Alumina growth behaviour on the surface-modified NiCoCrAl alloy by Pt and Hf at high temperature

Abstract

The growth behaviour of the modified surface of NiCoCrAl alloy by Pt and Hf was investigated at 1050 °C in air atmosphere. The undoped NiCoCrAl alloy exhibited an extremely serious oxide scale spallation. Compared to the undoped alloy, the Hf and Pt depositing on the surface of NiCoCrAl can greatly increase the alumina scale lifetime. Furthermore, altering the deposition order of Pt and Hf influences the cyclic oxidation resistance. The higher content of Hf on the alumina scale of NiCoCrAl alloys resulted in the formation of spinel (NiCr2O4). The spinel as a second phase in the oxide layer of NiCoCrAl + Hf alloys led to the internal oxidation. Internal defects were caused by the diffusion of Al during the oxidation process. Due to the phase transformation and grains growth, the internal stress of alumina scale increased, so that the spallation occurred on the surface of NiCoCrAl + Pt alloys. Pt particles agglomerated on the NiCoCrAl + Hf + Pt alloy surface to form irregular particles, and a lower TGO growth rate has been observed for the NiCoCrAl + Hf + Pt alloy.