Fabrication of stainless steel 316L/TiB₂ composite coating via friction surfacing

Stainless steel 316L/TiB₂ composite coatings were fabricated with different TiB₂ contents using friction surfacing (FS) on the stainless steel 304 substrate. One or two blind holes were drilled at different positions axially on the cylindrical 316L consumable rods for keeping micron-size TiB₂ powder as the reinforcement in the coatings. After FS, TiB₂ was found to be embedded into the austenitic matrix and also partially decomposed leading to the formation of FeB₂ and FeTi under high temperature and high strain rate. Compared with the friction-surfaced (FSed) 316L coating, the grain size of austenite in the TiB₂ reinforced composite coating was refined from 7.8 to 0.64 μm, where austenite grains closed to {111} tends to transform to FeTi. Compared with monolithic 316L coating, the hardness of the FSed 316L/TiB₂ coating was significantly increased from 219 to 1056 HV_0.2 owing to the presence of TiB₂ and intermetallic phases, finer austenitic grains and higher misorientation density. The pitting corrosion resistance of the FSed 316L coating was improved due to the elimination of MnS inclusions whereas the FSed 316L/TiB₂ coating possessed lower pitting resistance due to the presence of FeTi. Moreover, the passivity of the 316L/TiB₂ coating in 3.5% NaCl solution was preserved but the capability of re-passivation was degraded.