Wear- and Scaling-Resistant Coatings Based on TiCN

The composition, structure, and properties of coatings obtained by the high-velocity gas-flame spraying of composite powders based on TiCN with additions of SiC, AlN, SiC AlN/Al₂O₃ and a binder of NiCr based alloy were investigated. The working surfaces of coatings were studied by metallographic, petrographic, x-ray diffraction, electron-probe analyses, and scanning electron microscopy. It was determined that coatings 200 m in thickness had a typical finely dispersed lamellar structure with layers enriched in titanium alternating with layers of NiCr alloy. The tribological properties of developed coatings were superior to those of the standard WC + 8% Co alloy: under dry friction at a load of 2 MPa and sliding velocities in the range 5-15 m/sec the coefficient of friction was 0.17-0.11, and wear rate 3.4-8.5 m/km. The high oxidation resistance of the coatings is due to the presence, in the outer scale layer, of refractory compounds Al₂SiO₅, (Cr, Al)₂O₃, and Al₂TiO₅, which prevent the diffusion of oxygen into the substrate. The mass gain of the coating based on TiCN SiC AlN was 1.42 mg/cm₂ at 1450°C.     

Polythermal Ti-∑MoNi (9∶1) section of the ternary system Ti-Mo-Ni

Conclusions As a result of an investigation of the titanium corner of the system Ti-Mo-Ni, a partial phase diagram of the Ti + (0–55%) MoNi (91) section was constructed. The solubility of Mo and Ni in-Ti is 0.65% MoNi. Thea + phase field is bounded by MoNi contents of 0.65 and 17% at 600°C, 0.5 and 14% at 700°C, and 0.4 and 6% at 800°C. At MoNi contents of 55% and higher, there is a + Ti₂Ni field, the existence of which was confirmed by x-ray structural studies.Translated from Poroshkovaya Metallurgiya, No. 2 (110), pp. 33–37, February, 1972.     

Phase equilibria in the solidification range of alloys of the Ti-Ru-Ir system

Conclusions The processes taking place during solidification of the alloys of the Ti-Ru-Ir ternary system have been examined for the first time. The results show that the system contains three nonvariant quaternary equilibria with the liquid of the incongruent type: L + + at 2220°C, L + + at 1920°C, and L + + at 1465°C.In the region with the composition 0–50% Ti, the processes take place in the direction to the Ti-Ru side of the concentration triangle where they are also completed at the temperature of the binary eutectic L '+ equal to 1855°C. In the region with the composition 50–100% Ti the processes are completed at 1460°C at the nonvariant point corresponding to the eutectic reaction L + of the Ti-Ir binary system.Translated from Poroshkovaya Metallurgiya, No. 11(299), pp. 72–77, November, 1987.     

Kinetics and mechanism of oxidation of β-sialons

Conclusions We examined the behavior of two materials during high-temperature oxidation: the singlephase -sialon and the material based on -sialon containing up to 8% residual -Si₃N₄ and the glass phase produced by reaction sintering of the charge based on -modification of silicon nitride. The results show that the maximum oxidation resistance in the temperature range 800–1300°C is exhibited by the single-phase -sialon Si_5.5Al_0.5O_0.5N_7.5. The oxidation resistance decreases in the presence of the residual -Si₃N₄ and the glass phase in the material. The oxidation kinetics are also determined by the structure and composition of the oxide film. The kinetic curves are governed by a parabolic law which indicates that oxidation of the sialons is limited by the diffusion processes. No marked changes were detected in the lattice spacing of the sialon after oxidation.Translated from Poroshkovaya Metallurgiya, No. 6(306), pp. 69–73, June, 1988.     

The phase equilibria in W-Fe-Co-Ni system alloys. II. Isotherms of the solidus and the phase composition of alloys containing 10 and 20% (Fe + Co + Ni) at temperatures above 1200°C

Conclusions The isostructural intermediate -phases Fe₇W₅ and Co₇W₆ in the W—Fe—Co system form a continuous series of -solid solutions. In the 1640–1630°C range the L + (Fe₇W₆) peritectic equilibrium in this system changes to a similar L + (Co₇W₆) equilibrium, where is the tungsten-base boundary solution.In the W-Fe-Co-Ni polythermal tetrahedron in the 1470–1460°C range conversion of the L +(Fe₇W₆)+, peritectic equilibrium into the similar L + (Co₇W₆) + , where is the nickel-, -ironcobalt-base boundary solution, occurs.Upon completion of crystallization at 1400°C, the W-Fe-Co system alloys with 10–20% (Fe + Co) have a + phase composition, while the W-Fe-Co-Ni system alloys with 10–20% (Fe + Co + Ni) accordingly have + , + + or + . At temperatures below 1215°C in alloys rich in iron, FeW may be formed instead of -phase and therefore the alloys may have an + FeW, + + FeW, + + + FeW and + + FeW phase composition.Translated from Poroshkovaya Metallurgiya, No. 5(281), pp. 86–89, May, 1986.     

Enthalpy of Mixing and Excess Volume of Binary Metallic Melts of Eutectic Systems

The enthalpies of mixing H and excess volumes V were analyzed in alloy formation from binary metallic eutectic systems. Three types of systems can be distinguished: I with H > 0, V > 0; II with H > 0, V 0; III with H < 0, V 0. The hypothesis is discussed that another yet unstudied group IV exists in which H < 0, V < 0.     

Special features of the ductile-brittle transition in iron-based powder materials. II. Physicomechanical model of the ductile-brittle transition in cracking resistance tests

Conclusions The presence of pores in the material leads to the redistribution of stresses in the material and to localization of strains in small volumes between the pores. The susceptibility to ductile failure increases with increasing porosity.At –196°C, the failure mechanism of the porous materials based on iron changes from ductile to brittle (cleavage) with decreasing porosity. The dependence of cracking resistance on the porosity of these materials is nonmonotonic and the maximum cracking resistance is recorded at porosity values at which the failure mechanism changes. The nonmonotonic nature of cracking resistance reflects the high sensitivity of this characteristic to the change of the stress state in the material. The change of the stress state in the ductile-brittle transition temperature range can be described by the condition _f = _T. In the porous materials examined this condition is valid because of the specific form of the _f- and _T- dependences. The model of the ductile-brittle transition proposed in this work can be used to determine the analogy between the cold brittleness temperature T_br and the critical value of porosity _c corresponding to the point of intersection of the _f- and _T- curves for the porous materials.Translated from Poroshkovaya Metallurgiya, No. 3(303), pp. 39–42, March, 1988.     

Mechanical properties and microstructure of sintered titanium alloys

Conclusions A study was made of the mechanical properties and microstructure of titanium alloys in the sintered state. The influence of alloying elements was evolved. It was established that for alloys used in the sintered state it is favorable to use vanadium, aluminum, and molybdenum as alloying elements.The titanium alloy containing 3% Al and 3% V, made by the method of combined reduction of oxides of TiO₂, Al₂O₃, V₂O₅ by calcium hydride (_B-774.2 MN/m², -15%, -26%, a_k-25.4 joules/cm²) and also the alloy Ti+3% Al+3% V+2% Mo (_B-857.5 MN/m², -14.3%,-27%, a_k-24.5 joules/cm²) can be recommended for the manufacture of components by methods of powder metallurgy.     

Strength characteristics of matrials produced by hot forming of porous powder compacts. I. The influence of porosity,carbon content,and the method of compacting on the tensile,shear, and compressive yield strengths

Conclusions The mechanical characteristics (_t, ) of powder metallurgy steels depend upon the porosity as a weakening factor and work hardening as a strengthening one. The tensile strength is more sensitive to porosity and less susceptible to work hardening than the shear strength. The compressive yield strength depends practically only upon work hardening and the size of the metal cross section.In comparison with hot rolled of the same composition, powder metallurgy low-porosity steels possess higher characteristics _t, , and _0.2 ^comp , which may be explained by the strengthening action of work hardening.Powder metallurgy steels produced by extrusion have higher values of _t than hot formed as the result of improvement in the quality of the intergranular contacts and orientation of the nonmetallic inclusions while there is practically no difference in the characteristics and _0.2 ^comp of these materials.Translated from Poroshkovaya Metallurgiya, No. 3(279), pp. 88–91, March, 1986.     

The Solidus Surface in the Ti ― Ni ― Hf System in the Ti ― TiNi ― HfNi ― Hf Region

Studies have been done on the phase equilibria at subsolidus temperatures in the Ti TiNi HfNi Hf region of the Ti Ni Hf ternary system. The phases based on binary compounds and solid solutions of these components are accompanied in the equilibria by a phase based on an equiatomic ternary compound. This new phase belongs to the family of Laves phases and has a hexagonal crystal structure of MgZn₂ type. The solidus surface in the Ti TiNi HfNi Hf subsystem consists of the surface of the ternary phase alone, the surfaces of the six solid solutions based on the components and binary intermediate phases, the planes of five conode triangles, and the corresponding lineated surfaces.     

Effect of P,B4C,and (Ti,Cr)C Additives on the Kinetics of High-Temperature Oxidation of Chromium Carbide Alloys at 1000°C

We have used the thermogravimetric method to study the effect of B₄C, (Ti, Cr)C, and phosphorus additives on the kinetics of oxidation of chromium carbide alloys of the type 85% Cr₃C₂ 15% Ni (KKhN15) and 85% Cr₃C₂ 15% (Ni P) (KKhNF15), in air under isothermal heating conditions at 1000°C from 0 to 5 h. We have established that the alloys are characterized by insignificant increase in mass in the initial oxidation period (3 h), after which the degree of oxidation increases somewhat. The nature of the oxidation kinetics for KKhNF15 alloys, containing 0.016-0.64% B₄C, varies from some mass increase in the initial period (20 min) to later mass loss in connection with formation of CO, CO₂ and rapid evaporation of boron anhydride B₂O₃. The maximum resistance to oxidation is exhibited by alloys of the type KKhN15 and KKhNF15, the mass increase of which is 0.128-0.256 mg/cm² after 5 h of heating at 1000°C.     

Physicochemical processes occurring in nitride and oxide-nitride composites with phosphate binders during heating

Conclusions The hardening of compositions based on aluminum and silicon nitrides is a result of the chemical reaction of their phosphate binder with the nitrides, while additions of, e.g.,-corundum act as inert fillers up to a temperature of 570K. The reaction products are amorphous acid mono- and disubstituted aluminum and silicon phosphates, which on heating at first condense, forming poly- and metaphosphates, and then, at temperatures above 870K, decompose, forming (depending on their composition) aluminum orthophosphate or silicon pyrophosphate.Aluminum nitride initially, after being combined with the phosphate binder, vigorously reacts with it, which may lead to clotting or rapid swelling of the composition. However, gradual mixing under conditions of cooling (or without it) enables masses of any consistency to be obtained.In the mechanism of hardening of the compositions investigated a dominant role is played by the hydrogen bond. With rise in temperature the OH groups evaporate and the role of the hydrogen bonds diminishes, but a new, more powerful mechanism becomes operative, linked with the polymerization of the phosphates. Above 970K the polymer structure, which attains its maximum development at 870–970K, gradually disintegrates, but at the same time a new process-sintering-commences. Accordingly, as has been demonstrated by our investigation into the temperature dependence of the strength of the compositions, all the materials investigated pass through stages of hardening (470K), strengthening (470–970K), partial strength loss (by 30–40% in the range 970–1270K), and high-temperature sintering.The end products of the thermal decomposition of the polyphosphates up to 1520K are (depending on the nature of the nitride filler) aluminum orthophosphate or silicon pyrophosphate, present in amounts of 5–10%.At 1270–1370K a liquid phase (aluminum metaphosphate or silicon polyphosphate) forms in the compositions and then gradually disappears as a result of its further reaction with the fillers. Under these conditions an additional amount of AlPO₄ or SiP₂O₇ is formed.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 50–54, May, 1982.     

Stability and Heat Resistance of Silicide Coatings on Refractory Metals. Part 2. Stability and Heat Resistance of Silicide Coatings on Tungsten and Molybdenum at 1500-2000°C

The kinetics of diffusion redistribution of phases within the system WSi₂ W on heating tungsten silicide in air in the temperature range 1500-2000°C is studied. The stability and heat resistance of silicide coatings on tungsten is mainly governed by the diffusion of silicon towards the interphase boundaries W W₅Si₃, W₅Si₃ WSi₂, and WSi₂ SiO₂, formation at them of diffusion barriers of lower silicide W₅Si₃, and also a protective SiO₂ film at the outer boundary of the silicide coating. It is established that the transition rate for the higher to the lower tungsten silicide WSi₂ W₅Si₃ is on average four times slower than the transition rate for MoSi₂ Mo₅Si₃. It is shown that an increase in silicon concentration in the WSi₂ surface layer stimulates formation of diffusion barrier compounds at interphase boundaries. This leads to an increase in the stability of the phase composition and heat resistance of a silicide coating on metals. In particular at 1700°C the transition rate for molybdenum silicide on tungsten MoSi₂ (Mo, W)₅Si₃ is about twenty times slower than the transition rate for MoSi₂ Mo₅Si₃, and less by a factor of about eleven than the transition rate for WSi₂ W₅Si₃. Here there is also an increase in the heat resistance of silicide coatings on tungsten and molybdenum. It is shown that the SiO₂ film on tungsten silicide does not lose its protective properties up to 2000°C.     

Corrosion of Titanium-Aluminum Intermetallides. Part 2. Electrolytic Oxidation of γ‐TiAl,TiAl3, and α2‐Ti3Al in Sea Water

Potentiodynamic polarization, XRD, Auger electron spectroscopy, and scanning electron microscopy have been applied to determine the mechanisms of electrolytic corrosion of the intermetallides TiAl, TiAl₃, and ₂Ti₃Al in 3% NaCl solution with the addition of MgSO₄ in comparison with the corrosion of the pure metals (Al and Ti). There is comparatively high corrosion resistance in TiAl and Ti₃Al because of the protective action from thin films of rutile TiO₂. Evidence is obtained for the differences between these intermetallides from the appearance of pure titanium on deep anodic polarization (above +0.15 V for TiAl and +0.7 V for Ti₃Al): the aluminum and titanium enter the solution in the forms of Al³⁺ and TiO²⁺ and intermetallides dissolve rapidly. The final solid-state products from anodic oxidation in that case are rutile, magnesium aluminate, and also magnesium and sodium titanates. In addition to pure titanium, TiAl and ₂Ti₃Al as constructional materials may be recommended for use in sea water.     

Correlation between the particle size,pore size,and porous structure of sintered tungsten

Conclusions It has been established that the maximum size of pore channel constrictions D₁ is close to the mean size of pore sections in microsections of porous skeletons (-=22–44%) from tungsten powders of 1- to 5-m mean particle size. A rapid method of assessment of an integral fineness characteristic of a tungsten powder is proposed consisting in the determination of the pore size D₁ in a compact (-_c=25–45%), followed by the calculation of the mean size of agglomerated particles with Kozeny's formula. The densification of compacts from tungsten powders of 4-m particle size at sintering temperatures of about 0.6 T_melt is a result of decrease in the number of pores and increase in the equivalent size of agglomerated particles. In this process the mean pore section size determined by the metallographic method remains unchanged during sintering, which corresponds to a statistical model of a porous solid in the rheological theory of sintering.Translated from Poroshkovaya Metallurgiya, No. 12(312), pp. 24–31, December, 1988.     

Sintering of constructional powder materials by high-frequency currents

Conclusions The results are presented of a study into the possibility of sintering powder materials of complex composition by means of high-frequency currents. Relationships have been found between the critical temperature of specimens and the graphite and chromium contents of the starting charge. The microstructure has been investigated, and the mechanical properties determined for specimens of various compositions sintered at the critical temperatures.Presented to the Fifth Republican Scientific-Technical Conference on Powder Metallurgy, Kiev, March 29–31, 1966.Translated from Poroshkovaya Metallurgiya, No. 12, pp. 15–20, December, 1966.     

Production and properties of constructional parts from copper and copper alloy powders. A review

Conclusions Conventional methods of manufacture enable constructional copper alloy parts to be produced with a porosity of 10–15%. However, such parts do not exhibit high electrical conductivity and corrosion resistance, good brazing qualities, and stability of properties with time and at ambient temperature fluctuations. To improve their characteristics, it is necessary to reduce their porosity to not more than 3–5%. This can be achieved by employing high-energy methods of densification, in particular hot and cold forging. There is therefore an urgent need to study the processes of deformation of sintered blanks, determine optimum chemical compositions of materials, and develop methods of determining optimum blank sizes and shapes for forging.-Brasses are ductile at room temperature, but at 500–700°C they become less ductile than -brasses. At temperatures above 500°C the latter are less strong and hence more ductile than at room temperature. To obtain the best results, parts from -brass powders should be produced by cold forging and those +-brasses by hot forging. For hot forging it is best to use compacts from powders with a zinc content of 32–38%, which at room temperature are of the -modification and possess good formability. After heating for forging the -phase (an unordered solid solution) appears in their structure, which improves the workability of compacts in the hot state. Under these conditions their hightemperature ductility increases twofold. Hot-forged parts are also amenable to heat treatment (aging).Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 44–53, March, 1982.     

Static and cyclic strength of a uniaxially reinforced material in bending (part 1)

Conclusions A built-up degree of damage =f/f_o 8% has virtually no effect on the static strength of an AD33-B CM operating in air. The arbitrary fatigue limit corresponding to this volume of damage on a basis of 2–10⁵ cycles may be taken to be equal to (0.5–0.55) _t. Accelerated buildup of damage on a basis of 2–10⁵ cycles is observed at _a > (0.5–0.55) _t.Translated from Poroshkovaya Metallurgiya, No. 7 (259), pp. 65–67, July, 1984.     

Effect of Rhenium on Formation of the Structure of Eutectic Alloys Based on β-NiAl + γ-Re

We have studied phase equilibria and plotted the partial phase equilibria diagram for Ni Al Re in the region of compositions ranging from 0.2 to 14 at.% rhenium. We have established the dependence of the structure and the phase composition of the alloys in the Ni Al Re system on the rhenium concentration. We have determined the optimal ratio of the components at which the alloys have the maximum melting point. We have shown that the structure of the alloys is a composite consisting of a NiAl-based matrix and -Re fibers.     

Mechanical properties of multilayer steel-copper composites

Conclusions The tensile strength _t and fatigue limit _–1 of powder metallurgical and cast MLCs grow with decreasing mean layer thickness h starting from 5000 Å. In cast Type 45 steel/copper composites high tensile strength _t (222 kgf/mm²) combines with high impact strengtha _n (8 kgf-m/cm²) and hardness (42–45 HRC). With powder metallurgical and cast MLCs, at any given life NG the cycle stress necessary for fatigue fracture grows with decreasing mean layer thickness (within the h = 5000-500 Å range investigated).Translated from Poroshkovaya Metallurgiya, No. 11(203), pp. 33–37, November, 1979.