Thermal stability and oxidation resistance of laser clad TiVCrAlSi high entropy alloy coatings on Ti-6A1-4V alloy

TiVCrAlSi high entropy alloy coatings were deposited on Ti-6A1-4V alloy by laser cladding. SEM, XRD and EDS analyses show that, the as-clad coating is composed of (Ti,V)(5)Si-3 and a BCC solid solution. After annealing at 800 degrees C for 24 h under vacuum, the coating is composed of (Ti,V)(5)Si-3, Al-8(V,Cr)(5), and a BCC solid solution. The temperature-dependent phase equilibrium for the coating material calculated by using the CALPHAD method, indicates that above 880 degrees C the stable phases existing in the coating material are a BCC solid-solution and (Ti,V)(5)Si-3. When the temperature is below 880 degrees C, the stable phases are (Ti,V)(5)Si-3, Al-8(V,Cr)(5), and a BCC solid solution. In order to validate the calculation results, they were compared with TiVCrAlSi alloy samples prepared by arc melting, encapsulated in quartz tubes under vacuum, annealed at 400-1100 degrees C for 3 days and water-quenched. XRD analysis shows that the experimental phase composition agrees with the thermodynamic calculations. After vacuum annealing, there is a small increase of hardness for the laser clad TiVCrAlSi coating, which is due to the formation of Al-8(V,Cr)(5). The oxidation tests show that the TiVCrAlSi coating effectively improves the oxidation resistance of Ti-6A1-4V at 800 C in air. The formation of a dense and adherent: scale consisting of SiO2, Cr2O3, TiO2, Al2O3 and a small amount of V2O5 is supposed to be responsible for the observed improvement of the oxidation resistance. (C) 2011 Elsevier B.V. All rights reserved.