Preparation And Properties Of Two Kinds Of NiCrAlY Powder And Coatings

Thermal barrier coatings (TBCs) is widely used in aero-engine turbine blades, due to their excellent high temperature oxidation resistance. However, NiCrAlY alloy is adopted as the bonding layer because of the incompatibility of thermal expansion coefficient between thermal barrier coating and matrix.The composition of NiCrAIY alloy is a key factor on performances of bonding layer including the growth rate of thermal oxidation layer, composition, integrity, and the adhesion strength of the matrix and spalling behavior in the process of thermal cycling. So the composition of metal bonding layer is very important to the service life of thermal barrier coatings. In this paper, two ingredients NiCrAlY alloy powder and the coatings were prepared and their performances are compared. And we have obtained the below conclusions:Firstly, the best NiCrAlY powder preparation technology was obtained by optimizing the ultrasonic atomization equipment process. That is, atomization temperature is 1520～1540 ℃, atomization pressure is 8-10 MPa, gas flow rate is 10～15 m3/min, alloy liquid flow is 2～ 4 kg/min, atomizing medium is pure argon.Secondly, two powders, Ni69.5Cr25Al5Y0.5(Ni25CrAlY) and Ni67Cr22Al10Y1.0 (Ni22CrAlY), were prepared by ultrasonic atomization technology. It is studied that the microstructure, the particle morphology, the chemical composition, the apparent density and the liquidity, the thermal stability. And the performance difference of these two powders were compared. It is found that the two powders both contain γ-Ni and γ’-Ni3Al phases and their internal structure is as-cast dendrite structure. The β-NiAl phase only exists in the Ni22CrAlY powder. The as-cast dendrite structure in Ni22CrAlY powder is smaller than that of Ni25CrAlY powder. Other specifications all satisfy the requirements of coating preparation.Finally, two NiCrAlY coatings were prepared on the surface of nickel based superalloy DZ40M by HVOF. Their basic performance differences were analyzed. The oxidation and hot corrosion behaviors of the two coatings were compared in the environment of high temperature and thermal corrosion. It is found that the two kinds of coatings are composed of A1Ni3, A19Ni42.2, and a large number of metal elements. No apparent difference between roughness and hardness exists. But the compactness of Ni22CrAlY coating is better than that of Ni25CrAlY coating. In the environment of high temperature, the weight of Ni22CrAlY coating oxidation increases faster, less time spent to achieve constant weight, coating oxidation’s time is longer, so it has better oxidation resistance. In the environment of hot corrosion, the hot corrosion weightlessness rate of Ni25CrAlY coating is slower, the time for corrosion resistant and cracking failure is longer. So it has better thermal corrosion resistance.