Preparation of NiCrAlY coating electro-spark deposited on GH4169 alloy

NiCrAlY coatings with different Al contents were prepared by electro-spark deposition (ESD) on GH4169 alloy. For increasing the thickness of the coating, the coated samples were annealed in vacuum. The weight change of the coating with deposition time was tested. The microstructure was observed by a scanning electron microscope. The phases in the coatings were investigated by an X-ray diffractometer. The influences of Al contents and annealing on the microstructure of the NiCrAlY coatings were investigated. The results show that there was a limit thickness for NiCrAlY coating with high Al content. After annealing, the thickness increased with further electro-spark deposition. After four times of annealing+ESD, the thickness of the coating reached the maximum value of about 45 μm, and its hardness was 440 HV. While there was no limit thickness for NiCrAlY coating with low Al content. The high Al content coating consisted of β-NiAl and α-Cr phases before annealing. After annealing, the Ni₃Al phase appeared because the thickness of coating increased continually. The NiCrAlY coating with low Al content was mainly composed of Ni₃Al phase. Compared with NiAl, the thermal expansion coefficient of Ni₃Al is closer to that of GH4169, which is beneficial for the increase of thickness.