Creep rupture in a nickel-based superalloy

Smooth bar creep rupture tests were conducted under constant loads at 1033 and 1144 K using RENé 80. Creep deformation occurred dominantly by the dislocation creep mechanism, but creep rupture proceeded by the continual nucleation and growth of cavities. Rupture times were well predicted by the constrained diffusive growth model of Riedel, particularly at low applied stresses, but their temperature dependence and the Monkman-Grant product were better related to the unconstrained diffusive growth models. Interruption tests showed development of micro- cracks in the tertiary stage of creep and sometimes revealed edge cracks, the growth of which provided the creep crack growth rate.     

A process model for the distortion induced by the electron-beam welding of a nickel-based superalloy

A process model suitable for the prediction of the distortion induced during the electron-beam welding of nickel-based superalloys is described. For the purposes of model validation, processing trials on WASPALOY have been carried out using an industrial-scale welding apparatus. Particular emphasis has been placed on the effect of altering the focal position of the beam. The heat transfer occurring during welding has been characterized, and values of the thermal efficiency are reported. The thermal cycles experienced by material in the heat-affected zone (HAZ) are reproduced accurately. The resulting modes of distortion, both angular and camber, have been analyzed. For one of the welds, the residual-stress state has been determined using the neutron diffraction technique, and it is shown that the predictions are in reasonable agreement with the observations. While there are some discrepancies, the model is capable of rationalizing the modes and extent of distortion and the manner in which these depend upon the focal position of the beam.     

Inertia welding nickel-based superalloy: Part II. Residual stress characterization

The next generation of Ni-based alloys for aeroengines are richer in γ′ than existing alloys and are more difficult to weld by conventional means. Inertia welding is currently being developed as a joining technique for these alloys. Steep microstructural gradients have been observed in nickel-based superalloy RR1000 tube structures welded by inertia friction welding,^[1] and in this article, the concomitant residual stresses are mapped at depth using neutron diffraction. One tube in the aswelded and two in the postweld heat-treated (PWHT) condition have been investigated. In the case of the as-welded specimen, it was necessary to establish the variation of the stress-free lattice parameter, a ₀, across the weld line to infer elastic strain from lattice spacing changes. A biaxial sin² ψ measurement on thin slices was used to determine a ₀ as a function of the axial position from the weld line. This was in excellent agreement with the variation inferred by imposing a stress balance on the axial measurements. The change of a ₀ across the weld line can be rationalized in terms of the observed variation in the element partitioning effect between the matrix (γ) and the precipitates (γ′). It was found that the residual stresses in the weld and heat-affected zone generated by the welding process are large, especially close to the inner diameter of the welded ring. The experimental results have shown that, in order to relax the residual stresses sufficiently, the heat-treatment temperature must be increased by 50 °C over the conventional heat-treatment temperature. This is due to the high γ′ content of RR1000.     

含Hf和Ta新型镍基高温合金粉末中碳化物相

对含Hf和Ta新型镍基高温合金FGH98Ⅰ等离子旋转电极(PREP)雾化原始和不同温度下预热处理粉末中的碳化物相进行了研究.结果表明:原始粉末中MC'型碳化物可分为两类,一类为富Ti、Ta和Nb,另一类为含Ta、Hf和Zr.两类碳化物均含有一定量非碳化物形成元素Co和Ni及中等强碳化物形成元素Cr和Mo,并以块状、粒状分布于枝晶或胞晶间;随着预热处理温度升高,粉末中富Ti、Ta和Nb的MC'型碳化物转变为MC型碳化物,且其所含Ti、Ta和Nb的总量增大;含Ta、Hf和Zr的MC'型碳化物发生分解和转变,析出稳定的M₂₃C₆、M₆C和MC型碳化物,M₂₃C₆碳化物的析出和溶解温度为950℃和1150℃,M₂₃C₆和M₆C碳化物共存温度为1000～1100℃.另外,粉末中微量元素Hf和Ta主要以碳化物和γ'相参与碳化物反应.     

On the oxidation resistance of a powder metallurgy nickel-based superalloy

Abstract

To evaluate the influence of reactive minor elements on oxidation resistance of a nickel-based superalloy, 0?5w/o Si, and/or 0?1w/o Y were added in various combinations to a quaternary powder metallurgy alloy that consisted of a ternary master alloy, Ni–12Cr–9Fe+6w/o Al (w/o). The processing included production of transverse rupture strength (TRS) bars by uniaxial pressing followed by sintering to 1300°C and Gleeble thermo-mechanical deformation to reduce porosity. Sectioned TRS bars were then oxidised (static) at 900°C in air for times up to 1000 h and the influence of the Si/Y additions on oxidation resistance was determined via a combination of weight gain data and microstructural examination. It was found that the addition of 0?5w/o Si to the quaternary Ni–Cr–Fe–Al powder metallurgy system provided a measureable improvement in oxidation resistance both in terms of thickness of oxide layer and in overall weight gain. Conversely, 0?1w/o Y provided little benefit when added with the Si and was shown to be detrimental in the absence of Si. Interestingly, little difference was noted in final microstructures. Specifically, variation in %γ′ between samples was minimal (58?3–61?7 v/o) and a distinct precipitate free zone was always present between the oxide and the γ+γ′ matrix.

Afin d’évaluer l’influence des oligoéléments réactifs sur la résistance à l’oxydation d’un superalliage à base de nickel, on a ajouté 0?5% en poids de Si et/ou 0?1% en poids d’Y en combinaisons variées à un alliage quaternaire de la métallurgie des poudres qui consistait en un alliage ternaire maître, Ni–12Cr–9Fe+6% en poids d’Al. Le traitement incluait la production de barres de résistance à la rupture transversale par pressage uniaxe, suivi par le frittage à 1300°C et par la déformation thermomécanique de Gleeble pour réduire la porosité. Les barres sectionnées de TRS étaient ensuite oxydées (en statique) à 900°C à l’air jusqu’à 1000 h et l’influence des additions de Si/Y sur la résistance à l’oxydation était déterminée par l’intermédiaire d’une combinaison de données de gain de poids et d’examen de la microstructure. On a trouvé que l’addition de 0?5% en poids de Si au système quaternaire Ni–Cr–Fe–Al améliorait de façon mesurable la résistance à l’oxydation, tant en termes de l’épaisseur de la couche d’oxyde que de son gain global en poids. Réciproquement, 0?1% en poids d’Y avait peu de bénéfices lorsque ajouté avec le Si et l’on a montré qu’il était nuisible en absence de Si. De façon intéressante, on notait peu de différence dans les microstructures finales. Spécifiquement, la variation entre les échantillons du% de γ′ était minime (58?3 à 61?7% en volume) et une zone distincte sans précipités était toujours présente entre l’oxyde et la matrice de γ+γ′.     

电感耦合等离子体质谱法测定镍基高温合金中锗

镍基高温合金中的低熔点元素锗会对镍基高温合金力学性能和组织产生有害影响,因此需对其中锗的含量进行检测和严格限制.实验采用体积比为1 ∶ 1的HF-HNO3混酸在密闭体系中微波消解样品,选择72Ge作为分析同位素和动能歧视(KED)模式克服质谱干扰,采用基体匹配法绘制校准曲线和铑内标校正克服基体效应和仪器漂移的影响,建立...     

选择性激光熔化镍基高温合金的工艺优化

采用实验设计田口法及响应面法,对镍基高温合金选择性激光熔化过程中的三个工艺参数(激光功率、扫描速度和扫描间距)进行优化,以成形样品的相对密度作为评价标准,研究工艺参数对最终试样相对密度的影响.基于方差分析、信噪比、主效应图、响应曲线图等,分析各因素及其之间的相互作用对样品相对密度的影响.研究结果表明,不同工艺参数对试样...     

Viscoplastic constitutive model of a nickel-based superalloy under multiaxial loading conditions

Based on Chaboche constitutive model, a viscoplastic constitutive model of nickel-based alloy under multiaxial loading is proposed by introducing Lemaitre damag...     

Microstructures and mechanical properties in powder-based additive manufacturing of a nickel-based alloy

In powder-blown additive manufacturing, the microstructure and mechanical characteristics of the deposited layers are influenced greatly by the process parameters used. The microstructures and mechanical properties of the 1718 nickel alloy processed by additive manufacturing were investigated in this research. The samples were subsequently used to prepare metallographic specimens for observations by optical microscopy and scanning electron microscopy, and hardness test. It was found that the fine equiaxed grains are presented in the build and side surface. There is no difference of the microstructure along the build direction. Subsequently, the hardness is uniform along the thickness and the value is around 260 HV. The potential application includes imitation jewelry and holloware.     

Thermodynamic analysis of the oxidation period of making a nickel-based multicomponent superalloy

The oxygen activity is studied by oxygen sensors during the oxidation period in experimental heat of a superalloy in a 5-t electric arc furnace. The results of chemical analysis of metal and slag samples are used to calculate the activities of the metallic and oxide solution components using the energy parameters of the models of a pseudosubregular solution for the melt and a pseudoregular ionic solution for the slag, which were determined and presented in our earlier works. Equations are derived for the activity of oxygen in equilibrium with all melt components simultaneously and with each component individually. The entire oxidation process and the oxidation reaction of each metallic solution component are analyzed by comparing the actual and equilibrium oxygen activities in the metal at the beginning, middle, and end of the oxidation period of heat. The driving forces of the oxidation process are calculated from the difference between the actual and equilibrium chemical potentials of oxygen.     

Phase composition and phase stability of a high-chromium nickel-based superalloy,IN939

The experimental techniques of atom probe time of flight mass spectrometry, field emission STEM X-ray microanalysis, and electron probe X-ray microanalysis have been used to investigate the composition and stability of the various phases in alloy IN939 as a function of heat treatment and long-term exposure. The results show a need for some refinement of phase stability calculations, in particular, to take into account the incomplete partitioning of alloy elements between phases and the effects of different exposure conditions during service. The effects of segregation during casting have also been investigated.     

长期时效对GH4586A合金组织及拉伸性能的影响

研究了GH4586A合金在750℃、800℃长期时效过程中室温拉伸性能与组织变化的关系.利用扫描电镜对合金显微组织进行了观察;利用透射电镜对析出相进行了鉴定;通过物理化学相分析方法定量分析了长期时效过程中合金中相的质量分数.结果表明,该合金在750～800℃时效有μ相和σ相析出,并且随时间延长数量增加;在750～800℃长期时效过程中M23C6碳化物析出.M23C6主要在晶界析出且其析出量受时效温度及时间的影响;合金在750℃、1 500 h之内使用,强度和塑性可以匹配,超过1 500 h后由于μ相和σ相析出量明显增多,塑性迅速下降,合金不能作为转动件使用.     

Metal injection moulding of nickel-based superalloy CM247LC*

Metal injection moulding (MIM) is a promising new production technology for small- to medium-sized parts with high complexity for high-temperature applications like aero engines or turbochargers. This study concerns the feasibility of manufacturing parts from nickel-based superalloy CM247LC via MIM. CM247LC poses a serious challenge for MIM processing. Because of its high aluminium content, the strength potential is very high, but the sintering capability is severely restricted. Differential scanning calorimetry and dilatometry measurements as well as ThermoCalc simulations are used to optimise the sintering step of the MIM process route. Carbon, nitrogen and oxygen contents of the powder and the as-sintered specimens are measured to evaluate the pick-up of impurities during processing. The microstructure of the as-sintered specimens is characterised with respect to residual porosity, grain size, carbide content and γ′ precipitation size and morphology. Ways to further improve the microstructure and strength will be discussed.     

On the microstructural instability of an experimental nickel-based single-crystal superalloy

The susceptibility of an experimental nickel-based single-crystal superalloy to the precipitation of topologically close-packed phases (TCPs) is considered. Its composition has been chosen to be enriched with regard to molybdenum with no tungsten being present, in order to promote microstructural instability and to allow this to be studied. Two conditions are examined: (1) as-cast and (2) as-cast with a solutioning and aging treatment. In the as-cast condition, it is shown that the interdendritic region is already prone to TCP formation, and that further heat treatment in the vicinity of 1000 °C increases the extent of this severely. This is attributed to the partitioning of Ta, which causes an increase in the γ′ volume fraction in the interdendritic regions and a concomitant enrichment of the γ matrix with respect to Mo and particularly Cr. In the solutioned and aged state, TCPs form after heat treatment in the range from 800 °C to 1100 °C and form preferentially at the dendrite cores; this is due to the presence of residual Re, which does not diffuse as quickly as Ta in the opposite direction. The different TCP particles exhibit very different morphologies. At 1000 °C, the P phase is prevalent; around 850 °C, the P phase is still found, but μ is predominant and is found in association with σ. The experimental data are compared with the predictions of thermodynamic software and a database of thermodynamic parameters; the predictions are reasonable, although some discrepancies are noted.     

Inertia welding nickel-based superalloy: Part I. Metallurgical characterization

This article describes a quantitative study of the microstructure of nickel-based superalloy RR1000 tube structures joined by inertia welding. One as-welded and three post weld heat-treated (PWHT) conditions have been investigated. The samples were characterized mechanically by measuring the hardness profiles and microstructurally in terms of γ grain size, γ′ precipitate size and volume fraction, stored energy, and microtexture. Electron backscatter diffraction (EBSD) was used to characterize high-angle grain boundaries (HAGB) and the variation of microtexture across the weld line. The coherent γ′ precipitates were investigated over a range of scales on etched samples in a field emission gun scanning electron microscope (FEGSEM), using carbon replicas in a transmission electron microscope (TEM) and from thin slices by means of high-energy synchrotron X-rays. Dramatic changes in the microstructure were observed within 2 mm of the weld line. In this region, the hardness profile is influenced by changes in grain size, γ′ volume fraction, γ′ particle size, and the work stored in the material. Further away, the observed hardness variation is still significant although only minor microstructural changes could be observed. In this region, the correlation of microstructure and hardness is less straightforward. Here, a combination of small microstructural changes appears to give rise to a significant change in strength. No significant texture or grain distortion was observed in the extensively plastically deformed region due to recrystallization.     

Mechanisms of damage and fracture in high-temperature,low-cycle fatigue of a cast nickel-based superalloy

In cast Udimet 500 subjected to high-temperature, low-cycle fatigue, localized oxidation at grain boundaries plays an important role in crack nucleation and propagation. Evidence is presented of a surface ridging and pronounced grain boundary penetration due to oxidation, a denudedγ′ zone adjacent to the oxide, and cracking of the oxide. The ridging is selective, and is presumed to occur on those boundaries where high stress exists. The phenomenon is viewed as analogous to stress-corrosion cracking.     

多元光谱拟合-电感耦合等离子体原子发射光谱法测定含铌镍基高温合金中铜

样品经盐酸、硝酸和氢氟酸溶解后,选择Cu 327.393 nm作为分析线,选用多元光谱拟合(MSF)校正谱线干扰,建立了使用电感耦合等离子体原子发射光谱法(ICP-AES)测定含铌镍基高温合金中铜的方法。结果表明,含铌镍基高温合金中的共存元素铌对测定元素铜存在严重的谱线干扰,使ICP-AES测定结果存在较大误差,而使用MSF可有效校正铌对铜的谱线干扰,铜的质量分数在0.001 5%~0.025%范围内与发射强度呈线性,校准曲线线性相关系数R²=1.000 0;方法检出限为0.000 2%。按照实验方法测定含铌镍基高温合金标准样品中的铜,结果的相对标准偏差(RSD,n=8)为2.1%,测定值与认定值相符。     

镍基高温合金GH4738的凝固偏析和碳化物析出行为

高温合金铸锭凝固过程内部各区域散热条件不同,冷却速率存在明显差异。采用差示扫描量热分析(DSC)、高温共聚焦显微镜(HT-CLSM)原位观察和定向凝固(DS)的方法,研究了宽冷速范围下GH4738合金的凝固偏析和碳化物析出行为。结果表明, GH4738合金的凝固顺序为L→γ+L,L→γ+L+MC,L→γ+MC+η+(γ+γ′),其中MC型碳化物、η相和(γ+γ′)共晶相为合金凝固过程中的主要偏析产物;Ti、Mo元素是合金的主要枝晶间偏析元素;提高冷却速率能有效降低凝固前沿残余液相中的溶质富集程度;铸态组织中的的碳化物主要为富Ti的MC型碳化物(TiC、Ti(N)C)和以TiN或Al₂O₃为核心的MC型复合碳化物(Al₂O₃-TiC、TiN-TiC);随着冷却速率降低,碳化物平均尺寸增大,体积分数减小,形貌由小块状向长条状、汉字状和大块状演变。     

热挤压对FGH96镍基粉末高温合金微观组织的影响

研究了热挤压温度、挤压比、挤压速度、挤压前预处理对FGH96镍基粉末高温合金微观组织的影响规律,确定了获得晶粒尺寸小于10 μm的超塑性细晶组织的热挤压方法.研究结果表明,热等静压后FGH96合金发生了再结晶,实现了粉末的完全致密化成形,但晶粒大小极不均匀,且存在明显的原始颗粒边界(PPB)缺陷.采用热挤压前预处理工艺...     

烧结镍基高温合金丝网多孔材料的抗氧化性能研究

采用静态增重法,测试了两种不同尺寸的烧结镍基高温合金丝网多孔材料样品及致密单丝样品在900℃下的氧化动力学曲线与氧化速率;采用9410型全自动压汞仪测试多孔小样品的表面积,同时通过透气系数计算其表面积,并据此对多孔小样品的氧化速率进行修正;用SEM、EDS及XRD等手段观察分析多孔样品氧化100 h后的显微形貌与氧化物的组成情况。结果表明:经过100 h氧化实验,大、小多孔样品的氧化速率为单丝样品的7倍左右;多孔小样品修正后的氧化速率远远小于修正前的氧化速率,也小于单丝样品的氧化速率;多孔样品的表面氧化物呈球形,分布较为均匀,其组成主要为Ni Cr_2O_4。