Temperature Dependences of Static Mechanical Properties of an MDK-3 Laminated Composite

Abstract

The structure, hardness, strength, and plasticity of a laminated composite nanomaterial of the copper-zirconium-yttrium-molybdenum system obtained by electron-beam evaporation and layered vapor condensation over a temperature range of 290-1070 K are studied. Correlation between the hardness and strength of the composite was established.Introduction. Nowadays laminated composites based on copper, molybdenum, and rare earth metals are used more and more extensively as electrocontact materials for heavy-duty switching devices. These materials are formed by high-rate vacuum evaporation and condensation of a mixed vapor flow on a rotating disk. Such a composition determines their unique physicomechanical and operating properties. Dispersion-hardened MDK composites of the Cu-Zr-Y-Mo system (TU U 20113410.001-98) with molybdenum contents from 2.5-5.0 to 8.1-12.0 wt% and the total zirconium and yttrium contents no more than 0.8 wt% are currently manufactured at Gekont Science&Technology Company (Ukraine) [1][2][3][4].In operation, the materials of contacting pairs in high-current switching devices are subjected not only to corrosion and electrical erosion but also to mechanical loads at elevated temperatures. Therefore, studies on their mechanical properties over operating temperature ranges are of definite scientific and practical interest.The present publication covers data on experimental investigations of the structure, strength, hardness, and plasticity of the most promising laminated composite MDK-3 with a molybdenum content of 11 3 0 2 . . ± wt% over a temperature range of 290-1070 K.Test Methods. The structure of the composite material was investigated by optical and scanning electron microscopy. Mechanical characteristics were determined from the results of tensile tests in vacuum on standard sheet specimens with a 15-mm calculated test portion using a 1246-P unit [5] according to . The specimens were cut from the prepared composite 0.9-1.4 mm thick as-received (after vacuum annealing at 1170 K for 3 h). The tests were performed on 3-6 specimens at 100 K intervals. Their deformation rate was 2 mm/min, which corresponded to a relative strain rate of~. 2 2 10 3 1 ⋅ − − s . During the tests deformation diagrams were recorded to determine the yield strength σ 0 2 . , the ultimate strength σ u , the elongation δ, and the uniform elongation δ u . Moreover, the reduction of cross-sectional area ψ was evaluated.Hardness was estimated by Vickers indentation. The pyramidal point was made of a synthetic corundum single crystal. Indentation loads were 10 N. The tests were carried out in vacuum at a pressure no more than 0.7 MPa on a UVT-2 unit [7] according to DSTU 2434-94 [8].Experimental data were statistically processed. The average sample value (mathematical expectation) x, the sample standard deviation S, the coefficient of variation w, and the confidence limits Δx for the mathematical expectation were calculated at a significance level of α = 0 05 . .

Relationship between composition, structure, and mechanical properties of a condensed composite of copper–tungsten system

“…For a copper-molybdenum condensed composite material MDK-3 with a microlayered gradient structure the hot brittleness takes place in the temperature range between 770 and 970 K [21]. As evident from the data given in Table 2 for T = 870 K, the strength characteristics of the copper-tungsten composites at hand grow, which is 431 attributable to an increase in the tungsten content in the range 5-35 wt.%, the improvement being 1.3-2.0 times that for the composite at room temperature (Table 1).…”