快速凝固Al－Fe－W－Si－RE耐热铝合金的研究

研究了用多级快速凝固技术制取的Ａｌ－１１．５Ｆｅ－３．８Ｗ－２．３Ｓｉ－ＲＥ（质量分数）合金粉末的室温和高温组织结构及性能，结果表明，该合金有利于形成所谓“无特征区”组织，确定了合金的相变和第二相粒子大小为３０～８０ｎｍ，并获得了室温和高温拉伸性能优良的新合金。     

热等静压技术在镍基单晶高温合金中的应用研究进展

 通过总结目前热等静压对镍基单晶高温的应用研究进展，阐释了热等静压对镍基单晶高温合金中的疏松等孔洞类缺陷的消除作用，分析了孔洞的愈合机理，并分别展示了应用热等静压后合金的拉伸、持久、疲劳等力学性能变化情况，同时介绍了热等静压对已服役制件组织力学性能恢复处理的研究进展、计算模拟在指导热等静压工艺研究中的作用，展望了中国热等静压技术的未来发展。     

晶体取向对镍基单晶DD6合金蠕变性能的影响

针对航空发动机镍基单晶涡轮叶片高温服役下蠕变寿命的取向敏感性难题，开展了DD6单晶合金［001］、［011］与［111］3种典型取向在980^oC下的蠕变试验，获得了服役温度下单晶合金的蠕变寿命、伸长率，均为［111］取向>［001］取向>［011］取向；通过对蠕变过程中微观组织演化以及蠕变断裂后断口形貌进行分析，揭示了不同取向下单晶合金的蠕变失效机理；基于晶体塑性理论，建立了DD6单晶考虑取向敏感性的粘塑性本构及损伤方程，能够较好地拟合不同晶体取向单晶的蠕变过程，为单晶叶片的强度分析与寿命预测提供参考。     

镍基单晶高温合金表面再结晶控制技术的研究进展

针对镍基单晶高温合金构件的表面再结晶控制技术,结合国内外相关工作的研究状况,从单晶高温合金构件表面再结晶的形成机理、再结晶的表面效应、基于再结晶预防的构件设计、单晶构件热成型过程和冷加工过程再结晶控制技术等几方面,对镍基单晶高温合金构件的表面再结晶控制技术领域取得的研究成果进行总结和分析。重点论述了各国单晶再结晶控制技术,提出中国镍基单晶高温合金构件的表面再结晶控制技术存在的差距及未来研究重点。     

CMSX－3镍基单晶高温合金的蠕变－疲劳行为

对镍基单晶高温合金ＣＭＳＸ－３在９００℃、较高应力幅下进行蠕变－疲劳交互作用试验。结果表明，循环蠕变的保持时间显著地影响材料的断裂寿命和断裂应变；应变量与总保持时间有对应关系。可用γ强化的单晶高温合金蠕变－疲劳交互作用机制对此作出解释。     

镍基单晶高温合金蠕变机制研究进展

 叶片在服役过程中主要承受〈001〉轴向的离心载荷，由离心应力导致的蠕变损伤是叶片的主要失效机制之一。基于单晶叶片的典型服役条件，总结了国内外关于高温低应力和中温高应力蠕变变形损伤机制的研究现状，指出深入开展含典型缺陷单晶高温合金蠕变行为、氧化和热腐蚀对单晶合金蠕变-疲劳变形损伤机制影响研究十分必要。     

单晶高温镍合金循环加荷情况下变形和破坏的结构特性

直到不久以前，提高弥散硬化镍合金热弼洼主要的方向是改变合金元素的含量以求得合金元素最佳的密度，该密度能保证合金某种规定的综合性能。因而现代工业用的高温镍合金含有大约10—15种合金元素和微合金元素，而在强化相中各成分达到了极限溶解度。但是提高高温材料抗蠕变性和抗破坏性的课题还没有完全解决，因为对于多晶的铸件来说，与施加载荷轴心线垂直的晶界处出现的破坏比较典型。本文对单晶高温镍合佥在循环加荷情况下的组织和性能进行了研究。     

高温破碎烧结磁体制取各向异性NdFeB磁粉(Ⅱ)

在较高温度下对烧结NdFeB磁体进行机械破碎制取了磁粉．实验结果表明：当破碎温度升高到合金的三元共晶温度附近时，所得磁粉的矫顽力显著高于室温破碎磁粉的矫顽力．高温破碎磁粉矫顽力的升高与磁体破碎时由低温下穿晶断裂向高温下沿晶断裂的转变直接相关．原因在于高温破碎磁粉中，表层穿晶裂纹数量减少，表面较均匀地被富Nd相包覆，以及颗粒中尖锐棱角部位明显减少．高温破碎磁粉的矫顽力经过适当热处理还能进一步提高．     

CMSX—3镍基单晶高温合金的蠕变—疲劳行为

对镍基单晶高温合金ＣＭＳＸ－３在９００℃、较高应力幅下进行蠕变－疲劳交互作用试验。结果表明，循环蠕变的保持时间显著地影响材料的断裂寿命和断裂应变；应变量与总保持时间有对应关系。可用γ＾１强化的单晶高温合金蠕变－疲劳交互作用机制对此作出解释。     

C_(60)单晶制备和微观机制

Ｃ６０单晶制备中的粉末残留问题是影响该实验成功和单晶品质的一个重要问题．我们经过大量实验，研究出一种在高真空管式炉中生长出较好质量单晶的工艺条件，克服了粉末残角问题．还对这一工艺中单晶生长的动力学非平衡过程的微观机制进行了分析，为制备大的Ｃ６０单晶提供了理论依据．此工艺也为制备其它材料的单晶提供了一个可借鉴的实验方法．     

Influence of minor boron on the microstructures of a second generation Nibased single crystal superalloy

Boron is added into single crystal superalloys as a micro-alloying element to strengthen low angle grain boundaries.However,systematic investigations on the effect of boron on microstructures of single crystal superalloys are limitedly reported.The effect of boron on as-cast and heat-treated microstructures was investigated in two experimental Ni-based single crystal superalloys containing 3 wt% Re.The current results indicated that the volume fraction of(γ+γ′)eutectic and M_3B_2 borides was evidently increased,while the number of micropores was evidently decreased with the addition of 0.02 wt% boron.The(γ+γ′)eutectic could not be dissolved completely due to the lower incipient melting temperature caused by the formation of M_3B_2 borides.Meanwhile,the M_3B_2 borides were found to be enriched with indispensable strengthening elements Cr,Mo,W and Re,and this may lower the strengthening effect and cause stress concentration during high temperature creep.     

Alloying effects of refractory elements in the dislocation of Ni-based single crystal superalloys

The alloying effects of W, Cr and Re in the [100] (010) edge dislocation cores (EDC) of Ni-based single crystal superalloys are investigated using first-principles based on the density functional theory (DFT). The binding energy, Mulliken orbital population, density of states, charge density and radial distribution functions are discussed, respectively. It is clearly demonstrated that the addition of refractory elements improves the stability of the EDC systems. In addition, they can form tougher bonds with their nearest neighbour (NN) Ni atoms, which enhance the mechanical properties of the Ni-based single crystal superalloys. Through comparative analysis, Cr-doped system has lower binding energy, and Cr atom has evident effect to improve the systemic stability. However, Re atom has the stronger alloying effect in Ni-based single crystal superalloys, much more effectively hindering dislocation motion than W and Cr atoms.     

硼对第二代镍基单晶高温合金显微组织的影响

硼(B)是强化镍基单晶合金小角度晶界的重要微量元素,但目前关于B对镍基单晶合金显微组织影响的系统报道非常有限。通过对3种不同B含量(质量分数分别为0、0.01%、0.02%)的第二代镍基单晶合金DD11铸态及热处理态组织定量表征,研究了B对相转变温度、(γ+γ′)共晶组织、硼化物的影响。结果表明:B显著降低合金的固液相线,提高铸态共晶组织体积分数;0.01%B的加入,合金中未出现M3B2型硼化物相;而0.02%B的加入,显著促进了骨架状硼化物的形成,降低合金初熔点,引起残余共晶含量的大幅度提高;骨架状硼化物吸收较多的Cr、Mo和W等元素,降低合金的固溶强化效果,可导致单晶合金基体的蠕变性能大幅度降低。研究结果对认识单晶合金中微量元素B的作用机理及优化B成分范围具有理论指导意义。     

High temperature creep mechanisms of a single crystal superalloy: A phasefield simulation and microstructure characterization

The high temperature creep behavior of a single crystal Ni-based superalloy was studied by combined experimental and numerical methods. The creep test results showed that the creep curves exhibited a three-stage feature. The qualitative explanations for each stage of the creep curves were carried out based on the microstructure characterizations of γ/γ′ phases and dislocations. An elastoplasticity incorporated phase-field model was developed to provide quantitative understanding on directional coarsening(rafting) of γ′ phase. The simulation results showed that the directionality of γ′ coarsening was induced by both dislocation activity in γchannels and elastic inhomogeneity between γ and γ' phases, therein the dislocation activity played a major role.This findings provide new insights into the design of novel single crystal superalloys with improved creep properties.     

Unit-cell design for two-dimensional phase-field simulation of microstructure evolution in single-crystal Ni-based superalloys during solidification

Phase-field simulation serves as an effective tool for quantitative characterization of microstructure evolution in single-crystal Ni-based superalloys during solidification nowadays. The classic unit cell is either limited to γdendrites along 001 crystal orientation or too ideal to cover complex morphologies for γ dendrites. An attempt to design the unit cell for two-dimensional(2-D) phase-field simulations of microstructure evolution in single-crystal Ni-based superalloys during solidification was thus performed by using the MICRESS(MICRostructure Evolution Simulation Software) in the framework of the multi-phase-field(MPF) model,and demonstrated in a commercial TMS-113 superalloy. The coupling to CALPHAD(CALculation of PHAse Diagram) thermodynamic database was realized via the TQ interface and the experimental diffusion coefficients were utilized in the simulation. Firstly, the classic unit cell with a single γ dendrite along 001 crystal orientation was employed for the phase-field simulation in order to reproduce the microstructure features.Then, such simple unit cell was extended into the cases with two other different crystal orientations, i.e., 011 and 111 . Thirdly, for 001 crystal orientations, the effect of γ dendritic orientations and unit cell sizes on microstructure and microsegregation was comprehensively studied, from which a new unit cell with multiple γdendrites was proposed. The phase-field simulation with the newly proposed unit cell was further performed in the TMS-113 superalloy, and the microstructure features including the competitive growth of γ dendrites,microsegregation of different solutes and distribution of γ′ grains, can be nicely reproduced.     

Effect of the withdrawal rate on the microstructure and thermal durability of a third-generation single crystal superalloy

Single crystal Ni-based superalloys are the typical structural materials for high-pressure turbine blades, and their microstructure is critical in determining their mechanical properties. The withdrawal rate is a key parameter affecting the microstructure during the single crystal growth process. In the present work the effect of the withdrawal rate on the microstructure of a third-generation single crystal superalloy containing 6.8 ?wt% Re has been investigated, and the creep resistance of the alloy determined. The results showed that increased withdrawal rate refined the dendritic structure, reduced dendritic arm spacing, promoted the growth of secondary tertiary dendrites and decreased solidification segregation with a reduced size of γ′ phase. The porosity density of the as-cast alloy first decreased and then increased with the withdrawal rate, while the minimum porosity densityoccurred when the alloy was under the solidification condition of withdrawal rate of 4.5 ?mm/min. The maximum creep rupture life of 326.4 ?h of the heat-treated alloys under the test condition of 1100 ?°C/140 ?MPa also appeared at the alloys under the withdrawal rates of 4.5 ?mm/min. It is believed that the minimum porosity density and reduced size of the γ′ phase may be the main reasons for the enhanced creep rupture life of the alloys with withdrawal rates of 4.5 ?mm/min. This investigation provides theoretical support and a practical basis for the development of third-generation single crystal superalloys.     

Effect of trace boron on microstructural evolution and high temperature creep performance in Re-contianing single crystal superalloys

The effect of trace B on the microstructure and creep properties under 1100 °C/130 MPa in three single crystal superalloys with various levels of B(0, 0.01 and 0.02 wt %) additions was investigated. Compared with the boron-free alloy, the creep rupture life decreased slightly for the alloy with 0.01 wt % B, but dropped obviously for the 0.02 wt% B contained alloy. The low B addition had a slight effect on the main element compositions ofγ/γ′ by the high precision atom probe tomography(APT) analysis and no significant change of γ/γ′ misfit was observed. However, the contents of Re, Mo, Cr in γ phase were decreased with the high B addition, resulting in the decrease of γ/γ′ misfit and increase of the spacing of γ/γ′ interfacial dislocation networks. Meanwhile, the residual(γ+γ′) eutectics and borides with a large volume fraction obviously decreased the creep rupture properties in the high B addition alloy. This study is helpful for understanding the boron's role of strengthening mechanism in high temperature creep of Ni-base single crystal superalloys.