Laser cladding of Ni-Cr-AI-Hf on Inconel 718 for improved high temperature oxidation resistance

Abstract

In situ Ni-Cr-Al-Hfalloy has been developed by laser surface cladding with a mixed powder feed for improved high temperature oxidation resistance. Oxidation-resistant materials for operation at elevated temperatures must satisfy two requirements: diffusion through the oxide scale must occur at the lowest possible rate, and the oxide scale must resist spallation. Formation ofan Al₂O₃ protective scale fulfils the former requirement but its adherence is poor. A reactive metal such as Hfis added to improve adhesion. A l0 KW CO₂ laser was used for laser cladding. Optical, SEM and STEM microanalysis techniques were employed to characterize the different phases produced during the cladding process. Microstructural studies showed a high degree ofgrain refinement, increased solid solubility ofHfin the matrix and the formation of Hf-rich precipitates. A thermogravimetric analysis was carried out to determine the oxidation properties ofthese clad alloys with an extended solid solution of Hf Considerable improvement over the base metal was observed. This paper discusses microstructural development in this laser clad alloy and its effect on oxidation.