Effects of post-annealing on microstructure and mechanical properties of plasma sprayed Ti-Si-C composite coatings with Al addition

Abstract

In this study, Ti-Si-C composite coatings were fabricated by plasma spraying using Ti/SiC/C/Al powder mixtures, and then these coatings were annealed at 500–900 °C in an Ar atmosphere. The influences of post-annealing on the microstructure and mechanical properties were analyzed via X-ray diffraction (XRD), scanning electron microscope (SEM) and micro-hardness tester. Results showed that the annealing treatment hardly changed the phase structure of the composite coatings. Coatings before and after annealing were composed of Ti 5 Si 3 , Ti 3 SiC 2 and TiC phases. Compared with coatings without annealing, the peak intensity of Ti 3 SiC 2 increased, the porosities decreased and the microstructure became more uniform after annealing. The composite coatings showed an increased microhardness and fracture toughness , which reached the maximum value of 1232 HV 0.2 and 3.19 MPa·m 1/2 when annealed at 700 °C. The improvement of mechanical properties was mainly attributed to the more uniform microstructure and the toughening effect of closed micro-cracks.