Microstructure, phase and microhardness distribution of laser-deposited Ni-based amorphous coating

Ni₅₉Zr₁₆Ti₁₃Si₃Sn ₂Nb₇ amorphous material was deposited by laser cladding onto Ti-3Al-5Mo-5V-4Cr-2Zr titanium alloy. Despite trials with wide range of process parameters, the present experiments were unable to retain complete amorphous surface microstructure after laser cladding. So, the mixed structure with amorphous phase, intermetallic compounds and borides were obtained. X-ray Diffraction (XRD) results showed that the amorphous phase fraction of the coatings was measured up to about 50% depending on the laser cladding parameters. Differential Scanning Calorimetry (DSC) curve showed that glass transition temperature (T_g) and onset crystallisation temperature (T_x) was observed around 757 K and 800 K, respectively, which indicated that the Ni-based amorphous alloy coating had high thermal stability. The nanocrystalline grains were about 40-100 nm in size, precipitated from amorphous phase or interface between amorphous and borides. The Vickers hardness of coating depended on the amount of various phases that were present in different locations of coating.