含Hf的NiAl基共晶合金的氧化及力学性能的研究

【作者】 张仕臻；

【导师】 周文龙； 郭建亭；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2004， 硕士

【摘要】 本文采用传统的Bridgeman定向凝固技术制备NiAl-28Cr-5.85Mo-0.15Hf合金，借助于扫描电镜（SEM）、透射电镜（TEM）及X射线衍射（XRD）等分析手段，研究了定向凝固NiAl-28Cr-5.85Mo-0.15Hf合金的微观组织形貌、韧脆转变、高温变形行为和拉伸蠕变行为。此外，还研究了稀土元素Ce和Nd对NiAl-28Cr-5.5Mo-0.5Hf共晶合金组织及氧化性能的影响。 定向凝固技术制备的NiAl-28Cr-5.85Mo-0.15Hf合金是由NiAl相和层片状Cr（Mo）相组成的胞状共晶组织，在胞界处存在粗大的先共晶NiAl相，此外，白色的Hf固溶体不连续地分布于胞界。拉伸测试实验，合金呈现明显的韧脆转变温度（BDTT）。BDTT以上时，合金呈现典型的塑性断口形貌。该合金拉伸蠕变曲线由较短的减速蠕变阶段和较长的稳态蠕变阶段以及加速蠕变阶段组成。从应力指数n和蠕变激活能Q推断，该合金的蠕变变形是由位错攀移机制所控制的。蠕变断裂受孔洞及裂纹的形成和扩展所控制，且蠕变断裂数据符合Monkman-Grant关系。 研究了稀土Ce和Nd对NiAl-28Cr-5.5Mo-0.5Hf共晶合金氧化性能的影响。不同稀土含量合金1100℃的恒温氧化动力学曲线均近似服从抛物线规律。不同Ce和Nd含量合金的氧化增重呈现出相同的规律，即含量较少合金的氧化增重小于基体，当含量增大到0.5wt％时，氧化增重急剧增大。Ce含量为0.05wt％和Nd含量为0.1wt％时，分别获得了最小的氧化增重。Nd含量为0.005、0.05wt％的合金氧化膜中，存在有针状的θ-Al₂O₃，其它含量合金的表面氧化膜中的Al₂O₃为α-Al₂O₃，没有出现θ-Al₂O₃。当Ce、Nd含量达到0.5 wt％时，表面氧化膜中分别出现了CeO₂和Nd₂O₃的氧化物。稀土的加入，改变了合金表层氧化膜中各组成氧化物的含量，消除或减轻了氧化膜中的空隙和开裂，并且消除了合金中的内氧化。更多还原

【Abstract】 Multiphase intermetallic NiAl-based alloy with the composition of NiAl-28Cr-5.85Mo-0.15Hf has been directionally solidified(DS) by conventional Bridgeman apparatus. The microstructure, BDT, elevated temperature compressive deformation and tensile creep are investigated by XRD, SEM and TEM. Furthermore, The effect of RE on the oxidation behavior of NiAl-28Cr-5.5Mo-0.5Hf alloy is also studied.The (DS) NiAl-28Cr-5.85Mo-0.15 alloy prepared by conventional DS technique is composed of three phases, which are NiAl matrix, lamellar Cr(Mo) phase and semicontinuousely distributed Hf solution phase. The tensile results indicate that NiAl-28Cr-5.85Mo-0.15Hf alloy exhibits apparent brittle-to-ductile transition temperature(BDTT). At temperature just above the BDTT, the fracture morphology changed from NiAl cleavage and debonding along the NiAl and Cr(Mo) phase boundary to completely dimple in nature. The tensile creep curve is composed of the typical primary creep stage, steady-state creep stage and the accelerated creep stage. Based on the stress exponent and the activation energy for creep, the dominant creep deformation mechanism is controlled by the dislocation climb. The creep fracture is controlled by the crack formation and crack propagation. The creep fracture data can be analysed by the Monkman-Grant relationship.The effect of RE on the oxidation behavior of NiAl-28Cr-5.5Mo-0.5Hf alloy is studied. The isothermal oxidation kinetics of the alloy containing various content REEs obeys the parabolic law at 1100癈. The weight gain of the alloy containing small addition is lower than that of the matrix alloy. When the addition is up to 0.5wt%, the weight gain dramatically increases. The weight gain of the alloy containing 0.05wt%Ce and 0.1 wt% Nd is lowest among that of the Ce-doped and Nd-doped alloy, respectively. The oxidation scale of 0.005, 0.05wt%Nd alloy includes small portion of e-Al2O3. The CeO2 and Nd2O3 form in theoxidation scale of 0.5Ce- doped and 0.5wt%Nd-doped alloy, respectively. The RE addition results in a change of the constituent scales contents, gets rid of the microhole in the oxidationscale and eliminates the internal oxidation.更多还原