Friction stir processing of austenitic stainless steel cold spray coating deposited on 304L stainless steel substrate: feasibility study

In this work the feasibility test of friction stir processing (FSP) of 1.5 mm thick austenitic stainless steel cold spray coating deposited on 304L stainless steel substrate was performed using tungsten carbide tool. Applied FSP parameters (advance speed 50 mm/min, rotation speed 300 rpm, axial force 20 kN, tilt angle 1.5°) allowed to perform FSP treatment with a higher depth than the coating thickness. As a result, the material mixing at the coating/substrate interface was observed. The microstructure observation revealed that the coating microstructure in the stir zone was significantly modified. EBSD analysis confirmed that full material recrystallization during FSP allowed to formation of dense and uniform fine-grain structure with the mean grain size 1.9 mm. Average coating microhardness was decreased from 406 HV to 299 HV. Further FSP parameters optimization should be carried out in order to improve the process reliability and avoid any coating failure during treatment.