一种无铼单晶高温合金组织与性能研究

IMR OpenIR

	一种无铼单晶高温合金组织与性能研究
	张小强
学位类型	硕士
导师	楼琅洪
	2011
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	材料学
关键词	无铼单晶高温合金持久蠕变低周疲劳氧化 Free-re Single Crystal Superalloy Stress Rupture Creep Low Cycle Fatigue Oxidation
摘要	"本论文采用金相显微镜（OM）、扫描电镜（SEM）、电子背散射衍射技术（EBSD）、透射电镜（TEM）、能谱分析（EDS）、X射线衍射（XRD）等分析方法对一种无铼单晶高温合金铸态/热处理态组织、拉伸/压缩变形组织、持久变形组织、疲劳变形组织以及氧化组织进行了研究。主要内容包括以下几个方面：采用金相显微镜、扫描电镜、电子背散射衍射技术对实验合金铸态组织及热处理态组织进行分析表明，合金铸态组织一次枝晶间距约为370±25μm，二次枝晶间距约为60±10μm，共晶百分含量约为4.0±1.0%，热处理态γ'相大小约为0.3~0.4μm，面积百分数约为65%。实验合金经过760℃拉伸变形后，发生脆性断裂，碳化物为主要裂纹源，扫描电镜观察表明，合金组织没有发生明显的筏化。但是，合金经过950℃拉伸变形后，断口呈韧窝状，裂纹多在碳化物周围形成。实验合金经过760℃/850MPa低温高应力以及1070℃/160MPa高温低应力持久变形后，采用扫描电镜及透射电镜分析变形组织。研究发现合金在低温高应力时持久断口呈阶梯状，微观组织主要以层错为主，并且层错互相反应形成层错锁，高温低应力时断口呈韧窝状，微观组织主要为位错网。分析表明，在低温高应力变形条件下，产生了两种不同方向的堆垛层错。在高温低应力条件下合金变形主要受控于位错滑移和交滑移，变形的特征是形成位错网。实验合金经过950℃，不同应变幅以及不同应变速率条件下的低周疲劳变形后，采用扫描电镜及透射电镜分析变形组织。研究发现当应变幅不同时，合金断口扩展区和瞬断区面积比例没有发生明显的变化，位错由低应变幅时的束状向位错网转化。在不同应变速率条件下，合金断口扩展区比例随着应变速率的增加而增大，位错也由低应变速率时的位错网向高应变速率时的束状位错转化。通过分析疲劳稳定滞后回线可知，当应变幅较低或应变速率较高时，合金主要以弹性变形为主，滑移系开动的较少，因此只有少量束状位错萌生于γ基体通道中。当应变幅较高或应变速率较低时，合金的蠕变塑性变形比较明显，根据映像规则，合金开动了更多的滑移系，进而形成位错网。采用扫描电镜、能谱分析、X射线衍射等手段分析了实验合金1100℃氧化后的组织。分析发现合金的表面氧化物分三层，外层主要是由NiCr2O4、NiCo2O4和Co2TiO4等尖晶石结构组成，中间层主要由NiCr2O4尖晶石和Al2O3组成，内层主要是Al2O3。另外，合金还发生了内氮化，主要产物为(Al，Cr，Co)N。"
其他摘要	"In this dissertation, the as-cast and heat-treated microstructure, as well as the microstructure evolution during tension, compression, creep and low cycle fatigue of a Re-free nickel-base single crystal superalloy have been systematically investigated by using optical microscopy (OM), scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray. The primary coverage is as follows: The as-cast and heat-treated microstructure of tested alloy was analysised through metallographic microscope and scanning electron microscope. The primary dendritic arm spacing was approximately 370±25μm, the secondary dendritic arm spacing was approximately 60±10μm, the volumn fraction of eutectic was approximately 4.0±1.0%, the dimension and area fraction of γ' phase were 0.3~0.4μm and 65%. The characterization of fracture surface was brittle, the majority of cracks initiated at the carbides after the 760℃ tensile test of the tested alloy. However, when tested at 950℃, the fracture surface changed into ductility from brittle. After creep test at 760℃/850MPa, the fracture surface was similar to the tensile test and no rafting was found, but two kinds of intrinsic or extrinsic stacking faults with different direction were found in the γ' phase and the stacking fault lock was formed by reaction of those faults. The characteristic of fracture surface was ductility and the major pattern of microstructure was dislocation networks when tested at 1070℃/160MPa. At 760℃/850MPa, it was found that two type dislocations cut into the γ' particles and two different direction superlattice stacking faults generated. At 1070℃/160MPa, it was found that creep deformation was controlled by slip and cross slip in the matrix channels. The creep was characterized by formation of dislocation networks. During the low cycle fatigue test at 950℃ with R=-1, the areas of instantaneous rupture region on the fracture surface had little change and the dislocation pattern changed from bundle at low strain amplitude to network at high strain amplitude. With the increasing of strain rate, the areas of instantaneous rupture region decreased on the fracture surface and the dislocation pattern also changed from network at low strain rate to bundle at high strain rate. After analysizing the hysteresis loops at different strain amplitudes and strain rates, we consider that more plasticity deformation leads to more slip systems moving and the network formed at high strain amplitude or low strain rates. The microstructure after 1100℃ oxidization was analysized through the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray. Three layers formed on the surface of the tested alloy. The outer layer was constituted by NiCr2O4、NiCo2O4 and Co2TiO4. The major compounds in the intermediate layer were NiCr2O4 and Al2O3. Al2O3 was the only production in the inner layer. Otherwise, inner nitridation phenomenon occurred and the compound was (Al, Cr, Co)N."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64407
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	张小强. 一种无铼单晶高温合金组织与性能研究[D]. 北京. 中国科学院金属研究所,2011.