Ultrashort-time liquid phase sintering of high-performance fine-grain tungsten heavy alloys by laser additive manufacturing

Abstract

Liquid phase sintering (LPS) is a proven technique for preparing large-size tungsten heavy alloys (WHAs). However, for densification, this processing requires that the matrix of WHAs keeps melting for a long time, which simultaneously causes W grain coarsening that degenerates the performance. This work develops a novel ultrashort-time LPS method to form bulk high-performance fine-grain WHAs based on the principle of laser additive manufacturing (LAM). During LAM, the high-entropy alloy matrix (Al0.5Cr0.9FeNi2.5V0.2) and W powders were fed simultaneously but only the matrix was melted by laser and most W particles remained solid, and the melted matrix rapidly solidified with laser moving away, producing an ultrashort-time LPS processing in the melt pool, i.e., laser ultrashort-time liquid phase sintering (LULPS). The extreme short dwell time in liquid (~1/10,000 of conventional LPS) can effectively suppress W grain growth, obtaining a small size of 1/3 of the size in LPS WHAs. Meanwhile, strong convection in the melt pool of LULPS enables a nearly full densification in such a short sintering time. Compared with LPS WHAs, the LULPS fine-grain WHAs present a 42% higher yield strength, as well as an enhanced susceptibility to adiabatic shear banding (ASB) that is important for strong armor-piercing capability, indicating that LULPS can be a promising pathway for forming high-performance WHAs that surpass those prepared by conventional LPS.