Laser-clad Ni70Al20Cr7Hf3 alloys with extended solid solution of Hf: Part I. Microstructure evolution

Coatings for superalloys for extended service in atmospheres at high temperature are of great interest at present. The addition of reactive elements (RE’s) such as Hf to these coatings has a pronounced effect on their high-temperature oxidation resistance. A laser-cladding technique was used to produce Ni-Al-Cr-Hf alloys with an extended solid solution of Hf in a nearstoichiometric Ni₃Al matrix. A 10 kW CO₂ laser with mixed powder feed was used for the cladding process. Scanning electron microscope (SEM), transmission electron microscope (TEM), and scanning transmission electron microscope (STEM) were employed for studies of microstructural evolution of alloys produced during the laser-cladding process. Microstructural studies reveal the formation of dendrites with a solid solubility of about 11 to 14 wt pct Hf and also a eutectic structure. Convergent-beam techniques and X-ray spectroscopy have been applied to characterize the phases formed during the cladding process.