Microstructure, wear and high-temperature oxidation resistance of laser clad Ti₅Si₃/γ/TiSi composite coatings on γ-TiAl intermetallic alloy

Mixed NiCr-Si precursor powders on γ-TiAl intermetallic alloy (Ti-48Al-2Cr-2Nb) have been investigated for laser cladding treatment to modify the tribology and high-temperature oxidation properties of the material simultaneously. The alloy samples are pre-placed with NiCr-50% and NiCr-40%Si (wt.%), respectively, and laser treated at the same parameters, i.e., laser output power 2.8 kW, beam scanning speed 2.0 mm/ s, beam dimension 1 × 18 mm. The treated samples underwent tests of microhardness, full dry sliding wear and high-temperature oxidation. The results showed that laser cladding with different constitution of mixed precursor NiCr-Si powders improve the surface hardness in all cases. Laser cladding with NiCr-40% Si precursor mixed powders results in the better modification of tribology and high-temperature oxidation behavior. However, with NiCr-50%Si precursor powders shows decreased wear resistance compared to the original TiAl alloy due to the existence of a large amount of hard and brittle Ti₅Si₃ and TiSi compounds. Optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS) analyses indicated that the formation of the reinforced primary Ti₅Si₃, γ/TiSi eutectics and the refinement of the microstructure and both the continuous and dense Al₂ O₃, SiO₂ hybrid oxide scales are supposed to be responsible for the modification of the relevant properties. Laser cladding with NiCr-Si mixed powders is anticipated to be a promising wear- and oxidation-resisting surface modification technique for TiAl intermetallic alloy.