Effect of Overheating Events on Microstructure and Low-Cycle Fatigue Properties of a Nickel-Based Single-Crystal Superalloy

Micro-mechanical response to overheating events is an important factor when considering the serviceable life of aero-engine components. A key lifing consideration is the low-cycle fatigue (LCF) behavior of nickel-based single-crystal superalloy components. In this study, the LCF response was investigated at different overheating temperatures (1100 to 1300 °C) and times (30 to 120 min). The overheating events had an impact on the γ' phase content, which was observed to decrease with the increase in overheating temperature and time (fully dissolving at 1300 °C). Due to the dissolution of γ' precipitates, the average γ' size was shifted to larger values, however, the subsequent cooling post the overheating events resulted in the formation of tertiary γ' and a bimodal particle distribution. During the LCF tests, that were performed after the overheating exposure, either cyclic hardening or softening was observed. It could be concluded that overheating exposures had no significant effect on the fracture features. However, overheating events resulted in a decrease of LCF properties, which was correlated to the local dislocation response.

     

Microstructure Characterization and Mechanical Properties of FGH 95 Turbine Blade Retainers

FGH 95 is a powder metallurgy (P/M) processed superalloy,which was developed in the 1980s in China.One of the applications of FGH 95 was high pressure turbine blade retainers.The manufacturing processes used to produce FGH 95 blade retainers consisted of atomization by plasma rotating electrode process (PREP),hot isostatic pressing (HIP) at super-solvus temperature and a sub-solvus solution heat treatment.The material had an equiaxed grain structure (ASTM 6.5-7.5).The γ′ precipitates in as-HIP FGH 95 showed a tri-model distribution.Carbides in the alloy were MC type and precipitated at grain boundaries.The prior particle boundaries (PPB) in the material originated mainly from γ′ phase.Statistics of the mechanical properties data from batch production of the FGH 95 blade retainers were investigated.The as-HIP FGH 95 blade retainers showed high strength at room temperature and 650 ℃,excellent creep resistance and outstanding stress rupture strength at 650 ℃.     

Formation of an Intermediate Layer Between Grains in Nickel-Based Superalloy Turbine Blades

Metallurgical and Materials Transactions A - The boundary region formed on the surface of nickel-based single-crystal turbine blades was investigated by high-resolution microscopy observation....     

Influence of Static Magnetic Field on the Microstructure of Nickel-Based Superalloy by Laser-Directed Energy Deposition

Metallurgical and Materials Transactions A - The influence of a static magnetic field on microstructure evolution during laser direct energy deposition was studied. Our results reveal that dendrite...     

镍基高温合金HIP扩散连接的组织和性能

采用热等静压扩散连接工艺,获得了DD402单晶合金与FGH95合金的扩散偶。研究了热等静压温度对扩散偶的持久性能、组织结构的影响。结果表明,不同温度热等静压的扩散偶均实现了冶金结合;结合界面区形成了一个组织过渡区,DD402单晶合金中的γ′相粒子在HIP过程中发生了筏形化;热处理后结合界面区的γ′相形貌和尺寸未发生明显变化。1 166℃热等静压扩散偶的650℃持久性能偏低,断口在DD402单晶合金侧,断裂面从结合界面区的大尺寸γ′相起始,沿{111}滑移面向筏形γ′相区扩展。     

铝和钛含量对镍基铸造高温合金性能的影响

研究了拉伸和持久强度提高,塑性、冷热疲劳和焊接性能相应降低,尤其是Ti元素的作用尤为明显.还发现合金中的γ'相、MC相和(γ+γ')共晶组织的数量和尺寸是影响合金性能的重要因素.     

Microstructure and Properties of an Advanced Nickel-base PM Superalloy

The need for nickel-base powder metallurgy （PM） superalloy turbine discs is becoming increasingly evi dent. With the eventual aim of improving thrust-to-weight ratio of aeroengines for power generation, well integration of significantly high strength, high damage tolerance and high-temperature capability would be reasonably required. An advanced PM superalloy, which was designed for applications up to 815- 8 5 0 ℃, was experimentally investigated. Emphasis was primarily put on microstructure and mechanical properties. The results indicated the measured phases in the sample were composed of γ,γ＇, MC, and Ma B2. With uniform coarse grain microstruc ture （ASTM 5-6）, the sample appeared to exhibit overwhelming superiority over the prior art materials FGH95, FGH96, FGH97 and FGH98. The dominant embodiments consisted of high tensile strength （Rm = 1000 MPa and Rp0.2 800 MPa at 850℃）, strong creep resistance （ξp 0.12% at 815 ℃/400 MPa/50 h）, and considerable stressrupture life （τ=457.4 h at 815 ℃/450 MPa）. The technical practicability of applications up to 815-850 ℃ of this alloy was conclusively proved.     

GH871合金涡轮盘件的力学性能

对ＧＨ１３２的改型合金ＧＨ８７１涡轮盘件在接近使用条件下的力学性能进行了研究，结果表明，与ＧＨ１３２合金盘件相比较，ＧＨ８７１合金显著提高盘件拉伸强度，持久强度及疲劳蠕变交互作用条件下的断裂寿命，降低稳态蠕变速率，但持久塑性所下降，裂纹扩展速率较快。     

Microstructural Characterization of the White Etching Layer in Nickel-Based Superalloy

Microstructural characterization of the white etching layer (WEL) formed during milling in a fine-grained IN100 Ni-based superalloy was conducted. The microstructure of the layer depended on milling parameters, and under typical machining conditions, where moderate surface speed was used, the white layer exhibited nanostructure character. Fast surface speed produced partial amorphization of the outermost layer. Limited notched low cycle fatigue (LCF) testing was performed, and it was demonstrated that the fatigue properties deteriorated significantly in the specimens where WEL was present in the notch-root surface.     

氩气雾化镍基高温合金粉末的氧化特性研究

采用氩气雾化法(AA法)制备出FGH96高温合金粉末,将筛分后的粉末在真空和氩气保护下存储,对储存条件、储存时间以及粉末特性对粉末中氧含量的影响进行研究,分析气雾化高温合金粉末的氧化特性.结果表明,随着储存时间的延长,粉末中的氧含量均呈现增长趋势,真空下粉末的氧含量变化曲线最趋平缓,储存一个月,氧含量由88.3×10(-6)增加至110×10(-6),适合做较长时间的储存;氩气气氛下,短时间内粉末的储存效果较好,随着时间延长储存效果下降,氧含量增长较快,储存一个月达到137×10(-6).AES分析结果表明粉末表面存在氧化造成的成分偏析以及碳、氧元素污染,氧元素主要与富集表面的Ti,Cr等元素生成氧化物,粉末表面状态对单个粉末的氧化特性有较大的影响,粉末表面越粗糙,粘附的卫星颗粒越多,粉末的氧含量越大,粉末的氧含量呈现先增加后减小的趋势,表现为高斯分布,其中氧的富集层厚度最大约为38 nm,粉末表面越光滑则氧含量越少,氧含量沿深度分布曲线表现为单调减小,氧元素以物理吸附为主.     

Recovery of Nickel from Nickel-Based Superalloy Scraps by Utilizing Molten Zinc

Metallurgical and Materials Transactions B - With the purpose of developing a new process for recycling nickel (Ni) directly from superalloy scraps, a fundamental study on the extraction and...     

喷射成形GH742y合金的组织和性能

研究了喷射成形GH742y合金沉积坯的组织和性能以及热变形特性.研究结果表明,氮气雾化喷射成形GH742y合金沉积坯整体致密、成分均匀、无宏观偏析、组织细化、氧含量低,而且具有较好的力学性能,其主要力学性能超过技术指标的要求.同时,由于晶粒细小均匀,所以该合金具有较好的热变形性能.     

镍基高温合金IN-738组织与性能的关系

介绍了IN-738合金及其改型IN-738LC和IN-738FC合金的成分、性能和用途;给出了IN-738X合金的各种制造工艺参数;论述了IN-738X合金中电子空位数(Nv)对组织和性能的影响,得知IN-738合金的临界电子空位数为2.38;分析了IN-738X合金热处理过程中的组织结构,特别是γ'相和碳化物的变化;介绍了无氧化物弥散强化和有氧化物弥散强化的粉末IN-738X合金的若干重要研究成果;简要介绍了IN-738X合金的耐热腐蚀性和硫侵蚀的研究结果.     

不同HIP温度下镍基高温合金粉末的组织形貌

研究了镍基高温合金粉末在不同热等静压温度下成形的组织形貌,分析讨论了析出相对晶粒度和形成PPB、残留枝晶的影响,以及消除PPB、残留枝晶所采取的措施.     

Microstructure Evolution and Analysis of A [011] Orientation, Single-Crystal, Nickel-Based Superalloy During Tensile Creep

By means of the elastic?Cplastic finite-element method (FEM) for calculating the distribution features of the von Mises stress and strain energy density, the influences of the applied stress on the von Mises stress of the ????/?? phases and the rafting of the ???? phase for the [011] orientation, single-crystal, nickel-based superalloy are investigated. The results show that, after being fully heat treated, the microstructure of the [011] orientation, single-crystal, nickel-based superalloy consists of the cuboidal ???? phase embedded coherently in the ?? matrix, and the cuboidal ???? phase on (100) plane is regularly arranged along a 45?deg angle relative to the [011] orientation. Compared with the matrix channel of [010] orientation, the bigger von Mises stress is produced within the [001] matrix channel when the tensile stress is applied along the [011] orientation. Under the action of the larger principal stress component, the bigger expanding lattice strain occurs on the (001) plane of the cuboidal ???? phase along the [010] direction, which may trap the Al, Ti atoms with a bigger atomic radius for promoting the directional growth of the ???? phase into the stripe-like rafted structure along the [001] orientation. The changes of the interatomic potential energy, misfit stress, and interfacial energy during the tensile creep are thought to be the driving forces of promoting the elements?? diffusion and directional growth of the ???? phase.     

On the Time-Temperature-Transformation Behavior of a New Dual-Superlattice Nickel-Based Superalloy

Recent research has identified compositions of nickel-based superalloys with microstructures containing appreciable and comparable volume fractions of γ′ and γ″ precipitates. In this work, an alloy capable of forming such a dual-superlattice microstructure was subjected to a range of thermal exposures between 873 K and 1173 K (600 °C and 900 °C) for durations of 1 to 1000 hours. The microstructures and nature of the precipitating phases were characterized using synchrotron X-ray diffraction and electron microscopy. These data have enabled the construction of a T-T-T diagram for the precipitating phases. Hardness measurements following each thermal exposure have identified the age-hardening behavior of this alloy and allowed preliminary mechanical properties to be assessed.     

Nano-scale Mechanical Properties and Microstructure of Irradiated X-750 Ni-Based Superalloy

This study investigates the effect of irradiation on the mechanical properties of a Ni-based superalloy, X-750. 40 MeV Ni⁺ ions were used to irradiate the X-750 up to 1 dpa with and without 5000 appm helium pre-implantation at room temperature and 400 °C. Nano-indentation hardness tests were carried out at room temperature in the depth range of 200 to 1400 nm before and after irradiation. Cross-sectional TEM observations were performed on the irradiated materials to correlate the mechanical results with the microstructural evolution. The results show that helium pre-implantation enhances the irradiation-induced hardening due to generating a high density of small cavities and promoting the formation of larger Frank loops. In addition, nano-scale mechanical tests reveal that changing the subsequent Ni ion irradiation temperature from room temperature to 400 °C, leads to changing of the mechanical response from a softening behavior to an irradiation-induced hardening. The γ′ precipitates became disordered after irradiation at room temperature, whereas the γ′-phase remained ordered during irradiation at 400 °C. The softening effect of the γ′ instability outweighed the hardening impact of irradiation-induced defects such as cavities and Frank loops, leading to a hardness reduction for the room-temperature-irradiated material. Three different obstacle-hardening models were employed to assess the individual impact of each type of defect on the material’s overall strength enhancement. Furthermore, the superposition principle was used for each model to estimate the overall irradiation-induced strengthening, which is compared to the results from the nano-hardness measurements.     

Microstructure and Properties of Plasma-Nitrided Fe-Based Superalloy Fe-25Ni-15Cr

Fe-based superalloy Fe-25Ni-15Cr was plasma nitrided at a low temperature of 723 K (450 °C). The nitrided layer was characterized by optical microscopy (OPM) and scanning electron microscopy (SEM) and X-ray diffraction (XRD) through stepwise mechanical polishing and transmission electron microscopy (TEM). The results indicated that the double expanded austenite (γ _N1 and γ _N2) was developed on the nitrided surface. Energy-dispersive X-ray spectrum (EDS) revealed that separate expanded austenite layers with distinctly different nitrogen contents occurred: high (18.98 to 11.49 at. pct) in the surface layer and low (5.87 to 5.32 at. pct) in the subsurface. XRD analysis indicated that large lattice expansion and distortion relative to the untreated austenite of an idea face-centered-cubic (fcc) structure occurred on the γ _N1, but low expansion and less distortion on the γ _N2. No obvious lattice distortion on the γ _N1 was determined by calculating its electron diffraction pattern (EDP), except for detectable lattice expansion. Inconformity between XRD and EDP results suggested that the high compressive residual stress in the γ _N1 was mainly responsible for the lattice distortion of the γ _N1. TEM indicated that the γ _N1 layer exhibited the monotonous contrast characteristic of an amorphous phase contrast to some extent, and corresponding EDP showed a strong diffuse scattering effect. It was suggested that the pre-precipitation took place in the γ _N1 in the form of strongly bonded Cr-N clusters or pairs. Decomposition of the γ _N1 into CrN and γ occurred at the grain boundaries, and the orientation of both phases remained cubic and cubic relationship, i.e., the planes and the directions with identical Miller indices in both phases were parallel. The nitrided surface was found to have significantly improved wear resistance. Further, the nitrided surface showed no adverse effect in the corrosion resistance but slight improvement in the 3.5 pct NaCl solution.