航空发动机燃油调控系统用高硅镍铜合金的研究

IMR OpenIR

	航空发动机燃油调控系统用高硅镍铜合金的研究
	张洪宇
学位类型	硕士
导师	郑启 ; 于金江
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料工程
关键词	高硅镍铜合金微观组织带状组织 Ni3si 热处理 Ni-cu-si Alloys Microstructures Banding Structure Ni3si Heat Treatment
摘要	" 针对现有发动机燃油调控系统零件用的材料强度和硬度偏低，经常出现粘着磨损失效，导致发动机故障的问题，本文研究了航空发动机燃油调控系统用零部件用先进耐磨结构材料及其制备工艺。开发研制出新型高强度、高耐磨和抗粘合性能良好的高硅镍铜合金材料。通过研究高硅镍铜合金的凝固特征，观察合金的微观组织结构及其断裂特征，建立新的铸造工艺，解决了高硅镍铜合金铸造裂纹和加工开裂的难题。同时确定了合理的热处理流程，提高了工件可靠性。研究结果表明：高硅镍铜合金主要是由富Ni固溶体、Ni3Si沉淀相颗粒和少量共晶组成，Ni3Si颗粒弥散分布于基体当中作为主要的强化相。合金在凝固过程中，由于热应力的作用，合金内部生成大量位错，位错通过运动聚集形成位错墙。位错墙的形成为元素扩散和沉淀相的形核提供了良好条件，致使Ni3Si颗粒在此部位优先沉淀析出和生长，最终沿着位错墙形成由粗大Ni3Si颗粒相组成的带状组织。这种带状组织与合金中微裂纹关系紧密，裂纹通常是沿合金中的带状组织生成并扩展。解决合金铸造裂纹的关键是控制合金凝固过程的热应力产生，抑制带状组织的析出。通过建立新铸造工艺，控制合金的凝固过程和冷却速度，可有效解决合金脆断和内裂纹的难题。在高硅镍铜合金中，Si元素作为主要的强化元素，随着其含量的增加，合金基体中Ni3Si体积分数增加，Ni3Si颗粒趋于粗化。Ni3Si体积分数增加致使第二相强化作用增强，合金的强度和硬度明显升高。但合金的塑性在试验成分范围内并没有显著下降，主要是由于Ni-Cu合金基体本身具有良好塑性；同时富Ni固溶体（α）相与Ni3Si（β）相属于共格关系，且Ni3Si主要以细小颗粒状在基体中弥散分布；特别是采用新工艺后，抑制了带状组织和粗大Ni3Si析出，使Si在有限范围内增加时对合金塑性影响不大。该合金随着固溶温度提高，冷却速度加快，合金更趋向单相组织，铸态沉淀相可得到更充分的溶解，在1050℃温度下铸态沉淀相可以完全分解。固溶后随冷却速度降低，合金硬度增加。快速冷却抑制Ni3Si硬化相析出，容易诱发裂纹。时效过程主要是消除应力，不同固溶温度条件下的合金试样时效后硬度水平相当，选择较低温度固溶对避免热处理裂纹有利。热处理工艺可以进一步改善析出相的形貌，消除带状组织，提高材料使用可靠性。关键词：高硅镍铜合金，显微组织，带状组织，Ni3Si，热处理 "
其他摘要	" Failure often occurs in a fuel-controlled system of engines due to the low strength and hardness of the material used which can easily lead to adhesion abrasion. In order to solve this problem, the advanced wear-resistance structural material, Ni-Cu-Si alloy, and the new technology for its fabrication were investigated in the present study. Through investigation of its solidification process, observation of microstructure and evaluation of properties of alloys, a new casting technology was developed. By adopting this new casting process, formation of crack during the casting or mechining processes was completely avoided. Meanwhile, reasonable heat treatment was also determined. Based on the systematic investigation, some useful results are listed as follows: The Ni-Cu-Si alloy is mainly composed of Ni-base solid solution, Ni3Si precipitated particles, and a small amount of tiny Ni3Si particles which are evenly dispersed in the Ni-base solid solution matrix and act as strengthening phase. During the solidification process, lots of dislocations formed due to thermal stress. The dislocations moved and gathered, leading to formation of dislocation walls (DWs). The dislocation wall is favorable to the precipitation of Ni3Si phase because it is much easy for diffusion of oversaturated Si atoms in α phase through the DWs. The Ni3Si precipitates in the DWs preferentially, and forms band-like structure along the DWs. The band Ni3Si precipitates are closely related to micro-cracks in the alloy. The micro-cracks often nucleate and propagate along the banding structure. Based on the above observation, it is proposed that the casting cracks can be controlled by reducing the thermal stress during solidification and suppressing the formation of band-like structure. That is to say, the problems of brittle fracture and internal cracks can be settled by establishing a new casting process by controlling solidification process and cooling rate. In Ni-Cu alloys containing high amount of Si, Si acts as the main strengthening element. As the content of Si increases, the volume fraction of Ni3Si precipitates increases, and the Ni3Si precipitates become coarsening. The increased fraction of Ni3Si precipitates enhance the strengthening effect, leading to an increase in the strength and hardness of the alloy. The plastic of the alloy, however, does not show significant decline within the scope of the test compositions. Several reasons are responsible for this phenomenon: the intrinsic plastic of the Ni-Cu alloy, the crystallographic coherent structure of the Ni-rich solid solution (α) and the Ni3Si (β) precipitates, especially the evenly distribution of tiny Ni3Si precipitates and the prohibition of banding structure which is obtained through strictly controlling preparation process. As the solid solution temperature increases, particularly at 1050℃, the precipitates forming during solidification can be dissolved completely. If fast cooling rate is also applied, the single-phase structure should be obtained much easier. The slower the cooling rate after solid solution, the higher hardness the alloy gets. Rapid cooling suppresses the precipitation of Ni3Si strengthener, and leads to cracks. Aging process is adapted to eliminate stress, and does not have an influence on the hardness of the alloy. A lower aging temperature benefits the crack avoidance during heat treatment. The appropriate heat treatment process can improve the microstructure of the precipitates, eliminate banding structure, and increase the durability of the alloy. Keywords: Ni-Cu-Si alloys, microstructures, banding structure, Ni3Si, heat treatment "
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64566
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	张洪宇. 航空发动机燃油调控系统用高硅镍铜合金的研究[D]. 北京. 中国科学院金属研究所,2012.