【作者】 谢鹏；

【导师】 刘明；

【作者基本信息】 福州大学 ， 车辆工程（专业学位）， 2023， 硕士

【摘要】 由于优异的抗疲劳和抗蠕变性能,镍基单晶高温合金广泛应用于航空发动机的涡轮叶片中,并且长期在高温高压等恶劣环境下服役,因此对具有卓越力学性能的镍基单晶高温合金进行深入研究具有重要意义。镍基单晶喷丸强化后的喷丸强化层层深较浅,无法采用传统的方法对其力学性能进行表征,而仪器化压入可以弥补其不足,能在小范围区域内进行实验,广泛应用于工业及科研领域。目前对镍基单晶高温合金喷丸强化层的各种力学性能分析的研究相对较少。本文采用中国航发北京航空材料研究院研制的喷丸镍基单晶高温合金DD6,对其基体及喷丸强化层表面形貌、组织结构、微米硬度、局部微观疲劳及蠕变性能进行表征。首先对DD6喷丸前后的表面进行了形貌表征和XRD分析,对喷丸强化层进行了形貌、以及显微硬度分析,结果表明喷丸表面喷丸覆盖率超过了100%,镍基单晶衍射峰数量增加,择优取向明显弱化;喷丸强化层内,离喷丸表面越近,材料的塑性变形程度越高,努氏与维氏硬度由于喷丸强化的影响均得到了提升。其次对喷丸DD6基体、喷丸强化层及纯铝进行仪器化循环压入实验,研究了加载速率、循环次数对循环压入行为的影响。结果表明:加载速率越大,DD6基体与纯铝的硬度越小,说明较小的加载速率会使材料发生应变硬化,DD6的抗疲劳性能优于纯铝。喷丸强化层内,DD6不同喷丸深度的硬度和弹性模量随着加载次数的增大而线性减小,出现了软化现象或疲劳微损伤,硬度及弹性模量随喷丸深度的增大先增大后线性减小,最后在基体区域趋于平稳,说明喷丸后的DD6抗疲劳性能等力学性能均得到了加强。最后对喷丸DD6基体、喷丸强化层及五种常规纯金属(Cu、Fe、Mo、Sn和W)进行仪器化压入蠕变实验,研究加载速率、峰值载荷、保载时间对不同材料压入蠕变行为的影响,研究发现:仪器化压入蠕变实验均出现初始蠕变和稳态蠕变阶段,峰值载荷对蠕变位移有显著的影响,验证了压痕蠕变的普遍性。各种金属在不同实验参数下的稳态蠕变应力指数不同,说明仪器化压入只能在一定的范围内表征材料的蠕变性能。DD6喷丸强化层的硬度、弹性模量及稳态蠕变应力指数均随着喷丸深度的增大先增大后减小,最后在基体区域趋于平稳,说明喷丸强化提高了DD6表层抗蠕变等力学性能。更多还原

【Abstract】 Due to the excellent fatigue and creep resistance,Nickel-based single crystal superalloys are widely used in turbine blades of aero-engines with long-term service in harsh environments with high temperature and high pressure.Therefore,it is crucial to research extensively Nickel-based single crystal superalloys of excellent mechanical properties.Because of shallow layer depth,the properties of shot-peening layer of Nickel-based single crystal after shot-peening cannot be characterized using conventional methods.The insufficient can be made up by instrumented indentation,which can be conducted in the small region,and widely used in industry and scientific research.The various mechanical properties of the shot-peening layer of Nickel-based single crystal superalloys have not been investigated extensively.Therefore,in the current work,the the surface morphology,structure,microhardness,local micro-fatigue,and creep properties of the matrix and shot-peening layer of the shot-peened nickel-based single crystal superalloy DD6,developed by the Beijing Institute of Aerospace Materials of the China Aerospace Development,are characterized.Firstly,the surface morphology and XRD of DD6 before and after shot-peening were analyzed,and the structure and microhardness of shot-peened layer were characterized.The results show that after shot-peening,the shot-peening coverage of shot-peening surface is larger than 100%,the number of Nickel-based single crystal diffraction peaks increase,the selective orientation was weakened significantly;with the decreases in shot peening depth,the extent of plastic deformation increases;the Knoop and Vickers hardness increase due to shot-peening process.Secondly,instrumented cyclic indentation tests were conducted on the matrix and shot-peened layer of DD6 and pure aluminum to investigate the effects of loading rate and cycle number on the instrumented cyclic indentation behavior.The results show that with the increase in loading rate,the hardness of both DD6 matrix and pure aluminum decrease,which indicates that strain hardening of materials can be induced under small loading rate;DD6 exhibits higher fatigue resistance than pure aluminum.Within the shot-peened layer,the values of both the hardness and elastic modulus of DD6 of different shot-peening depth decreased linearly with the increase in cyclic numbers,and softening phenomena or fatigue microdamage occurred;with the increase in shot-peening depth,hardness and elastic modulus increase,followed by the linear decrease,and reached constant levels within the matrix,which indicates that the mechanical properties such as fatigue resistance of DD6 have been improved after shot-peening process.Finally,instrumented indentation creep tests were carried out on the matrix and shot-peened layer of DD6,and 5 conventional pure metals(i.e.,Cu,Fe,Mo,Sn,and W)to investigate the effects of loading rate,peak load,and holding time on the indentation creep behaviors of different materials.The results show that initial and steady creep stage can be observed,and creep displacement can be affected significantly by peak loads,which validates the universality of indentation creep.The steady creep stress exponent of various metals varies with experimental parameters,which indicates that instrumented indentation can be used to characterize creep properties of materials only within a certain range.With the increase in the shot-peening depth,the hardness,elastic modulus,and steady creep stress exponent increases,followed by the decrease,and reaches constant level within the matrix,indicating that mechanical properties of DD6 surface such as creep resistance can improved by shot-peening process.更多还原