恒载荷下TiNi和TiNiCu形状记忆合金弹簧的热稳定性

TiNi基形状记忆合金弹簧是一种有广阔应用前景的形状记忆合金驱动元件.研究了在电流加热方式下,不同加热温度,不同恒载荷作用下TiNi和TiNiCu记忆合金弹簧的热稳定性.研究表明,恒定载荷下,最初的几次循环后,弹簧的行程变小,而在循环次数超过一定次数后,弹簧的行程不随着循环次数的增加而发生明显变化.对于TiNi和TiNiCu记忆合金弹簧,过热和过载均会向弹簧中引入不可逆的塑性变形,导致其热稳定性的下降.由于Ti3Ni4相粒子的析出强化了基体,在恒载荷下,TiNi合金弹簧较TiNiCu合金弹簧显示出更加良好的热稳定性.     

Plastic deformation behavior of ZK60 magnesium alloy with addition of neodymium

The hot deformation simulation of a ZK60 magnesiuln alloy at different temperatures from 373 to 673 K and different strain rates of 0.1, 0.01 and 0.002 s^-1 was studied by using the Gleebe-1500 simulator. The plastic deformation behavior was measured and the deformation activation energy was calculated. The microstructures of ZK60 magnesium alloy with an addition of neodymium during the deformation process were observed by using Polyvar-MET optical microscope and Tecnai G^2 20 TEM. The results show that the working hardening, the dynamic recovery and the dynamic recrystallization occur during the plastic deformation process at different temperatures and strain rates. The dynamic recrystallization starts when the temperature is over 473 K and the DRX grain size after hot deformation is only 5-10 μm. So the refined grains improve both the tensile strength and the elongation of alloys at room temperature. Neodymium is added into the alloy and a precipitate phase Mg12Nd that impedes the movement of dislocations is formed, which benefits to increasing mechanical properties of ZK60 magnesium alloy.     

Martensitic stabilization and defects induced by deformation in TiNi shape memory alloys

Martensitic stabilization caused by deformation in a TiNi shape memory alloy was studied.Special attention was paid to the deformed microstructures to identify the cause of martensitic stabilization.Martensitic stabilization was demonstrated by differential scanning calorimetry for the tensioned TiNi shape memory alloy.Transmission electron microscopy revealed that antiphase boundaries were formed because of the fourfold dissociation of [110]B19' super lattice dislocations and were preserved after reverse t...     

Al-5Fe-1.2Si-1Mg-0.6Cu-0.5Mn合金轧制变形行为及组织性能

为了细化Al-5%Fe基合金中粗大的脆性针状或针片状富铁相,采用电磁搅拌及固态挤压技术制备Al-5%Fe-1.2%Si-1%Mg-0.6%Cu-0.5%Mn合金轧制坯锭,研究Al-5%Fe基合金的轧制变形能力及合金的组织性能,并用热压缩实验模拟了铝铁合金在783~693K、变形速率为0.01~10s^-1条件下的热变形行为.结果表明：该合金高温变形时存在明显的稳态流变特征,流动应力对应变速率和温度敏感.板材力学性能较挤压态有大幅度提升,其室温下的抗拉强度和伸长率最高达到354.5MPa和7.6%,比挤压态分别提高了105.6%和184.6%.轧制对铝铁合金中富铁相的破碎作用十分明显.     

M5锆合金塑性变形行为

了解锆合金塑性变形行为,为M5合金的工程应用提供数据.试验采用静态拉伸试验方法对国产及法国产M5锆合金核燃料包壳管在室温和400℃下的拉伸性能进行了研究.结果表明,国产及法国产M5合金的拉伸性能无显著差异.在均匀塑性变形阶段,室温拉伸时法国产M5的形变硬化指数稍高于国产M5,400℃拉伸时两种材料的均匀塑性变形阶段均分为两个阶段,前均匀塑性变形阶段(n1)和后均匀塑性变形阶段(n2),法国产M5的n1明显高于国产M5的n1,法国产M5的n2稍高于国产M5的n2.     

Reverse Transformation Behavior of TiNi Shape Memory Alloys Prestrained in the Parent Phase

1 IntroductionShape memory alloys (SMAs) prestrained at a tem-perature belowAs(the reverse martensitic transformationstartingtemperature) can generate a large stress or me-chanical energy when constrainedly heated at aboveAf(the reverse martensitic transformation finishing tempera-ture) ,therefore they are regarded as one of the most im-portant actuatorsinsmart composites[1-4].The relationshipbetweenthe prestrain level and the reversible martensitictransformationof TiNi SMAs has beenstudie…     

Flow stress behavior of Al-Cu-Li-Zr alloy containing Sc during hot compression deformation

The flow stress behavior of Al-3.5Cu-1.5Li-0.25（Sc＋Zr） alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s^-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa^-1 and 1.51×10^16 s^-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.     

Surface properties of nitrogen-ion-implanted TiNi shape memory alloy

X-ray diffraction （XRD）, auger electron spectroscopy （AES）, and X-ray photoelectron spectroscopy （XPS） were used to characterize the surface properties of the N^ ＋-ion-implanted TiNi alloy. There is a high nitrogen content region at the outermost surface of the N^＋-ion-implanted TiNi alloy. The detected nitrogen exists mainly in the form of TiN. Small amounts of Ti305 and TiO2 also exist on the surface of the N^＋-ion-implanted TiNi sample. The modified layer of the N^＋-ion-implanted sample can work as an obstacle layer of the nickel＇s dissolution, which obstructs Ni dissolving from the TiNi surface effectively.     

Actuation Mechanism of Two-step Reverse Transformation Behavior in TiNi Alloys Deformed at Parent Phase

1　IntroductionTiNishapememoryalloys (SMAs)arethepromisingfunctionalmaterialstobeusedasimportantactuatorsinmicromachinesandintelligentmachinesduetotheirlargeoutputstrainorstress[1,2 ] .ItiswellknownthattheSMAsdeformedatmartensiticphasehaveacapableofgeneratingforceormotionwithanenergyinputbyheating .Theac tuationcharacteristicoftheSMAsiscloselyrelatedtotheirdeformationformationandtemperature (thestateoftheSMAs) .Inotherwords ,theactuationcharacteristicoftheSMAsisdependentontheirreversema…     

Deposition of DLC Coating on Biomedical TiNi Alloys by Plasma Based Ion Implantation to Improve Surface Properties

1Introduction Diamond likecarbon(DLC)isbeingconsideredfor widespreadclinicaluseasasurfacecoatingforcoronary stents,heartvalvesandorthopaedicimplants.Sucha coatingofmedicalimplantshashighpotentialbenefits suchasreductionofmetalionreleasewhichleadstoare ductionofcoronarystent associatedthrombosis;lowfric tioncoefficientwhichensureslesswearparticlesreleaseof orthopaedicimplants;goodbiocompatibilitywhichlowers theriskofimplantfailure.Uptodate,DLChavebeen successfullycoatedon316Lstainlesssteel[1…     

温度和应变速率对ZK60镁合金压缩变形行为的影响

在应变量为0.6（ε=0.6）、不同温度（523~723 K）和应变速率（0.001~10 s-1）条件下,利用Gleeble-1500D热模拟试验机,对铸态ZK60镁合金进行热压缩变形行为的研究,分析变形温度和应变速率对ZK60镁合金压缩变形行为的影响规律,即在相同应变速率条件下,随着变形温度的升高,合金的峰值应力降低。在相同温度条件下,随着应变速率的增大,合金的流变应力增大。计算其应变速率敏感指数m值为0.14和表观激活能Q值为226~254 kJ/mol。研究表明,在温度为573~673 K、应变速率为0.001~0.1 s-1时,合金发生动态再结晶。     

TiNi和TiNiCu记忆合金薄膜的温度记忆效应研究

在形状记忆合金的相变过程中,如果温度升至TS后停止升温,并降温至马氏体相变结束温度Mf以下,则在下一次完全相变循环中出现动力学停顿,而这一动力学停止温度点与上次的停止温度密切相关,这一现象被称为温度记忆效应。该文通过示差扫描量热法对TiNi和TiNiCu合金薄膜进行一次或连续几次不完全相变,系统地研究了温度记忆效应。结果表明,不仅温度记忆效应是形状记忆合金固有现象,而且温度记忆效应与马氏体变体间的弹性能及母相和马氏体相之间的共格应变密切相关。     

TC4钛合金在不同温度下的剪压缩失效

利用Fallwerk试验装置,在高应变率(102s-1)下,采用动态剪压缩试验研究TC4钛合金不同温度下的剪压缩失效现象。通过试验发现:相同温度下,流变应力随应变的增大不断增加,到达峰值后发生应力塌陷,即剪切失效;相同应变下,温度越高,材料的屈服强度和流变应力均明显下降,且峰值应力向应变增大的方向移动,即塑性变形能力逐渐加强;温度升高,材料的剪切失效能力减弱,在673 K至873 K温度区间内存在一个温度极限值。在该极限值以下,材料易发生剪切失效。同时,根据试验数据拟合了峰值应力和最大塑性应变与温度的曲线方程,为钛合金的研究提供了理论依据。     

出口通道背部摩擦力对工业纯钛室温ECAP变形影响的有限元分析

工业纯钛的等径弯曲通道变形(Equal Channel Angular Pressing,简称ECAP)通常在350~450℃实现,为研究工业纯钛室温ECAP变形的可行性,提高其细化效率,本文利用三维有限元商品软件Marc.Super-form对工业纯钛方形试样的一道次室温ECAP变形过程进行模拟.研究并分析了模具出口通道背面摩擦对工业纯钛(Commercial Pure Titanium,CP-Ti)试样变形、应变速率及挤压载荷分布的影响规律.研究表明,增大模具出口通道背部摩擦可使工业纯钛ECAP变形区的应变速率分布更均匀,使试样内应变分布均匀性提高.在此基础上通过改善外部摩察工艺条件成功地实现工业纯钛室温ECAP变形,获得变形均匀的ECAP试样.     

Flow stress behavior and processing map of Al-Cu-Mg-Ag alloy during hot compression

The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate and temperature, the flow stress equation is estimated to illustrate the relation of strain rate and stress and temperature during high temperature deformation process. The processing maps exhibit two domains as optimum fields for hot deformation at different strains, including the high strain rate domain in 623-773 K and the low strain rate domain in 573-673 K.     

Flow stress equation for multipass hot-rolling of aluminum alloys

Ｔｈｅｆｌｏｗｓｔｒｅｓｓｏｆａｍａｔｅｒｉａｌｒｅｌａｔｅｓｎｏｔｏｎｌｙｔｏｔｈｅｓｔｒａｉｎ ,ｓｔｒａｉｎｒａｔｅ ,ａｎｄｔｅｍｐｅｒａｔｕｒｅｏｆｄｅ ｆｏｒｍａｔｉｏｎ,ｂｕｔａｌｓｏｔｏｔｈｅｍｉｃｒｏｓｔｒｕｃｔｕｒｅ .Ａｓａｎｅｓｓｅｎｔｉａｌｉｎｐｕｔｆｏｒｃｏｍｐｕｔｅｒｍｏｄｅｌｉｎｇｔｈｅｒｍｏｍｅ ｃｈａｎｉｃａｌｐｒｏｃｅｓｓｉｎｇｏｐｅｒａｔｉｏｎｓｕｓｉｎｇｆｉｎｉｔｅｅｌｅｍｅｎｔｍｅｔｈｏｄｓ,ａｎａｃｃｕｒａｔｅｆｌｏｗｓｔｒｅｓｓｖａｌｕｅｏｒｆｌｏｗｓｔｒｅ…     

Al-Mg-Si合金热压缩变形的流变应力方程

为了给制定和优化热加工工艺参数提供理论依据,采用Gleeble-1500热模拟机研究了含锆Al-Mg-Si合金在变形温度为653~803 K、变形速率为0.01~10s^-1条件下的热压缩变形的流变应力行为,并通过回归法建立材料变形的流变应力数学模型.结果表明：该合金为正应变速率敏感材料,真应力-真应变曲线存在明显的稳态流变特征;流变应力随着变形速率的增加以及变形温度的降低而增加;在较低变形温度条件下,真应力〖CDF*3〗真应变曲线为动态回复曲线;在较高变形温度条件下真应力-真应变曲线为动态再结晶曲线.该合金流变应力σ可用包含Arrhenius项的Zener Hollomon参数的函数来描述,式中A、α和n的值分别为1.89×10¹⁰s^-1、0.024MPa^-1和7.46,热变形激活能Q为166.85kJ/mol.     

Deformation Behavior of 6063 Aluminum Alloy During High-Speed Compression

The deformation behavior characteristics of 6063 aluminum alloy were studied experimentally by isothermal compression tests on a Gleeble- 1500 thermal-mechanical simulator. Cylindrical specimens of 14mm in height and 10mm in diameter were compressed dynamically at temperatures ranging from 473 to 723K and at higher strain rntes from 5 to 30s^-1. It is fouud that the flow curves not only depend on the strain rate and temperature but nlso on the dynamic recovery aud recrystallization behavior. The results show that the flow stress decreased with the increase of temperature, while increased with the increase of strain rate. The discontinuous dynamic recrystallization （DDRX） may take place at a high strain rate of 20s^-1 under the tested conditions. At 30s^-1 , the flow curve can exhibit,flow softening due to the effect of temperature rise that raised the temperature by aboat 32K in less than 0.05s.     

Flow stress behavior and constitutive modeling of 20MnNiMo low carbon alloy

The hot deformation behavior of 20 Mn Ni Mo low carbon alloy was investigated by isothermal compression tests over wide ranges of temperature(1223-1523 K) and strain rate(0.01-10 s~(-1)). According to the experimental true stress-true strain data, the constitutive relationships were comparatively studied based on the Arrhenius-type model, Johnson-Cook(JC) model and artificial neural network(ANN), respectively. Furthermore, the predictability of the developed models was evaluated by calculating the correlation coefficient(R) and mean absolute relative error(AARE). The results indicate that the flow stress behavior of 20 Mn NiM o low carbon alloy is significantly influenced by the strain rate and deformation temperature. Compared with the Arrhenius-type model and Johnson-Cook(JC) model, the ANN model is more efficient and has much higher accuracy in describing the flow stress behavior during hot compressing deformation for 20 Mn Ni Mo low carbon alloy.     

Property and microstructure analysis of ZK60 alloy superplastic sheet

It was investigated that the superplastic mechanical properties of fine-grained ZK60 magnesium alloy sheets at the temperature range of 200-420 ℃ and strain rate range of 5.56 × 10-4 -5.56 ×10-2 s-1 by tensile tests.And the microstructure evolution during the superplastic deformation of ZK60 magnesium alloy was examined by metallurgical microscope and transmission electronic microscope (TEM).The results showed that fine-grained ZK60 magnesium alloy starts to exhibit superplasticity from 250 ℃ and the maximum elongation is about 1106% at 400 ℃ and 5.56 × 10-4 s-1.The strain rate sensitivity is significantly enhanced with the increase of temperature and with the decrease of strain rate.The predominate superplastic mechanism of ZK60 magnesium alloy is grain boundary slide (GBS) at the temperature range of 300-400 ℃.The grains of ZK60 alloy remain equaxial after superplastic deformation,and dynamic continuous recrystallization (DCRX) is an important softening mechanism and grain stability mechanism during the superplastic deformation of the alloy.The curved grain boundaries and crumpled bands at grain boundaries after deformation prove GBS generates during superplastic deformation of ZK60 magnesium alloy.