预氧化真空度对冷喷涂CoNiCrAlY涂层高温氧化行为的影响

Effect of Pre-oxidation Vacuum Degree on the High Temperature OxidationBehavior of Cold Sprayed CoNiCrAlY Coatings

利用冷喷涂技术制备了CoNiCrAlY涂层,并对涂层进行了不同真空度下的预氧化处理。结合XRD、SEM和EDS等方法研究了预氧化处理真空度对CoNiCrAlY涂层在1050℃下氧化行为的影响。结果表明,冷喷涂CoNiCrAlY涂层含氧量为0.12%(质量分数),孔隙率小于0.36%(体积分数)。真空预氧化处理提高了涂层致密度,使涂层由γ-Matrix单相结构转变为γ-Matrix和β-(Ni,Co)Al双相结构,并在涂层表面生成连续、致密的α-Al_(2)O_(3)单一氧化膜。高温氧化过程中,涂层表面TGO的生长速度随预氧化处理时真空度的减小而降低。当真空度小于或等于10^(-3) Pa时,预氧化处理时的真空度对涂层表面TGO的生长速度影响较小。真空预氧化处理使涂层氧化过程中形成的Al_(2)O_(3)膜具有更大的晶粒和更少的缺陷,减少了Al元素和O元素进行扩散的晶界面积,从而降低了Al_(2)O_(3)的生长速度并抑制了尖晶石氧化物的形成,提高了冷喷涂CoNiCrAlY涂层的抗氧化性能。

ACoNiCrAlY coating was prepared by cold spray and pre-oxidized in a vacuum environment under different vacuum degree.The effect of vacuum degree of pre-oxidation on the oxidation behavior of CoNiCrAlY coatings at 1050℃was studied by XRD,SEM and EDS.The results show that the as-sprayed coating presents a dense structure with low porosity(less than 0.36vol%)and low oxygen content(0.12wt%).Vacuum heat treatment improves the density of as-sprayed coating,converts the single-phase(γ)as-sprayed coating to a two-phaseγ-Matrix/β-(Ni,Co)Al microstructure,and forms a continuous,dense and singleα-Al_(2)O_(3)layer.During the course of oxidation,the growth rate of TGO formed on CoNiCrAlY coating decreases with the decrease of vacuum degree.When the vacuum degree is less than or equal to 10^(-3) Pa,vacuum degree has little influence on the growth rate of TGO.An Al_(2)O_(3)layer with larger grain size and less defect is formed on the surface of pre-oxidized coating during the oxidation process,which can decrease the diffusion area for Al and O.As a result,the growth rate of Al_(2)O_(3)decreases and thus the formation of spinel oxide is suppressed.It is concluded that the oxidation resistance of cold-sprayed CoNiCrAlY coating has been greatly improved by vacuum pre-oxidation treatment.