TiNi合金在恒应力约束下的不完全相变

利用DSC对预应变TiNi形状记忆合金丝在恒应力约束下的马氏体不完全逆相变进行了研究,发现不完全相变热循环样品在第二次自由态加热过程中出现两步马氏体逆转变和两段应变回复现象.分析认为:经过恒应力约束下的不完全逆相变后,TiNi样品中存在不同的马氏体,在随后的加热过程中先后逆转变,产生两段回复应变.     

长期约束条件下TiNi合金超弹性衰减研究

研究了在长期约束条件下TiNi合金超弹性的衰减规律,结果表明,超弹性衰减随时间呈类抛物线规律;约束应变越大,衰减量越大,约束应变较小时不发生明显衰减;应力-应变循环处理可显著降低超弹性衰减幅度.在阐明超弹性衰减襄律的基础上,讨论了衰减机制.     

Effects of strain and electropulse duration on elastic modulus of TiNi alloy

The elastic modulus of TiNi alloy was tailored by electroplastic rolling deformation and the effects of rolling strain and electropulse duration on the elastic modulus of electroplastic rolled TiNi alloy were systematically investigated. With rolling strain increasing from 0 to 1.70, the elastic modulus decreases from 61 to 30?GPa, which can be attributed to the increase in dislocation density and deformation-induced low modulus B19^′ martensite phase. With electropulse duration increasing from 80 to 120?µs, the elastic modulus first decreases due to the volume fraction increase in low modulus B19^′ martensite phase and then slightly increases on account of the dynamic recovery of dislocation and reverse martensite transformation resulted from electroplastic effect induced by high-energy electropulse.     

马氏体相变温度变化对TiNi合金磨损性能的影响

利用等通道转角挤压工艺原理，在挤压模具通道转角为90°，温度为750、850℃，挤压速率为25mm／s条件下，对TiNi合金进行晶粒细化加工处理。在干摩擦条件下对细晶TiNi合金的磨损特性进行了实验研究。结果表明，原态钛镍合金的晶粒由60μm细化到小于10μm，晶粒细化后的TiNi合金的耐磨性能得到显著提高。分析了马氏体相变温度变化对TiNi合金耐磨性能的影响机理。     

富镍TiNi形状记忆合金析出物的形态与组成

用光学显微镜、扫描电镜（ＳＥＭ）和能谱仪（ＥＤＸ）系统研究了富镍ＴｉＮｉ形状记忆合金铸态及固溶、时效处理后组织中析出物的形态、分布与组成，给出了Ｎｉ含量和热处理对析出物组织特征的影响规律。     

Effect of Ho on the microstructure and compressive properties of NiAl-based eutectic alloy

The effect of various holmium content on the microstructure and compressive behavior of NiAl-28Cr-6Mo-0.15Hf eutectic alloy has been investigated by using combination of SEM, TEM and compression test. The results suggest that appropriate Ho addition improves the compressive ductility at room temperature and the high temperature strength at 1273 K of the alloy significantly. In addition, lamellar microstructure inside of eutectic cell and eutectic cell get refinement gradually, but the intercellular region become coarse, with increase of Ho content. Furthermore, Ni₂Al₃Ho phase, with hexagonal crystal structure, is observed in the alloy.     

Effects of electropulsing treatment on mechanical properties in Ti rich TiNi shape memory alloy

Abstract

The influence of electropulsing treatment on thermomechanical behaviour in terms of transformation temperatures and mechanical properties of a cold worked Ti rich TiNi shape memory alloy was studied. The results showed that the transformation temperatures increase with increasing current intensity. The superelasticity of the alloy is improved after the electropulsing treatment, and the hardness of the alloy decreased with increasing current intensity. The microstructure of the alloy showed that the above changes can be attributed to the decreasing dislocation density due to the current pulses.     

Effect of cooling aging on microstructure and mechanical properties of an Al–Zn–Mg–Cu alloy

In the present work, Al–Zn–Mg–Cu alloy was aged by non-isothermal cooling aging treatment (CAT). At high initial aging temperature (IAT), the hardness was decreased with the decreased cooling rate. However, when IAT was lower than 180 °C, the hardness was increased with the decreased cooling rate. Conductivity was increased with the decreased cooling rate regardless of IAT. The tensile strength, yield strength and conductivity of Al alloy after (200–100 °C, 80 °C/h) CAT were increased 2.9%, 8.1% and 8.3% than that after T6 treatment, respectively. With an increase of IAT and decrease of cooling rate, the fine GP zone and η′ phase were transformed to be larger η′ and η precipitates. Moreover, continuous η phase at grain boundary was also grown to be individual large precipitates. Cooling aging time was decreased about 90% than that for T6 treatment, indicating cooling aging could improve the mechanical properties, corrosion resistance and production efficiency with less energy consumption.     

外磁场对Ni-Mn-Ga磁性形状记忆合金相变应变及显微组织的影响

研究了外磁场对Ni52Mn24.6Ga23.4(%,原子分数)单晶马氏体相变及其相变应变的影响,并对磁场增强相变应变的微观机制进行了探讨。研究结果表明无外加磁场时,NiMnGa合金发生马氏体相变时可产生约0.3%的收缩形变,沿单晶[100]方向施加外磁场,其相变应变随磁场的增加而呈近线性增加。当外磁场强度为6.37×105A/m时,应变量达到最大值(3.5%)。磁场作用下冷却形成的马氏体虽然孪晶亚结构不变,但自协作组态消失,并伴随有孪晶板条的增厚。磁场对马氏体相变应变的增强效应来自于磁场作用下的马氏体变体的择优取向。     

电子辐照影响TiNi形状记忆合金R相变的研究

用能量为1.7MeV不同注量的电子辐射了TiNi形状记忆合金,通过温度控制使辐照在合金的R相状态进行,发现辐照使合金和奥氏体逆转变开始温度As和结束温度Af升高,随着辐量的增加有增大的趋势,且奥氏体转变滞后也有所增大,R相转变开始点Rs和转变结束点Rt略有增加。XRD结果表明电子辐射成了R相点阵畸变,随辐照注量的增加有增大的趋势。这一变化被认为是辐照引入的点缺陷导致了R相稳定化,并且部分缺陷打打扎了R相界面造成的。这一结果为记忆合金相变点的调节提供了新方法。     

高能球磨时间和退火温度对制备TiNi合金粉的影响

为获得高能球磨时间和退火温度对TiNi机械合金粉特性的影响机制,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、差示扫描量热法(DSC)等分析方法对TiNi合金粉进行了研究。结果表明,机械合金的相成分随着在氩气保护气氛中的球磨时间和退火温度的不同而发生变化。球磨22h的产物是非晶态TiNi合金、Ti的固溶体、Ni的固溶体,球磨27h的产物是非晶态TiNi合金粉和Ni固溶体相,球磨30h发生了明显的固相反应,生成了TiNi、Ni3Ti、Ti3Ni4等物相;在650℃/5h和1000℃/5h下的退火产物都是Ni3Ti、Ti2Ni、TiNi2、TiNi和TiC,但在上述2个退火温度下TiNi并不是主要物相,其中在650℃退火时TiNi的含量明显更低。     

Cu-Cr-Zr-Mg合金时效组织与性能

为了研究时效工艺对Cu-0.3Cr-0.15Zr-0.05Mg合金显微组织及性能的影响,在时效温度400～650℃和时效时间1～11h条件下,得到时效工艺参数与硬度和电导率的曲面关系,并利用透射电镜分析合金时效后的微观形态和析出相.研究结果表明:合金固溶后470℃时效4 h,硬度和电导率可达HV108和45 S·m-1,析出相为Cr、Cu4Zr和有序的CrCu2(Zr,Mg)相;550℃时效1 h后硬度和电导率仍具有HV106和46.8 S·m-1,析出相完全转变为Cr和Cu4Zr.     

PLGA携载紫杉醇涂层包被TiNi合金的表面特性与生物性能

系统研究了PLGA携载紫杉醇包被TiNi合金的表面特性与生物性能。采用原子力显微镜(AFM)和X射线光电子能谱(XPS)研究了药物涂层的表面形貌及化学成分;采用高效液相色谱(HPLC)研究了在pH为7.4的PBS溶液中紫杉醇从TiNi合金表面涂层中释放特性,并通过血小板粘附试验研究了药物涂层的血液相容性。试验结果表明经涂覆后TiNi合金表面化学组成及结构随着载药量的增加而改变。紫杉醇在涂层降解初期释放较快,随着时间的延长,累积释放量增加缓慢。血小板粘附试验表明载药量为0%、10%、20%和30%时涂膜样品表面血小板粘附数量均小于未涂膜样品表面。而随着载药量的增加,涂膜样品表面粘附的血小板数量增加,血小板变形严重,当载药量为30%时,血小板出现明显的聚集现象。     

Two-stage superelasticity of a Ce-added laser-welded TiNi alloy

Microstructure, phase transformation and stress-strain behaviors of a Ce-added laser welded TiNi alloy have been studied. An Nd:YAG laser was used for butt fusion of two Ti-50.9Ni alloy plates with a (Ti-50.9Ni)-5Ce stripe pre-assembled between their joint. Microstructure, phase constitution, phase transformation and stress-strain behavior of several TiNi alloy specimens were researched with SEM, XRD, DSC and tensile test, respectively. Unlike the typical monotonous superelasticity of base metal and Ce-free welded TiNi, the Ce-added welded TiNi specimen shows a peculiar two-stage superelasticity. Based on results of SEM, XRD and DSC tests, a mechanism for the two-stage superelasticity has been discussed.     

Study on effect of residual stress distributions on kinetics of static strain aging after cold rolling

Abstract

In the present research, the effect of residual stress distribution on the static strain aging (SSA) phenomenon in cold rolled steel was investigated. A three-dimensional model was employed to evaluate the residual stress distributions within the rolled strips, and hole drilling experiments were also performed to verify the data obtained from the mathematical model. Hardness and tensile tests were then performed on the cold rolled samples at different temperatures and aging periods, and the results of these tests were utilised to assess SSA behaviour after different rolling programs. The results show that SSA occurs within the cold rolled steel in the employed aging period, and its kinetics is affected by residual hydrostatic stresses. Additionally, the variation in residual hydrostatic stress distribution due to deformation path, e.g. single- and two-pass rolling layouts, slightly affects the activation energy of SSA and changes the kinetics of SSA after cold rolling.     

Effect of further water curing on compressive strength and microstructure of CO2-cured concrete

This study aims to investigate the effects of further water curing on the compressive strength and microstructure of CO₂-cured concrete. The results showed that concrete with a residual w/c ratio of 0.25 showed the most rapid strength development rate upon further water curing due to hydration of uncarbonated cement particles. Thermogravimetric, IR-spectrophotometric and scanning electron microscope examinations indicated that further hydration of the cement particles could form C-S-H gel and ettringite crystals. The results showed that the calcite formed during the initial CO₂ curing was consumed during the further hydration of C₃A, and produced calcium monocarbonaluminate hydrate. Also, Ca(OH)₂ was not detected due to its reaction with the formed silica gel. Mercury intrusion porosimetry test results indicated that the porosity and pore size of the CO₂ cured mortar decreased further after water curing.     

Effect of Incomplete Thermal Cycle on Transformation Behavior of Deformed TiNi Thin Film

Compared with the undeformed TiNi film,the martensite-austenite transformation(M-A) of the deformed one is elevated to a higher temperature on the first heating,but it nearly returns back to the original temperature on the second heating.An incomplete M-A transformation of the deformed TiNi film on the first heating divides the total martensite population into the self-accommodating martensite M2 and the oriented martensite M1.Thus,two transformations corresponding to M1-A and M2-A transition occur on the second heating.However,the forward transformation is not affected by the incomplete thermal cycle.     

电化学抛光时间对常规和超细晶TiNi合金生物活性的影响

研究了电化学抛光时间(60、180s)对常规和超细晶TiNi合金表面形貌与生物活性的影响。结果表明,电化学抛光时间从60s增加到180s时,常规Ti-Ni合金表面纳米尺度蚀坑数量增多,但仅轻微提高了其生物活性(模拟体液中Ca-P层的生长速率),而超细晶TiNi合金表面纳米蚀坑数量大幅减少,生物活性虽大幅降低,但仍显著高于常规TiNi合金。结果表明,除了增加纳米尺度蚀坑形貌外,组织超细化也是提高生物活性的一个有效方法。     

Effect of overheating treatment on the microstructure of NiAl-based alloy

The effect of melt overheating treatment on the microstructure of the alloy NiAl-28Cr-5.9Mo-0.1Hf(at.%)-0.05Ho(wt.%) has been investigated. Overheating treatment resulted in the decrease of the amount of primary NiAl from 12% in the normal sample to 8% in the overheated sample and in the refinement of NiAl/Cr(Mo) lamellar. The size of eutectic cell was increased from 37 μm to 63 μm after the treatment. Another significant change of the microstructure was the morphological instability of precipitates: the morphology of Cr(Mo) precipitates in primary NiAl was dendritic in the normal alloy but was cubic/spherical in the overheated alloy. The mechanisms responsible for these changes were discussed.     

时效对Cu-3.2Ni-0.75Si-0.30Zn合金组织和性能的影响

研究了时效温度和时效时间对Cu-3.2Ni-0.75Si-0.30Zn合金组织和性能的影响.结果表明,合金经900℃固溶,不同时间时效处理后,第二相呈弥散分布.合金经不同冷变形后时效,能获得较高的显微硬度与导电率,当时效温度达到500℃时,其显微硬度达到253.7Hv,导电率达到40%IACS.同时建立了该合金在500℃下,关于时效时间的一元导电率方程.时效前的预冷变形能够有力的促进合金在时效过程中第二相的析出,从而提高合金的显微硬度和导电率.