IC-6高温合金的氧化性能与防护

测定了IC－6高温合金在900℃－1100℃的氧化动力学曲线。结果表明：900℃，IC－6合金的氧化膜主要由α－Al2O3、NiAl2O4和NiO构成并含有少量的NiMoO4和MOo2.1050℃和1100℃氧化时，IC－6合金表面生成了挥发性很强的MoO3，发生了氧化失重，IC－6合金上沉积NiCoCrAlY涂层后，900℃，涂层的氧化膜主要为α－Al2o3；1050℃时，氧化膜主要为α－Al2O3和Cr2O3，大大改善了合金的抗氧化性；1100℃时，氧化膜主要由α－Al2o3、NiAl2O4和NiO构成，涂层虽然有一定的保护性，但效果不如900℃和1050℃时显著，形成以α－Al2O3和Cr2O3为主的氧化膜是使合金沉积NiCoCrAlY涂层后抗氧化能力大大提高的直接原因。     

Combined pre-annealing and pre-oxidation treatment for the processing of thermal barrier coatings on NiCoCrAlY bond coatings

A combined pre-annealing and pre-oxidation treatment was developed for the processing of partially yttria stabilized (PYSZ) thermal barrier coatings (TBC) on top of NiCoCrAlY bond coatings (BC). To develop this pre-treatment, the influence of the oxygen potential during pre-annealing and pre-oxidation on the life span and failure mechanisms of the entire high temperature coating system upon thermal cycling was investigated. The results of this study showed that the service life of the coating system depended strongly on the composition and microstructure of the thermally grown oxide (TGO) after pre-oxidation. The longer life spans were obtained if the TGO thickened very slowly during thermal cycling due to a large α-Al₂O₃ grain size. Such a slow-growing TGO corresponded with a pre-treatment for which θ-Al₂O₃ was formed during pre-oxidation and for which the yttrium was located within a high density of pegs along the TGO/BC interface after pre-oxidation. If the yttrium was present on top of the TGO after pre-oxidation, a thick mixed alumina-zirconia layer formed upon thermal cycling. This mixed oxide layer contributed significantly to the total oxide layer thickness, resulting in short life spans. The formation of NiAl₂O₄ spinel in between the TBC and the α-Al₂O₃ should be avoided, since this can lead to premature failure along the spinel/α-Al₂O₃ interface.     

Synthesis and oxidation behavior of nanocrystalline MCrAlY bond coatings

Thermal barrier coating systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a metal bond coat (MCrAlY, M = Ni, Co) and a ceramic top layer (ZrO₂/Y₂O₃). In this work, the oxidation behavior of conventional and nanostructured high-velocity oxyfuel (HVOF) NiCrAlY coatings has been compared. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed on a nickel alloy foil to form a nanocrystalline coating. Freestanding bodies of conventional and nanostructured HVOF NiCrAlY coatings were oxidized at 1000 °C for different time periods to form the thermally grown oxide layer. The experiments show an improvement in oxidation resistance in the nanostructured coating when compared with that of the conventional one. The observed behavior is a result of the formation of a continuous Al₂O₃ layer on the surface of the nanostructured HVOF NiCrAlY coating. This layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions present in the conventional coating. The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.     

冷喷涂CoNiCrAlY涂层在Na_2SO_4熔盐中的热腐蚀行为

利用冷喷涂技术制备CoNiCrAlY涂层,并对涂层进行了真空预氧化处理。结合X射线衍射,扫描电镜,能谱分析等方法研究预氧化处理前后的CoNiCrAlY涂层在900℃的Na2SO4熔盐中的热腐蚀行为。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0.28%(体积分数)。真空预氧化处理在涂层表面生成厚约0.26μm连续、致密的α-Al_2O_3氧化膜;喷涂态涂层和预氧化涂层在热腐蚀150h后表面均生成了以α-Al_2O_3为主的致密连续氧化膜,保护了基体免受腐蚀破坏;真空预氧化处理有效减缓了S和O等元素向涂层内扩散的速率,从而提高了涂层的抗Na2SO4熔盐热腐蚀性能;高温热腐蚀对涂层的破坏作用远大于高温氧化。在相同温度下,涂层在单一Na2SO4熔盐中腐蚀时,Al的消耗速率约为高温氧化时的2倍。     

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。     

Electrolytic Co-deposition of Ni-CrAlY Composite Coatings Using Different Deposition Configurations

With the aim of seeking an alternative low-cost process for the fabrication of MCrAlY coatings, an electrolytic co-deposition process was employed to form a composite coating consisting of a Ni matrix and CrAlY particles. Three configurations were investigated in the co-deposition process, including a vertical setup, a horizontal arrangement, and a rotating barrel. The CrAlY volume fractions in the resultant composite coatings were compared. The advantages and disadvantages of each configuration were discussed. Among the three configurations studied in this paper, the rotating barrel demonstrated the best overall performance, with the capability of producing coatings with more uniform CrAlY particle incorporation of up to 40 vol.%.     

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.     

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.