镍基单晶高温合金晶格错配度及叶片残余应力分析

IMR OpenIR

	镍基单晶高温合金晶格错配度及叶片残余应力分析
	王有道
学位类型	硕士
导师	吴二冬 ; 王苏程
	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	材料物理与化学
关键词	镍基单晶高温合金晶格常数晶格错配度残余应力 X射线衍射 Nickel-base Single-crystal Superalloy Lattice Constants Lattice Misfit Residual Stress Xrd
其他摘要	" 本文通过采用X射线衍射法对镍基单晶高温合金的晶格常数、晶格错配度和柱状晶高温合金中残余应力进行探索性地测量分析。试验中首先采用单晶片减薄方法并利用X射线四轴衍射仪测定了处于不同应力状态的镍基单晶高温合金DD10基体相（γ）和沉淀强化相（γ′）的晶格常数。根据合金减薄过程中两相间约束条件的变化发现存在一个临界厚度tc。当单晶片厚度达到tc后，沉淀强化相（γ′）的晶格常数随厚度减小而减小，但基体相（γ）的晶格常数几乎没有变化，两相的晶格错配度随厚度减小而变大，由此，可得出合金从接近三维应力状态的表面应力状态向平面应力状态转化达到失稳状态的临界厚度以及与表面应力状态和平板应力状态对应的晶格错配度，并推算出与无相间约束对应的无应力状态下两相的晶格常数。分析结果表明：合金减薄达到临界厚度后，单晶片减薄过程伴随γ/γ′两相间约束的减弱和相间应力松弛，晶格取向差和晶体嵌镶度增大，测量的表面应力状态从表面应力状态向平面应力状态转化。测量得到的临界应力状态与无应力状态的晶格错配度可为高温合金单晶材料的应用设计和应力测试提供参考。其次，通过使用不同的腐蚀方法对镍基单晶高温合金片进行选择性腐蚀，在腐蚀掉γ/γ'两相中任意一相后，利用XRD掠入射的方法，使用小角度入射角测量在表面未被腐蚀的另一单相的晶格常数，发现γ/γ'两相晶格常数减小，特别是γ相大幅度减小，γ/γ'两相间的晶格错配度变正，并与PDF卡片中Ni和Ni3Al的晶格常数接近。扫描电镜和EDS发现选择性腐蚀的γ/γ'两相各自本身的组织形态及组成成分都发生了一定程度的变化，特别是两相晶界偏析元素Mo大幅度减少，这一结果表明除了γ/γ′两相相界的约束作用外，两相相界的组份也对晶格错配度起到重要作用。最后，采用XRD技术对单晶高温合金压痕应变进行估算。通过与应变模拟的对比验证了其方法的可靠性后，进一步采用XRD技术在DZ125L定向凝固高温合金涡轮叶片的不同位置测量其表面残余应力状态。结果表明，DZ125L合金涡轮叶片在表面经轻微腐蚀后不同部位的平面宏观残余应力均为压应力，但其具有一定的各向异性，即沿叶片横向的应力均小于沿叶片纵向的应力，而且某一部位沉淀相γ'相的应力值均小于相应基体γ相的应力值。测试表明，喷丸处理后，在涡轮叶片表面层形成了对表面具有保护作用的压应力状态层，使其在常规条件下不易破坏。" ; " In this study, the lattice constants and misfits of phase γ'/γ in a nickel-based single alloy, and the residual stresses in the blade with columnar crystal superalloy have been measured and analysed by X-ray diffraction (XRD). Firstly, by using single-chip thinning method and four-axis X-ray diffraction goniometer, the lattice constants of both matrix phase γ and precipitation strengthening phase γ' in a nickel-based single crystal superalloy DD10 were determined. Based on the changes of the restriction conditions between the two phases during thinning process, a critical thickness was revealed. After the thickness of single-chip reached the critical thickness, the lattice constant of γ' phase decreased linearly with the decrease of thickness. However, the lattice constant of γ phase kept almost constant, which resulted in the increase of the absolute value of the lattice misfit. In the transformation from the surface stress state (near three-dimensional stress state) to plane stress state, the critical thickness to reach an unstable state, the lattice misfits in the surface stress state and in the plate stress state, and the lattice constants of the two phases under non-stress state associated to the non-phase-constraints were derived from the measurements. The results showed that, after reaching the critical thickness, the crystal lattice misorientation and the mosaicity increased and the measured surface stress state turned to plate stress state, accompanied by the reduction of the γ/γ′ inter-phase restraint and the relaxation of the inter-phase stress. The calculated lattice misfits in the critical stress state and in the non-stress state could provide references for the applicational design and the stress measurement of the single crystal superalloy. Secondly, the γ/γ′ phase in the nickel-based single crystal superalloy chip was selectively corroded by different etching solutions. The lattice constant of the preserved phase γ or γ′ was determined by the grazing incidence X-ray diffraction. The lattice constants of the preserved phases, especially the γ, decreased significantly, approached to the values of Ni and Ni3Al in the PDF cards, and the γ/γ′ lattice misfit changed to possitive. The certain changes of microstructure and components of the etched γ/γ′ phase were observed by the SEM and EDS. In particular, the element Mo segregated on the phase boundary decreased significantly after selective corrosion. The results suggested that the composition of the phase boundary played an important role in the lattice misfits, in addition to the restraint of the phase boundary. Thirdly, the impact indentation strains of single crystal superalloy were evaluated by the XRD technique, and the credibility of XRD technique was confirmed by the comparion of the two techniques. The surface residual stresses in different locations of the blades made from DZ125 superalloy were further measured by XRD. The results showed that the surface macroscopic residual stresses at the different locations of the blade under slightly corrosion condition were compressive and anisotropic. The stresses perpendicular to growth direction are larger than the stresses along the growth direction, and the stresses in γ' phase are less than the stresses in γ phase. The measurements confirmed that a layer under compressive stress on the surface of the blade was formed upon shot peening treatment, which protected the blade from damage under routine conditions."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64509
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	王有道. 镍基单晶高温合金晶格错配度及叶片残余应力分析[D]. 北京. 中国科学院金属研究所,2012.