the basis of experimental data on phase equilibria, calculated the phase diagram of the Cu-Al system. The values of the calculated temperatures of phase transformations practically coincide with the data of the work.
Copper - beryllium
The phase diagram of copper - beryllium has been studied by many researchers. It is built over the entire concentration range (Fig. 2). The crystallization curves of the alloys consist of four branches corresponding to the crystallization of the α, β, δ and β-Be phases. The β-phase crystallizes along a curve with a minimum at a temperature of 860 °C and 5.3% (by weight) Be. At 870 °C the β-phase is formed by a peritectic reaction, and at 578 °C the β-phase decomposes by a eutectoid reaction. There is evidence of a higher eutectoid transformation temperature - 605 °C.
The solubility of beryllium in copper at the eutectoid transformation temperature is 1.4% (by weight). With decreasing temperature, the solubility of beryllium decreases and is: at 500 °C - 1.0% (by weight), at 400 °C - 0.4% (by weight), at 300 °C - 0.2% (by weight) . In the concentration range of 50.8...64.3% (at.) Be at 930 °C, a peritectic reaction of the formation of the β"-phase occurs, and at 1090 °C the eutectoid transformation β ↔α-Be +δ takes place. Phase boundaries regions δ/δ + α-Be and δ + α-Be/α-Be pass through 81.5 and 92.5% (at.) Be at 1000 °C, at 900 °C - 81.0 and 93.0 % (at.) Be, at 700 °C - 80.8 and 95.5% (at.) Be, respectively.
Phase δ is formed by a peritectic reaction at a temperature of 1239 °C. The copper-based solid solution (α-phase) has a fcc lattice with a period α = 0.3638 nm at 2.1% (by mass) Be, the δ-phase has a disordered bcc lattice with a period α = 0.279 nm at 7.2% (by mass) Be, the β′-phase has an ordered body-centered cubic lattice of the CsCl type with a period α = 0.269...0.270 nm, the δ-phase has a cubic lattice of the MgCu 2 type with a period α = 0.5952 nm. The β-Be phase is a high-temperature phase, and the α-Be phase is a low-temperature modification of a beryllium-based solid solution.
According to the data, which shows part of the diagram up to 50% (at.) Cu, the δ-phase (Be 4 Cu-Be 2 Cu) melts congruently at 1219 °C and 22% (at.) Cu. The β-phase has a MgCu 2 type structure and changes the lattice parameter in the homogeneity region from α = 5957 nm to α = 0.5977 nm at 25 at.% Cu.
Copper - iron
The copper-iron phase diagram has been studied by many researchers. The results of these studies are analyzed in detail in the works. The main contradictions relate to the question of the complete or partial miscibility of copper and iron in the liquid state. As a result of experiments, it was found that in the copper-iron system there is no stratification, but for the supercooled state (100 °C) stratification does occur. The separation region is almost symmetrical to the axis corresponding to the equiatomic composition, and the critical mixing temperature lies 20 °C below the liquidus temperature at equiatomic composition.
In Fig. Figure 3 shows a diagram of the state of copper - iron according to the data. Two peritectic and one eutectoid transformations were established at temperatures of 1480; 1094 and 850 °C. Solubility of iron in copper at 1025; 900; 800 and 700 °C is 2.5; 1.5; 0.9; 0.5% (by mass) Fe respectively. The lattice parameter of the copper-based solid solution for the alloy with 2.39 at.% Fe is 0.3609 nm. The lattice parameter of α-Fe (bcc) increases from 0.28662±0.00002 to 0.28682 nm with the addition of 0.38 at.% Cu.
Copper - cobalt
The state diagram of the copper - cobalt system is shown in Fig. 4 . It agrees well with the results of earlier studies of this diagram. In this system, as a result of supercooling by 100 °C or more, a region of immiscibility in the liquid state appears, which is almost symmetrical about the axis corresponding to the equiatomic composition. With this composition, the critical mixing temperature lies 90 °C below the liquidus curve.
The Cu-Co system is of peritectic type. The temperature of the peritectic reaction is 1112 °C. Data on the solubility of cobalt in a solid solution based on copper (β) and copper in a solid solution based on cobalt (a) in the temperature range 900...1100 °C are given in Table. 1.
Copper - silicon
The state diagram of copper - silicon is shown in Fig. 5 (based on the totality of works). The system contains an α-solid solution based on copper, β-, δ-, η-phases, as well as K-, γ- and ε-phases formed by peritectoid reactions.
The region of existence of the β-phase [bcc lattice with α = 0.2854 nm at 14.9 at.% Si] is in the temperature range 852...785 °C; it is formed by a peritectic reaction with a peritectic transformation point of 6.8% (by mass) Si. The region of existence of the β-phase covers the temperature range 824...710 °C and is formed by a peritectic reaction; peritectic transformation point 8.65% (by mass) Si. Phase η has two modifications: η′ and η″. In the temperature range 620...558 °C the transformation η↔η′ takes place, and in the range 570...467 °C the transformation η′↔η″ takes place. The η-phase lattice is similar to the γ-brass lattice.
Phase K is formed by a peritectoid reaction at +842 °C and exists up to 552 °C, the peritectoid point corresponds to 5.9% (by mass) Si. The K phase has a close-packed hexagonal lattice with α = 0.25543 nm and c = 0.41762 nm at 11.8 at.% Si and α = 0.25563 nm and c = 0.41741 nm at 14.6% (at.) Si. Phase γ is formed by a peritectoid reaction at 729 °C and is stable up to room temperature; the peritectoid point corresponds to 8.35% (by mass) Si.
The γ phase has a cubic lattice of the β-Mn lattice type with a period α = 0.621 nm.
The ε phase is also formed by a peritectoid reaction at 800 °C and exists in a narrow concentration range of 10.6...10.7% (by mass) Si, stable up to room temperature. It has a bcc lattice with α = 0.9694 nm. The solubility of copper in silicon is negligible and amounts to 2.810 -3; 2·10 -3; 5.5·10 -4; 8.5·10 -5; 5.3·10 -6% (at.) at temperatures 1300; 1200; 1000; 800 and 500 °C respectively. The solubility of silicon in copper is significant and amounts to ∼5.3% (by weight) at 842 °C.
Copper - manganese
The state diagram of the copper-manganese system is constructed over the entire concentration range. Here it is given according to the data (Fig. 6). Copper and manganese form a minimum on the liquidus curve at a content of ∼37% (at.) Mn and a temperature of 870±5 °C. Transformations in the solid state are associated with ordering processes in alloys on the part of copper and allotropic modifications of manganese. The solid solution (α-Cu, γ-Mn) is ordered at ∼16 at.% Mn (MnCu 5) and 400 °C and at ∼25 at.% Mn (MnCu 3) and 450 °C.
The solubility of copper in the α-Mn and β-Mn phases is insignificant. The system undergoes a continuous transition from a face-centered cubic lattice of a copper-based solid solution (α-Cu) to a face-centered tetragonal lattice of γ-Mn.
Copper - Nickel
The state diagram of the copper-nickel system is a system with a continuous series of solid solutions. Figure 7 shows the results of experimental studies that are in good agreement with each other. In the solid state there are transformations associated with magnetic transformations in nickel. All alloys of the Cu-Ni system have a fcc lattice. Assumptions about the existence of CuNi and CuNi 3 compounds in the system were not confirmed in later works. Alloys of this system are the basis of industrial alloys of the cupronickel type.
Copper - tin
In Fig. Figure 8 shows a state diagram based on a large number of works. The system has established the existence of a number of phases formed both during primary crystallization and during transformation into the solid state. Phases α, β, γ, ε, η are formed during primary crystallization, phases ζ and δ - in the solid state. Phases β, γ and η are formed by peritectic reactions at temperatures of 798, 755 and 415 °C. The lattice period of the α phase increases from 0.3672 to 0.3707 nm. Phases β and γ are crystallographically similar and have a bcc lattice.
The ε phase exists based on the Cu 3 Sn compound and has an orthorhombic lattice. The η-phase corresponds to the Cu 6 Sn 5 compound. It is ordered at 189...186 °C. Phase ζ has a hexagonal lattice with the expected composition Cu 20 Sn 6 . The δ-phase has the structure of γ-brass, it is an electronic compound and corresponds to the formula Cu 31 Sn 8 at 20.6 at.% Sn.
The solubility of tin in copper, according to X-ray spectral analysis, is, % (at.) Sn [% (by mass) - in parentheses]: 6.7 (11.9); 6.5 (11.4); 5.7 (10.10) at temperatures 350; 250; 150 °C respectively. The solubility of copper in tin in the solid state at the eutectic temperature is 0.01% (at.) (according to Tokseitov et al.).
Copper - lead
The state diagram of copper - lead, constructed over the entire concentration range, is shown in Fig. 9 according to the work. The state diagram of the copper-lead system is characterized by the presence of monotectic and eutectic transformations. The temperature of the monotectic transformation is (955±0.5) C, and the extent of the immiscibility region at this temperature is 15.7-63.8% (at.) Pb. The eutectic point corresponds to 0.18% (at.) Pb, and according to the data - a temperature of 326 °C and 0.2% (at.) Pb. The solubility curve between the monotectic temperature and the melting point of lead has been determined quite carefully. It has been established that this curve intersects the monotectic horizontal at a lead content of 67% (at.). The solubility of lead in copper in the solid state at temperatures above 600 °C is no more than 0.09% (at.). The solubility of copper in lead in the solid state is less than 0.007% (by weight).
Copper - antimony
The state diagram of copper - antimony is presented according to the data in Fig. 10.
In the alloys of this system, a high-temperature β-phase with an fcc lattice of the BiF 3 type was discovered, which melts congruently at 684 °C and the alloy contains 28.6 at.% Sb. At 435 °C, the β-phase decomposes eutectoidally into phase k and Cu 2 Sb. The eutectoid point corresponds to 24% (at.) Sb. Maximum solubility of β-phase 20...32%) (at.) Sb. Other intermediate phases - η, ε, ε′ and k-are formed by peritectoid reactions at temperatures of 488 °C (η), 462 °C (e). The ε′-phase has a hexagonal lattice with periods α = 0.992 nm, c = 0.432 nm and exists in the temperature range ∼375...260 °C. The k-phase has an orthorhombic Cu 3 Ti type structure, exists in the range 450...375 °C and decomposes into the ε-phase and Cu 2 Sb at a temperature of 375 °C or the ε′-phase and Cu 2 Sb (according to other authors ). Phase η has a homogeneity region from 15.4 to 15.8% (at.) Sb at 426 °C. The intermediate phase Cu 2 Sb is formed by a peritectic reaction at 586 °C and has a narrow homogeneity region of 32.5...33.4% (at.) Sb. It has a tetragonal lattice. The maximum solubility of antimony in copper in the solid state at temperatures of 600; 550:500; 450; 400; 360; 340 and 250 °C is 5.79; 5.74; 5.69; 5.44; 4.61; 3.43; 3.02; 1.35% (at.) or 10.53; 10.44; 10.37; 9.92; 8.48; 6.38; 5.64; 2.56% (by mass), respectively.
Copper - phosphorus
The state diagram of the copper - phosphorus system is shown according to the data in Fig. 11. Based on the results of later work, two compounds were discovered in the system: Cu 3 P and Cu P 2. The temperature of formation of the Cu 3 P compound directly from the melt is given by different authors in different ways: 1005; 1018 or 1023; 1022 °C. The homogeneity range of the Cu 3 P compound is 31% (at.) P at eutectic temperature and 27.5% (at.) P at 700 °C. The Cu 3 P compound has a hexagonal lattice with parameters α = 0.695 nm, c = 0.712 ± 0.02 nm, c/α = 1.02.
The CuP 2 compound crystallizes directly from the melt at 891 °C. A eutectic reaction occurs between the Cu 3 P compound and copper at 714 °C, the eutectic point corresponds to 15.72% (at.) P.
There is eutectic equilibrium between the compounds Cu 3 P and Cu P 2 at 833 °C. The composition of the eutectic point is 49% (at.) R.
In the region of the diagram between phosphorus and the CuP 2 compound, the existence of a degenerate eutectic at 590 °C is assumed.
The solubility of phosphorus in copper is given in table. 2.
(Note. Phosphorus content is indicated in parentheses as a percentage by weight.)
Copper - chrome
The copper-chromium phase diagram has been studied most thoroughly in the copper-rich region. It is given in full in the work of G.M. Kuznetsova et al. based on thermodynamic calculation data and data on the parameters of the interaction of components (Fig. 12). The structure of the alloys contains two phases: solid solutions based on copper (α) and chromium (β). At 1074.8 °C, a eutectic transformation occurs at a chromium content of 1.56% (at.). The solubility of chromium in copper according to various authors is given in table. 3.
The solubility of copper in chromium in the solid state varies from 0.16% (at.) at 1300 °C to 0.085% (at.) at 1150 °C.
Copper - zinc
In copper alloys, the elements of group II of the periodic table of D.I. are of greatest practical interest. Mendeleev represents zinc. The copper-zinc phase diagram has been studied by many researchers over the entire concentration range. In Fig. Figure 13 shows a state diagram constructed from a set of works in which methods of thermal, x-ray, metallographic, electron microscopic analyzes and determination of liquidus temperature were used.
The liquidus line of the copper-zinc system consists of six branches of primary crystallization of phases α, β, γ, δ, ε and η. There are five peritectic transformations in the system, % (at.):
1) F (36.8 Zn) + α (31.9 Zn) ↔ β (36.1 Zn) at 902 °C;
2) F (59.1 Zn) + β (56.5 Zn) ↔ γ (59.1 Zn) at 834 °C;
3) F (79.55 Zn) + γ (69.2 Zn) ↔ δ (72.4 Zn) at 700 °C;
4) F (88 Zn) + δ (76 Zn) ↔ ε (78 Zn) at 597 °C;
5) F (98.37 Zn) + ε (87.5 Zn) ↔ η (97.3 Zn) at 423 °C.
The solubility of zinc in a copper-based solid solution first increases from 31.9% (at.) at 902 °C to 38.3% (at.) at 454 °C, then decreases and amounts to 34.5% (at.) at 150 °C and 29% (at.) at 0 °C.
In the region of existence of the α-phase, two modifications α 1 and α 2 are defined. The region of existence of phase β ranges from 36.1% (at.) Zn at 902 °C to 56.5% (at.) Zn at 834 °C and from 44.8% (at.) Zn at 454 °C up to 48.2% (at.) Zn at 468 ° C. In the temperature range 454...468 ° C, transformation or ordering occurs.
The β′ phase decomposes according to the eutectoid reaction β′↔α + γ at a temperature of ~255 °C. The β-phase exists in four modifications: the γ′′′-phase up to temperatures of 250...280 C, above 280 °C the γ″-phase is stable, which at 550...650 °C transforms into the γ′-phase; above 700°C there is a γ phase. The δ phase exists in the range 700...558 °C, decomposing eutectoidally according to the reaction δ↔γ + ε at 558 °C.
The solubility of copper in a zinc-based η-solid solution decreases from 2.8% (at.) at 424 °C to 0.31% (at.) at 100 °C. The lattice parameters of the copper-based α-solid solution increase with increasing zinc concentration.
The β phase has a body-centered cubic lattice of the W type, the β′-phase has an ordered body-centered lattice of the CsCl type. The lattice period of the β′-phase increases from O 2956 to 0.2958 nm in the concentration range of 48.23...49.3% (at.) Zn.
The γ phase has a γ-brass type structure. Its composition corresponds to the stoichiometric composition of Cu 5 Zn 8 . The γ″′ phase has an orthorhombic lattice with periods α = 0.512 nm, b = 0.3658 nm and c = 0.529 nm.
The γ″ phase has a cubic lattice with a period α = 0.889 nm. The structure and lattice parameters of the γ′ and γ phases have not been determined. Phase 3 has a bcc lattice with a period α = 0.300 nm at 600 °C for an alloy with 74.5 at.% Zn. The ε phase has a hexagonal Mg-type lattice.
Alloys based on the copper-zinc system (brass) are widely used in various industries: they are characterized by high manufacturability and corrosion resistance. The production of various parts and castings from alloys of this system is not particularly difficult. Alloys of grades L96, L90, L85, L80, L75, L70, L68, L66, L63, L59 - simple brass - are processed by pressure in a cold and hot state and have a single-phase structure, which is a solid solution based on copper (a) for alloys with copper content of at least 61% (by mass) and two-phase (α + β) for alloy L59. Single- and two-phase alloys (α, α + β, β), alloyed with aluminum, iron, manganese, silicon, tin, lead, are used to produce castings using various methods.
REPORTS OF THE ACADEMY OF SCIENCES OF THE REPUBLIC OF TAJIKISTAN _____________________________________2007, volume 50, No. 3_________________________________
ELECTROCHEMISTRY
UDC 669.71:620.193
Corresponding Member of the Academy of Sciences of the Republic of Tajikistan I.N. Ganiev,
B.Sh.Narziev, A.M.Safarov INFLUENCE OF SMALL ADDITIVES OF ZIRCONIUM AND ITS ANALOGUES ON THE ELECTROCHEMICAL BEHAVIOR OF ALUMINUM
Elements of the titanium subgroup are widely used as modifiers of aluminum alloys. They are also included in the majority of complex alloys, which contain a large number of dispersed intermetallic particles, which are potential substrates for the crystallization of the alloys they process. According to the state diagrams of aluminum with titanium, hafnium and zirconium, on the aluminum side, crystallization of intermetallic compounds of the compositions T1L13, N/L13 and 2gL13 takes place. The solubility of titanium and hafnium in aluminum in the solid state does not exceed 1.5% wt. .
Zirconium, being an effective modifier, also has a rare universal property: it sharply increases the recrystallization temperature of aluminum and aluminum alloys both after hot and cold deformation, significantly increases the corrosion resistance and stability of the solid solution in aluminum alloys.
In the AIg system, in an area rich in aluminum, a peritectic reaction occurs, in which a liquid containing 0.11% 2g interacts with the 2gL13 compound and forms an aluminum solid solution. The maximum solubility of zirconium in solid aluminum at the temperature of invariant transformation (660°C) is 0.28 wt. %.
Taking this into account, the composition of the alloys was chosen to cover the region of solid solution of titanium, zirconium and hafnium in aluminum and beyond, that is, from 0.01 to 0.5% by mass.
There is limited information in the literature on the influence of hafnium and zirconium on the electrochemical properties of aluminum, and reports regarding the influence of titanium are presented in the works. What is known is mostly from studies in different environments.
The purpose of this work is a comparative study of small additions of zirconium and its analogues on the electrochemical behavior of aluminum grade A995 in an electrolyte environment of 3% NaCl.
Methods for studying alloys are described in the work. The synthesis of alloys was carried out in a laboratory resistance shaft furnace of the SShVL type from aluminum grade A995 and alloys containing 3 wt.% titanium, hafnium and zirconium, respectively. From the resulting alloys, cylindrical rods with a diameter of 8 mm and a length of 100 mm were cast at 850-900°C, the end part of which served as a working electrode.
Studies of the electrochemical properties of alloys were carried out using a potentiostat PI-50-1.1.
In Fig. Figure 1 shows changes in the electrode potentials of aluminum alloys with titanium and hafnium over time. It can be seen that the largest shift in the potential value is observed at the initial moment of time, that is, when the electrode is immersed in the solution, a gradual formation of a protective oxide film on the working surface occurs, the speed of which is determined by time and the concentration of the alloying component. If for aluminum-titanium alloys the most intense protective oxide film is formed in the first 15-20 minutes after immersion in the solution, then for aluminum-hafnium alloys this process lasts from 20 to 45 minutes, depending on the chemical composition of the alloy.
In aluminum alloys with titanium and hafnium, as the component content increases, an increase in passivation ability is observed, as evidenced by a shift in the free corrosion potential to the positive region. So, for an aluminum alloy with 5% titanium, this shift is about 60-80 mV.
The anodic polarization curves of aluminum alloys with titanium and hafnium at a potential sweep rate of 10 mV/s are presented in Fig. 2, and the coordinates of characteristic points on these curves at a potential sweep rate of 20 mV/s are given in Table. 1. It can be seen that, regardless of the rate of development of aluminum alloying with titanium and hafnium, the free corrosion potential (within 30 min of exposure), the critical passivation potential and the complete passivation potential shift to the positive region.
Additions of alloying elements have different effects on the magnitude of the pitting potential of aluminum. At concentrations of titanium and hafnium up to 0.1%, the pitting potential shifts to the positive region, and at higher concentrations (up to 5%) to the negative region or is at the level of the parent metal.
Additions of titanium and hafnium within the solubility range in aluminum (up to 0.84 wt.%) somewhat reduce the critical passivation current and complete passivation current densities, which is apparently due to their high modifying effect and the associated grain refinement of the aluminum solid solution. The primary crystallization of intermetallic compounds T1L13 and N/L13 is associated with an increase in the densities of the critical passivation current and the complete passivation current in alloys containing 0.8% or more titanium and hafnium (Table 1)
Studies of the dependence of the free corrosion potential of aluminum-zirconium alloys on time have shown that zirconium additives shift the potential of aluminum to a more negative region (Table 2). When alloy samples are immersed in the test 3% NaCl solution, the free corrosion potential has a high negative value, but during the first 5-20 minutes it shifts to the positive side. Further exposure for 1 hour leads to the establishment of an almost stationary potential, which is associated with the formation of oxide films on the studied alloy surfaces.
Rice. 1. Dependence of free corrosion potential (- E, B) on time for aluminum containing (wt.%) titanium (a): 1 - 0, 2 - 0.1, 3 - 2.5, 4 - 5.0, and hafnium (b): 1 - 0, 2 - 0.1, 3 - 2.5, 4 - 5.0 in a 3% NaCl solution.
Rice. 2. Anodic potentiodynamic curves of aluminum grade A995 and its alloys with titanium (a): 1 - 0, 2 - 0.05, 3 - 0.1, 4 - 2.5, 5 - 5.0, and hafnium (b): 1 - 0, 2 - 0.05 , 3 - 0.1, 4 - 2.5, 5 - 5.0, potential sweep rate 10 mV/s.
Table 1
Electrochemical characteristics of aluminum alloys with titanium and hafnium
(potential scan rate 20 mV/s)
0.01 Ti 0.990 1.70 1.38 0.650 0.715 1.16 0.34
0.05 Ti 0.948 1.70 1.30 0.650 0.710 1.08 0.42
0.1 Ti 0.981 1.70 1.30 0.650 0.710 1.05 0.42
0.3 Ti 0.983 1.69 1.39 0.680 0.720 1.32 0.44
0.8 Ti 0.979 1.69 1.39 0.680 0.730 1.70 0.46
2.5 Ti 0.972 1.63 1.39 0.690 0.740 1.80 0.56
3.0 Ti 0.960 1.63 1.39 0.690 0.740 1.82 0.70
5.0 Ti 0.958 1.61 1.30 0.690 0.750 1.92 0.90
0 1.035 1.71 1.43 0.680 0.720 1.90 0.50
0.01 N 0.994 1.70 1.44 0.640 0.715 1.05 0.32
0.05 N 0.990 1.70 1.43 0.640 0.710 1.04 0.34
0.1 N 0.995 1.70 1.43 0.640 0.710 1.00 0.41
0.3 N 0.986 1.69 1.42 0.680 0.720 1.32 0.43
0.8 N 0.986 1.69 1.42 0.680 0.730 1.70 0.44
2.5 N 0.950 1.65 1.35 0.690 0.740 1.80 0.55
3.0 N 0.946 1.65 1.35 0.690 0.740 1.82 0.74
5.0 N 0.943 1.56 1.33 0.690 0.750 1.90 0.86
In table Figure 3 shows the electrochemical characteristics of alloys of the A1-2g system. As can be seen, with increasing zirconium concentration in alloys, the potentials for complete passivation and pitting shift to the positive region. In this case, the width of the passive region expands by 40-100 mV. The introduction of zirconium into aluminum in the range of up to 0.3 wt.% slightly reduces the density of the critical passivation current, the complete passivation current, and the dissolution current from the passive state.
table 2
Change in the free corrosion potential of alloys of the A1 - 2g system in an electrolyte of 3% NoC1
Alloy composition -Esv. Change in potential (-E, V) over time -E set-
bov, wt.% cor., (min.) new.,
Zr AI V 1 5 3G 6g V
G.G1 rest. 1.G2 G.92 G.82 G.72 G.71 0.70
G.G5 -"- 1.G2 G.86 G.8G G.75 G.75 0.75
G.1G -"- 1.1b 1.1G 1.G9 G.96 G.91 0.87
G.3G -"- 1.14 1.12 1.G9 G.96 G.92 0.89
G.5G -"- 1.G4 1.G2 G.98 G.94 G.92 0.89
1GG 1.G9 1.G5 G.93 G.81 G.75 0.73
Table 3
Electrochemical characteristics of alloys of the AT-2g system in an electrolyte environment of 3% KaCI
(Potential scan rate 20 mV/s)
Alloy composition, wt.% E n.p. E p.p. E p.o. i cr.p. i p.p.
Zr AI V 2 mA/cm
G.G1 rest. 1.45 1.3G 1.5G 0.35 0.68
G.G5 -"- 1.46 1.37 1.60 0.30 0.67
G.1G -"- 1.45 1.38 1.65 0.30 0.65
G.3G -"- 1.45 1.31 1.70 0.35 0.65
G.5G -"- 1.45 1.25 2.10 0.45 0.64
1GG 1.42 1.32 2.10 0.37 0.68
Thus, small additions of zirconium, titanium and hafnium can be used to improve the electrochemical characteristics of high purity aluminum, although this reduces the width of the passive region on the potentiodynamic curves, which is undesirable.
Institute of Chemistry named after. IN AND. Nikitina Received 03/05/2007
Academy of Sciences of the Republic of Tajikistan,
Tajik Technical University named after. M. S. Oshimi
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4. Gerasimov V.V. Corrosion of aluminum and its alloys. M.: Metallurgy, 1967, 114 p.
5. Umarova T.M., Ganiev I.N. Corrosion of double aluminum alloys in neutral environments. Dushanbe: Donish, 2007, 258 p.
I.N.Ganiev, B.Sh.Narziev, A.M.Safarov TASHIRI ILOVAI KAMI SIRCONIUM VA ELEMENTAL BA ON MONAND BA RAFTORI ELECTROCHEMISTRY ALUMINUM
Natichai omuzishi mikdori kami sirconium wa elemental guruhi titanium ba hosiyathoi electrochemistry aluminum dar muhichi neutral 3% NaCl omuhta shudaast.
I.N.Ganiev, B.Sh.Narziev, A.M.Safarov INFLUENCE OF THE SMALL ADDITIVES ZIRCONIUM AND ITS ANALOGUES ON ELECTROCHEMICAL BEHAVIOR OF ALUMINUM
In the present work the comparative researches of the small additives zirconium and titanium group elements on electrochemical behavior of aluminum in environment electrolyte 3% NaCl are under investigation.
When zirconium dioxide is introduced into the electrolysis bath, an aluminum-zirconium alloy should be formed. The alloy formation that occurs has a significant impact on the entire technological process and, first of all, on the electrochemical separation of aluminum. In addition, since the reduction of zirconium dioxide dissolved in the electrolyte is possible both electrochemically and aluminothermally, it is necessary to consider the effect of alloy formation on a possible shift in the potential for zirconium release, as well as on the course of the aluminothermic reduction reaction. The absence of difficulties in the electrochemical reduction of aluminum in the presence of zirconium will allow the process to be carried out with energy costs close to those in the production of aluminum. At the same time, due to the low solubility of ZrO2 in cryolite-alumina melts, the completeness of the reaction of aluminothermic reduction of zirconium dioxide is of significant importance, which necessitates the assessment of the residual concentration of ZrO2 in the electrolyte. To solve these issues, it is necessary to have information about the thermodynamic properties of the resulting aluminum - zirconium alloys. A characteristic feature of zirconium expected on a liquid aluminum cathode is its chemical interaction with aluminum. As the phase diagram shows, it can form a number of compounds with aluminum in solid form. This, in turn, will in a certain way affect the physical and chemical properties of the resulting alloy and influence the technology of the electrolysis process. The state of the general theory of metal alloys and, in particular, the theory of metal solutions, does not allow calculations of the thermodynamic properties of alloys based on data for pure aluminum and zirconium. Setting up experiments to study the thermodynamic characteristics of alloys involving zirconium and aluminum is very difficult due to their high chemical activity, and therefore the data available in the literature is far from complete. In the work of Yu.O. Esin and his colleagues, the heats of mixing of liquid aluminum alloys with zirconium in the concentration range from 0 to 60% at. Zr were determined by the calorimetric method. The obtained data are presented in Table 3.1. The data presented in Table 3.1 indicate that very large deviations from Raoult’s law are observed in melts of the Al-Zr system. A decrease in the absolute value of DHZr and DHAl with an increase in the concentration of zirconium or aluminum in the alloy indicates a strong interaction of zirconium with aluminum. In other words, the Al-Zr bond is much stronger than Al-Al and Zr-Zr. The strong interaction of these two elements is also evidenced by the Al-Zr phase diagram, in which congruent compounds are formed that melt without decomposition. Similar formations of aluminum and zirconium atoms are preserved in liquid alloys even at high overheating relative to the liquidus line. For a complete thermodynamic characterization of alloys, it is necessary to have the activity values of the components in the alloy. To determine the thermodynamic properties of alloys, several methods are mainly used: the method of measuring the saturated vapor pressure above the alloy; calorimetric method and method based on determining the distribution coefficient, the method of electromotive forces.
The double phase diagrams bounding the zirconium angle are investigated.
Composition and mechanical properties of technical gitanium (GOST 9853 - 61.| The influence of some elements on the strength of Ti. All known double phase diagrams of Ti-based alloys are divided into three large groups according to the nature of the liquidus and solidus lines near the Ti ordinate (approximately 30 - 40% of the weight alloying additive), and each of these groups is divided into subgroups according to the nature of transformations in the solid state.
Composition and mechanical properties of technical titanium (GOST 9853 - 61.| Influence of Sn and AI on the tensile strength of titanium alloys. All known double state diagrams of Ti-based alloys are divided into three large groups according to the nature of the liquidus and solidus lines near the Ti ordinate (approximately 30 - 40% of the weight of the alloying additive), and each of these groups is divided into subgroups according to the nature of transformations in the solid state.
The similarity of double phase diagrams and the same crystal structure of niobium, tantalum, molybdenum and tungsten and the resulting silicides predetermine the similarity in the patterns of formation and structure of the diffusion layer.
The nature of the double state diagrams of metals of groups V-VI or, in a broader aspect, groups III-VIII and the patterns observed in these systems are primarily due to the similarity of the electronic structure of the outer shells of their atoms.
Analysis of double state diagrams of refractory transition metals of groups IV-VI with interstitial elements (B, C, N, O) shows that, as a rule, the metal component forms a eutectic with the nearest intermediate compound. Such systems are characterized by a relatively low solubility of interstitial elements in the base metal (see Fig. 38), which increases with increasing temperature. In multivalent, highly ionizing metals of groups IV-VI, the valence electrons of interstitial impurities are itinerant and therefore the solubility of B3, C, N3, O4 ions is determined by the ratio of atomic radii rx / gm.
When constructing double phase diagrams, the composition of the alloy is plotted along the horizontal axis in percent, and the temperature in degrees Celsius is plotted along the vertical axis. Thus, each point in the diagram corresponds to a certain composition of the alloy at a certain temperature under equilibrium conditions.
This series of double state diagrams is convenient to use when analyzing the influence of the nature of the interaction of soldered metal A with solder B on their compatibility. With this consideration, it is necessary to take into account that phase diagrams characterize the phase composition of alloys and the composition of alloy phases under equilibrium conditions.
Scheme of a closed region of austenite.| Scheme of a diagram with continuous solubility of Fe a (8 and an alloying element. | Scheme of a diagram with continuous solubility of t - iron and an alloying element. | Expanded, limited region of t - solid solution. A feature of all double state diagrams of iron with other elements is the presence of recrystallization in the solid state due to polymorphic transformations of iron. Modifications a and b have the same body-centered cube lattice. In the temperature range (910 - 1401) there is a y-modification, which has a cube lattice with centered faces.
The line rule in dual phase diagrams can only be applied in two-phase regions. In the single-phase region there is only one phase; any point inside the region characterizes its concentration.
The line rule in dual phase diagrams can only be applied in two-phase regions.
The answer to these questions is given by the double state diagrams presented in Fig.
The answer to these questions is given by the double state diagrams of titanium - alloying element, presented in Fig. 374 in the form of a classification scheme.
The answer to these questions is given by the double phase diagrams of titanium - alloying element, presented in Fig. 374 in the form of a class-sn circuit diagram.
Solderable metals and solder metals forming double phase diagrams, the components of which are insoluble in each other, neither in the liquid nor in the solid state (see Fig. 4) or are limitedly soluble in the liquid state, but insoluble in the solid state (see . Fig. 4), can form only adhesive type connections.
In Fig. Figures 58 and 59 show dual phase diagrams of aluminum with copper and magnesium. In both cases, with increasing temperature, a significant change in the solubility of alloying elements in aluminum is observed. A similar change in solubility is observed in multicomponent systems, which provides the possibility of strengthening heat treatment. However, in complex alloys, phases of complex composition and structure will be in equilibrium with the aluminum solution according to the corresponding phase diagrams.
Externally, vertical section diagrams are similar to double state diagrams. Only the liquidus and solidus curves do not intersect in the general case on the ordinates of vertical sections.
It summarizes new data on 1719 double phase diagrams and crystal structures of phases published in 1957 - 1961, as well as old works not reflected in the reference book.
To characterize phase equilibria in cast iron, double phase diagrams are used primarily.
The structure of lead babbitts should be analyzed based on the double phase diagram of Pb - Sb (Fig.
Externally, the section diagram (Fig. 117) is similar to the double state diagram. The difference is that instead of the eutectic horizontal, an area e a c appears on the section in the form of a triangle, the sides of which are curved lines formed at the intersection of the section plane with the ruled surfaces of the three-phase volume.
The surfaces of the beginning of crystallization of double eutectics pass through the corresponding eutectic horizontals of double phase diagrams.
It is easy to see that the section under discussion does not really have the properties of a double phase diagram, since it contains, in addition to equilibria with phases 8 and y, equilibria in which phase (3, released from the liquid in the region above the formation temperatures of the solid solution of the compound and then turning into the latter.
A variant of the phase diagram shown in 468 when the V - fl cut becomes partially double.| A variant of the phase diagram shown in 469 when the VtA region becomes partially double. Between points A and p, this cut has all the properties of a double phase diagram. Beyond the point p r it contains elements of the state that are not directly related to the AVZ system, and therefore loses in this part the properties of a double system.
Therefore, the 22-year period that elapsed between the first and second editions of the Dual Phase Diagram Handbook would now be unacceptable. Anderko, the United States Air Force Space Research Laboratories 1 have been asked to support the publication of this handbook.
The phase and structural changes that occur at the diffusion stage of the process can be predicted using double phase diagrams if only two elements are involved in the diffusion interaction. It is assumed that the diffusion process is not intensified and the resulting diffusion zone is in an equilibrium state.
Using the method of vertical sections of a triple state diagram, using the example of the diagram under discussion, we will trace the gradual transition from a double state diagram of one type to a double state diagram of another type.
Zirconium angle of the phase diagram of the zirconium - vanadium - nickel system. At a temperature of -770, there is a eutectoid four-phase equilibrium p6 ta3 Zr2Ni ZrV2, which is formed from the second class of equilibrium P2 - β4 - Zr2Ni ZrV2 departing from the four-phase equilibrium indicated above and two eutectoid equilibria p4 a1 Zr2Ni and P53 a2 ZrV2, emanating from the corresponding double phase diagrams.
In order to determine the joint influence of niobium and aluminum on the properties of zirconium, work was undertaken to study the ternary phase diagram of a part of the zirconium-niobium-aluminum system rich in zirconium. In the double state diagram of the zirconium - aluminum system in the temperature range from 1395 to 975 C, the chemical compounds closest to zirconium are Zr5Al3, Zr2Al and ZrsAl. At a temperature of 1350 C, 9 5% aluminum dissolves in p-zirconium. There are a total of nine chemical compounds in this system. Below 980 C, the p-solid solution decomposes into two solid solutions rich in zirconium and niobium, respectively. With decreasing temperature, the region of separation in the solid state expands up to the monotectoid temperature of 610 C.
The left side of the dual state diagram Cu - A1 is shown in Fig.
Scheme of changes in the content of a low-melting component in a soldered joint made of metal A during diffusion soldering. Diffusion soldering of titanium and its alloys with solders rich in copper, silver, and nickel is promising. Judging by the data in Table. 30 and double state diagrams, the widest regions of solid solutions in these alloys are in the temperature range of existence of p-solid solutions. Silver is quite fusible, and copper and nickel form relatively low-melting eutectics with titanium. Intermetallic compounds formed in solder seams of titanium joints made with solders containing these metals are also relatively low-melting.
But this similarity is only external. In fact, there is a profoundly fundamental difference between the vertical sections of a ternary system and a double phase diagram.
Position of vertical cuts. in the state diagram.| Vertical section diagram I.| Vertical section diagram. Section in Fig. 90, while outwardly similar to the double phase diagram, differs significantly from it in this sense.
The scientific basis of steel heat treatment technology is the joint analysis and application of state diagrams (phase diagrams) and decomposition diagrams of supercooled austenite. To date, double phase diagrams are known for iron-based alloys; and for the majority of alloys and steels widely used in industry - and ternary diagrams.
Variant of the state diagram of a system with an incongruent for a melting ternary chemical compound in the case where one of the cuts from the compound to the components is not double.| Vertical section diagram of CS. In Fig. 476 shows a vertical section of the state diagram along line AS. Consequently, beyond point p the cut AS loses the properties of a double state diagram. The dotted lines show the most stable parts of the liquidus and solidus of the 8-solid solution with a common hidden maximum.
Vertical section diagram along line VC.| Isothermal section of the phase diagram at the temperature corresponding to the eutectic point e5 in the binary system VC.
From the above it follows that the vertical section of the phase diagram along the line VC (Fig. 439) has the properties of a double phase diagram, since the V e & and C e liquidus lines are conjugate with the V d9 and C c3 solidus lines.
The question naturally arises about the origin of this graphite. It was already indicated above (§ 44) that to explain the origin of graphite, there are two theories, based either on a double state diagram or on a single one.
Isothermal sections below the eutectic point c5.| Isothermal calculation at a temperature corresponding to the triple eutectic point E. Due to these properties of the vertical section VC, it and similar sections are called quasi-binary, sometimes also pseudo-binary, indicating their similarity with diagrams of binary systems. They should, however, be called simply double cuts, since the prefix quasi means supposedly, as if, and the prefix pseudo means false, false, which rather casts doubt on the similarity of QUIET cuts with double state diagrams, rather than emphasizing it.
Alloys of copper and tin containing up to 12% Sn have practical application in mechanical engineering. The left side of the copper-tin dual phase diagram is shown in FIG.
The formation of solid solutions leads to a change in transformation temperatures. To assess the influence of alloying elements on titanium, it is important to establish how they affect the polymorphic transformation of titanium and whether they form chemical compounds with titanium. The answer to these questions is given by the double state diagrams presented in Fig. 356 in the form of a classification scheme.
For ternary systems, the phase rule is written in the form / 4 - p; Compared to double systems, one additional degree of freedom appears. Three-phase ternary alloys have one degree of freedom; these alloys occupy the corresponding volumes in the spatial state diagram. As in the case of two-phase regions in double phase diagrams, the temperature of a three-phase ternary alloy can be varied, but at any given temperature the compositions of all three equilibrium phases turn out to be quite definite. In two-phase volumes of the spatial diagram of the state of a ternary system, temperature and composition can be changed independently of each other. In a single-phase volume, the number of degrees of freedom of a ternary alloy reaches a maximum value of three: here you can change the temperature, as well as the concentrations of two of the three components. Since the concentrations of all three components in total are equal to 100%, only two concentrations can be changed independently of each other, since the content of the third component is determined by the difference between 100% and the sum of the concentrations of the remaining two components.
Vertical section. The beneficial effect of molybdenum is explained by the fact that in its presence the formation of the chemical compound TiCra is difficult. The maximum solubility of chromium in a-titanium, in accordance with the double state diagram Ti-Cr, is 0 5% wt.
This book is a textbook on heat treatment of metals for mechanical engineering colleges. To study heat treatment using this book, the student is required to know the basics of metal science in the volume of the book by A. I. Samokhotsky and M. P. Kunyavsky Metal Science or the book by M. S. Aronovich and Yu. M. Lakhtin Fundamentals of Metal Science and Heat Treatment, or books by B. S. Natapov Metal Science, which are also textbooks for technical schools. It is assumed that the student is well acquainted with the main types of double phase diagrams, with the crystalline structure of metals and alloys, with the elementary structures of steels and cast irons, with metallographic research techniques and mechanical tests. These issues are not discussed at all in this book. The first chapter briefly, but in somewhat more detail than in the mentioned metal science textbooks, examines the classification and characteristics of steels and the state diagram of iron-carbon alloys.
Phase diagram with a continuous series of solid solutions with a maximum point on the liquidus and solidus surfaces.| Projection of the phase diagram shown in 69 onto the concentration triangle. In this sense, isothermal cuts are no different from a double phase diagram. However, the significant difference between them is that the double diagram allows one to judge equilibria. The fundamental difference between isothermal and vertical cuts is clear from the above.
Typically, vertical sections are constructed along the composition lines of ternary alloys, which contain a constant amount of one of the components. A, which exceeds the content of this component in the triple eutectics and in the double eutectics e and e3, is shown in Fig. The lower part of this section superficially resembles a double phase diagram of the eutectic type, if you do not pay attention to the designations of the various phase regions.
Let us pay attention to the fact that straight line SUg in Fig. 470 passes through the lines ee, d d, EZE1 of the three-phase equilibrium x Y - b 8 between the liquid and solid solutions of component C and compound Yr. The lines of intersection with these surfaces (Fig. 472) are not elements of the double state diagram CVlt; therefore, beyond point p, the cut loses the properties of the double state diagram.
With the development of new branches of science and technology, the requirements for the properties of aluminum alloys are also expanding. This leads, as a rule, to complications in their composition. Increasingly, additives of such refractory elements as zirconium, manganese, chromium, titanium, vanadium, boron and others are being used as alloying components.
The works of M.V. Maltsev, V.I. Dobatkin, A. Kibula and other authors show that the latter, when introduced into the melt, contribute to grain refinement of ingots, eliminate structural heterogeneity, significantly improve the casting and mechanical properties of alloys, and ensure the production of large-sized forgings and stampings , as well as other semi-finished products manufactured with a low degree of deformation from alloys D16, ACM, 1911,1915. For such casting alloys as VAL-1, VAL-5, AL4M and others, the feasibility of using refractory alloying components has also been shown.
Zirconium, which, like other transition metals, has a pronounced modifying effect, has become widespread for alloying aluminum alloys.
The phase diagram of the Al-Zr system is of the peritectic type. As the diagram, Fig. 1.1 shows, between the liquid (0.11% zirconium) on the side of pure aluminum and the ZrAl 3 compound, a peritectic reaction occurs with the formation of a solid solution of aluminum (0.28% zirconium). The reaction temperature is 660.5 °C.
The work indicates that the study of double phase diagrams characterizing the interaction between aluminum and alloying components allows one to judge the effectiveness of a particular element as a modifier. The most effective modifiers are those metals that form peritectic or eutectic phase diagrams with aluminum with refractory compounds, the liquidus of which is significantly shifted towards aluminum. An example of such a diagram is the Al-Zr diagram.
In addition to its ability to refine grains, zirconium can significantly influence the recrystallization temperature of aluminum alloys. The latter action is associated with the formation and decomposition of solid supersaturated solutions of zirconium in aluminum. As a rule, the finished product does not contain supersaturated solid solutions. During the technological cycle of production of semi-finished products, associated with numerous heating of the alloy, alternating with deformations, the decomposition of these solid solutions occurs with the release of secondary aluminides. The degree of decomposition of the solid solution, dispersion and nature of distribution of decomposition products ultimately determine the influence of transition metals on the mechanical properties of deformed semi-finished products.
Elagin, in his work, considering the influence of transition metals on the recrystallization temperature, indicates that dispersed metals have the greatest effect on the recrystallization temperature intermetallic compounds — decomposition products of solid solutions. Undissolved solid solutions increase the recrystallization temperature to a lesser extent. And the coagulation of decomposition products of solid solutions leads to a completely opposite effect. Solid solutions of various transition metals differ in their stability. The most stable is a solid solution of zirconium and aluminum. In the main volume of this solution, decomposition proceeds very slowly. Coagulation of decomposition products is also slowed down compared to other comparable alloys.
Thus, the work notes an increase in the fluidity of Al-Mg alloys. In the AL27-1 alloy, zirconium additives reduce the tendency to crack formation and reduce the hydrogen content.
According to Kozlovskaya, replacing part of the manganese in the D16 alloy with zirconium helps to obtain a strongly pronounced press effect, the absence of a coarse-crystalline rim and increased plasticity in the transverse direction.
In alloys of the Al-Zr-Mg system, zirconium additives significantly reduce stress corrosion and also increase the corrosion resistance of aluminum alloys in aggressive environments.
The information provided, which is far from complete, about the role of zirconium in aluminum alloys indicates that zirconium is increasingly used as an alloying element.
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