Evading stress-property tradeoff in a SMA/PZT laser cladding coating via phase transformations

Tradeoff between residual stress and properties is the primary obstacle which hinder the practical application of laser cladding technology. Herein, a Fe-based SMA/PZT (shape memory alloy/lead zirconate titanate piezoelectric ceramic) composite coating was fabricated by laser cladding. To explore the optimal PZT doping amount and its performance enhancement mechanism of the composite coating, microstructure, phase composition, stacking fault probability (SFP), residual stress, microhardness and wear resistance of the coating were investigated. The results reveal that the composite coatings are composed of PZT (Pb(ZrTi)O3) phase, γ austenite phase and ε martensite phase. Among which the coating with 1 wt% PZT doping amount possesses the highest microhardness as well as the best wear resistance. The grain size and stacking fault energy (SEF) of the coating have been reduced after doping with PZT. Ultramicroscopic structure unveils that the γ → ε phase transition occurred in the SMA/PZT composite coating during the laser cladding process, high-density dislocation accumulation zone appears around the PZT particles. PZT doping has an interesting effect on both promoting and hindering the transformation of γ → ε in the composite coating. Doping of PZT increases the amount of martensite in the local area of the composite coating, reduces the residual stress, and significantly improves the microhardness and wear resistance.