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Study on the Preparation and Caviation Erosion of Ti-Ni Coatings

Author: ZhangMengZuo
Tutor: LiuLiBin
School: Central South University
Course: Materials Science
Keywords: Ti-Ni coating low temperature High Velocity Oxygen Fuel heat treatment cavitation erosion
CLC: TG174.4
Type: Master's thesis
Year: 2013
Downloads: 13
Quote: 0
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Abstract


Ti-Ni coatings were deposited on316L steel by new type low temperature High Velocity Oxygen Fuel process (LT-HVOF). The effects of heat treatment process on the microstructure, phase compositions and performance for Ti-Ni coating were systematically investigated. The fundamental performance of Ti-Ni coating such as the composition, microstructure, microhardness, oxygen content were characterized by means of SEM, XRD, EDS and other testing methods. The cavitation erosion resistance performance for Ti-Ni coatings were tested by ultrasonic treatment instrument. Cavitation erosion resistance performance and the corrosion mechanism for Ti-Ni coating were characterized by microstructure,3D morphology by comparing with HVOF WC coating. The results were as follows:(1) Ti-Ni coatings were prepared by low temperature High Velocity Oxygen Fuel with Ni clad Ti power as feedstock. When the fuel/oxygen ratio was2.54and the combustion chamber pressure was15.3bar, the Ti-Ni coating with high deposition rate, less than1%porosity rate, and as low as0.59%of the oxygen content was obtained. Ti-Ni coating prepared by LT-HVOF was composed of Ti and Ni phase.(2) With the increase of heat treatment temperature, more NiTi phase with a small amount of Ti2Ni, Ni3Ti phase was formed, but a large number of pores was found after quenching. High-temperature multi-stage heat treatment and annealing treatment were effective way to reduce the pores. The optimized heat treatment process for Ti-Ni coating was:heat treatment at950℃for5h, after cooling in furnace to850℃, then keeping at850℃for1h, and finally water quenching. The coating applied by the optimized heat treatment owned more NiTi phase and a relatively small amount of Ni3Ti and Ti2Ni phase, and few pores and oxide layer were observed in the coating. (3) The study on cavitation erosion of Ti-Ni coatings revealed that unalloyed Ti-Ni coating exhibited poor cavitation erosion performance due to great mass loss. Many deep pits were observed for unalloyed Ti-Ni coating after cavitation erosion test. The cavitation erosion resistance performance was significantly improved after coating heat treatment. Small and uniform corrosion pits were found on the coating surface. The optimized heat treated Ti-Ni coating offered the best cavitation erosion resistance performance, and even showed better performance than that of conventional HVOF WC coating.(4)The cavitation erosion mechanism for as sprayed coating was governed by the repeated impact of the vacuoles, and the failure was first started at the Ni location, which finally led to the delamination of Ti due to the loss of Ni binder. Cavitation erosion of the alloyed coatings was occurred firstly at the microporous location and oxide layer interface, and the cavitation damage was extended along the holes or around the oxide layer. Finally the coating was peeled off. Ni3Ti phase was not found as preferential corroded phase even as a type of brittle phase.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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