Influence of post-treatment on the microstructural evolution of thermally sprayed Fe-base MMC containing TiC and Cr3C2

In this study, ledeburitic cold-work tool steel X220CrVMo13-4 (AISI D7) was admixed with TiC and Cr3C2 and the resulting feedstock powder was deposited on an austenitic substrate X5CrNiMo17-12-2 (AISI 316L) by the High Velocity Oxy Fuel (HVOF) process. The coatings exhibited low porosity and good adhesion to the substrate material. Further improvement of the material and tribological properties of the deposited coatings was achieved by hot isostatic pressing (HIP) and heat treatments. HIP treatment, which was carried out without encapsulation, led to a fully dense MMC coating. Further heat treatment to secondary peak hardness of the ledeburitic cold-work tool steel increased the hardness and thus the tribological properties. Diffusion reactions and the embedding behavior of the hard particles in the steel matrix were investigated with respect to the post-treatment processes by means of diffusion calculations and microstructural examinations. The results indicated that diffusion processes at the hard particle/metal matrix interface exert a strong influence on the embedding behavior of TiC and Cr3C2 particles in the coating microstructure. During HIP and heat treatment, new phases with a larger amount of metallic bonding were formed, thus improving particle adhesion to the metal matrix.