不同回复加热温度对NiTiNb合金回复应力的影响

对不同回复加热温度条件下Ni47Ti44Nb9合金的回复应力进行测定,分析了其与温度的关系。结果表明,不同的回复加热温度,冷却时产生的回复应力rσm随加热温度的上升而增加。并得出在管接头等应用中,回复加热温度在200℃左右为宜。     

碳含量对不同淬火态Fe-Mn-Si-Cr-Ni-C系记忆合金回复应力的影响

研究了碳含量对不同淬火态Ｆｅ－Ｍｎ－Ｓｉ－Ｃｒ－Ｎｉ－Ｃ系记忆合金回复应力的影响,结果表明,在６５０℃淬火时,碳元素的加入能显著提高合金加热时产生的最大回复应力,σｈ,提高了７６％,不同碳含量的合金,加热后冷却室温产生的回复应力σｃ达到最大值的淬火温度是不同的。在最佳淬火温度下,碳元素的加入能显著提高合金加热后冷却到室温时的回复应力σｃ提高了４２％,在任一淬火温度下,含碳不同的Ｆｅ－Ｍｎ－Ｓｉ－ｃ     

Ni-Ti-Nb合金不同状态下的回复应力

对在冷拔态、非真空热处理、真空热处理3种状态和不同的回复加热温度条件下Ni47Ti44Nb9合金的回复应力进行测定,分析了回复应力与温度的关系。结果表明,非真空热处理、真空热处理这两种热处理方式的最大回复应力σr^m变化不大,而冷拔态下合金的最大回复应力值σr^m远远高于其他两种状态的回复应力。     

两种不同变形方式对NiTi合金回复特性的影响

研究了马氏体再取向(MR)和应力诱发马氏体转变(SIM)两种不同变形方式对Ni50.2Ti49.8合金拉伸性能及预应变后加热回复特性的影响.结果表明:拉伸变形中,MR变形方式的应力平台结束时的应变值较SIM变形方式大.在拉伸预应变处于应力平台阶段时,两种变形方式在相同预应变后加热回复有相同的记忆能力;在拉伸预应变大于应力平台时,两种变形方式在相同预应变后加热回复,SIM变形方式的逆相变温度和回复应变略高于MR变形方式.     

NiTi形状记忆合金回复力-温度模型改进与实验研究

摘要: 针对NiTi形状记忆合金的马氏体不完全逆转变现象带来的回复力模型预测误差,开展了NiTi形状记忆合金一维回复应力-温度模型研究。在Brinson的形状记忆合金(SMA)一维本构模型基础上,增加马氏体回复因子为内变量,给出了马氏体回复因子与预应变的关系,综合考虑温度和应力对马氏体体积分数的影响,构造NiTi形状记忆合金回复应力-温度改进模型,通过实验测试了不同预应变量的NiTi合金回复应力与温度关系曲线。研究表明：本文提出的改进模型预测的NiTi形状记忆合金回复应力-温度曲线,与实验结果曲线吻合较好,本研究结果对于提高NiTi形状记忆合金回复力预测精度具有重要意义。     

热处理对Fe17Mn5Si8Cr5Ni形状记忆合金回复应力的影响

研究了热处理对Fe17Mn5Si8Cr5Ni0.5NbC形状记忆合金回复应力的影响。结果表明:(1)随着淬火温度的升高,合金的回复应力增加,在750℃左右时,合金的回复应力(加热时的最大回复应力"h和冷却到室温的回复应力"r)最大;(2)合金经1100℃×30min固溶后再进行时效处理,时效温度在450～600℃(时效时间为1h)时,合金的回复应力达到最大;时效时间(时效温度为600℃)对"h影响不大,对"r有显著的影响,当时效时间为360min时,"r达到最大,然后又降低。     

时效时间对Fe-Mn-Si-Cr-Ni-C记忆合金回复应力的影响

本文研究了时效时间对Ｆｅ－１４Ｍｎ－５Ｓｉ－８Ｃｒ－４Ｎｉ－０．２Ｃ记忆合金回复应力的影响。实验结果表明,在１１２３Ｋ时效时,合金加热时产生的最大回复应力σｈ随时效时间的增加而升高,在３００ｍｉｎ时达到最大值,比固溶态提高了１０２％;当时效时间大于影响规律不同。σｈ没有影响。时效时间对合金加热后冷却到室温时回复应力σｃ的影响规律与其对σｈ的影响规律不同。σｃ随时效时间的增加而增加,在１２０ｍｉｎ时     

Ti—Ni形状记忆合金回复应变率和回复力测定的研究

较详细地叙述了用拉伸试验法测量Ti-Ni形状记忆合金的回复应变和回复力特征的研究结果,并分析了Ti-Ni合金回复应变率和回复应力同低温马氏体状态下残余变形程度之间的关系。     

快速加热过程中冷轧钢板的回复和再结晶行为

利用X射线衍射技术研究了一种超低碳冷轧钢板快速加热过程中的回复和再结晶行为。结果表明加热速率对试样退火过程中的回复和再结晶行为影响显著:640℃退火时,不同加热速率退火条件下的试样均处于回复阶段。X射线衍射峰型的不同表明快速加热时因可用于回复的时间缩短而使试样的回复过程被推迟。720℃退火时,快速加热条件下的试样处于再结晶开始阶段,而慢速加热条件下的试样已基本完成再结晶,处于晶粒长大阶段。760℃退火时,慢速加热条件下试样已完成再结晶,而快速加热处理的试样在板中心处仍存在少量轧态纤维组织。原因主要在于快速加热导致可用于回复和再结晶的时间缩短,而使试样的回复及再结晶行为被推迟。     

热处理对TiNi形状记忆合金回复稳定性能的影响

研究了热处理对TiNi合金回复稳定性能的影响。结果表明,马氏体相变温度Msσ和Mfσ随热机械循环次数增加而上升,而马氏体逆相变温度Asσ和Afσ随热机械循环次数的增加而下降。随着热机械循环次数的增加,相变温度逐步稳定。退火温度小于500℃,热机械循环下TiNi合金的回复性能稳定,退火温度达550℃时,TiNi合金组织长大,应力诱发马氏体变形时容易发生滑移,回复应变随热机械循环次数增加而下降,回复稳定性能变差。     

退火工艺对NiTi形状记忆合金恢复力的影响

通过力学性能测试、显微组织观察和预应变后约束下的恢复力测试等手段,研究了退火工艺对Ni50.2Ti49.8合金恢复力的影响.结果表明,预应变为12%时,恢复力达到最大;退火温度升高,恢复力下降.合金的屈服强度是影响恢复力的重要因素,屈服强度越高,在马氏体逆相变过程的相界面迁移能力越强,恢复力就越大.     

Recovery stress characteristics of TiNi alloy wires after partial martensitic transformation under different constraint conditions

The recovery stress characteristics of a TiNi shape memory alloy wire under different constraint conditions were studied. The results show that the recovery stress rate (da/dT) in the second heating cycle increases significantly with the increasing constraining-spring coefficient in the first heating cycle. As a result, a distinct discontinuity appears on the recovery stress curves of the TiNi alloy wires in the second heating process. Also, the results of differential scanning calorimeter(DSC) measurements show that after the thermomechanical process, the heating curve of the TiNi alloy wire consists of two independent endothermic peaks.     

Recovery,recrystallization and grain growth in ordered alloys

The recovery, recrystallization and grain growth behavior of ordered alloys are reviewed from a phenomenological viewpoint. These processes are essentially similar to those occurring in metals except that below the critical ordering temperature their kinetics are much slower, particularly due to the ordered nature of the grain boundaries. Recovery in weakly-ordered compounds below their critical temperature is associated with strain-age hardening whereas more strongly-ordered compounds exhibit recovery softening. An alloy deformed in the ordered state recrystallizes more rapidly than one deformed in the disordered state, a feature associated with a higher stored energy of cold work in the ordered state. Competition between ordering and recrystallization in some strained initially-disordered compounds can cause them not to easily recrystallize in certain temperature ranges, even though they recrystallize readily at both higher and lower temperatures. Antiphase boundaries are relatively scarce in strongly-ordered compounds, but common in weakly-ordered compounds after recrystallization, a feature that may arise because of the (partial) disorder of grain boundaries in the latter materials. Deviations from the stoichiometric composition, because of the increasing disorder, and hence, faster diffusion, generally lead to faster recrystallization and grain growth than at the stoichiometric composition.     

Recovery as a measure of oriented crystalline structure in poly(l-lactide) used as shape memory polymer

Semicrystalline poly(l-lactide), or PLLA, has been reported as possessing shape-memory effect [1], [2], [3], [4], [5]; however, the mechanism responsible for the shape recovery has not been well addressed. Therefore, in this paper, we attempted to investigate the structural evolution in PLLA during the shape memory process by means of differential scanning calorimetry, dynamic mechanical analysis (DMA), optical birefringence and wide-angle X-ray diffraction measurements. The shape recovery behaviour and recovery stress as a function of stretch ratio and deformation temperature were quantified. Based on the present results, shape recovery decreases with increasing stretch ratio and deformation temperature. It is suggested that the shape recovery is associated with the disorientation of oriented amorphous chains formed during stretching and the drop in recovery is attributed to the strain-induced crystallization and the formation of highly oriented microfibrillar structure, hindering the mobility in the amorphous phase and thus impeding recovery. In particular, the validity of the stress-optical law is considered. It is shown that the stress-optical properties show divergence from the Gaussian theory for stretch ratio greater than ～1.5.     

Influence of pre-strain on recovery stress of annealed NiTi thin wire during isothermal holding

The present research aims to understand the recovery stress of NiTi wires generated during heating and isothermal holding under constrained condition. Both pre-strain and isothermal holding temperature have significant effects on the evolution of recovery stress during heating and isothermal holding. In general, increasing isothermal holding temperature and/or pre-strain causes an increase of recovery stress reduction or relaxation. This effect can be attributed to different dislocation densities and mobility of dislocations generated in those conditions.     

Al-Mg-Si合金线导电率演变规律与机制

通过不同温度退火处理模拟架空输电用Al-Mg-Si合金线的热服役环境,对不同退火温度下Al-Mg-Si合金线的导电率演变规律与机制进行了研究。结果表明,Al-Mg-Si合金线的导电率随着退火温度的升高呈现3阶段特征,第一阶段温度为90~150 ℃,Al-Mg-Si合金线导电率略微增大,缺陷的回复是本阶段Al-Mg-Si合金线导电率增大的原因;第二阶段温度为150~200 ℃,析出相的长大和固溶原子的析出导致Al-Mg-Si合金线导电率大幅增大;第三阶段温度为200~300 ℃,晶粒长大是Al-Mg-Si合金线导电率缓慢增大的主要原因。     

一种新型水平连铸Al-Mn-Si-X合金热压缩变形流变应力

采用圆柱体在Gleeble-1500热模拟机上进行热压缩实验,对一种新型水平连铸Al-Mn-Si-X合金热变形流变应力行为进行研究,变形温度为350℃~500℃,应变速率为0.01s-1~10s-1。结果表明,流变应力先随应变的增大而增大,达到峰值后则逐渐减小并趋于平稳,表现出流变软化特征;而应力峰值是随着温度的升高而减小,随应变速率的增大而增大。应用包含Zener-Hollomon参数的Arrhenius双曲正弦关系描述合金热压缩变形流变应力,其变形激活能Q=159.2kJ/mol。     

海上某油田高温高压水蒸汽对热采井管柱腐蚀问题研究

随着稠油开采的投入逐年增大,稠油热采技术成为石油行业研究的热门。稠油热采中,蒸汽吞吐通常作为油田规模蒸汽驱开发之前的先导开发方式。但是,高温高压蒸汽进入油管后,可能会对油管造成腐蚀和结垢。尤其在氮气纯度不够时,会携带有氧气,这样会对热采井管柱造成严重腐蚀。再者,考虑到热采井套管承受高温、高压引起的交变热应力的影响,腐蚀后的管柱管壁减薄或者局部穿孔,这些情况极易造成管柱形变和断裂。因此对高温高压氧腐蚀研究的开展就显得尤为重要。本文从不同氧含量、不同高温、不同水质情况等因素研究了高温高压蒸汽对热采井管柱腐蚀问题。