低层错能Ni-Co基高温合金动态应变时效研究

IMR OpenIR

	低层错能Ni-Co基高温合金动态应变时效研究
	田成刚
学位类型	硕士
导师	孙晓峰 ; 崔传勇
	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	Ni-co基高温合金动态应变时效置换固溶原子可动位错激活能层错 Ni-co Base Superalloy Dynamic Strain Aging Substutitional Solutes Mobile Dislocations Activation Energy Stacking Fault
摘要	"先进镍钴基(TMW)合金综合使用了固溶强化、沉淀强化及细晶强化等常规强化手段以及通过降低合金的层错能引入大量孪晶结构的非常规强化手段，是比较典型的新一代先进变形高温合金。但在其通常使用温度区间(300?C?550?C)，TMW合金存在着动态应变时效现象，关于该合金锯齿状塑性失稳机理及其对力学性能的影响，目前仍不清楚。本文采用Ni-Co基高温合金为实验材料，利用光学显微镜（OM）、扫描电镜（SEM）、透射电镜（TEM）研究了固溶处理以及及Co含量对镍钴基高温合金动态应变时效的影响规律。首先研究了该合金经亚固溶（低于??溶解温度）处理后的室温至600?C的拉伸性能。实验结果表明：在300-350℃为常规动态应变时效，在400-500℃为反常动态应变时效。在锯齿流变区发现应变速率敏感性指数(m)都为负；亚固溶热处理后合金的屈服强度、抗拉强度、延伸率、加工硬化指数在锯齿流变发生的区间变化不大。通过分析表明常规的动态应变时效是由间隙C原子与可动位错的作用造成的，反常的动态应变时效是由置换固溶原子在合金中的可动位错处的规则排列形成钉扎气团阻碍其运动造成的，且这一过程受热激活控制；当温度高于550℃时锯齿流变消失，原因可能是温度高元素扩散加快破坏了置换固溶原子在可动位错处的排列。通过改变合金的热处理制度研究了合金过固溶（高于??溶解温度）处理后的动态应变时效现象。实验结果表明：在400℃和450℃为反常动态应变时效；过固溶热处理后的锯齿流变现象是由置换固溶原子和合金内可动位错的相互作用引起的。亚固溶热处理和过固溶后锯齿流变的临界应变量的差别与合金内二次g￠的间距有关，其应力差值的区别可能是由合金内位错密度和由晶界控制的扩散有关。通过改变合金中Co含量研究了的三种不同Co含量合金的动态应变时效现象。实验结果表明：随着Co含量的降低，合金室温时的层错能升高。三种合金拉伸时都有常规和反常的两种动态应变时效发生，且常规动态应变时效是由间隙C原子与可动位错的作用造成的，反常动态应变时效是由置换固溶原子和可动位错作用造成的。随着合金中Co含量降低，合金发生动态应变时效的温度区间向低温移动。层错能对动态应变时效的发生有一定的影响。 "
其他摘要	"The newly developed Ni-Co base superalloy, which is strengthened by solid-solution strengthening, precipitation strengthening, grain refining strengthening and twinning strengthening, is a typical wrought superalloys. In the application temperature, the alloy exhibits dynamic strain aging (DSA). However, the DSA mechanism is still unkown. In this paper, the Ni-Co base superalloy was employed to investigate the dynamic strain aging (DSA). The microstructure of the alloy after different heat treatments and with different Co concents was studied by using optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). After subsolvus heat treatment, the alloy exhibited normal DSA behavior in the temperature region ranging from 300 to 350℃ and inverse DSA behavior in the temperature region ranging from 400 to 500℃. The analysis suggested the interaction between C atoms and mobile dislocations should be responsible for serrates flow in normal DSA regime and the ordering of the substitutional solutes around mobile dislocations due to the thermal activated process may cause the serrations in inverse DSA regime. Negative strain-rate sensitivity of flow stress was observed in the DSA regime. The yield strength, ultimate tensile strength, elongation, work hardening index and fracture features were unaffected by the temperatures and strain rates in DSA regime. The stress-strain curves are smooth when the tested temperatures are above 550?C. After supersolvus heat treatment, the alloy exhibited inverse DSA behavior in the temperature regime ranging from 400 to 450℃, which was caused by the interaction between substitutional solutes and mobile dislocations. The variation of critical strain of serrated flow after subsolvus and supersolvus solutions may be related to different spacing between secondary g￠ and different densities of mobile dislocations during plastic deformation. The different densities of mobile dislocations and the diffusion controlled by grain boundary were responsible for the variation of stress drop of serrated flow after two solution treatments. Three alloys with different Co contents were employed to study the effect of Co content on dynamic strain aging. The stacking fault energy of the alloy decreased with Co content reducing at room temperature. Normal and inverse DSA behaviors were found in three alloys, the normal DSA behavior was caused by the interaction between C atoms and mobile dislocations and the inverse DSA behavior resulted from the ordering of the substitutional solutes around mobile dislocations. The temperature regime for DSA moved to low temperature region with Co content decreasing in the alloy. It was assumed that stacking fault energy affected dynamic strain aging in the alloy.
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64553
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	田成刚. 低层错能Ni-Co基高温合金动态应变时效研究[D]. 北京. 中国科学院金属研究所,2012.