The Influence Of Temperature On Diffusion Behavior And Microstructure Properties Of Ni-Ti Cold Spray Layer

NiTi intermetallic compound can be potentially used in various applications such as water turbines, propellers and other over-current component due to its excellent corrosion resistance and erosion wear resistance performance. However, processing of NiTi alloys is difficult, so the fabrication of spraying coatings on the base metal is a solution. In order to study the formation mechanism of NiTi intermetallic compound, Nickel and Titanium powders as well as its mechanical alloying powders were adopted to make different Ni/Ti diffusion couples in this paper. The preparation by cold spraying Ni/Ti coating and the process of Ni and Ti diffusion in the interface was observed and analyzed. The formation mechanism of intermetallic and atom diffusion behavior mechanism in the coating by cold spraying were studied on focus. This provides a theoretical basis for the fabrication of high-performance NiTi intermetallic compound coatings by cold spraying.The results showed that the composition and microstructures of cold spraying coatings were consistent with the milled poweds as same dense and non-oxidizing. The effect of heat treatment conditions on the cold spray Ni/Ti diffusion couple coating structure and phase structure was obvious. The Ni/Ti interface morphology after diffusion through SEM showed that Ni3Ti, Ti2Ni and NiTi intermetallic compound coating thickness increased significantly as the thermal diffusion temperature increased and the formation of Ni3Ti and T12N1was priority. The growth of NiTi intermetallic compound was base on the parabolic growth rules, while the growth of NiTi, Ti2Ni were little effect with the increasing of heat treatment holding time. The mechanical milling time significantly affects the layered structure thickness of the Ni/Ti powder. The alloy powder milled7.5h Ni/Ti under the lower temperature was more accessible to form NiTi intermetallic compounds as the reason of the thermal diffusion. Through comparative analysis of vibration cavitation erosion test, the cavitation erosion resistance of NiTi coating was improved by proper heat treatment.