Fracture resistance and contact damage of TiN particle reinforced Si 3N4 ceramics

Abstract

The R-curve behavior, spherical Hertzian contact damage and cyclic contact damage of a bearing grade Si3N4 ceramic reinforced with TiN particle dispersion are investigated and compared with the performance of a reference Si3N4 ceramic without TiN but with a similar microstructure. These ceramics were produced by firing powder compacts of Si3N4, Y2O3 and Al2O3, with and without additional AlN and TiO2, at 1800°C for 2 h in 0.9 MPa N2, followed by hot isostatic pressing at 1700°C. The ceramic without TiN has an R-curve with an initial value around 5.5 MPam 1/2, which slowly rises to 6.5 MPam1/2 after a crack extension of 300 μm. In contrast, the Si3N4 ceramic with TiN particles has a higher initial KR value but the R-curve remains relatively flat during subsequent crack growth. The latter ceramic exhibits a higher critical stress for permanent deformation and for ring-crack formation on the indented surfaces. It also demonstrates a better retention of the residual strength after single and repeated Hertzian indentation. The superior performance of the TiN-reinforced ceramic is attributed to the strengthening of grain boundary by TiN particles. Specifically, the resistance against contact and fatigue damage of this bearing grade Si3N 4 is explained in terms of the effect of high grain boundary strength on the R-curve behavior, grain boundary microcracking, and the balance between crack shielding accumulation and degradation by grain boundary sliding during cyclic loading.