Investigation On Microstructures And Wear Properties Of Laser-Cladded Ti-Al/Ceramics Composite Coatings On Titanium Alloys

The excellent physical and chemical properties, such as high specific strength, high specific modulus and good resistance to corrosion of the titanium alloys made them widely used in the fields of biological medicine, aeronautics and aviation industries, etc.. Nevertheless, the titanium alloys show poor wear resistance, limiting its potential application. Laser cladding is an important surface modification technique of titanium alloys due to the advantages of the close combination to the substrate and the pollution-free. The Ti-Al intermetallics exhibit the properties of high specific strength and good oxidation resistance, which are recognized as the most development prospects of the light materials in the fields of the aeronautics and aviation industries.Titanium alloy is the development prospect advanced material in the aviation industry. Ti-Al intermetallics+ceramic hard phases (TiC, TiB2, TiN, etc.) laser-cladded coatings were formed on titanium alloys substrate, which reinforced the surface performance of the substrate, and also had a metallurgical bonding to the substrate, the microstructures and wear properties of the laser-cladded coatings were investigated in this study. This research provided essential experimental and theoretical basis to promote the application of the laser cladding technique in the fields of the aviation, national defense and military equipment, which owned the important strategic significance to the development of the aviation industry in our country.In order to increase the wear resistance of the titanium alloy substrate, laser-cladded Ti-Al intermetallics/ceramics composite coatings were formed on the substrate, which was the main line in this study. And the laser cladding process parameters and powder mixture ratio were optimized in order to fabricate the high quality Ti-Al/ceramics composite coatings on T1-6A1-4V alloys. The relationship of the microstructures, micro-hardness and wear properties of the laser-cladded Ti-Al/ceramics composite coatings with addition of Cu,Y2O3-Al2O3,YPSZ (Yttria Partially Stabilized Zirconia), also in nitrogen atmosphere were researched. And the influence of the Al2O3and the rare earth oxide Y2O3on the in situ formation mechanism of the ceramic phases in the laser-cladded composite coatings, and the strengthening mechanism to the substrate were also revealed. The brittleness of the Ti-Al/ceramics composite coatings decreased by mean of the adjustment of the powder ratio in the pre-placed coatings, leading to the improvement of the wear resistance. In this study, the wear mechanism of the laser-cladded Ti-Al/ceramics composite coatings was researched by means of calculation of the wear mass/volume losses.Series research results indicated that during the laser cladding process, Al3Ti reacted with Ti which came from the substrate, leading to the formation of Ti3Al, leading to the improvement of the wear resistance of titanium alloys. Addition of YPSZ decreased the probability of the production of the micro-crack in the laser-cladded Ti-Al/ceramics composite coatings, which improved the the strength, toughness and tribological properties of the coatings. Moreover, in nitrogen atmosphere, a large amount of TiN was produced in the surface of the laser-cladded Ti-Al/ceramics composite coatings, which further increased the wear resistance of the titanium alloys.During the laser cladding process, Cu was able to react with Ti and Ti-Al, leading to the formations of Ti-Cu intermetallics and Ti(CuAl)2, which improved the wear resistance of the laser-cladded coatings. Moreover, Cu addition also promoted that growth of the titanium boron compounds in the Al3Ti-C-TiB2laser-cladded coatings. Ti(CuAl)2was dispersed in the coatings, which was beneficial in increasing the micro-hardness and wear resistance of the laser-cladded coatings. Nevertheless, when the Cu content exceeded13wt.%in the pre-placed coating, the toughness of the laser-cladded coating decreased, leading to the production of the micro-crack.During the laser cladding process, a portion of Al2O3can react with TiB2, leading to the formations of Ti3Al,O2and B. In fact, the chemical reaction between Al2O3and TiB2consumed a portion of the ceramic phases, leading to the enhancement of the dilution rate of the substrate to the coating, favouring the melting and precipitation of the remained ceramic phases, which improved the micro structure and wear resistance of the laser-cladded coatings.1wt.%Y2O3addition can significantly improve the microstructures and wear resistance of the Al2O3-TiB2reinforeced Ti-Al/ceramics composite coatings. Aggregation of Y2O3was present in the laser-cladded coating, which retarded the growth of Al2O3and TiB2. The microstructures of the laser-cladded coatings became uniform with addition of Y2O3, and Y2O3also reinforced the crystal boundary of the coatings.Laser cladding of Al3Ti+TiB2/(Ni-coated WC) pre-placed powders on Ti-6A1-4V alloy can form the Ti-Al/ceramics composite coating. The X-ray diffraction (XRD) analysis indicated the micro-hardness of this composite coating was only2～3times higher than that of the substrate, and the improvement of the wear resistance was also limited due to the actions of the productions of a large amount of M6C (Ni2W4C) brittle phases and the coarse microstructure. Addition of10wt.%AL2O33-1.5wt.%Y2O3refined the microstructures of the composite coatings, and also decreased the M6C content, the micro-hardness of the coating increased to1300～1450HV0.2, and its wear resistance also increased.Ceramics and Ti-Al intermetallics which owned the propertis of light weight and excellent performance were fabricated on the titanium alloys by mean of the laser cladding, which formed the high quality intermetallics/ceramics composite coatings. Laser-cladded Ti-Al/ceramics composite coatings can be used to repair varies failure parts, such as the aviation engine blade. In this study, the wear mechanism and the influence factors of the Ti-Al/ceramics composite coatings were reseached, and the intrinsic regularities of the microstructure, phase constituent and wear properties of the coatings were also revealed, which provided the essential experimental and theoretical basis to prepare the high performance metals ceramics composite coatings on titanium alloys.