固溶热处理对一种第三代镍基单晶高温合金组织及高温持久性能的影响

研究了固溶热处理对一种Re含量为6.5%(质量分数)的第三代单晶高温合金组织及持久性能的影响,实验结果表明:合金铸态下存在明显的凝固偏析,枝晶间区域存在大量的(γ+γ′)共晶组织。固溶过程中,共晶组织在1 335℃以上开始快速溶解,但难熔元素,尤其是Re元素的偏析需要在1 360℃以上才能有明显改善;经过1 365℃固溶后疏松含量增加至0.21%(体积分数),接近铸态下疏松含量的5.2倍。铸态及经1 360℃和1 365℃固溶热处理后合金的持久性能测试结果显示:固溶热处理显著改善了合金的持久性能,且固溶温度越高,持久性能越高。在高温持久加载过程中,铸态合金的裂纹主要沿枝晶间分布,在(γ+γ′)共晶组织处萌生;当固溶温度较低时,且枝晶干处析出了较多的TCP(topologically close-packed)相,未能充分降低Re元素的偏析可能是导致枝晶干处TCP相大量析出的主要原因;当固溶温度较高时,TCP相析出量较少。     

Inconel 718微铣削加工表面残余应力有限元仿真

刃口圆弧半径和每齿进给量显著影响微铣削镍基高温合金残余应力,因此进行了基于ABAQUS的Inconel 718微铣削三维仿真研究.基于J-C本构方程模拟材料应力应变关系,得到相同单元在S11和S22两个方向的残余应力值,进而研究每齿进给量对表面残余应力的影响规律.进行Inconel 718微铣削实验,通过X射线衍射法测量不同每齿进给量切削过程中工件进给和垂直进给两个方向上的残余应力.进给方向的表面残余应力实测值与仿真结果最大误差为21.1%,平均误差为8.9%;垂直进给方向的表面残余应力实测值与仿真结果最大误差为31.0%,平均误差为12.3%,验证了Inconel 718微铣削加工三维有限元仿真模型的准确性.     

新型定向凝固高温合金750℃抗热腐蚀性能

研究了涂有75%Na2SO4+25%NaCl盐膜的新型定向凝固镍基高温合金在750℃的热腐蚀行为,采用X射线衍射仪和带能谱的扫描电镜分析腐蚀产物相组成以及微观结构.结果表明:该合金在开始阶段腐蚀速率较大,随着腐蚀时间的延长以及合金腐蚀层厚度的增加,腐蚀速率降低.腐蚀层可分为3个区域:外层是以TiO2和Cr2O3为主相对疏松的氧化层,中间层具有保护性的是富Cr层,内层是以Al,Ti为主的氧化物以及点状分布的硫化物.合金的热腐蚀主要由氧化-硫化共存伴随着表面腐蚀物挥发形成,在此过程中腐蚀持续向合金基体推进,使得腐蚀层不断增厚.     

长期时效对FGH96合金组织与力学性能的影响

研究了长期时效热处理制度对FGH96合金的显微组织、析出相、拉伸性能、持久性能及蠕变性能的影响.采用光学显微镜分析了合金的晶粒组织,用扫描和透射电镜分析了γ'相、碳化物和硼化物的形貌、尺寸和含量.通过力学性能测试分析了拉伸、持久和蠕变性能.结果表明在时效温度550℃和650℃下,时效时间在100 h至7500 h变化时,FGH96合金的晶粒尺寸、γ'相形貌尺寸、MC型碳化物和M3 B2型硼化物相含量、拉伸性能、持久性能等基本保持不变.时效温度为650℃时,随着时效时间的延长,γ'相及Cr23 C6碳化物的含量相比550℃略有增大,导致蠕变性能降低,残余应变增大.     

Microstructure-based hot extrusion process control principles for nickel-base superalloy pipes

The properties of nickel-base superalloy pipes are determined by microstructure, and the microstructure can be tuned by hot extrusion process. There are two major questions in hot extrusion: one is how to successfully extrude pipes without apparent defects, the other is how to make the microstructure under control. However, up to now, there is no systematical report about hot extrusion process and microstructure control for nickel-base superalloys. In present study, a series of technical control principles for hot extrusion are proposed basing on practical manufacture facts, large amounts of experimental studies and finite element simulation of several typical nickel-base superalloys. The common used technical control principles can be applied for hot extrusion parameters determination to maintain safety hot extrusion and microstructure control. In the investigation of microstructure control based hot extrusion principles, the action rules of different working parameters on hot extrusion field quantities were established. The upper and lower limits of different principles were obtained in consideration of materials characteristics and extruder conditions. The limitations were overlapped on the action rules to determine the optimized hot extrusion parameters. The microstructure-based control principle proposed in present work can provide theoretical guidance for hot extrusion parameter determination and optimization.     

Dendrite morphology and evolution mechanism of nickel-based single crystal superalloys grown along the o0014 and o0114 orientations

Nickel-based single crystal superalloys oriented along the o0014 and o0114 lattice directions were produced by a bottom seeding technique in an attempt to understand the evolution mechanism of the dendrite grown along different orientations in the present study. The changes in primary dendrite arm spacing for single crystal with different orientations are also discussed. It was found that the dendrite morphologies of single crystal superalloy grown along o0114 were different from that of o0014. Firstly, the dendrites showed the irregular cruciforms and array in rows in a transverse section. Secondly, no typical primary dendrites were observed but the dendrite morphologies appeared like the letter ‘‘V’’ or ‘‘W’’ in a longitudinal section. The primary dendrite arms grew along the o0014 orientation from the bottom of the sample in the o0014 orientation. However, in the o0114 orientation, the single crystal developed by continuous side-branching along the [001] and [010] orientations. The primary dendrite arm spacing was as the function of the deviation angle f. It indicates that with the increase in the deviation angle f, the primary dendrite arm spacing first increased, and then decreased.     

Effect of long term aging on microstructure and stress rupture properties of a nickel based single crystal superalloy

A nickel based single crystal superalloy with [001] orientation was prepared by the screw selecting method in the directionally solidified furnace. The long term aging (LTA) of the alloy after full heat treatment was performed at 1040 1C for 200–800 h. The microstructure and stress rupture properties at 980 1C/250 MPa and 1070 1C/140 MPa of the alloy long term aged (LTAed) for different time were investigated. The coarsening g0 phase and the broadening g matrix channel are observed in the samples LTAed at 1040 1C, but the g0 morphology is still in cubic shape after LTA for 800 h. No TCP phase precipitates after LTA for 400 h, while needle shaped and granular TCP phase forms in dendritic core of the alloy after LTA for 600 h. With increasing aging time, the volume of the TCP phase increases and it grows from the dendritic core to the interdendritic region along a fixed direction. The composition of the TCP phase is mainly composed of Re and W. With increasing aging time the rupture life of the alloy at 980 1C/250 MPa and 1070 1C/140 MPa all turns shorter. Finally, the relationship between the microstructure and the stress rupture properties is discussed.     

镍基单晶高温合金微磨削形貌仿真及实验研究

基于单个磨粒微磨削几何运动学规律和最小值函数,推导出全局磨粒的微磨削运动轨迹表达式,建立工件微磨削加工表面的包络线函数集合,得出磨削加工微观形貌仿真预测模型,并通过开展DD5镍基单晶高温合金微磨削加工工艺实验验证模型结果的正确性.实验结果表明:仿真预测微观形貌与实际微观形貌具有相似特征,仿真预测线轮廓高度与实际加工微磨削线轮廓高度误差为0.2~0.3μm;不同磨削参数下的表面粗糙度对比结果也表明预测模型与实验所得的表面粗糙度变化趋势一致.     

拉伸载荷下镍基粉末高温合金中夹杂物行为

采用扫描电镜原位拉伸方法,跟踪观察了人工植入A12O3夹杂物的镍基粉末高温合金P/MRene95中夹杂物导致裂纹萌生、扩展乃至断裂的过程.结果表明,在单轴拉伸载荷下,裂纹首先萌生于脆性非金属夹杂物A12O3处,大于一定尺寸的夹杂物,还会使该裂纹扩展成为导致合金断裂的主裂纹,从而大大降低合金的屈服强度及断裂强度.