Graded Ti(C,N)-based cermets fabricated by mechanical activation and in situ carbothermal reduction: Investigation of nitrogen sintering pressure on microstructure and mechanical performance

Abstract

Ti(C,N)-based cermets with a surface graded layer were obtained by nitrogen sintering under different nitrogen pressures at temperatures from 1300 to 1400 °C. The influence of nitrogen pressure in the range of 50–250 mbar on microstructure and mechanical performance of cermets were then systematically investigated and it was found that coarser solid solution grains formed at the surface of the cemets after sintering the Ti-rich and Ni-poor graded layer. Furthermore, tending with increasing nitrogen pressure, the overall grain sizes and surface region of the cermets became finer, and the surface graded layer thickness increased (the thickest graded layer was 194 μm). The formation of the graded layer and the increase in the thickness of the graded layer were all attributed to the high nitrogen activity on the surface during sintering. Moreover, nitrogen sintering allowed the Ti(C,N)-based cermets to increase the surface hardness of the cermets with a lesser reduction in strength. The maximum surface hardness and TRS (Transverse Rupture Strength) value of cermets after nitrogen sintering was about 14 GPa following a nitrogen pressure of 150 mbar, and 2267 MPa following nitrogen pressure of 100 mbar.