Consolidation of WC-Co by simple shear

Abstract

Equal channel angular extrusion (ECAE) has the capability of introducing large amounts of plastic strain into bulk material and powders in a fairly uniform way with the added advantage of no reduction in workpiece cross-section. The objective of this research is to investigate the potential of ECAE for consolidating particulate blends of tungsten carbide and cobalt. The process included two extrusions at temperatures between room temperature and 1200C̊ on 4.5inx1inx1 in pure nickel and stainless steel hollow billets containing five different stoichiometric WC-Co powders. The investigated compositions were WCxwt%Co, x = 11 and 14, with particle sizes ranging from 0.2 to 10[]m. The as-received powders, ECAE consolidated material and corresponding sintered sample were characterized for structure, particle size, impurity content, void fraction, composition and hardness. The phases and properties of the ECAE processed WC-CO materials were compared with those of conventionally sintered material and with recent literature review results, for evaluation purposes. Full formation / compaction was achieved after two extrusions at 1200C̊ and subsequent argon annealing at 1400C̊. The most important findings of this ECAE consolidation research are as follows. a) For ECAE compacted and annealed WC11wt%Co, 1% porosity, 1450 HV hardness and grain sizes of 1.6 am were observed and compared with 7.5% porosity, 1320 HV and 2.01 []m grain size for the conventionally sintered sample. b) For submicron WC14w1%Co starting powder samples, ECAE consolidation and annealing produced materials with an average grain size of 1.1 []m, 2% porosity and 1650 HV hardness. c) Formation / consolidation of MA W+C+Co metal powders produced cemented carbides with an average hardness of 1350 HV. d) The creation of substructure during these high temperature extrusions is indicated with particle refinement and no significant grain growth for most samples. e) MA of elemental WC-CO powders does not appear to improve consolidated properties. These results compare favorably with most studies in the current literature. The above findings corroborate that ECAE can successfully consolidate WC-CO powders into hard and strong cemented carbides of interest to the cutting tool and the oil field industry.