Properties Of Pseudoalloys Research Articles

Peculiarities of hardening of steel – copper alloy pseudo-alloys obtained by infiltration during hot plastic deformation

The influence of the regimes of plastic deformation of steel – copper alloy pseudo-alloys obtained by infiltration on their structure, mechanical properties and anisotropy of properties is investigated. It has been established that hot forging of pseudo-alloys at a temperature of 700–950 °C provides an increase in strength by 1.5–3 times, impact strength by 1.5–2.5 times, plasticity by 1.5–2 %, and at 1100–1150 °С (above the melting point of copper) – leads to cracking of the material. It is shown that the properties of pseudo-alloys based on steel alloyed with chromium are lower than those based on steel alloyed with nickel, which is associated with the formation of chromium oxides due to its increased affinity for oxygen. The formation of macro-texture in pseudo-alloys after hot stamping has been established, which leads to secondary anisotropy of properties, the level of which is determined by the degree of deformation and temperature, but does not exceed 15–20 %. The deformation curve of the pseudo-alloy during hot forging was constructed, which revealed the optimum temperature (700–900 °С) and the limiting degree of deformation (65 %) depending on the composition of the pseudo-alloy. With an increase in the degree of deformation, microcracks form at the interface between the iron and copper phases, which in turn leads to a decrease in strength, ductility, as well as a 1.5–2-fold decrease in the impact strength of pseudo-alloys with a copper phase content of 15 % and destruction of pseudo-alloys with a 25 % copper content phases, in which the length of interphase iron-copper boundaries is much greater. The achieved mechanical properties of hot-forged steel-copper alloy pseudo-alloys make it possible to use them for parts of heavily loaded friction units, as well as parts for structural purposes.

Influence of heat treatment on the structure and properties of pseudo-alloy steel – copper alloy obtained by infiltration

The paper presents the results of studies of the effect of heat treatment regimes on changes in the structure and properties of steel-copper alloy pseudo-alloys obtained by infiltration. It is shown that, depending on the composition and initial density of the steel skeleton, the strength of the material increases by 1.3–1.8 times, the hardening effect is realized when the carbon content in the steel skeleton is 0.3–1.5 % and is achieved due to changes in the structure and phase composition of the steel base and copper phase. It has been established that during heating for quenching and during tempering, redistribution of carbon occurs in the iron phase, which is more pronounced in the frame of the pseudo-alloy made of medium-carbon steel. The formation of a “crust” structure in the grains of the skeleton is noted, while in the skeleton made of medium-carbon steel this occurs at a tempering temperature of 200 °C, in low-carbon steel – at a temperature of 500–650 °C. In a high-carbon steel skeleton, carbon stratification in the grain body is less pronounced. An increase in the strength of pseudo-alloys at tempering temperatures of 500–650 °C is associated with the formation of the α′-phase, the precipitation of the Fe3C carbide phase and the metastable Fe2C phase in the iron phase, as well as the precipitation of dispersed phases Fe4Cu3, Fe4Cu3, η-Cu6Sn5 and δ-Cu3Sn8 in the copper phase. Due to the precipitation of phases, the microhardness of the infiltrate in the form of copper in pseudo-alloys after tempering at 550 °C increased from 820–880 to 950–980 MPa, in the form of tin bronze – from 1450 to 1750 MPa. The use of heat treatment leads to an increase not only in the strength, but also in the tribotechnical properties of the pseudo-alloy: the friction coefficient of the pseudo-alloy with a frame of 80 % density made of FeC0.8 steel decreases to 0.008–0.009, the seizure pressure doubles and the wear resistance increases by more than 2.5 times.

Investigation into the Peculiarities of Structure Formation and Properties of Copper-Based Powder Pseudoalloys Modified by ZnO and TiN Nanoparticle Additives

Comprehensive investigations into Cu–ZnO (nano) and Cu–TiN (nano) copper-based materials by standard methods in combination with metallographic and electron microscopy investigations using energy-dispersive and thermal analyses make it possible to identify stable correlation relations between the content of nanoparticle additives, microstructural parameters, and mechanical-and-physical properties of pseudoalloys. Process procedures of increasing the distribution uniformity of modifying additives of ZnO and TiN nanoparticles over the pseudoalloy bulk excluding their conglomeration are developed and substantiated. Novel original methods of nanoparticle introducing into a matrix material in the form of a master alloy made of Cu–Al–ZnO or copper powders coated with TiN nanoparticles are proposed. A high specific surface and reactivity of nanopowders make it possible to lower the ceramic phase in electrocontact materials (down to 2.0–3.0% instead of 10–15% when compared with known commercial brands). This results in the conservation of the main properties characteristic of the matrix material (copper) such as thermal and electrical conductivity at a rather high level, while the general level of physicomechanical characteristics (hardness, strength, and wear resistance) and operational properties of composite pseudoalloys simultaneously increases. The main characteristics of copper-based composite materials are as follows: electrical resistance (ρ = 0.025 μΩ m), bonding strength to the contact support material (σ ~ 2 MPa), and dispersed ceramic phase inclusions. They reduce the electroerosive wear (up to a factor of 2.5) when compared with conventional materials.

INVESTIGATION OF STRUCTURE FORMATION FEATURES AND PROPERTIES OF COPPER-BASED POWDER PSEUDOALLOYS MODIFIED BY ZnO AND TiN NANOPARTICLE ADDITIVES

The multi-method investigation of Cu–ZnO (nano), Cu–TiN (nano) copper-based materials using standard mechanical testing methods along with metallographic, electron-microscopic research using energy-dispersive and thermal analysis allowed to identify stable correlative relationships between the content of nanoparticle additives, microstructure parameters and mechanical-and-physical properties of pseudoalloys. Processing technologies are suggested and justified to improve the uniform distribution of ZnO and TiN modifying nanoparticle additives over the pseudoalloy volume eliminating their conglomeration. The paper proposes novel original methods of nanoparticle introduction to the matrix material as master alloys of Cu–Al–ZnO or copper powders coated with TiN nanoparticles. High surface area and reactive capacity of nanopowders provides for reduced ceramic phase in electrocontact materials (down to 2,0–3,0 % instead of 10–15 % compared with known commercial ones). In this way, general properties typical for matrix materials (copper), i.e. heat and conductivity, remain significantly high, and at the same time, the general level of mechanical-and-physical properties of composite pseudoalloys such as hardness, strength and wear resistance as well as their operational properties is increased. Main properties of copper-based composites include resistivity (ρ ~ 0,025 μΩ·m), strength of bonding to Тугоплавкие, керамические и композиционные материалы 20 Известия вузов. Порошковая металлургия и функциональные покрытия  4  2017 the contact support material (σ ~ 2 MPa), dispersed ceramic phase inclusions that reduce electroerosive wear (2,5 times) in comparison with conventional materials.

Effect of steel skeleton composition on the triboengineering properties of steel-copper pseudoalloys produced by infiltration

The effect of the composition of the skeleton made from steel powder on the triboengineering properties of pseudoalloys produced from copper alloy infiltration is analyzed. It is established that the steel-copper pseudoalloys possess a low friction coefficient depending on the concentration of graphite and additives of solid greases in the steel skeleton and on its original density. Higher copper phase concentration in the pseudoalloys boosts their heat conductivity and alters the structural morphology, thus promoting the triboengineering properties.

Calculation of the thermophysical properties of tungsten-copper pseudoalloys

In the calculation of the thermophysical properties of the pseudoalloy it is necessary to take into account its porosity, which is determined by the structure of its tungsten skeleton and by the difference in the coefficients of thermal expansion of W and Cu. The thermal conductivity of the TCPA depends only on the amount of copper in it, and not on the latter's character of distribution. A continuous Cu structure may form in the TCPA at a volume copper content as low as 12%.

Tungsten carbide pseudoalloys and their potential applications

An investigation was carried out into the effect of composition on the structure and some properties of pseudoalloys based on tungsten carbide. It was established that Group VIII elements and oxides increase the short-time hot hardness. and oxidation resistance of WC-Cu composites in the temperature range 300–800°C. Pseudoalloys based on tungsten carbide possess adequate ductility: Their tough-to-brittle transition occurs at subzero temperatures. The loss of ductility exhibited by the pseudoalloys is due to the low strength of their phase boundaries and tungsten carbide grain boundaries in agglomerates. Electrodes made in these pseudoalloys have excellent processing properties and long life in contact welding, and may be recommended for extensive trials under larger-series production conditions.