HVOF制备MCrAlY涂层过程中WC杂质颗粒的演变遗传行为研究

在热喷涂工业生产过程中,喷涂制备不同材料体系的涂层之前需要对送粉路径(送粉罐、送粉盘、搅拌器、送粉管路、送粉针)进行清理,但由于送粉路径内部结构复杂且存在静电吸附效应,使得残留于喷涂系统的粉末无法被完全去除,通常以微量杂质颗粒的形式被带入新涂层,进而影响新涂层的性能。为此,本文研究了在单晶基材表面采用高速火焰(HVOF)喷涂制备MCrAlY涂层过程中,送粉路径残留的WC杂质颗粒(WC-10Co4Cr)在涂层及涂层与基材界面处的遗传演变行为,分别采用SEM、EDS分析了WC杂质在喷涂态、热处理态涂层中的微观组织和相组成。研究结果表明,WC杂质颗粒确实存在于MCrAlY涂层中,并在后期热处理及氧化试验中进一步分解而固溶于涂层中,甚至扩散至单晶基材内部引起含W碳化物的生成,影响涂层及单晶基材的显微组织,改变局部的成分均匀性。同时,本文还采用ThermoCalc软件进行了热力学计算模拟,辅助分析了WC分解及W与C元素在显微组织中的遗传特性。对于WC类粉末和MCrAlY粉末共用的HVOF喷涂设备,建议给MCrAlY粉末配备单独的送粉路径,以确保涂层的纯净度与质量。     

Investigation of spitting behaviour of NiCoCrAlY type materials during electron beam evaporation

ABSTRACT

Spitting behaviour of four casted and powder metallurgy ingots used in the fabrication of NiCoCrAlY-type environmental protective coatings by electron beam physical vapour deposition was investigated and correlated with ingot microstructures and compositions. Spits found in the coatings mainly consisted of the Ni₅Y phase precipitated in the β-NiAl matrix while their typical size exceeded 50?µm. Spitting was less pronounced for ingots having a higher Cr content, larger size of γ-Ni(Co, Cr) precipitates formed within β-NiAl grains and narrower transitional zone formed at the interface between molten and unmolten ingot regions and consisting of coarsened β grains. Large (above 100?µm) agglomerates of the Ni₅Y phase detected below the zone were identified as the main spit precursors.     

粉末冶金靶材多弧离子镀HY3涂层抗氧化性能

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1 100 ℃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5 μm,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1 100 ℃、200 h的高温氧化,P涂层的氧化增量为1.01 mg/cm²,低于铸造靶材制备的涂层(C涂层,1.10 mg/cm²)。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Y2Hf2O7,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−Al2O3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。     

飞机APU涡轮导向叶片高温防护涂层失效模式分析

利用扫描电镜(SEM)、能谱分析仪(EDS)等分析了国内某型在役APU涡轮导向叶片的结构特征与热防护机理,研究了叶片失效件中高温防护涂层的厚度变化与失效模式。结果表明:飞机APU导向叶片中存在渗铝涂层+MCrAlY涂层与单一渗铝涂层2种不同的涂层结构;APU导向叶片失效件的MCrAlY涂层厚度从叶片尾缘—叶盆—前缘区域呈先增大后减小的趋势;受叶片构型影响,叶片尾缘区域涂层的氧化程度较严重,而叶盆区域越靠近前缘的位置涂层氧化损伤程度越低,但叶片前缘区域由于受CMAS腐蚀与高温氧化的耦合作用使得该区域涂层损伤最为严重。     

Failure mechanism of MCrAlY coating at the coating‐substrate interface under type I hot corrosion

MCrAlY coatings are widely used to provide protection of hot component in modern gas turbine engines against high‐temperature oxidation and hot corrosion. Coating‐substrate interface, where the substrate is only partially covered by the ?coatings, is vulnerable to the hot corrosion attack. The accelerated degradation at the coating‐substrate interface can cause fast spallation of the coating, leading to the early failure of the gas turbine components. In this paper, MCrAlY powder was deposited on IN792 disks by high‐velocity oxygen‐fuel spraying. The hot corrosion behavior of the coated sample was investigated using (0.8Na, 0.2K)₂SO ₄ salt deposition at 900°C in lab air. Results showed a minor attack in the coating center, however, an accelerated corrosion attack at the coating‐substrate interface. The fast growth of corrosion products from substrate caused large local volume expansions at the coating‐substrate interface, resulting in an early coating spallation.     

Si对MCrAlY涂层微观结构及性能的影响

本文制备了Si含量分别为0,2%及5%的CoCrAlSiY合金涂层,研究了Si元素的添加对合金粉末及涂层的组织、结构及性能的影响,初步探讨了Si元素对涂层高温性能的作用机理。研究结果表明：Si元素主要分布在涂层的β相中,通过影响β相的含量和分布对涂层的高温性能产生影响,Si推进了合金由内氧化向外氧化发生的过程,促进了保护性氧化膜的形成,但Si含量过高,会引起氧化膜的PBR值增加,氧化膜的应力变大,不利于涂层高温抗热震性能的提高。     

Corrosion of MCrAlY: Pt composites prepared by spark plasma sintering

Cyclic oxidation tests of sintered MCrAlY:Pt composites were carried out at temperatures of 1223 and 1273?K. Composite tablets were previously produced by spark plasma sintering. To assess an effect of platinum dispersed, microstructural characterisation was performed on the tablets before and after the cyclic oxidation treatment. Scanning electron microscopy analysis of the oxide layer showed that the presence of typical α-Al₂O₃ and NiAl₂O₄ spinel had structure columnar and equiaxial in both samples. Fine sintered microstructure and addition of Pt into the MCrAlY matrix enhanced the resistance of the material to cyclic oxidation.     

真空热处理对多弧离子镀NiCoCrAlY涂层高温氧化行为的影响

采用多弧离子镀技术在镍基高温合金上沉积NiCoCrAlY涂层,通过真空热处理消除涂层内部孔洞.研究了950、1000和1050℃热处理后的涂层在1000℃下的氧化实验,以探究最优的热处理温度.采用XRD、SEM和EDS观察分析涂层的物相组成和表截面形貌.结果 表明,真空热处理后,基体与涂层结合紧密,氧化增重相对缓慢,涂...     

Effect of manufacturing related parameters on oxidation properties of MCrAlY‐bondcoats

The effect of MCrAlY‐bondcoat manufacturing parameters prior to TBC deposition on the bondcoat oxidation behavior and TBC lifetime was studied. The studied material was a NiCoCrAl(Y/Hf) free‐standing coating. It was found that variation of oxygen partial pressure during vacuum plasma spraying and the vacuum heat treatment procedure significantly affects the yttrium and hafnium distribution in the coating. In coatings sprayed at high pO₂, yttrium and hafnium were mainly tied up into oxide precipitates. This effect is apparently responsible for an early alumina scale spallation and failure of the initially studied TBC system during cyclic oxidation. In contrast, the coating sprayed at low pO₂ revealed an overdoping effect, i.e. extensive yttrium and hafnium incorporation into the scale resulting in an accelerated scale growth rate and internal oxidation. It was shown that by variation of the vacuum heat treatment parameters the yttrium and hafnium distribution in the near‐surface regions of the low oxygen coating can be modified. The latter result demonstrates the potential of minimizing the negative overdoping effect on the scale growth in the thermal‐sprayed MCrAlY coatings with low oxygen and/or high reactive element contents by optimization of the vacuum heat treatment procedure.     

Temperature Effect on Early Oxidation Behavior of NiCoCrAlY Coatings: Microstructure and Phase Transformation

Initial oxidation behavior of NiCoCrAlY coating prepared by arc-ion plating has been studied in air at 900, 1000 and 1100 °C. The results showed that phase transformation from transient θ-Al₂O₃ to α-Al₂O₃ was highly related to the temperature and oxidation time. The oxide scale in the initial stage was mainly composed of θ-Al₂O₃ at 900 °C. Instead, more amount of α-Al₂O₃ emerged out with increasing oxidation temperature. The elemental distribution after oxidation confirmed that faster chromium diffusion to the oxide scale played an important role in the speedy transformation from θ-Al₂O₃ to α-Al₂O₃. Y segregation at scale/coating interface resulted in less cavity formation and hence improved the oxide scale adherence.