Microstructural and texture evolution of copper-(chromium, molybdenum, tungsten) composites deformed by high-pressure-torsion

Julian M Rosalie,Pradipta Ghosh,Jinming Guo,Oliver Renk,Zaoli Zhang

doi:10.1016/j.ijrmhm.2018.04.008

Abstract

Cu-refractory metal composites containing Cr, Mo or W were subjected to severe plastic deformation using room temperature high-pressure torsion (HPT). A lamellar microstructure developed in each of the composites at equivalent strains of ∼75. The refractory metals developed {hkl}⟨111⟩ fibre textures with a slight tilt to the tangential direction. This texture was stronger and more clearly defined in Mo and W than in Cr.By applying additional HPT deformation to these samples, perpendicular to the original shear strain, it was found that the lamellar structure of Cu30Mo70 and Cu20W80 (wt%) composites could be retained at high equivalent strains and the refractory layer thickness could be reduced to 20–50 nm in Cu20W80 and 10–20 nm in Cu30Mo70. Although neighbouring regions of the microstructure were aligned and there was evidence of local texture in both composites, the bulk texture of Cu30Mo70 became weaker during this second step of HPT deformation. This was attributed to the refractory metal lamellae being discontinuous and imperfectly aligned.This work shows that it is possible to form ultrafine composites of Cu-group VI refractory metals via high-pressure torsion, with namolamellar structures being possible where there is a sufficient volume fraction of Mo or W.

Highlights

Copper-refractory metal composites are important industrial materials consisting of varying proportions of copper and one or more of the refractory metals, namely Nb, Ta, Cr, Mo, W and Re
The Cu20W80 composite was harder than Cu30Mo70 in the as-received condition, the latter composite became substantially harder after high-pressure torsion (HPT) deformation, owing to more extensive microstructural refinement, as is shown
Each of the refractory metal composites developed a lamellar structure during step 1 HPT deformation, with the refractory layer spacing ranging from 400 nm (Cu30Mo70) to 1.3 μm (Cu57Cr43) at ǫ ∼75 (See Table 3)

Summary

Introduction

Copper-refractory metal composites are important industrial materials consisting of varying proportions of copper and one or more of the refractory metals, namely Nb, Ta, Cr, Mo, W and Re. The high melting points (from 1907◦C(Cr)– 3422◦C (W))[5] and low thermal expansion coefficients (4.5–7.3 μm m−1 K−1)[6] of the refractory elements provide the required high temperature strength and dimensional stability. Nanostructured forms of these composites have been produced by severe plastic deformation (SPD). The ability to develop nanolamellar composites of refractory elements in Cu matrix will open-up the possibility for developing high strength, tough and thermally stable components for high temperature applications

Results

Discussion

Conclusion