Study of high-temperature deformation features of binderless tungsten carbide with various initial particle size

Abstract

The mechanism of high-temperature creep deformation during compression tests of binderless tungsten carbide specimens with different initial particle size was studied. Tungsten carbide samples with high relative density (96.1 – 99.2 %) were obtained by high-speed spark plasma sintering (SPS) from nano-, submicron-, and micron-sized α-WC powders. The creep tests were carried out in two modes: isothermal soaking at different temperatures (1300 – 1375 °C) at a given stress, allowing to estimate the activation energy of creep, and tests by “stress jumps” at 1325 °C, allowing to estimate the value of the coefficient n in the creep equation. It is shown that the value of creep activation energy in ultrafine grained tungsten carbide with grain size ~ 0.15 µm sintered from plasma chemical nanopowders is ~ 31 kTm. This value is 1.5 – 2 times higher than the creep activation energy in fine-grained tungsten carbide samples obtained by SPS from submicron (~ 0.8 μm) and micron (~ 3 μm) industrial powders. It was found that the value of the coefficient n varies from 2.4 to 3.1, which corresponds to the case of motion of lattice dislocations in the field of uniformly located point obstacles. It has been suggested that one of the reasons for the increase in creep activation energy in tests of tungsten carbide is an increased volume fraction of W2C low carbide particles formed during high-speed sintering of plasma-chemical α-WC nanopowders with an increased concentration of adsorbed oxygen.