Creep of un-doped and Cr-doped WC-Co at high temperature and high load
M.A. Yousfi, A. Nordgren, Susanne Norgren, Jonathan Weidow, H.-O. Andrén, L.K.L. Falk
Abstract
Un-doped and Cr-doped WC-10 vol% Co cemented carbides with a WC grain size of 1.4 μm have been investigated before and after hot compressive creep tests under an applied load of 900 MPa at 1000 °C and 300 MPa at 1100 °C. The Cr-doped material showed a much higher creep resistance at 1000 °C and a somewhat higher creep resistance at 1100 °C than the un-doped material. Quantitative microscopy showed that WC grain growth occurred in the plane perpendicular to the load axis during creep deformation and that the growth process was slower in the Cr-doped material. In addition, binder phase redistributed and a number of WC grain boundaries were infiltrated with binder phase. This suggests that accommodated WC grain boundary sliding occurred during creep deformation. The formation of intergranular cavities implies that also unaccommodated grain boundary sliding occurred, especially at 1000 °C. It is suggested that WC grain growth perpendicular to the load axis is rate limiting in the creep deformation process, and that Cr segregation to WC/binder phase boundaries hinders grain growth. The weak effect of Cr on creep resistance at 1100 °C at 300 MPa is explained by Cr giving a larger volume fraction of binder phase and therefore a larger number of infiltrated grain boundaries, facilitating grain growth.