The γ′-Ni3(Al,Ta) phase triggered strengthening of the Ni-Ta-Al-Cr-C coating layer, deposited on austenitic stainless steel

The aim of this work was to analyse the effect of the gamma'-Ni-3(Al,Ta) phase on the strengthening of the Ni-Ta-Al-Cr-C coating layer, deposited on austenitic stainless steel AISI 310. The hardfacing alloy was deposited using the Gas Tungsten Arc Welding process. The specimens were analysed in the as-welded, solution treated and aged states. The investigations involved a wide range of experimental techniques, that included scanning electron microcopy, electron probe microanalysis, microhardness measurements and single direction wear testing using the nanoindentation technique to characterize the effect of the gamma'-Ni-3(Al,Ta) phase on the strengthening of the investigated coating layer. Additionally, the block-on-ring wear test was performed in order to determine the macroscopic wear mechanism of the deposit during sliding wear under harsh conditions. The obtained results show that heat treatment (solution treatment + aging) did not significantly affect the chemical distribution along the first layer, but clearly reduced local intradendritic segregation and brought about a more uniform distribution and size of the gamma' phase in comparison to the as-welded state. An increase of Fe within the coating layer reduced the gamma' phase's nucleation driving force and its final volume fraction. It was found that the MC carbides exhibited a greater tendency to fracture during the single direction wear test in comparison to M7C3 carbides. The heat treatment procedure used in this work allowed to increase the volume fraction of the gamma' phase in the coating layer. This manifested itself in a significantly enhanced microhardness and increased values of displacement into the surface vs the scratch distance made by the indenter during the wear test, which is associated with the improvement of abrasive wear resistance.