Influence of Sputtered NanocrystaUine Coating on Oxidation and Hot Corrosion of a Nickel-based Superalloy M951

The isothermal and cyclic oxidation behaviors in air and hot corrosion behaviors in Na2SO4 ＋ 25 wt% K2SO4 salt of M951 cast superalloy and a sputtered nanocrystalline coating of the same material were studied. Scanning electron microscopy, energy dispersive X-ray spectroscope, X-ray diffraction, and transmission electron microscopy were employed to examine the morphologies and phase composition of the M951 alloy and nanocrystalline coating before and after oxidation and hot corrosion. The as-sputtered nanocrystalline layer has a homogeneous y phase structure of very fine grain size （30-200 nm） with the preferential growth texture of （111） parallel to the interface. Adherent AI203 rich oxide scale formed on the cast M951 alloy and its sputtered coating after isothermal oxidation at 900 and 1000 ℃. However, when being isothermal oxidized at 1100℃ and cyclic oxidized at 1000 ℃, the oxide scale formed on the cast alloy was a mixture of NiO, NiAl2O4, Al2O3 and Nb205 and spalled seriously, while that formed on the sputtered coating mainly consisted of Al2O3 and was very adherent. Nanocrystallization promoted rapid formation of Al2O3 scale during the early stage of oxidation and enhanced the adhesion of the oxide scale, thus improved the oxidation resistance of the substrate alloy. Serious corrosion occurred for the cast alloy. The sputtered nanocrystalline coating apparently improved the hot corrosion resistance of the cast alloy in the mixed sulfate by the formation of a continuous Al2O3 and Cr2O3 mixed oxide layer on the surface of the coating, and the pre- oxidation treatment of the coating led to an even better effect.     

High-Temperature Oxidation Behavior of a Ni-Cr-W-Al Alloy

A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-Al alloy in air at 1250℃ with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure and composition of the oxide scale were investigated by means of scanning electron microcopy and X-ray diffraction. The results showed that the oxide scales of the alloy were a compact and continuous outer Cr2O3 and NiCr2O4 layer and an inner Al2O3 layer that was in dendrite shape. Oxides scales with good adherence were formed on the surface of the alloy, which made the alloy perform excellent high-temperature oxidation resistance.     

Analysis of Surface Oxide Films Formed in Hydrogenated Primary Water on Alloy 690TT Samples With Different Surface States

Oxidation of Alloy 690 TT samples either manually ground to 400 and 1500 grit, mechanically polished, or electropolished was performed in a solution of 1500 10 6B and 2.3 10 6Li with 2.5 10 6dissolved H2, at 325℃ and 15.6 MPa for 60 days. The oxide films grown on samples with different surface states were analyzed using various techniques. Results show that a triple-layered structure was formed after immersion： an outermost layer with large scattered oxide particles rich in Fe and Ni, an intermediate layer with small compact oxide particles rich in Cr and Fe for the ground surfaces and loose needle-like oxides rich in Ni for the polished surfaces, and an inner layer with continuous Cr-rich oxides. The surface state was found to affect not only the surface morphology, but also the corrosion rate. Grinding accelerated the growth of protective oxide films such that the ground samples showed a lower oxidation rate than the polished ones.Samples of ground Alloy 690 TT showed superior resistance to intergranular attack（IGA）.     

Influence of Water Vapor on the Isothermal Oxidation Behavior of Thermal Barrier Coatings

The oxidation of specimens with thermal barrier coating (TBC) consisted of nickel-base superalloy, low-pressure plasma sprayed Ni-28Cr-6AI-0.4Y (wt pct) bond coating and electron beam physical vapor deposited 7.5 wt pct yttria stabilized zirconia (YSZ) top coating was studied at 1050℃ respectively in flows of 02, and mixture of O2 and 5%H2O under atmospheric pressure. The thermal barrier coating has relatively low oxidation rate at 1050℃ in pure O2. Oxidation rate of thermal barrier coating in the atmosphere of O% and 5%H2O is increased The oxidation kinetics obeys almost linear law after long exposure time in the presence of 5% water vapor. Oxide formed along the interface between bond coat and top coat after oxidation at 1050℃ in pure O2 consisted of Al2O3, whereas interfacial scales formed after oxidation at 1050℃ in a mixture of O2 and 5%H2O were mainly composed of Ni(AI,Cr)2O4,NiO and AI2O3. It is suggested that the effect of water vapor on the oxidation of the NiCrAlY coating may be attributed     

Solid-state cold spraying of FeCoCrNiMn high-entropy alloy:an insight into microstructure evolution and oxidation behavior at 700-900℃

About 3 mm thick five-element equimolar high-entropy alloy(HEA) FeCoCrNiMn was successfully deposited by solid-state cold spraying(CS).The high-temperature oxidation behavior of the CSed HEA was investigated at 700-900℃.Heat treatment was performed on the CSed HEA before oxidation to heal the incomplete interfaces between the deposited particles.Results show that the microstructure of the CSed HEA is characterized by grain refinement and abundant interparticle incomplete interfaces.Post-spray heat treatment promotes recrystallization and grain growth in the CSed HEA.After oxidation testing,the oxide scales are composed of multi-layers:a Mn₂O₃(or Mn₃O₄) outer layer,a Mn-Cr spinel intermediate layer and a Cr₂O₃ inner layer.The CSed HEA exhibits higher parabolic rate constants and more favorable internal oxidation than the bulk HEAs that have similar compositions in the literature.Such a discrepancy becomes pronounced at higher temperatures.The grain refinement and numerous particle boundaries are responsible for such a distinctive performance of the CSed HEA.     

Oxidation Resistance Coatings of Ir – Zr and Ir by Double Glow Plasma

Oxidation resistance coatings of Ir-40 at.% Zr and Ir were produced onto Mo substrates by double glow plasma technology. The oxidation resistances of the coatings were evaluated at high temperature. Ir-Zr coating consisted of two layers： the primary layer close to the substrate was composed of dense columnar grains and the second layer was composed of dense grains of nanometric size. The mass gain of Ir coating above 800℃ was about 1.35% due to the formation of solid IrO2. The mass loss of Ir coating was about 5.3% due to the formation of gaseous oxide IrO3 when being held at 1227 ℃ for 30 min. The substrate was protected more effectively by multilayer than monolayer coating of Ir in oxidizing environment. The Ir-Zr coating was well bonded to the substrate after oxidation at 800℃. After oxidation at 1000℃, the Ir-Zr coating was poorly bonded to the substrate. The oxidation resistance of Ir-Zr coating was poor due to high content of Zr.     

Short-time Oxidation of Alloy 690 in High-temperature and High-pressure Steam and Water

The oxidation behavior of alloy 690 exposed to high-temperature and high-pressure steam and water at 280 ℃ for 1 h was investigated by scanning electron microscopy(SEM),atomic force microscopy(AFM) and X-ray photoelectron spectroscopy(XPS).In high-temperature and high-pressure steam,the oxide film is composed of an outermost Ni-rich hydroxides layer,an intermediate layer of hydroxides and oxides enriched in Cr,an inner oxide layer.The film formed in high-temperature water is similar to that in steam,except for missing the Ni-rich hydroxides layer.Samples with different surface finishes(electropolished,mechanically polished,ground,and as-received) were prepared for comparison.A general increase of the oxide thickness with the degree of surface roughness is observed.The equivalent oxide thicknesses lie in the range of 100-200 nm for the as-received samples,150-250 nm for the samples ground to 400# and 10-20 nm for the samples ground to 1500#,mechanically polished,and electropolished.     

Oxidation Behavior of Pd-Modified Aluminide Coating at High Temperature

(Ni,Pd)Al coating, prepared by low pressure pack cementation on the Ni-base superalloy M38 where Pd-20 wt pct Ni alloy was predeposited, consists of a single β-(Ni,Pd)Al phase. The initial isothermal oxidation behavior of (Ni,Pd)Al coating was investigated by TGA, XRD, SEM/EDS at 800～1100℃. Results show that oxidation kinetics accord preferably with parabolic law at 800, 900 and 1100℃, but not at 1000℃.θ-Al2O3 was observed at 800～1100℃. It is found that Pd plays an important role in accelerating the diffusion of Ti from the substrate to the coating surface in the aluminide coating.     

Surface Microstructure and High Temperature Oxidation Resistance of Thermal Sprayed NiCoCrAlY Bond-Coat Modified by Cathode Plasma Electrolysis

The surface properties of the air-plasma sprayed bond-coat have been modified by cathode plasma electrolysis(CPE). After modification, a re-melted layer without obvious pores and oxide stringers is formed,the gain size of re-melted layer is approximately 80–120 nm. It is shown, from cyclic oxidation at 1100℃,that a thin oxide scale mainly composed of α-Al_2O_3 has been formed on the modified bond-coat and the oxidation resistance of the modified bond-coat has been significantly improved. Such beneficial result can be attributed to following effects: during CPE process, the plasma discharges with high temperature take place on the bond-coat surface. With plasma discharge treatment, the surface is melted and quickly re-solidified, the grain size decreases, and the pores and oxide stringers disappear. During cyclic oxidation, owing to the above modification of surface properties, the critical content of Al for selective oxidation is significantly decreased. Therefore, a continuous Al_2O_3 scale is formed.     

Effects of rejuvenation heat treatment on microstructure and creep property of a Ni-based single crystal superalloy

Both surface and internal microstructures of a second-generation Ni-based single crystal(SX) superalloy were studied after creep and rejuvenation heat treatment(RHT).It is indicated that the microstructures,such as the dislocation network,the γ phase and the γ' phase,can be recovered to those after the standard heat treatment(SHT).It is found that RHT affected zone(RAZ) formed at the surface is composed of theγ'-free layer,the transition layer and the recrystallization(RX),which are less than 20 μm in depth totally.Such depth of the RAZ doesn't affect the properties of the superalloy.The morphology of γ' phase at the RAZ is related to the composition of the elements.The average creep life after RHT is close to the average life after SHT.It is concluded that RHT could effectively repair SX parts and increase the total life of the sample after a damage by creep.     

310S耐热钢的高温氧化行为EI北大核心CSCD

采用静态氧化不连续增重法研究晶粒尺寸和成分存在差异的两种310S耐热钢(1#和2#)在800~1100℃下的氧化动力学与膜结构,比较两者的氧化性能差异,阐明氧化膜的生长机制和差异形成原因。结果表明:800~900℃时氧化膜均由富Si氧化层和富Cr氧化层组成,1#试样的氧化速率更低;1000℃时氧化膜中增加了Cr-Mn氧化物层并在1100℃时转变为Cr-Mn-Fe氧化层,并且两者的氧化速率接近;整体上2#试样的氧化膜在所有温度下更加致密、平整,黏附性更好,保护能力更强。特别在1100℃时,两者的富Cr氧化层和Cr-Mn-Fe氧化层的形态分化较大,2#试样的氧化膜形态更有利于长期的抗氧化性能。总体上,2#试样的抗氧化性优于1#试样。2#试样所具备的更小的平均晶粒尺寸和更均匀的晶粒提高了择优氧化元素的扩散通量并降低氧化膜的非均匀生长,造成两者氧化性能的差异。     

High temperature oxidation and sulfate induced corrosion of an oxide dispersion strengthened Ni base superalloy

The oxidation and sulfate induced corrosion behavior of an oxide dispersion strengthened nickel base superalloy, MA 6000, has been studied at 900°C and 1000°C. The experimental program involved thermogravimetry. X-ray diffraction and scanning electron microscopy. The kinetics of high temperature oxidation in air increased with increasing temperature. The experimental activation energy for oxidation in air indicated that a chromia-rich scale formed the protective oxide layer. In the case of sulfate induced corrosion, however, increasing temperature decreased the scale growth rate. This result has been explained by considering the relative stability of nickel sulfide at 900° and 1000°C. Metallographic studies of the scales are also presented.     

钴基合金铝化物涂层在高温氧化过程中的主要退化方式

铝化物涂层在高温氧化过程中主要以两种方式退化,一是涂层的表面氧化退化,二是涂层的内扩散退化,DZ40M钴基高温合金铝化物涂经900℃和1000℃两个温度下高温氧化后的组织结构变化表明,该涂层在900℃时起的退化为主,而在1000℃时则以内扩散引起的退化为主,通过理论分析可知,涂层以何种退化方式为主,既取决于氧化温度,也取决于涂层本身的组成和结构。     

TiAl合金表面Si-Al-Y共渗层的组织及高温抗氧化性能

通过在1050℃下Si-Al-Y扩散共渗0~4 h在TiAl合金表面制备了Al、Y改性的硅化物抗氧化渗层, 分析了共渗层的结构及相组成, 并对其组织形成机理及高温抗氧化性能进行了研究。结果表明: 1050℃共渗4 h所制备的共渗层具有多层结构, 由外向内依次为TiSi₂外层、(Ti,X)₅Si₄及(Ti,X)₅Si₃(X表示Nb, Cr)中间层、TiAl₂和γ-TiAl内层及富Al的过渡层, 其中Y元素主要富集于共渗层的外层和中间层。不同时间共渗的结果表明, Si-Al-Y共渗层的形成是一个在基体表面先沉积Al, 后沉积Si的有序过程。经1000℃高温氧化20 h后共渗层表面形成了由TiO₂外层及SiO₂·Al₂O₃次外层组成的致密氧化膜; Y的氧化物主要存在于氧化膜与残余共渗层的界面处, 能够有效地增强膜层的附着力。     

High temperature oxidation behaviour of directionally solidified nickel base superalloy CM–247LC

Abstract

The present paper describes the isothermal and cyclic oxidation behaviour of the technologically important nickel base directionally solidified superalloy CM-247LC in air in the temperature range 1000-1200°C. This superalloy behaves as a transition nickel base alloy under isothermal oxidation conditions and exhibits a fairly long transient oxidation period (~20 h at 1100°C). Irrespective of the temperature of exposure and nature of oxidation (isothermal or cyclic), a composite oxide scale develops on CM-247LC. While the outer portion of the oxide scale consists of either spinel (NiAl₂O₄) or a mixture of spinel and NiO, depending on oxidation temperature, the inner portion is always constituted of alumina. Beyond the transient period, the alloy is found to follow parabolic oxidation kinetics. The oxide layer that forms is invariably very non-uniform in thickness, and is dispersed with two types of oxide particles. While tantalum rich oxide particles are found scattered in the outer zone of the oxide layer, hafnium rich oxide particles lie close to the oxide/metal interface. Results also reveal that the nature of oxidation associated with the CM-247LC superalloy causes entrapment of metal islands in the oxide layer.     

Ni-Cr-Ta-Al-Co-Mo合金在900℃和1000℃的恒温氧化行为

用热重分析法测定了氧化动力学曲线,并采用XRD和SEM（EDAX）等手段,研究了Ni12.59Cr6.74Ta4.04A15.16Co1.35Mo6.29W合金在900℃和1000℃的高温氧化行为。结果表明,在氧化初期合金的氧化质量增加较快,随着氧化时间的延长质量增加的速率逐渐降低,其氧化动力学曲线符合抛物线规律。在9...     

HP40Nb钢热浸镀Al-Si高温氧化行为及组织研究

为提高高温抗氧化性能,对HP40Nb钢进行了热浸镀Al-10%(质量分数)Si,并进行不同温度扩散处理,研究了不同扩散处理试样在1000℃条件下的高温氧化行为,通过SEM,EDS和XRD分析了经不同扩散处理后的渗层在高温氧化过程中的组织结构变化.结果表明:经800℃/4h扩散处理,渗层由内层(NiAl+ Cr3 Si)...     

Adhesion of thermal barrier coatings systems after long term oxidation : influence of preoxidation temperature and surface state of the bond coat

Abstract

The aim of this study was to determine the effect of the pre-oxidation temperature and surface state of the bond coat on the microstructure of the oxide scale formed at the first stages of oxidation and on its adhesion after subsequent long-term oxidation (1000 h) at 1100–C. Short-term isothermal oxidations of 1 h were performed at several temperatures (900–C, 1100–C) on a Pt-modified NiAl bond coat with two different surface states (as-aluminized or grit-blasted) deposited on a superalloy (AM1). The adherence of the different systems after an additional isothermal ageing treatment in air at 1100–C for 1000 h, was compared in order to deduce the initial oxide scale leading to the best resistance to spallation. Characterization was performed using SEM and analytical TEM. The crystalline structure and the morphology of the as-formed oxide scale were studied as a function of the different parameters.     

EBPVD制备ODS Ni基高温合金抗氧化性能研究

采用电子束物理气相沉积技术制备了微晶氧化物弥散增强Ni基高温合金,并研究了该合金的高温氧化行为.通过最小二乘拟合得到的合金氧化动力学模型近似遵循4次方规律,并在高温氧化过程中,合金能够生成单一的Al2O3氧化膜,而且氧化膜的粘附性好,不易脱落.稀土氧化物的添加可明显地改善合金的抗高温氧化性能,提高氧化膜的粘附性.