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The creep mechanism in the compression testing of the tungsten carbide withdifferent grain sizes has been studied. The WC samples with high density(96.1-99.2%) were obtained by SPS from nano-, submicron, and micron-grade WCpowders. The samples had a coarse-grained (CG) surface layers of ~0.3 mm inthickness and ultrafine-grained (UFG) central parts consisting of WC with asmall fraction of W2C. The creep tests were conducted in two regimes: (Mode #1)holding at different temperatures (1300-1375C) at 70 MPa; (Mode #2) tests atdifferent stresses (50, 70, 90 MPa) at 1325C. Tests in Mode #1 were done todetermine the effective creep activation energy Qcr while tests in Mode #2 - todetermine the coefficient n in the power law creep equation. The increasing ofthe fraction of the W2C particles from 1.7 up to 4% was found to result in adecrease in the Qcr from 17.5 down to 13 kTm. The coefficient n equals to3.1-3.7. The Qcr in the WC sintered from nanopowders was shown to be 31 kTm.This value is 1.5-2 times greater than the Qcr in the UFG samples obtained bySPS from commercial powders. The increased fraction of the W2C formed whensintering the nanopowders with increased adsorbed oxygen concentration wassuggested to be one of the origins of the increase in the Qcr when testing theUFG samples. The mechanical removing of the CG layers from the surfaces of thetungsten carbide sample was shown to result in an accelerated creep,insufficient decrease in the Qcr and coefficient n to 2.5-2.6. The creep rateof the samples was suggested to be determined simultaneously by the creepprocess in the CG surface layers and the creep process in the UFG central partsof the samples. The creep rate in the surface CG layers is determined byintensity of carbon diffusion in the WC crystal lattice while the creep rate inthe UFG central parts - by the intensity of grain boundary diffusion.

Low-temperature creep of binderless tungsten carbide with different grain sizes