Nitride coatings improve Ti-6Al-4V alloy behavior in creep tests

This study aimed to evaluate the effect of plasma-assisted PVD TiN and TiAlN/TiAlCrN coatings on the Ti-6Al-4V alloy under creep conditions at 600 degrees C. Microstructural and surface coating analysis were investigated using XRD, optical and scanning microscopy and isothermal oxidation. The results showed that the TiN coated sample showed the lowest secondary creep rate values for stresses greater than 222 MPa. Below 222 MPa, the TiAlN/TiAlCrN coated sample presented a secondary creep rate value higher than the TiN coated sample. This behavior was due to TiAlN/TiAlCrN oxidation resistance that, according to isothermal oxidation tests, did not suffer oxidation at 600 degrees C. The stress exponent analysis indicated that the main creep mechanism was controlled by climbing dislocations. The fracture mode is similar for all conditions studied and displayed transgranular fracture with decohesion of intergranular regions. Finally, the coated samples contribute to improved oxidation resistance, reduced damage tolerance parameter (lambda) and increased lifetime of Ti-6Al-4V alloy. (C) 2016 Elsevier B.V. All rights reserved.