Nanostructured gradient material based on Cu—Cr—W pseudo alloy prepared by high energy ball milling and spark plasma sintering

Abstract

This study was conducted to obtain nanostructured mechanically activated composite particles from immiscible metals Cu, Cr and 5÷70 wt.% W, nanostructured bulk materials based on them and Cu / Cu—Cr—W nanostructured gradient material with different tungsten content by combined short-term (up to 150 min) high-energy ball milling (HEBM) and spark plasma sintering (SPS). Cu— Cr—W mechanically activated composites were obtained by HEBM of Cu + Cr + (5÷70 wt.%)W powder mixtures in the Activator-2S ball planetary mill at the rotating speed of 1388 rpm for the grinding chamber and 694 rpm for the planetary disk in an argon atmosphere for 150 min. Cu—Cr—W mechanically activated composite particles were consolidated by SPS in the temperature range of 800— 1000 °C at a pressure of 50 MPa for 10 min. The nanostructured gradient sintered material based on Cu—Cr—W pseudo alloys was pressed layer by layer in the following sequence (from pure copper to pseudo alloy with increasing tungsten content): Cu / Cu—Cr—5%W / Cu—Cr—15%W / Cu—Cr—70%W and sintered at 800 °C for 10 min. The crystal structure, microstructure, and properties of Cu— Cr—W mechanically activated composites and consolidated materials based on them were studied depending on production conditions. It was shown that the nanostructure formed in mechanically activated composites at the short-term HEBM stage (up to 150 min) was preserved for all Cu—Cr—W (5÷70 wt.% W) compounds after SPS. Based on SEM and EDX, refractory particles of W (d ~ 20÷100 nm) and Cr ( d ~ 20÷50 nm) were uniformly distributed in the material volume (in the copper matrix). The hardness of Cu—Cr—W (15 wt.% W) bulk samples obtained from nanostructured powder mixtures (after 150 min HEBM) by SPS at 800 °C was approximately 6 times higher than the hardness of samples sintered from the mixture of starting components (without HEBM). For the Cu—Cr—70%W nanostructured compound ( t sps = 1000 ° С ) the hardness value was ~3 times higher than that for microcrystalline analogues. The highest re­lative density of 0.91 was achieved for Cu—Cr—15%W and Cu—Cr—70%W samples. Electrical resistivity for nanostructured Cu—Cr—W composites were 2 times higher than for microcrystalline samples. Apparently, this is due to an increase in grain boundaries and various defects accumulated in the material at the HEBM stage. The obtained results show that combined short-term HEBM and subsequent SPS is a promising way to produce nanocrystalline Cu—Cr—W composites and gradient materials based on them.