NiTi cladding on stainless steel by TIG surfacing process: Part I. Cavitation erosion behavior

NiTi was deposited on AISI 316 stainless steel by the tungsten inert gas (TIG) surfacing process, aiming at increasing cavitation erosion resistance. A thick deposit, with a 750 HV microhardness and dilution ratio of 14% was formed, with strong deposit/substrate interfacial bonding. Small pores (size ≤20 μm, total volume fraction less than 1%), and some second phase precipitates were present in the deposit. Even with the presence of such pores, the cavitation erosion rate of the deposit in NaCl solution was lower than that of AISI 316 by a factor of more than nine, and even lower than that of AISI 316 laser-clad with NiCrSiB, a common hard-facing material. The large increase in erosion resistance could be attributed to the partial retention of superelasticity, and also to the high hardness of the deposit. In this preliminary study on the efficacy of the TIG process for NiTi deposition, the main problem identified was the presence of small pores in the deposit, the elimination of which, via more refined processing, would definitely further increase the cavitation erosion of the deposit.