Research On Technology And Properties Of Laser Cladding TiC/TiAl Composite Coatings On γ-TiAl Intermetallic Alloy

γ-TiAl intermetallic alloy (hereafter referred as TiAl alloy) is considered as one of attractive candidate structural materials for the future aeronautics and astronautics, gas turbine and automobile industries, because it possesses low density, high specific strength and stiffness, superior specific modulus and excellent high-temperature creep resistance. However, the practical application of TiAl intermetallic alloy is limited due to the poor surface hardness and wear resistance.The aim of the present research is to explore an advanced surface modification method to expand the application of TiAl intermetallic alloy. The feasibility of fabricating TiC reinforced TiAl matrix intermetallic cermet composite coatings on TiAl alloy using Ti-Al-TiC powders by laser cladding is investigated through a lot of trial tests. TiC reinforced TiAl matrix composite coatings which has good quality have been successfully synthesized under optimal laser parameters. The microstructure, phase composition, micro-hardness of the laser cladding composite coatings were investigated by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) as foundation of the constitution of the mixed powder pre-coatings, laser cladding parameters and granularity. The room-temperature dry sliding wear test of the laser cladding composite coatings and TiAl alloy were carried out on a Pin-on-disc wear testing machine. The wear mechanisms were also discussed based on the experimental results. The main results are as the following:1. High quality TiAl matrix intermetallic cermet composite coatings can be synthesized successfully under the appropriate condition, the continuous matrix was TiAl and the short-bar, particle shape or well developed dendritic phases were TiC.2. The microstructure and the micro-hardness of the coatings were sensitive to the laser parameters. The results revealed that with the increase of laser scanning rate, the morphology of reinforced TiC homogeneously dispersed in TiAl matrix and changed into short-bar and particle shape from well developed dendritic shape, meanwhile, the micro-hardness also enhanced by an increase in the scanning rate. With the increase of laser power, the morphology of reinforced TiC changed into well developed dendritic shape, the trend of micro-hardness increased firstly and then decreased.3. The amount of TiC in the mixed powder pre-coatings had the directly influence to the volume fraction of the reinforced TiC in the composite coating. However, the granularity influenced the morphology of the reinforced phase greatly.4. Under the room-temperature dry sliding wear test conditions, the composite coatings have much better wear resistant than the original TiAl alloy. There are different wear resistant mechanism between the composite coating and the original TiAl alloy.