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...

For a copper-tungsten microlayered composite material for electrical contact applications, which is prepared by electron-beam evaporation-condensation, the changes in its structure, conductivity, hardness, and mechanical properties in tension at room temperature and elevated temperatures are studied versus the tungsten content and heat treatment conditions. New morphological features of the condensed composite and the related changes in the material properties have been revealed. The conditions for the formation of structural defects and their influence on mechanical properties and fracture behavior of the material in tensile tests have been investigated. A relationship has been established between the tungsten content of the composite, its structure, strength, and hardness.Introduction. The present-day composite materials (CM) based on tungsten and copper were developed in the second half of the 20th century. These pseudoalloys which are usually prepared by powder metallurgy (PM) methods have been widely accepted for electrical, structural, and special applications. Despite a long-term experience of using these materials, the research efforts in this field are still pursued, which is due to an extension of technological potentialities for controlling the CM composition, dispersion, distribution of the refractory component inside the product, etc. [1][2][3][4][5][6][7]. Considering that electrical and thermal conductivities of tungsten are lower than those of pure copper, there arises the necessity to search for technological possibilities of producing combined products. In these products the Cu-W composite is used only for facing the contact components of electrical switchgear, which significantly changes the components' functionalities. The implementation of the combined product design presents some difficulties for the quality of the copper body/composite facing interface has to be thoroughly inspected. These difficulties as well as the necessity to separately prepare the facing and the contact component can be in some cases eliminated owing to the use of a technology with provides microlayer gradient composites.Fundamentally new possibilities for the production of these materials have arisen owing to the development of electron-bean units and the elaboration of a process of high-rate electron-beam evaporation of the CM components from separate water-cooled crucibles with subsequent layer-by-layer condensation of the mixed vapor flow onto a metal substrate [8][9][10][11][12]. The main and undeniable benefits offered by the electron-beam technology which provides new-generation electrical-contact composites based on copper and refractory metals are as follows:(i) the possibility of atomic-and molecular-level mixing of vapor flows of substances that have a limited mutual dissolubility and producing composite materials and coatings with a preset structure, chemical composition, physical-mechanical properties and performance, which cannot be achieved by any other available methods; 426 0039-2316/11/4304-0426 (ii) ...

A procedure and experimental equipment are developed to perform small punch testing of miniature disk specimens. The procedure is experimentally tested on specimens of 45 steel. A comparative analysis is made of the known procedures for determining the yield stress from the small punch load-displacement curves for miniature disk specimens.Keywords: small punch testing of miniature disk specimens, stress-strain curve, yield stress. Introduction.The method of small punch testing of miniature disk specimens, known as small punch test (SP-test), is based on the recording of the ball punch deformation of a miniature disk specimen (SP disk microspecimen) rigidly fixed along the perimeter in a special device in the coordinates of the load applied to the ball vs depth of punch indentation in the SP disk microspecimen.This method, in its essence, is similar to the method of instrumented indentation test. The difference is that the latter method refers to the nondestructive test methods, whereas the SP-test method requires special disk-shaped specimens whose geometry and surface roughness have to meet rather severe requirements. It is advisable to use this method if traditional tensile tests according to the standard GOST 1497-84 [10] are impossible because of the necessity of preparing specimens from miniature cut-outs. In the world practice, the method of punching SP disk microspecimens is used to determine the characteristics of strength s u , s 0 2 . [2-9] and fracture toughness J c I , K c