Preparing CuCr Pseudoalloys by the Deposition of Copper from a Solution onto Chromium Powders with the Simultaneous Mechanical Activation of the Mixture

Abstract

CuCr composite particles have been obtained using copper deposition from the solution of its sulfate onto chromium powder particles with the simultaneous mechanical activation (MA) of the mixture in an AGO-2 planetary ball mill for 5 min. The CuSO 4 ·5H 2 O concentration in the solution with complete copper reduction provides a molar ratio of Cu/Cr = 1. Since deposited fine crystalline copper is highly active and rapidly oxidizes to Cu 2 O oxide in air, the composite powders are washed, dried, and stored in an argon atmosphere. After drying, the mixture is subjected to additional MA for 5 min. During MA, composite particles with a laminate structure start forming in the solution. The powders are used to press tablets with a diameter of 3 mm, height of up to 1.5 mm, and density of 4.2–4.5 g/cm 3 . Samples are sintered in an argon atmosphere at 700–1400°С. To compare microstructures, we have also sintered samples from mixtures of Cr and Cu metal powders with a volume ratio of chromium to copper of 50 : 50, which were obtained by simple mixing in a porcelain mortar for 20 min and MA for 10 min. Three regions of the alloy structure formation can be distinguished depending on the heating temperature. When temperatures are heated below the eutectic melting point, composite particles are sintered at separate points. With heating temperatures above the liquidus temperature, the alloy melts with its phases separated; one part of the sample consists of copper enriched in chromium, and the other part consists of chromium enriched in copper. With intermediate heating temperatures, liquid phase sintering accompanied by phase separation is observed. Copper-enriched chromium particles become spherical and are located in a chromium-enriched copper matrix. A comparison of samples sintered under the same conditions from powder mixtures obtained by different methods showed that samples with deposited copper have a more uniform and fine-grained structure.