Friction and wear characteristics between cermet alloy and cast iron (Part 4): On the effect of N content of TiCN in a cermet alloy

Effects of N element content in TiCN cerment chips on frictional wear behavior by sliding them against FC250 cast iron roller have been investigated in air under without lubricated conditions. The mass% of TiN in TiCN cermet (= TiN_FR), which is proportional to N content in TiCN, was varied between from 0 % to 50%. The friction wear tests were performed under the following conditions: a normal load of 40 N, a sliding speed of 0.1 ms^-1, and a total sliding distance of 2000 m. The humidity condition inside of a testing machine chamber was changed in three ranges of about 20%, 30-50% and over 95%. Basically, the microstructure of the TiCN cermet chips was composed of three phases of core, rim, and Ni binder. However, in the cermet of TiN_FR = 0%, the remarkably coarse (W,Ti) C rim phases were formed during sintering and the fine TiC core and binder phases were segregated between these large rims. With addition of N element, the growth of the rim structure was suppressed. Thus, a uniformly mixed fine microstructure of TiCN core, (W, Ti)(C, N) rim and Ni binder phases was obtained in the cermet of TiN_FR = 25%. However, the further increase of TiN_FR resulted the distribution of W₄Ni₂C compound particles, which were formed by consumption of Ni binder. The amount of wear of TiCN chip (W₁,) was remarkably decreased with increasing of the humidity irrespective of the value of TiN_FR due to the lower friction coefficient. Furthermore, the cermet of TiN_FR = 25%, which has the fine and uniform three phase microstructure, showed the lower W₁, value irrespective of the humidity condition. The amount of wear in FC250 cast iron roller was increased during sliding against the cermet of TiN_FR higher than 25% at the three humidity conditions. As a result, the cermet of TiN_FR = 25% was considered to be better sliding materials against cast iron. The EPMA analysis showed the adhesion of wear debris including Ni and Fe elements on the friction surfaces of both chip and roller. The wear mechanisms for these cermets were discussed on the basis of wear surface microstructure considerations.