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。     

低应力／应变幅控制的对称拉压疲劳对Ti—49.6Ni合金相变行为的影响

采用电阻法研究了TiNi形状记忆合金在对称拉压应力或应变疲劳条件下的相变行为,结果表明,经过低应力/应变疲劳,材料发生R相变,试样的相变温度变得稳定,马氏体相变温度Ms和逆相变温度As低于未疲劳试样,随着循环次数的增加,应变疲劳后材料的Ms点、As点与循环次数无明显关系,材料具有良好的相变稳定性。     

应变约束相变对Ti44Ni47Nb9合金恢复应变的影响

研究了10％预应变Ti44Ni47Nb9合金应变约束相变加热温度Th对随后自由相变行为的影响，结果表明：经过约束相变循环的Ti44Ni47Nb9合金，在随后的自由相变过程输出两段恢复应变εr1和εr2，其值分别随约束相变加热温度Th升高而增加和减小，但合金总恢复应变εr(εr=εr1 εr2)却随Th。升高而降低．分析表明：恢复应变εr，的降低与约束逆相变过程中马氏体相在恢复力作用下拉伸变形导致合金产生了大量塑性变形有关，而两段恢复应变εr1和εr2的形成则与合金约束相变后形成应变量明显不同的M1和M2两部分取向马氏体逆相变相关．     

TiNi形状记忆合金薄膜马氏体稳定化研究

采用DSC法研究了TiNi合金薄膜变形后的相变行为及影响机制,结果表明变形导致TiNi薄膜马氏体发生稳定化现象,即TiNi薄膜第一次逆相变滞后,逆相变温度升高.但马氏体稳定化现象在经过一次完全相变循环后消失,且马氏体相变温度降低.变形引起TiNi合金薄膜相变行为的变化与马氏体变体储存的弹性应变能和相变不可逆能变化相关.     

TiNi合金不完全相变的温度记忆效应

通过示差扫描量热分析(DSC)研究了预应变及约束条件下TiNi形状记忆合金的温度记忆效应．结果表明，通过变形约束手段，可以大大拓宽TiNi合金的相变温度区间，使得TiNi合金的温度记忆效应能够在一个非常大的温度范围内发挥作用；同时，变形并约束后TiNi合金的温度记忆效应比自由态TiNi合金的温度记忆效应更加准确．分析表明，马氏体与母相界面处的位错以及界面处的弹性自适应过程是可能的温度记忆效应机制。     

Ti-50．8Ni-0．3Cr超弹性合金的相变与形变特性

用示差扫描量热仪、X射线衍射仪、拉伸实验和循环实验研究了退火温度、形变温度和应力-应变循环对Ti-50.8Ni-0.3Cr超弹性(SE)合金丝和弹簧相变、形变及应力循环特性的影响.350-600℃退火态Ti-50.8Ni-0.3Cr合金室温下呈SE特性,室温组织由母相B2和TiNi3组成.退火温度显著影响合金的相变类型,随退火温度升高,合金的马氏体相变温度升高,R相变温度先升高后降低,应力诱发马氏体应力先降低后升高;随形变温度的升高,SE弹簧的应力诱发马氏体切应力增加;随应力循环次数增加,SE弹簧的应变恢复率先快速衰减后趋于稳定.预循环训练可增加弹簧SE特性的稳定性.要使该合金弹簧具有良好的SE特性,退火温度应为400-550℃,使用温度应在室温以上.     

TiNi薄膜马氏体稳定化及其形状记忆效应研究

用DSC研究了预变形对Ti51Ni49形状记忆合金薄膜的相变行为的影响，结果表明：预变形后薄膜的马氏体发生了稳定化现象，第一次逆相变温度T^1A随预应变量增加而升高，而在第二次相变循环中，马氏体稳定化现象消失，逆相变温度T^2A基本恢复到变形前的温度值，马氏体相变温度随预应变量增大而降低，但R相变受预变形影响不大，形状记忆效应研究表明，Ti51Ni49合金薄膜的可恢复应变随预应变量的增加而增大，其最大值4．5％在预应变量为6％时获得。     

循环应力作用下TiNi形状记忆合金应力诱发相变行为演变的原位研究

利用马氏体相变有相变潜热释放的性质,通过精确测量TiNi形状记忆合金在不同变形条件下试样温度的变化波形,结合应力应变响应研究了循环应力作用下TiNi形状记忆合金相变行为的演变过程,对循环应力造成形状记忆合金超弹性退化的原因进行了探讨.结果表明:试样的温度变化比普通金属材料高许多,可以用温度法来研究马氏体相变在变形过程中的变化;在应力控制的循环应力作用下,试样内应力诱发马氏体相变量随着循环周次的增加而不断减小,每一周内应力诱发马氏体相变行为也在不断演化,发生应力诱发马氏体相变的临界应力不断减小,而由马氏体弹性变形所携带的应力增加.     

Ti49.4Ni50.6超弹性弹簧的相变和形变特性

用示差扫描量热仪、拉伸实验和应力-应变循环实验系统研究了退火温度、变形温度以及热循环和室温应力-应变循环对Ti49．4Ni50．6超弹性(SE)弹簧的相变和形变特性的影响。冷加工加中温退火态Ti49．4Ni50．6合金冷却→←加热时的相变类型为母相B2→←R相→←马氏体B19′。随退火温度升高，马氏体转变温度升高，R相转变温度降低。623-773K退火态Ti49．4Ni50．6弹簧室温下可获得SE特性，随变形温度升高，SE弹簧剐度增加；当退火温度超过823K后，SE持性变差。热循环时SE弹簧的切变量取值越小，其应变恢复率越高。预循环训练可增强SE的稳定性。     

TiNi及TiNiCu形状记忆合金的回复力特征

研究了TiNi二元与TiNiCu三元形状记忆合金的回复力特征,并通过示差扫描量热分析研究了合金的热弹性马氏体相变特征.结果表明:二元与三元合金在一定温度范围内的最大回复力随着预应变的增大而升高,但是当预应变达到或超过其最大可恢复变形极限时最大回复力反而减小.对于TiNi合金,回复力随温度增长的速率随着预应变的增加而增加,而TiNiCu合金的回复力随温度增长的速率随着预应变的增加而减小.通过对克劳修斯-克拉珀龙方程进行修正,分析了回复力和相变之间的关系.结果表明:TiNi二元合金的冷变形应变越大,相变温度区间越小,其回复力随温度增长的速率就越大;TiNi三元合金的冷变形越大,相变温度区间越大,其回复力随温度增长的速率就越小.     

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.     

MARTENSITE AND REVERSE TRANSFORMATION IN PRESTRAINED TiNi SHAPE MEMORY ALLOY THIN FILM

The effect of pre-strain on phase transformation of TiNi shape memory alloy film was studied by differential scanning calorimeter measurement (DSC). Compared with un-defarmed TiNi film, the reverse transformation of pre-strained specimens was elevated to a higher temperature on the first heating, but martensite and reverse transformation on subsequent thermal cycles occurred at a lower temperature. The evolution of transformation behavior in pre-strained TiNi film was related to the change of elastic strain energy, irreversible energy and internal stress field.     

Actuator Response of Improved Two-Way Memory TiNi Wires Evaluated by Weight Fraction Diagrams

This paper experimentally studies the improvement in the actuator response of TiNi shape memory wires brought about by thermal treatments. Heat-treated TiNi wires were thermally cycled at zero stress before being trained by constant stress to develop the two-way shape memory effect. Subsequently, the work output of these two-way memory TiNi shape memory alloys are measured during repeated thermomechanical cycling under various levels of constant stress. Changes in the phase transformation behavior in two-way memory and thermomechanically cycled TiNi shape memory alloy wires are quantified by x-ray diffraction as a function of temperature. The weight fraction diagrams of TiNi wires thermally cycled at zero stress before they were trained suggests that during constant stress training they develop a lower quantity of R-phase than samples that have not been thermally cycled at zero stress before being trained. This gives thermally cycled TiNi samples higher levels of transformation strain and work output during thermomechanical cycling than samples that have not been thermally cycled before training. These results suggest that for the best material performance—that is, significant transformation strain and, consequently, substantial work output—the TiNi wire should be thermally cycled at zero stress before training.     

Changes in martensitic transformation temperatures during thermal cycling in Ti−Ni−Zr shape memory alloys

Changes in the transformation behavior and transformation temperatures of a 40Ti-50Ni-10Zr (at%) alloy during thermal cycling have been investigated by means of differential scanning calorimetry, X-ray diffraction and thermal cycling tests under a constant load. A 40Ti−50Ni−10Zr alloy showed two stage transformation behavior, i.e., from the B2 to the B19 and then from the B19 to the B19, although they are not clearly separated. With the increasing of the number of thermal cycling, the decreasing rate of the transformation temperature corresponding to the B2–B19 was higher than that corresponding to the B19–B19, and consequently the former overlapped with the latter. Transformation temperatures of 40Ti−50Ni−10Zr greatly decreased (95K) during thermal cycling without applied stress, since only the thermal cycling effect which suppresses martensitic transformation had an influence on transformation temperatures. Decreases in transformation temperatures during thermal cycling with applied stress was smaller than that during thermal cycling without applied stress because both the structural refinement effect which assists martensitic transformation and the thermal cycling effect had an influence on transformation temperatures.     

Effects of thermomechanical cycling on the shape memory behavior and transformation temperatures of a Ni50.2Ti49.8 alloy

The effects of thermomechanical cycling on the shape memory behavior and transformation temperatures of a Ni50.2Ti49.8 alloy under a constant applied stress of 300 MPa were investigated.It is believed that thermomechanical cycling induces defects such as dislocations,which evidently affect the shape memory behavior and transformation temperatures.The recovery strain decreases with increasing number of thermomechanical cycles,whereas the irreversible plastic strain increases,especially in the initial few cycles.The stored elastic strain energy has an important influence on transformation temperatures,the Aso decreases and the Mso increases with increasing number of thermornechanical cycles.The recovery strain,irreversible plastic strain,Aso,and Mso reach a saturation value after several cycles.     

PHASE TRANSFORMATIONS IN RAPIDLY SOLIDIFIED TiNi SHAPE MEMORY ALLOYS

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预变形对TiNi薄膜相变行为的影响

用DSC法研究了预变莆对TiNi薄膜相变行为的影响,结果表明,预变形可使马氏体逆相变温度升高,马氏体发生了稳定化,经过一次完全相变循环后,这种稳定化现象消失,若TiNi薄膜在预变形后先经过一次不完全逆相变,则其后的热循环中,除第一次相变循环的逆相变是由两个独立的相变过程共同完成,其他相变循环的逆相变过程相同于变形的状态,由此可见,预变形造成的TiNi薄膜马氏体稳定化现象,经过完全相变循环后均可以消除,而与预变形后薄膜的相变历史无关。     

Super-Elasticity Characteristics of TiNi Alloy Processed by Equal Channel Angular Extrusion

A Ni-rich TiNi alloy was processed by Equal Channel Angular Extrusion (ECAE) at 500℃. After four passes ECAE treatment, microstructure of the alloy was refined but slightly inhomogeneous, to sub-micron scale, approximately 0.5～0.6 μm. Comparing with the solution-treated TiNi specimen, the martensitic transformations start (Ms) and peak temperatures (Mp) of TiNi specimens processed by ECAE were dramatically lowered. After ECAE treatment, the R-phase transformation was stimulated and separated from martensiti...