Microstructural evolution of titanium carbonitride based materials during oxidation

Ti(C, N) based materials represent a new class of hard and wear resistant structural materials. Nowadays, the main field of applications is focused on metal cutting and finishing operations. For these kinds of applications usually the mentioned materials work in oxidizing environments at high temperatures. The thermophysical stability under these conditions represents therefore a key factor that influences the materials performance, and consequently the tool life of the component in service. The present study aimed to investigate the oxidation behavior of two different Ti(C, N)-WC based materials, the first containing 0.9 wt% of Co and the second 6.2 wt% of Ni and 2.9 wt% of Co. Cycled oxidation tests (20 hours each) were conducted with a muffle furnace in laboratory static air at 1000 oC up to 100 hours. During the initial transitory stage the competition between the mass gain due to the formation of solid TiO2 (rutile) and the mass loss due to released volatile W oxides controlled the mass change; thereafter the oxidation process obeyed a linear law. Great microstructural modifications occurred an the (sub)surfaces of the oxidized samples: multiphase TiO2 based scales grew upon the external surfaces of the oxidized specimens. Kinetics and oxidation mechanisms were proposed and discussed. (author)