Nanostructured Gradient Material Based on the Cu–Cr–W Pseudoalloy Fabricated by High-Energy Ball Milling and Spark Plasma Sintering

Abstract

Nanostructured mechanical composites of immiscible metals Cu, Cr, and 5–70 wt % W; nanostructured consolidated materials based on them; and Cu/Cu–Cr–W nanostructured gradient material with various W contents are fabricated in this work by combining short-term (up to 150 min) high-energy ball milling (HEBM) and spark plasma sintering (SPS). To fabricate Cu–Cr–W mechanical composites, HEBM of Cu + Cr + (5–70 wt %)W is performed using an Activator-2S planetary ball mill with a revolution rate of drums of 1388 rpm and a planetary disc of 694 rpm in argon for 150 min. The Cu–Cr–W mechanical composites are consolidated by SPS at temperatures of 800–1000°C and pressure of 50 MPa for 10 min. The nanostructured gradient sintered material based on Cu–Cr–W pseudoalloys is compacted layer-by-layer in the following sequence (from pure copper to pseudoalloy with an increase in the tungsten weight fraction): 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 mechanical composites and consolidated materials based on them are investigated depending on fabrication conditions. It is shown that the nanostructure formed in mechanical composites at the short-term HEBM stage (up to 150 min) is retained after SPS for all Cu–Cr–W (5–70 wt % W) compositions. The SEM and EDS data evidence that W (d ~ 20–100 nm) and Cr (d ~ 20–50 nm) refractory particles are homogeneously distributed in the material bulk (in a copper matrix). The hardness of consolidated Cu–Cr–W samples (15 wt %) formed from nanostructured powder mixtures (after 150-min HEBM) by SPS at t = 800°C exceeds the hardness of samples sintered from the mixture of initial components (without HEBM) by a factor of ~6. The hardness for the nanostructured Cu–Cr–70% W composition (t_SPS = 1000°C) is higher by a factor of ~3 than for microcrystalline analogs. Samples Cu–Cr–15% W and Cu–Cr–70% W have the largest relative density up to 0.91. The resistivity of nanostructured Cu–Cr–W compositions exceeds this characteristic for microcrystalline samples approximately twofold. This can be caused by an increase in grain boundaries and the accumulation of various defects in the material at the HEBM stage. These results show the prospects of using the combination of short-term HEBM and subsequent SPS for the formation of consolidated nanocrystalline Cu–Cr–W composites and gradient materials based on them.