Enhancement of mechanical properties of Os0.9Re0.1B2 ceramics via buried boron powder assisted sintering

Abstract

Abstract As a new type of hard/super-hard materials, the consolidation of transition metal borides is very critical for obtaining bulk ceramics with excellent properties. In the present work, buried boron powder assisted pressures-less sintering was applied for preparation of Os 0.9 Re 0.1 B 2 ceramics with the aim for mechanical properties improvement. Os 0.9 Re 0.1 B 2 powders were firstly synthesized via mechanochemical technique with moral ratios of (Os + Re):B = 1:2.5 and 1:2.25, respectively. Bulk samples were then consolidated using buried powder sintering and exposed sintering, respectively, for comparison. The influence of buried boron powder sintering on the phase composition, microstructure, and mechanical properties (micro-hardness, nano-hardness, and Young's modulus) of Os 0.9 Re 0.1 B 2 ceramic samples were investigated. The results show that by employing buried powder sintering, B powders surrounded the sample during the sintering process, which on the one hand, inhibited decomposition of Os 0.9 Re 0.1 B 2 to (Os 0.9 Re 0.1 ) 2 B 3 , while on the other hand, decreased the grain size of the sample. Further, a columnar to equiaxial transition for the grains was found with grain size decreased when (Os + Re):B = 1:2.25. The samples prepared with buried powder sintering have higher mechanical properties as compared with those prepared with exposed sintering. The sample prepared from (Os + Re): B = 1:2.25 by buried powder sintering had the best mechanical properties among the four studied samples, along with the smallest grain size. The mechanical properties of the samples were greatly influenced by the grain size and relative density.