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ith the aim of investigating the evolution of the substructure, the rolling of a steel strip containing 0•13%C, 0•75%Mn, and 0•048%Nb (all wt-%) was interrupted and the partially rolled strip water quenched. Using X-ray diVraction spectra, subgrain size and dislocation density were determined for specimens taken before and after the rolling passes. Both these microstructural characteristics were related to the rolling temperature and the amount of NbC precipitation. T he distribution of precipitates was investigated via T EM. At lower rolling temperature, particles precipitated in rows in the austenite temperature range.MST /3964

We investigate the structure, hardness, strength, plasticity and fracture character of Cu-Cr microlayer composite material for electric contacts with prescribed microlayered structure and chemical composition in the temperature range from 290 to 1070 K. The correlation relationships between the hardness and strength characteristics have been established. Notation σ u -ultimate strength, MPa σ 0 2 . -offset yield stress, MPa δ -relative elongation, % δ pr -relative uniform elongation, % ψ -reduction of the cross-sectional area, % HV -Vickers hardness, MPa T -thermodynamic temperature, K U -plastic strain activation energy (enthalpy), eV ′ A -constant characterizing the material and strain rate c -proportionality factor, c H = σ H -hardness, MPa σ -characteristic of strength, MPa k -the Boltzmann constant G -shear modulus, MPa HV m -mean value of Vickers hardness, MPa S -root-mean-square deviation, MPa w -coefficient of variation, % ΔHV -reliable estimate at a 0.95 confidence level, MPa a b , -regression coefficientsIntroduction. Copper and chrome composites are widely used as the most efficient electric contact materials for arcing contacts of arc-extinguishing chambers in vacuum circuit breakers. In addition to the conventional methods of powder metallurgy, these materials are produced by high rate electron-beam evaporation/condensation of copper and chrome from separate water-cooled crucibles and layer-by-layer condensation on a metal substrate (a rotating steel disc). The electron-beam physical vapor deposition (EBPVD) technology makes it possible to produce, within one production cycle, sheet copper-chrome composite materials with a given microlayer structure and chemical composition, and condensates with the content of gaseous impurities no higher than that in the initial material, even in the case of evaporation of active metals such as chrome. One more peculiar feature of this method is that it allows the creation of combined contacts with a working layer of an arc-extinguishing composite material obtained by physical vapor deposition, which is cohesive with the copper substrate that provides heat removal from the working layer.The optimum content of chrome in these composites that provides the most favorable combination of electrical, mechanical and chemical characteristics of the material is from 30 to 40 mass%, the tensile strength of composites being 400 to 550 MPa, hardness from 1600 to 1800 MPa, and the resistivity not exceeding 2 5 10 8 . ⋅ − Ω ⋅ m. A high-temperature annealing of the condensed materials Cu-(30 to 40 mass%) Cr is responsible for the decrease in their strength and resistivity down to 30%, but, in fact, does not influence the hardness. Owing to the specific structure of these materials, their unique physico-mechanical and operating characteristics are formed. At present, condensed Cu-Cr microlayer composite materials have been produced as pilot lots by the "Gekont" Research and Production Enterprise (Vinnytsya, Ukraine) [1][2][3][4][5][6][7].In the process of operation, materials of co...

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Experimental data on high-temperature mechanical properties under uniaxial tension of commercially pure tungsten obtained by powder metallurgy have been analyzed. It has been found that for powder metallurgy tungsten in the high-temperature region~, (0.5 0.8) − T melt there is a close correlation among the characteristics of short-and long-term static strengths and creep resistance, which are described by a single functional relation. Introduction.The progress in a number of branches of modern engineering is related to the use of refractory metals and alloys, which can ensure strength of components and structural elements operating under conditions of extremely high temperatures (up to 2300-3300 K) and mechanical loads. Tungsten and tungsten-based alloys have the most unique range of physico-mechanical characteristics including heat resistance [1][2][3].In addition to short-term strength, the characteristics of long-term static strength and creep are the most important factors characterizing serviceability of metals at high temperatures. Complete experimental evaluation of such characteristics for refractory materials presents great difficulties and is unrealistic in many cases.It is known that temperature dependences of various mechanical characteristics that determine the resistance of metallic materials to deformation are qualitatively similar. Under short-term and long-term static loading, there are correlation dependences between strength characteristics of metals and alloys, which can be described by certain analytical expressions based on both empirical and physically justified approaches. They are undoubtedly of scientific and practical interest, because they make it possible to evaluate heat-resistance characteristics of advanced structural materials at minimum cost [4,5].In the present study, based on the analysis of experimental data obtained earlier, a generalized correlation dependence has been established between the characteristics of high-temperature short-term and long-term static strength and creep resistance of commercially pure tungsten produced by powder metallurgy (PM) technique.Theoretical Background. On the basis of numerous experiments it has been found that temperature dependence of any mechanical characteristics, which determine the resistance of metallic materials to deformation, is described quantitatively by the following equation [4]: