A Study on the Intermetallics Formation of Cold Sprayed Ni-Ti Composite Coating After Post Spray Heat-treatment

Offering deposition of dense coating at solid state, cold spray consolidating method can be used for deposition of a wide variety of composite coatings including metal-matrix composite coatings. In this research, deposition of Ni-Ti composite coating using cold spraying and formation of intermetallics after post spray heat-treatment were investigated. Ni and Ti powders were physically blended with equivalent volume ratio (68.3% at. Ni-31.7%at. Ti), sprayed as the feedstock powder and composite coating with 35.2 at. % Ni- 64.8 at. % Ti composition was obtained. Post heat-treatments were conducted at 740 ̊C, 900 ̊C, and two-step heat-treatment 740 ̊C and 960 ̊C for different times. Microstructural investigation showed that all three equilibrium intermetallics of binary Ni-Ti phase diagram including Ni3Ti, Ti2Ni and NiTi phases were formed at all heat-treatment experiments and fraction of Ni3Ti phase decreased with consumption of the Ni precursor. Additionally, it was found that cold sprayed composite coatings had fast intermetallics formation and growth kinetics compared with those of common press and sinter samples which was addressed through deformation enhanced interdiffusion and particle/particle bonding of cold sprayed coatings.