低铼高性能镍基单晶叶片组织优化与性能研究

发布时间：2018-06-09 04:50

  本文选题：低铼镍基高温合金 + 单晶涡轮叶片　； 参考：《江苏大学》2017年硕士论文

【摘要】：作为航空发动机中工作环境最恶劣、结构最为复杂的热端部件,航空涡轮叶片是发动机中最核心的部件之一,随着先进航空发动机的发展,涡轮叶片服役温度和工作载荷不断提升,先进单晶涡轮叶片的制造技术已经成为了航空工业的关键技术[1]。因而,研究新型高性能单晶涡轮叶片的制备、优化工艺,探讨其力学性能和失效机制具有重要的实用意义。本文主要针对一种低铼高性能镍基单晶高温合金,采用快速凝固法(HRS)制备单晶涡轮叶片,研究定向凝固参数对涡轮叶片组织的影响;另外还探讨了热处理工艺对合金微观组织和力学性能的影响;最后测定了单晶试样的室温强度和高温蠕变性能,分析其断裂机理。研究结果如下:单晶涡轮叶片凝固规律研究表明:对于新型高温合金和选定涡轮叶片结构,一次枝晶间距随抽拉速度的加快和型壳保温温度升高而减小,并且当抽拉速度为1mm/min和4mm/min时都会导致铸件出现杂晶。制备的涡轮叶片各部位组织不均,叶片壁厚较厚处一次枝晶间距、共晶相面积相对壁厚较薄处更大。枝晶臂处强化相尺寸远大于枝晶轴处。热力学模拟和实验研究表明:合适的热处理不仅能够消除低温共晶相,还可以极大的改善铸态合金不均匀的组织。工艺参数对热处理效果的影响表现为:较低的固溶温度无法完全消除共晶相和粗大的γ'相组织,较高的固溶温度会使得组织微熔。合金中析出的γ'相尺寸随时效温度的升高逐渐增加,立方度先增加后减少;固溶时间和时效时间过长都会导致γ'相边角圆钝。对合金的室温强度研究表明:枝晶组织的枝晶轴处的硬度最高,超过410HV,枝晶间的共晶组织显微硬度远低于枝晶内部,仅有约365HV;热处理能够消除这种性能差异并使合金最高硬度提升到450HV;热处理后合金室温抗拉强度能够达到1030MPa。室温下合金的断裂方式为脆性断裂。新型镍基单晶合金的高温蠕变性能研究表明:在1100℃/100MPa、1100℃/120MPa、1100℃/140MPa三种测试条件下寿命分别为450h、260h、100h左右。在此温度下,合金的蠕变第一阶段不明显,迅速进入第二阶段。第二阶段的持续时间随应力增加显著缩短。其断裂都是蠕变微孔聚集长大所引起的。在1100℃蠕变过程中合金组织发生了明显的垂直应力轴的形筏现象,随应力增加筏形组织不断增厚,形筏方向在靠近断口处产生小角度改变,断口处的筏形已经完全破碎。
[Abstract]:As one of the most difficult and complicated hot end parts in aero-engine, the aero-turbine blade is one of the core components in the engine. With the development of advanced aero-engine, With the increasing service temperature and working load of turbine blades, advanced manufacturing technology of single crystal turbine blades has become a key technology in aviation industry [1]. Therefore, it is of great practical significance to study the preparation, optimization process, mechanical properties and failure mechanism of new high performance single crystal turbine blades. In this paper, single crystal turbine blades were prepared by rapid solidification method for a high performance nickel base single crystal superalloy with low rhenium and high performance. The effect of directional solidification parameters on the microstructure of turbine blades was studied. In addition, the effect of heat treatment on the microstructure and mechanical properties of the alloy was discussed, and the room temperature strength and high temperature creep property of the single crystal sample were measured, and the fracture mechanism was analyzed. The results are as follows: the solidification law of single crystal turbine blade shows that for the new superalloy and selected turbine blade structure, the primary dendrite spacing decreases with the increase of the drawing speed and the heat preservation temperature of the shell. And when the drawing speed is 1mm/min and 4mm/min, the castings will appear heterocrystals. The structure of the turbine blade is uneven, and the primary dendrite spacing of the blade is thicker, and the area of eutectic phase is larger than that of the thin one. The size of the strengthened phase at the dendrite arm is much larger than that at the dendrite axis. The thermodynamic simulation and experimental study show that the suitable heat treatment can not only eliminate the eutectic phase at low temperature, but also greatly improve the inhomogeneous microstructure of the as-cast alloy. The effect of process parameters on heat treatment effect is as follows: lower solution temperature can not completely eliminate eutectic phase and coarse 纬 'phase structure, and higher solution temperature will make microstructure micromelt. The size of 纬 'phase in the alloy increases gradually with the increase of the effect temperature, and the cubic degree increases first and then decreases, and both the solution time and aging time lead to the obtuse of the edge angle of 纬' phase. The study on the room temperature strength of the alloy shows that the microhardness of the dendritic microstructure at the dendrite axis is the highest, which is more than 410 HV.The microhardness of the eutectic microstructure between the dendrites is much lower than that of the dendrite interior. Only about 365 HVT; heat treatment can eliminate this difference and increase the maximum hardness of the alloy to 450 HV.The tensile strength of the alloy at room temperature can reach 1030 MPA after heat treatment. The fracture mode of the alloy at room temperature is brittle fracture. The creep properties of the new Ni-base single crystal alloy at high temperature have been studied. The results show that the lifetime of the new Ni-base single crystal alloy is about 450 h / 260 h / 100 h at 1100 鈩，

本文编号：1999010