喷射成形FGH4095的热变形特征

研究了喷射成形高温合金FGH4095在温度为1010—1140℃、应变速率为0.001—10.0s^-1下的热变形行为,并使用双曲正弦模型建立了喷射成形FGH4095的本构方程.结果表明:本构方程预测结果与实验值符合较好,为喷射成形FGH4095热加工过程的数值模拟提供了较准确的模型.     

氮气喷射成形FGH4095的组织特征

以氮气为雾化气体采用喷射成形工艺制备了FGH4095高温合金沉积坯, 记录了沉积过程坯体表面温度曲线, 并采用定量金相法、排水法测试了坯体致密度, 观察了坯体晶粒及γ'相的形貌. 结果表明采用氮气作为雾化介质进行喷射成型喷射沉积坯基体致密度可达99%以上, 但也存在着较大的(1—2μm)的气孔, 经热等静压和近等温锻后宏观气孔闭合, 氮以尺寸不超过1 μm的碳氮化物形式存在. 喷射沉积坯以等轴晶组织为主, 坯体内部平均晶粒尺寸约为20—40 μm, 近表面区域晶粒较细, 约为13 μm; 一次γ' 相多数呈尺寸约0.3—0.5 μm不规则块状形貌. 喷射成形坯组织结构的形成与喷射成形过程的降温过程有密切关系.     

喷射成型FGH4095静态再结晶组织特征

为了研究喷射成型FGH4095高温合金经热等静压、近等温锻后固溶热处理的组织特征,采用喷射成型高温合金,经1170℃,120 MPa,3 h热等静压和75%压缩量的近等温锻,经1120℃,1140℃,1160℃保温10,20,40 min固溶热处理,再经油淬后研究其再结晶过程及晶粒尺寸、析出相的变化规律.结果表明,固溶温度强烈影响静态再结晶过程及固溶后的组织.在1120℃下固溶20 min,由于区域化的不完全再结晶,可形成项链组织;1140℃下固溶40 min可基本完成再结晶,并得到细化的再结晶组织,平均晶粒尺寸约为8μm;1160℃下固溶10 min即可基本完成再结晶,晶粒尺寸长大到约18μm.     

低密度Co-Ni-Al-Mo-Cr-Ti/Nb/Ta系列高温合金方形γ/γ′共格组织设计及其稳定性

利用团簇成分式方法设计系列低密度Co基高温合金[Al-(Co₈Ni₄)]((Al_0.5(Ti/Nb/Ta)_0.5Mo_0.5)(Mo_0.5Cr_0.5Co_0.5))(=Co_8.5Ni₄Al_1.5Mo_1.0Cr_0.5(Ti/Nb/Ta)_0.5),采用真空非自耗电弧炉制备合金铸锭,并对其在1300℃固溶15h,在900℃下进行长期时效处理,进而对时效态样品进行微观组织表征和力学性能测试.结果表明,当Ti/Nb/Ta,Ti/Nb和Ti/Ta以等物质的量比匹配时,3种合金的微观组织均表现为立方形γ’相均匀地分布在γ基体中,这取决于合金适中的γ/γ’点阵错配度(0.27%—0.34%).在900℃长期时效过程中,3种合金中的γ’相均具有较小的粗化速率,且合金的显微硬度随时效时间基本不发生变化(27...     

蠕变镍基单晶高温合金微观结构与界面特征的X射线小角散射研究

利用SAXS技术对蠕变过程中不同尺度范围的微观结构变化分析表明X射线小角散射(SAXS)与中子小角散射(SANS)测量的二维散射图具有明显的差异,由散射强度曲线的变化说明了蠕变过程中二次析出γ'相形貌和不同区域尺寸特征的改变情况.分析结果表明二次析出γ'相存在两类特征尺寸,在蠕变过程中沿[100]或[010]方向的变化趋势类似,均是在第一和第二阶段有所减小,在第三阶段又有所增大,相较而言,特征尺寸较大的γ'相变化也较为显著.二次析出γ'相在蠕变第二阶段元素扩散最严重,相表面最粗糙,在第三阶段两相界面又进一 关键词： 单晶高温合金 二次析出γ'相 X射线小角散射 微观结构     

高温合金活性剂激光微焊接接头的组织性能研究

采用配方均匀设计法,配制了SiO2-MnO2-CaO-TiO2-CaF2-NaF多组元活性剂,利用微型脉冲激光器对500 m厚GH4169高温合金进行了活性剂激光焊接试验。分析并讨论了焊接接头的显微组织和力学性能。试验结果表明,与传统激光焊相比,所配制的20种活性剂均增加了焊缝熔深,并且其中F12系混合活性剂增加熔深能力最为显著,使焊缝深宽比增加了159%,证明通过使用活性剂来增加微激光焊焊缝熔深,降低高温合金板激光焊接的成本是可行的。在活性剂作用下,焊缝显微组织仍由柱状晶和等轴晶组成,接头抗拉强度达到927 MPa,为母材强度的92.7%。     

高温合金活性剂激光微焊接接头的组织性能研究

采用配方均匀设计法,配制了SiO2-MnO2-CaO-TiO2-CaF2-NaF多组元活性剂,利用微型脉冲激光器对500 m厚GH4169高温合金进行了活性剂激光焊接试验。分析并讨论了焊接接头的显微组织和力学性能。试验结果表明,与传统激光焊相比,所配制的20种活性剂均增加了焊缝熔深,并且其中F12系混合活性剂增加熔深能力最为显著,使焊缝深宽比增加了159%,证明通过使用活性剂来增加微激光焊焊缝熔深,降低高温合金板激光焊接的成本是可行的。在活性剂作用下,焊缝显微组织仍由柱状晶和等轴晶组成,接头抗拉强度达到927 MPa,为母材强度的92.7%。     

高温合金活性剂激光微焊接接头的组织性能研究（英文）

采用配方均匀设计法,配制了SiO2-MnO2-CaO-TiO2-CaF2-NaF多组元活性剂,利用微型脉冲激光器对500μm厚GH4169高温合金进行了活性剂激光焊接试验。分析并讨论了焊接接头的显微组织和力学性能。试验结果表明,与传统激光焊相比,所配制的20种活性剂均增加了焊缝熔深,并且其中F12系混合活性剂增加熔深能力最为显著,使焊缝深宽比增加了159%,证明通过使用活性剂来增加微激光焊焊缝熔深,降低高温合金板激光焊接的成本是可行的。在活性剂作用下,焊缝显微组织仍由柱状晶和等轴晶组成,接头抗拉强度达到927 MPa,为母材强度的92.7%。     

水喷射淬冷高温壁面的传热实验研究

本文采用直接表面温度测量的方法对水喷射高温壁面的传热过程进行实验研究．系统地研究了射流出口速度、冷却水过冷度、喷嘴至加热面的间距、初始壁温以及水喷雾的流量密度等参数对淬冷表面的膜态沸腾、最小临界点、过渡沸腾、最大临界点等传热过程的影响，给出了有关实验结果，分析了它们的特点。     

Innovative technologies for powder metallurgy-based disk superalloys: Progress and proposal

Powder metallurgy(PM) superalloys are an important class of high temperature structural materials, key to the rotating components of aero engines. In the purview of the present challenges associated with PM superalloys, two novel approaches namely, powder preparation and the innovative spray-forming technique(for making turbine disk) are proposed and studied.Subsequently, advanced technologies like electrode-induction-melting gas atomization(EIGA), and spark-plasma discharge spheroidization(SPDS) are introduced, for ceramic-free superalloy powders. Presently, new processing routes are sought after for preparing finer and cleaner raw powders for disk superalloys. The progress of research in spray-formed PM superalloys is first summarized in detail. The spray-formed superalloy disks specifically exhibit excellent mechanical properties. This paper reviews the recent progress in innovative technologies for PM superalloys, with an emphasis on new ideas and approaches, central to the innovation driving techniques like powder processing and spray forming.     

Investigations on the growing, cracking and spalling of oxides scales of powder metallurgy Rene95 nickel-based superalloy

The surface and cross-sectional morphologies of powder metallurgy (PM) Rene95 nickel-based superalloy after 100 h oxidation in the temperature range of 700-1100 °C were investigated. It is shown that oxides nucleate first on the surface of the alloy and form an oxides scale. Afterwards, oxides scale endures decohesion, rumpling, cracking and finally spalling owing to the weak cohesive strength of the scale/alloy interface. The XRD and EDS analyses confirmed that the oxides scale of PM Rene95 superalloy is mainly composed by Cr₂O₃ at 800 °C and NiCr₂O₄ is the main spinel at 1100 °C. The subsequent analysis of internal stress verified that cracking and spalling are caused by growth stress and promoted by thermal stress. On these bases, improvement of the cohesive strength of the scale/alloy interface is considered to be the main way to increase the oxidation resistance of PM Rene95 superalloy.     

Oxidation behavior and mechanism of powder metallurgy Rene95 nickel based superalloy between 800 and 1000 °C

The oxidation behaviors of powder metallurgy (PM) Rene95 Ni-based superalloy in the temperature range of 800-1000 °C are investigated in air by virtue of isothermal oxidation testing, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the oxidation kinetics follows a square power law as the time extends at each temperature. The oxidation layers are detected to be composed of Cr₂O₃, TiO₂ and a small amount of NiCr₂O₄. The cross-sectional morphologies indicate that the oxidation layer consists of three parts: Cr-rich oxide layer, Cr and Ti duplex oxide layer, and oxidation affected zone. Theoretical analyses of oxidation kinetics and thicknesses of oxidation layers confirm that the activation energy of oxidation of PM Rene95 superalloy is 165.32 kJ mol⁻¹ and the oxidation process is controlled by diffusions of oxygen, Cr, and Ti. Accordingly, a diffusion-controlled mechanism is suggested to understand the oxidation behaviors of PM Rene95 superalloy at elevated temperatures.     

喷雾腔压力及喷嘴孔径对相变喷雾冷却性能的影响

为了满足大功率激光器件高热流密度及低表面温度的冷却需求,以R22为冷却工质,实验研究了在闭式系统中改变喷雾腔压力及喷嘴孔径对相变喷雾冷却中临界热流密度、冷却温度等冷却性能的影响,实验结果表明：在喷雾入口压力为0.8 MPa,喷雾高度为22 mm,入口温度为-3 ℃的实验条件下,当喷雾腔压力在0.2~0.4 MPa范围内变化时,随着喷雾腔压力的升高,临界热流密度值（CHF）先增大后减小,存在最优的临界热流密度,冷却壁面温度随着喷雾腔压力的升高而上升;当改变喷嘴孔径时,CHF存在最优值,过小及过大的孔径均会影响喷雾冷却性能;当喷嘴孔径为 0.4 mm,喷雾腔压力为0.34 MPa时, CHF值最高,为276.1 Wcm-2,其对应的被冷却表面温度为26.8 ℃,表面换热系数为 66 640 Wm-2K-1。     

Grain refinement and texture evolution during high precision machining of a Ni-based superalloy

Abstract

The grain refinement and texture evolution in the surface gradient microstructure of a Ni-based superalloy induced by high speed machining was studied in this research. The direct evidence of grain refinement induced by dislocation–twin interaction was revealed and the detailed grain refinement process was summarised as deformation twinning, dislocation-twin reaction, localied thinning of nanotwin lamellae and final fracture. The underlying dislocation–twin interaction mechanism was elucidated from the crystallographic perspective. Using electron backscatter diffraction and precession electron diffraction techniques, a multiscale texture analysis covering undeformed coarse grain region, ultrafine grain region and nanograin region was carried out. The texture evolution with decreasing depth to the machined surface was identified as cube in the bulk interior and a mixture of rotated cube {0?0?1}<1?1?0>, cube {1?0?0}<0?0?1>, copper {1?1?2}<1?1?1 > and Goss {1?1?0}<0?0?1> textures in the topmost 1.3-μm-thick nanograin layer. The intrinsic thermomechanical effects of high precision machining are responsible for crystallographic texture transformation.     

High cycle fatigue and fracture behaviour of a hot isostatically pressed nickel-based superalloy

Powder of a nickel-based superalloy, RR1000, has been hot isostatically pressed (HIPped) at a supersolvus temperature and post-HIP heat treated to produce different microstructures. Microstructures were investigated using a scanning electron microscope together with an energy dispersive X-ray spectrometer and a wave-length dispersive X-ray spectrometer. High cycle four-point bending fatigue and tension–tension fatigue tests have been performed on the fabricated samples. It was found that HIPped and aged samples showed the best four-point bending fatigue limit while HIPped and solution-treated and aged samples had the lowest fatigue limit. The four-point bending fatigue crack initiations all occurred from the sample surfaces either at the sites of inclusion clusters or by cleavage through large grains on the surfaces. The tension–tension fatigue crack initiation occurred mainly due to large hafnia inclusion clusters, with lower fatigue lives for samples where inclusions were closer to the surface. Crack initiation at the compact Al₂O₃ inclusion cluster led to a much higher fatigue life than found when cracks were initiated by large hafnia inclusion clusters. The tension–tension fatigue limits were shown to decrease with increased testing temperature (from room temperature to 700?°C).     

Gamma prime and TCP phases and mechanical properties of thermally exposed nickel-base superalloy

The effect of long-term thermal exposure and casting superheat on microstructure, topologically close-packed (TCP) phases, γ?′ precipitation and mechanical properties of an experimental Ni-base superalloy were studied. The investigated alloys were produced by investment casting process under two levels of superheat. After solution heat treatment, at 1180°C for 2?h followed by air cooling; the two alloys under investigation were isothermally exposed at 845°C for 24, 200, 1000, and 1500?h. The long-term thermal exposure conditions have a significant impact on the precipitation and morphology of TCP and γ?′ phases. The σ phase precipitated as needle and platelet shapes, whereas the μ phase formed in plate and agglomerated shapes. The μ phase has high concentration of Cr, Mo, W, and Co, while the σ phase has high percentages of Ni and Ti. The μ phase was precipitated after thermal exposure of 200?h in the case of high superheat specimen and after 1000?h in low superheat specimen. The η phase found was also a thick plate-like shape in the microstructure of both alloys in the interdendritic zones. The optimum size and volume fraction of γ?′ precipitates were obtained after being thermally exposed for 200 and 1000?h for high and low superheat alloys, respectively. Consequently, the highest hardness level was achieved at the optimum conditions of γ?′ precipitates in high and low superheat alloys.