（Ni,Cr）／Al2O3复合涂层制备工艺的研究

利用粉末热喷涂法制备（Ｎｉ，Ｃｒ）／Ａｌ２Ｏ３复合涂层，采用ＸＲＤ和金相对复合涂层的相结构和相组成进行分析，并分析了喷涂工艺对金属／陶瓷系复合涂层制备的影响。实验结果表明，Ａｌ２Ｏ３粉末的沉积率和喷涂参数是影响（Ｎｉ，Ｃｒ）／Ａｌ２Ｏ３复合涂层相结构和相组成的关键。     

溅射Ni—9Cr—1Al纳米晶涂层的高温氧化

对Ｎｉ－９Ｃｒ－１Ａｌ铸合金及其溅射纳米晶涂层进行了９００℃为时２００ｈ恒温氧化实验,结果表明：铸态合金及溅射涂层都生 由Ｃｒ２Ｏ３和Ａｌ２Ｏ３组成的外氧化物。通过断面观察发现两者都发生了内氧化现象,讨论了溅射涂层内氧化发生的机制。     

溅射Ni-9Cr-1Al纳米晶涂层的高温氧化

对Ｎｉ－ ９Ｃｒ－１Ａｌ 铸态合金及其溅射纳米晶涂层进行了９００ ℃为时２００ ｈ 恒温氧化实验,结果表明：铸态合金及溅射涂层都生成了由Ｃｒ２Ｏ３ 和Ａｌ２Ｏ３ 组成的外氧化物．通过断面观察发现两者都发生了内氧化现象．讨论了溅射涂层内氧化发生的机制．     

Ni3Al金属间化合物及溅射CoCrAlY涂层的高温热腐蚀

研究了Ｎｉ３Ａｌ金属间化合物及溅射ＣｏＣｒＡｌＹ涂层在９００～９５０℃空气中，表面存在（Ｎａ，Ｋ）２ＳＯ４盐膜时的热腐蚀行为，结果表明，Ｎｉ３Ａｌ遭受严重的热腐蚀，溅射ＣｏＣｒＡｌＹ涂层可以通过在表面迅速形成保护性Ａｌ，Ｃｒ氧化膜而显著改善Ｎｉ３Ａｌ的耐热腐蚀性能。     

Si＿3N＿4－Al＿2O＿3－ZrO＿2系陶瓷表面氧化层组成的EPMA分析

利用ＥＰＭＡ和ＸＲＤ的分析方法，研究了Ｓｉ＿３Ｎ＿４－Ａｌ＿２Ｏ＿３－ＺｒＯ＿２系陶瓷材料表面氧化层组成。结果表明，Ｓｉ＿３Ｎ＿４－Ａｌ＿２Ｏ＿３－ＺｒＯ＿２系陶瓷材料表面氧化层是由方石英相、ＺｒＳｉＯ＿４相和含有Ａｌ＿２Ｏ＿３、ＣａＯ等的ＳｉＯ＿２玻璃相所组成，其中ＳｉＯ＿２玻璃相中Ａｌ＿２Ｏ＿３、ＣａＯ等的含量，随着氧化时间的增加而逐渐增加。     

Ni_3Al(IC-6)合金防护涂层抗氧化性能研究

Ｎｉ３Ａｌ合金是一种新型高温合金，ＩＣ－６合金是不含Ｃｒ而含１４％Ｍｏ的Ｎｉ３Ａｌ合金。由于高温下Ｍｏ极易氧化升华，因此为使ＩＣ－６合金在高温下可靠工作，需选择ＮｉＣｒＡｌＸ涂层作为ＩＣ－６合金的保护涂层。采用磁控溅射技术，在专用装置上按通过系统研究提出的工艺涂覆ＮｉＣｒＡｌＸ涂层，并对其抗周期氧化性能进行了研究。试验表明：ＮｉＣｒＡｌＹＳｉ涂层对ＩＣ－６合金的防护是非常有效的。     

不同封闭处理ZrO2热障涂层抗热震性的研究

研究了用有机硅树脂,ＮｉＣｒＢＳｉ涂层和水玻璃封闭的ＺｒＯ２热障涂层的抗热震性能,试验表明,有机硅酸脂封闭的效果最好,ＮｉＣｒＢＳｉ涂层次之,水玻璃封闭效果不明显,当涂层氧化失效占主导地位时,涂层热震寿命短,当热应力导致涂层失效占主导地位时,涂层热震寿命较长。     

多弧离子镀MCrAlX涂层的高温性能研究

本文首次应用多弧离子镀技术沉积Ａｌ２Ｏ３保护性氧化膜形成类型的ＮｉＣｏＣｒＡｌＳｉＹＨｆ涂层和 ＣｏＮｉＣｒＡｌＴａＹ涂层，探讨了涂层质量和沉积工艺的关系，对两涂层的高温氧化性能和热腐蚀性能进行了试验研究，分析了涂层的高温防护衰退机制．     

溅射Ni3Al微晶涂层的抗氧化性能

研究了铸态Ｎｉ３Ａｌ合金及其微晶溅射涂层在１０００－１１００℃下等温氧化性能及１０００℃下的循环氧化性能，结果表明：铸态Ｎｉ３Ａｌ合金在氧化过程中形成Ａｌ２Ｏ３，ＮｉＯ和ＮｉＡｌ２Ｏ４的复杂氧化膜，微晶Ｎｉ３Ａｌ涂层在氧化过程中形成α－Ａｌ２Ｏ３和ＮｉＡｌ２Ｏ４尖晶石，不含ＮｉＯ，这种氧化膜的保护作用比含ＮｉＯ的氧化膜的保护作用好，使得其氧化增重比铸态合金小约１半，此外铸态Ｎｉ３Ａｌ合金在氧化过程     

Si及α－Al_2O_3超细粉对Al_2O_3－ZrO_2－C系材料显微结构的影

本文探讨了Ｓｉ及α－Ａｌ２Ｏ３超细粉对Ａｌ２Ｏ３－ＺｒＯ２－Ｃ系材料显微结构的影响．认为在Ａｌ２Ｏ３－ＺｒＯ２－Ｃ系材料中同时加入Ｓｉ和α－Ａｌ２Ｏ３超细粉，Ｓｉ粉除了与Ｃ生成了ＳｉＣ纤维外，其反应产物ＳｉＯ２还与α－Ａｌ２Ｏ３超细粉及ＺｒＯ２生成了莫来石（Ａ３Ｓ２）和Ａｌ２Ｏ３－ＺｒＯ２－ＳｉＯ２（ＡＺＳ）固溶体，这些新生成的矿物相对试样的显微结构产生重要的作用．     

YPSZ纳米结构热喷涂粉末材料工艺优化研究

热等离子体喷涂制备YPSZ纳米结构涂层必须首先进行YPSZ纳米结构粉末材料的研究.本文采用浆料分散、喷雾干燥、热处理的方法制备适于热等离子体喷涂纳米结构涂层的球形、致密YPSZ纳米结构粉末材料.测定浆料的粘度、沉降高度曲线表征浆料的均匀性和稳定性,利用扫描电子显微镜、x射线衍射分析对粉末材料的微观组织及相结构进行分析,利用热重/差热分析对热处理工艺过程进行分析.结果表明:采用优化的工艺成功制备出球形、结构均匀、致密的YPSZ纳米结构粉末材料,适于热喷涂制备YPSZ纳米结构涂层.     

The Application of Flame and Plasma Sprayed Coatings for Cast Iron Molds

Molds made of grey iron for casting iron are subjected to severe temperature fluctuations very similar to the die casting process except for the high pressure erosion that occurs due to molten metal. Therefore, the main life limiting damage for molds is the formation of surface cracks arising from thermal fatigue. Various flame and plasma sprayed coatings were investigated to extend the life of molds for casting iron. Coating materials studied include plasma sprayed ceramic coatings with bond coat (NiCrAl, NiCrAlY, and NiCrAlCoY) as well as powder flame sprayed oxidation resistant alloys (NiCr, NiAl, and NiCrAl). The results of simulated cyclic furnace tests from room temperature to 1100°C in air indicated that the failure occurred along the interface between the bond coat and the iron substrate due to iron oxidation rather than the interface between the ceramic coating and the bond coating for superalloy substrate. The results of field tests are also discussed.     

Application Study on Ceria Based Thermal Barrier Coatings

The industrial application of APS sprayed YPSZ coatings for thermal insulation is established in several branches. As the main potential to increase the efficiency of combustion processes is thermal efficiency and the state‐of‐the‐art systems are limited to surface temperatures below 1200°C for long term applications, there is interest in concepts, that allow an increase of the process temperature. Ceria and ceria based ceramics show an outstanding potential for use at temperatures exceeding 1200°C. A triple‐layer thermal barrier system in consideration of the established system – MCrAlY bond coat and YPSZ – and an additional ceria based top coating are investigated. TBC systems with two different ceria powders are produced by APS and HVOF spraying and evaluated with concern to the microstructure, bond strength, thermal shock behaviour and long term compatibility of the constituents. HVOF sprayed coatings contain more oxygen, are more dense than APS sprayed coatings and do not show segmentation due to cracks perpendicular to the surface. APS sprayed pure ceria coatings show a columnar morphology inside single splats forming the coating. The bond between YPSZ and ceria and the total bond strength of the thermal barrier system exceeds the cohesion inside the ceria coating. The thermal shock resistance of ceria coatings with high silica and sulphur content is low. Long term sintering investigations prove the compatibility of ceria and YPSZ at 1150°C.     

Temperature effect on the role of yttrium in oxidation behaviour of NiCrAl alloys

Temperature effect on the oxidation behaviour of NiCrAl and NiCrAl-Y alloys has been studied in the present work. Thermogravimetric analysis has been carried out at 900, 1000, 1100 °C for 210 h in order to investigate oxidation kinetics. Phase constitution of surface scales was determined by using X-ray diffraction, and microstructure was examined by using scanning electron microscope with energy dispersive spectra. Oxidation resistance of NiCrAl alloy has been found to be improved substantially by adding rare earth element yttrium at all the three experimental temperatures. But Y-rich inclusions result in higher initial oxidation rates as a result of oxidation of the inclusions.     

Thermal barrier coatings produced by laser cladding

A 2kW C0₂ laser has been used to clad a mild steel substrate with two different ceramic coatings, namely yttria partially stabilized zirconia (8 wt% YPSZ) or a mixture of YPSZ and pure alumina powder. A range of laser processing parameters has been investigated. Results have been obtained showing the possibility of using the laser beam for producing a clad layer of thermal barrier coating with different topography depending on the processing conditions.On leave from Scientific Research Council, Baghdad, Iraq.     

Optimising oxidation resistance of MCrAl coating systems using vapour phase alloy design

Abstract

The potential for developing new overlay coatings by codeposition from segmented or multiple sources has been investigated. The main focus of this work was the development of new NiCrAl based alloys with improved resistance to high temperature oxidation. Initially, studies concentrated on the deposition of a wide range of ternary alloy compositions by magnetron sputtering from a segmented target consisting of pure Ni, Cr, and Al segments. Hence, alloy compositions were produced by mixing of these source materials in the vapour phase. These coating compositions were deposited onto high purity Al₂O₃ to ensure that no interaction between the coating compositions and substrate occurred during subsequent oxidation trials. Oxidation trials at 950°C for periods up to 100 h have been undertaken. Modelling of the oxidation behaviour along quasibinary sections has allowed the construction of a ternary iso-oxidation contour map for the NiCrAl system. This approach has identified new oxidation resistant materials with a twofold improvement in oxidation resistance over typical commercial overlay coatings.

MST/1093     

Lifetime‐determining spalling mechanisms of NiCoCrAlRE / EB‐PVD zirconia TBC systems

The mechanisms that control the lifetime of thermal barrier coating (TBC) systems have been traced by two particular overlay bondcoats serving as model systems: superalloy pins (IN100, CMSX‐4) with two alternative NiCoCrAlRE (RE: Hf, Y) bond coat compositions (i) NiCoCrAlY without and (ii) with co‐dopants of silicon and hafnium. On top an electron‐beam physical‐vapor deposited (EB‐PVD) yttria partially stabilized zirconia (YPSZ) TBC commonly mixed with 2 wt.% hafnia, or, rarely with 10 wt.%, was applied. The test pins were thermo‐cycled at 1100 and 1150 °C until failure. Identical lifetimes in cyclic tests on YPSZ TBCs with 2 (relatively high sintering rate) and 10 wt.% hafnia (relatively low sintering rate) preclude an effect of diffusion mechanisms of the YPSZ TBC on lifetime. The fit of lifetimes and test temperatures to Arrhenius‐type relationships gives activation energies for failure. These energies agree with the activation energies for anion and cation diffusion in alumina for the respective bondcoat variant: (i) for the NiCoCrAlY/TBC system for O^2‐ diffusion in alumina, (ii) for the NiCoCrAlYSiHf/TBC system for Al³⁺ diffusion in alumina. SEM and EDS investigations of the thermally grown oxides (TGOs) confirm the mechanisms responsible for TBC failure as indicated by activation energies. Two categories of failure can be distinguished: (i) NiCoCrAlY coatings fail by an “adhesive mode of failure” along smooth bond coat/TGO interfaces driven by a critical TGO thickness. (ii) NiCoCrAlYSiHf coatings fail later and more reluctantly by a “cohesive” crack mode via de‐cohesion at the TGO/TBC interface. In the latter case a quasi‐integrity of the crack‐affected TGO is lengthily maintained up to failure by a crack‐pinning mechanism which runs via Al³⁺ supply from the bondcoat.     

喷雾干燥YPSZ纳米结构热喷涂粉末材料制备及表征

YPSZ纳米结构粉末材料的研究是热喷涂制备YPSZ纳米结构涂层必须首先进行研究的问题。本文采用喷雾干燥方法制备适合于热等离子体喷涂的YPSZ纳米结构粉末原料,同时采用等离子体喷涂制备涂层。利用扫描电子显微镜分析晶粒大小、颗粒形貌,X射线衍射分析相组成,对喷雾干燥后粉末进行热重-差热分析,测定粉末的松装密度、振实密度及流动性。结果表明制备的YPSZ粉末材料具有实心、流动性好、松装密度高、振实密度高、球形度高、单斜相少等优点,采用热等离子体喷涂沉积制备YPSZ纳米结构涂层。     

Hot Isostatic Pressing of Plasma Sprayed Thermal Barrier Coating Systems

Thermal barrier coatings (TBC) are important to aerospace and high performance gas turbine engines because they help to keep the temperature experienced by the base metal low; thus, prolonging the life span of the material. Plasma spraying is a technique commonly used to deposit the ceramic-based TBC. An intermediate layer is applied to enhance the bond between the substrate and the ceramic top coat. However, the oxidation of the bond coat due to the infiltration of gas through the porous ceramic layer is a major problem encountered in TBC. This in turn leads to spalling and eventual destruction of the whole coating system. Hot isostatic pressing (HIP) was performed on a number of plasma sprayed thermal barrier coating systems to investigate the effects the process has on micro structure and other physical properties. Due to the fact that the majority of TBC is exposed to thermal cycling and thermal fatigue, it is hoped that the changes brought about by HIP in the porosity and microstructure will improve the life span and performance of TBC. HIP was performed in the temperature range 750-1300° C and pressures of 50-200 MPa. The bond coats that were studied include Ni-5% Al, Ni-20 percnt; Al, NiCrAl and NiCrAlY, while the ceramic coat was Zr0₂-5 wt percnt; CaO. Characterization of the coatings was carried out using scanning electron microscopy (SEM) and image analyser. The results showed the porosity of the coatings to be dramatically reduced to near zero levels. In addition, the other physical properties like hardness and Young's modulus increased over a wide temperature range.     

Development of a low-expansion bond coating for Ni-base superalloys

Ternary NiCrAl alloys were modified by the addition of Ti and Si in order to adjust their coefficients of thermal expansion (CTE) to less than 15 × 10⁻⁶ K⁻¹ (from room temperature to 1000 °C) without sacrificing essential high temperature oxidation resistance. Vacuum induction melted cast alloy samples were investigated by dilatometry and thermogravimetry (TG). Oxidative TG was conducted isothermally at 900 and 1000 °C and cyclically between 600 and 1100 °C for 100 h respectively. The CTE is reduced mainly by Ti and secondly by Cr additions. Quinary alloys which showed optimal oxidation resistance essentially exhibit phase stability in the solid state at all temperatures. Approximately 4 at.% Si is needed to attain low oxidation rates and to prevent oxide spallation as well. The beneficial effect of Si on oxidation behavior is attributed hypothetically to its ability to initiate the formation of protective alumina and subsequently silica. High Cr contents lessen the beneficial effect of Si owing to the concurrent formation of chromia and/or titania.