Microstructure and properties of coatings prepared by reactive plasma spraying of Ti-Al milled powders
Reactive plasma spraying of Ti-Al mechanically milled powders on Q235 steel surface was performed to prepare composite coating of Ti-Al intermetallic compounds and to study its properties.The compositions and microstructure of the coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively,the bond strength, micro-hardness and corrosion resistance were also tested.The results show that the coatings consist of Al3Ti, TiN, Al2O3, a little TiAl and Ti3Al, residual Al and Ti.Even though mechanical milling can promote the reactions in the spraying, Al and Ti have not reacted completely during spraying, and they are easy to be oxidized and nitrified while being sprayed in air.Insert mechanical bonding is formed between the coating and the matrix.The average bond strength is 30.24 MPa, the average micro-hardness is 206.1 HV,and the corrosion resistance of the coatings is superior to that of the substrate.As a whole,the longer milling time, the higher spraying current, the longer spraying distance, and the lower gas flow rate, bring about the more thorough reactions in the spraying, the more uniform and compact microstructure of the coatings, and the higher bond strength, micro-hardness, and corrosion resistance of the coatings.
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