粉末冶金靶材多弧离子镀HY3涂层抗氧化性能

Oxidation Resistance of HY3 Coating Deposited by Arc Ion Plating with Powder Metallurgy Target

目的研究靶材制备工艺对多弧离子镀(Arc ion plating,AIP)MCrAlY涂层抗氧化性能的影响。方法采用粉末冶金方法制备NiCrAlYSi(HY3)靶材,然后采用AIP在DZ125合金基体上制备HY3涂层。在1100℃下对粉末冶金靶材制备涂层进行200 h的静态氧化实验,采用SEM、XRD等对靶材和氧化前后的涂层进行微观组织分析,并与传统铸造靶材进行对比。结果采用粉末冶金方法制备的靶材成分更加均匀,相尺寸约为5μm,相较于铸造靶材降低了1个数量级。采用粉末冶金靶材制备的涂层(P涂层)元素分布更均匀、β相含量更高。经过1100℃、200 h的高温氧化,P涂层的氧化增量为1.01 mg/cm^(2),低于铸造靶材制备的涂层(C涂层,1.10 mg/cm^(2))。在200 h后,P涂层表面的热生长氧化物(TGO)完整,而C涂层表面的TGO出现了剥落现象,P涂层的活性元素均匀分布,促进TGO内生成了少量弥散分布的钉扎氧化物Y_(2)Hf_(2)O_(7),提高了TGO的抗剥落能力。更高的β相含量促进了氧化初期θ-Al_(2)O_(3)的快速生成,有利于P涂层生成保护性能更好的TGO。结论粉末冶金靶材成分的均匀性优于传统铸造靶材,采用粉末冶金靶材制备的HY3涂层的抗高温氧化性能优于铸造靶材制备的HY3涂层。

MCrAlY coatings are commonly used to protect turbine blades against hot temperature attack.This work aims to investigate the effect of target preparation methods on the oxidation behavior of MCrAlY coatings fabricated by arc ion plating(AIP).NiCrAlYSi(HY3)targets prepared by powder metallurgy(PM)were used as raw material,and HY3 coatings were deposited on DZ125 substrates by AIP(denoted as P coating).Coating specimens were also deposited with casting target for comparison(denoted as C coating).Vacuum annealing was carried out at 960℃for 3 h to promote homogenization of the coatings subsequently.Microstructure of both targets and coatings before and after oxidation were analyzed with scanning electron microscope(SEM)equipped with energy spectrometer(EDS)and X-ray diffractometer(XRD).Isothermal oxidation tests were performed at 1100℃for 200 h.Then oxidation curves were obtained by plotting weight gains of coatings against oxidation time.Thermal grown oxide(TGO)formed after short-term oxidation(10 min)was analyzed by photo-stimulated luminescence spectra to reveal the possible mechanism.The results showed that the PM targets exhibited much smaller phase size of about 5μm,almost one order of magnitude lower than that of C target.Both coatings in annealed condition were uniform and dense,with a similar thickness of about 30μm,mainly composed ofγʹandβphases.However,results analyzed with Image J(an image processing software)indicated that the volume fraction ofβphase precipitated in the P coating was about 64%,which was significantly higher than the value of about 45%detected in the C coating.The finer microstructure of the P target resulted in the uniform distribution of Al in the coating,thus was responsible for the higher volume fraction ofβphase.The mass gain values of P and C coatings after 200 h oxidation were about 1.01 mg/cm^(2) and 1.10 mg/cm^(2),respectively.The mass gain values for the coatings were close to each other,but obvious spallation of TGO could be observed for the C coating.No peeling or spallation of oxides occurred to the P coating.Cross-sectional examination of coatings after 200 h oxidation demonstrated that the thickness of TGO grown on P coating was about 3.9μm,with a small amount of Y_(2)Hf_(2)O_(7) dispersion.TGO formed on the C coating was about 4.5μm thick,which was slightly thicker than that of the P coating.Pegs with larger size in the TGO of C coating were determined as HfO_(2).Similar to the aluminum distribution behavior,homogeneous yttrium in the P coating resulted in the formation of finely dispersed Y2Hf2O_(7) pegs in TGO,which improved the scale spallation resistance.As a comparison,larger HfO_(2) pegs could be observed in the oxidized C coating,as a result of the more severe segregation of yttrium and hafnium.The 10 min short-term oxidation test indicated that the TGO developed on the P coating containedα-Al_(2)O_(3) and a small amount ofθ-Al_(2)O_(3),which was different from the TGO of C coating with completely transformedα-Al_(2)O_(3).The retarded transformation ofθtoα-Al_(2)O_(3) can be attributed to the higher volume fraction ofβphase in the P coating.Nucleation ofθ-Al_(2)O_(3) is promoted by the rapid outward diffusion of Al along theγʹ/βphase boundaries at the initial stage of oxidation,which transforms into a more protectiveα-Al_(2)O_(3) subsequently.Consequently,the P coating reveals improves oxidation and scale spallation resistance than the C coating in isothermal oxidation tests performed at 1100℃.