Abstract

OLIVEIRA, F.A. Costa et al. Fracture behaviour of a new submicron grained cemented carbide. C.Tecn. Mat. [online]. 2008, vol.20, n.1-2, pp.52-59. ISSN 0870-8312.

In this work, the effect of increasing argon pressure applied on a post-sintering treatment from 3 MPa to 100 MPa on the mechanical properties of a newly developed hardmetal grade, namely, hardness, flexural strength and fracture toughness, is reported. The as-received material has been previously sintered at 1460ºC under 2 MPa argon pressure from powder mixtures of WC and 3.5 wt% Co together with minor additions of VC, graphite and a pressing lubricant. By increasing the argon pressure, a significant increase in flexural strength from » 1500 MPa to » 3000 MPa was observed, whilst hardness (HV30»2000) and fracture toughness (»8 MN.m^-3/2) remained practically unchanged. Both microstructural and fractographic studies revealed that this is mainly attributed to a decrease in the amount and size of microstructural defects (namely, pores and metallic inclusions). Furthermore, fracture has been found to occur mainly by intrinsic (bulk) defects rather than surface-related ones, suggesting that surface finishing did not affect flexural strength measurements. Hot isostatic pressing has been successfully used to consolidate WC-3.5wt% Co composites with submicron WC grains size confirming that porosity reduction results in flexural strength improvement.

Keywords : Hardmetal; Flexural strength; Fractography; Fracture toughness; Microstructure.

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