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

Abstract

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 Al2O3, 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.