On microstructure and fatigue characterisation of cast iron alloyed with PTA deposits

Abstract

In this paper, TiC–W–Cr powders were alloyed on grey cast iron by plasma transferred arc (PTA). The alloying samples were characterised with reference to the microstructure, microhardness, fatigue life and fatigue crack growth. From the results, it is indicated that two distinguishing region, i.e. alloying zone and heat affected zone, were formed on the surface after PTA alloying. The alloying zone mainly consists of primary austenite, martensite, a eutectic of (Fe,Cr)₇C₃ carbide and austenite as well as the uniformly distributed unmelted TiC particles. Plasma transferred arc alloying TiC–W–Cr eliminated the stress concentration at the edge of graphite and produced hard carbide, resulting in frequent crack deflection. As a result, the Weibull distribution of fatigue life demonstrated that PTA alloying TiC–W–Cr exhibited longer lives compared to matrix and PTA hardening without reinforcement, but more scattered. In addition, on the basis of the careful observation of fatigue crack growth, it was shown that the fatigue crack growth rate could be retarded by PTA alloying TiC–W–Cr at a low stress intensity, but speeded up at high stress intensity due to the brittleness.