Influences of 2.5wt% Mn addition on the microstructure and mechanical properties of Cu-Al-Ni shape memory alloys

The influences of 2.5wt% Mn addition on the microstructure and mechanical properties of the Cu-11.9wt%Al-3.8wt%Ni shape memory alloy (SMA) were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimeter (DSC). The experimental results show that Mn addition influences considerably the austenite-martensite transformation temperatures and the kind of martensite in the Cu-Al-Ni alloy. The martensitic transformation changes from a mixed xed β₁→β'₁+γ'₁ transformation to a single β₁→β'₁ martensite transformation together with a decrease in transformation temperatures. In addition, the observations reveal that the grain size of the Cu-Al-Ni alloy can be controlled with the addition of 2.5wt% Mn and thus its mechanical properties can be enhanced. The Cu-Al-Ni-Mn alloy exhibits better mechanical properties with the high ultimate compression strength and ductility of 952 MPa and 15%, respectively. These improvements are attributed to a decrease in grain size. However, the hardness decreases from Hv 230 to Hv 140 with the Mn addition.     

Martensite transformation, mechanical properties and shape memory effects of Ni-Mn-In-Mg shape memory alloys

The martensite transformation(MT), mechanical properties and shape memory effect(SME) of(Ni_(50)Mn_(35)In_(15))_((1-x))Mg_x(x = 0%, 0.08%, 0.3%, 0.6% at%) alloys were comprehensively investigated. The results showed that due to Mg doping the MT temperature shifted to higher temperatures and a worm-like secondphase precipitated at grain boundaries and inside the grains. With increasing Mg content, the amount of precipitates gradually increased, the thermal hysteresis was almost invariant, and the SME was not obviously affected at 3% pre-strain, even when the volume of the second phase reached up to 28.75%. Compressive stress and strain experiments showed that both the strain and strength of the Ni-Mn-In-Mg alloys were improved substantially(by 46.9% and 53.4%, respectively, at x = 0.6%) compared with those of the pure Ni_(50)Mn_(35)In_(15) alloy; this effect is nearly the same as that achieved by the directional solidification method. Because Mg is nonmagnetic, the magnetization difference of the alloy with Mg doping is much lower than that of the alloy without Mg doping. Overall, the results confirm that adding a small amount of Mg is a potentially viable method for improving the mechanical properties of Ni-Mn-In alloys without adversely damaging their functional properties.     

稀土元素Ce对Ti-Ni形状记忆合金力学性能的影响

采用拉伸试验研究了稀土元素Ce对Ti—Ni合金力学性能的影响,通过扫描电镜对Ti—Ni—Ce合金的断口形貌进行观察。实验结果表明,添加稀土元素Ce使Ti—Ni合金的应力-应变行为有显著影响。在马氏体状态拉伸时,当x（Ce）低于0．5％时,合金的应力-应变曲线出现明显的屈服平台;而当％（Ce）超过1％时,合金的应力-应变曲线上无明显的屈服平台,以连续屈服和强烈的加工硬化为特征。随Ce加入量增加,合金的延伸率降低、脆性增大,断裂类型由微孔聚集型的韧性断裂逐渐转变为沿晶脆性断裂。因此,Ce的加入量不能超过1％,否则将损害Ti—Ni合金的使用性能。     

中温处理对CuAlNiMnTi记忆合金热循环及力学行为的影响

用阻法、金相分析、电镜分析、Ｘ射线衍射及拉伸试验等研究了淬火后中温处理对ＣｕＡｌＮｉＭｎＴｉ形状记忆合金热循环特性及力学行为的影响。研究结果表明：合金淬火后经６００℃中温处理可产生适量α相，α相优先在晶界析出，保温时间延长，则晶内也析出α相，控制中温处理时间可以调整α相含量，从而调整相变点；经中温短时处理后，在随后的热循环过程中不再有ＮｉＡｌ基析出相，从而实现热循环过程中相变点基本稳定；中温处理时     

Microwave sintering effects on the microstructure and mechanical properties of Ti-51at%Ni shape memory alloys

Ti-51at%Ni shape memory alloys (SMAs) were successfully produced via a powder metallurgy and microwave sintering technique. The influence of sintering parameters on porosity reduction, microstructure, phase transformation temperatures, and mechanical properties were investigated by optical microscopy, field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), compression tests, and microhardness tests. Varying the microwave temperature and holding time was found to strongly affect the density of porosity, presence of precipitates, transformation temperatures, and mechanical properties. The lowest density and smallest pore size were observed in the Ti-51at%Ni samples sintered at 900℃ for 5 min or at 900℃ for 30 min. The predominant martensite phases of β2 and β19' were observed in the microstructure of Ti-51at%Ni, and their existence varied in accordance with the sintering temperature and the holding time. In the DSC thermograms, multi-transformation peaks were observed during heating, whereas a single peak was observed during cooling; these peaks correspond to the presence of the β2, R, and β19' phases. The maximum strength and strain among the Ti-51at%Ni SMAs were 1376 MPa and 29%, respectively, for the sample sintered at 900℃ for 30 min because of this sample's minimal porosity.     

Phase transformation behaviors and shape memory effects of TiNiFeAl shape memory alloys

Measurements of electrical resistivity, X-ray diffraction, and tensile test at room temperature and -196℃ were performed to investigate the effects of Al addition substituting Ni on the phase transformation behaviors, the mechanical properties, and the shape memory effects of Ti₅₀Ni₄₇Fe₂Al₁ and Ti₅₀Ni_46.5Fe_2.5Al₁ alloys. It is found that 1at% Al addition dramatically decreases the martensitic start transformation temperature and expands the transformation temperature range of R-phase for TiNiFeAl alloys. The results of tensile test indicate that 1at% Al improves the yield strength of Ti₅₀Ni₄₇Fe₂Al₁ and Ti₅₀Ni_46.5Fe_2.5Al₁ alloys by 40% and 64%, but decreases the plasticity to 11% and 12% from 26% and 27% respectively. Moreover, excellent shape memory effect of 6.6% and 7.5% were found in Ti₅₀Ni₄₇Fe₂Al₁ and Ti₅₀Ni_46.5Fe_2.5Al₁ alloys, which results from the stress-induced martensite transformation from the R-phase.     

Microstructural evolution and mechanical properties of aging high nitrogen austenitic stainless steels

The microstructural evolution of 18Cr18Mn2Mo0.77N high nitrogen austenitic stainless steel in aging treatment was investigated by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that hexagonal intergranular and cellular Cr₂N with a=0.478 nm and c=0.444 nm and body-centered cubic intermetallic χ phase with a=0.892 nm precipitate gradually in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular Cr₂N precipitation induces the decay of Vickers hardness, and the formation of cellular Cr₂N and χ phase causes the increase in the values. The impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. The tensile strength and elongation deteriorate obviously except for the sample aged for 1 h in yield strength. Stress concentration occurs when the matrix dislocations pile up at the precipitation and matrix interfaces, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage steps and accelerate the formation of cracks.     

Martensitic transfor mation involved mechanical behaviors and wide hysteresis of NiTiNb shape memory alloys

On the basis of thermoelastic martensitic transformation involved,the mechanical behaviors of NiTiNb shape memory alloys were experimentally studied and their wide hysteresis effect was theoretically d...     

铁磁形状记忆合金复合材料力学性能试验研究

通过机械研磨的方法,获得不同尺寸的NiMnGa合金颗粒,在常温条件下,将NiMnGa合金颗粒与E51环氧树脂混合均匀,静置固化得到复合材料试件。对不同的复合材料试件进行压缩-卸载试验,从细观力学的角度分析不同体积分数和不同尺寸各向同性的NiMnGa合金复合材料试件的应力-应变曲线,研究了NiMnGa合金颗粒对树脂基的增强效果。分析实验结果表明：在温度不变,外力相同条件下,复合材料相比NiMnGa合金而言,应变相同时需要的应力值更大,并且在压应力卸载为0 MPa后,复合材料会有较小的残余应变。因为环氧树脂基体包裹合金颗粒,所以NiMnGa合金颗粒在产生应变时会受到阻碍,由于基体的存在,传递到NiMnGa合金颗粒的外载荷较小,大部分载荷由环氧树脂基体承担,这样可以改善合金颗粒易碎的缺点。不同尺寸的NiMnGa合金颗粒影响复合材料的应力应变,但复合材料发生马氏体变体重取向的临界应力为40 MPa左右。随着合金颗粒含量的增加,压缩应力卸载后,复合材料产生的残余应变会更大。这样复合材料缓冲的效果更好。     

Microstructural evolution in Al-Zn-Mg-Cu-Sc-Zr alloys during short-time homogenization

Microstructural evolution in a new kind of aluminum (Al) alloy with the chemical composition of Al-8.82Zn-2.08Mg-0.80Cu-0.31Sc-0.3Zr was investigated. It is found that the secondary phase MgZn₂ is completely dissolved into the matrix during a short homogenization treatment (470℃, 1 h), while the primary phase Al₃(Sc,Zr) remains stable. This is due to Sc and Zr additions into the Al alloy, high Zn/Mg mass ratio, and low Cu content. The experimental findings fit well with the results calculated by the homogenization diffusion kinetics equation. The alloy shows an excellent mechanical performance after the short homogenization process followed by hot-extrusion and T6 treatment. Consequently, a good combination of low energy consumption and favorable mechanical properties is obtained.     

CuZnAl形状记忆合金超弹性的研究

研究了不同热处理工艺、晶粒束缚以及工作温度、应力循环、热循环和应力热循 环对 ＣｕＺｎＡｌ合金超弹性的影响。试验结果表明：合金常规淬火获得最佳超弹性的 淬火加热温度为８９０℃，对于所研究的线材试样而言，保温时间与线材直径有关；合 金采用双相区淬火，可获得较好的超弹性，其最佳淬火加热温度为７００℃，保温时间 为１０ｍｉｎ；晶粒束缚影响合金的超弹性，ｇｓ／Ｄ越大，晶粒束缚越小，超弹性越好； 合金的超弹性与工作温度有关，超弹性最佳值是在Ａｆ点以上一段温度范围内．其下限 温度为Ａｆ点以上１７～２２℃。合金在应力循环后出现了循环软化现象而不是循环硬 化现象，应力循环后，相变的熵及焓变降低；热循环和应力热循环均使合金的相变点 提高。     

形状记忆合金的宏观力学本构模型

结合作者提出的形状记忆因子的概念,阐述了形状记忆合金（SMA）超弹性和形状记忆效应的微观机理,将SMA的超弹性和形状记忆效应统一归结为形状记忆效应.重新定义了形状记忆因子,并明确了其物理意义.利用SMA在相变过程中马氏体体积分数和相变自由能间的微分关系,建立了描述SMA相变行为的形状记忆演化方程.该形状记忆演化方程能同时考虑相变峰值温度、相变开始和结束温度对SMA相变行为的影响,并能描述SMA从孪晶马氏体向非孪晶马氏体的转变过程,克服了现存SMA相变方程或形状记忆方程的局限性,能更全面准确地描述SMA的相变行为.从宏观力学角度,建立了能全面描述SMA实现形状记忆效应的热力学本构方程,在假设SMA为各向同性材料的基础上,将该本构方程从一维推广到三维.该本构方程中的所有材料参数都可以通过宏观实验测定,比现存三维本构方程更便于工程实际应用.     

CuZnAl形状记忆合金的拉伸曲线模型

采用电子万能拉伸试验机对CuZnAl形状记忆合金进行了拉伸试验．试验结果表明。拉伸曲线的骨架曲线与滞回曲线因为残余马氏体量不同而形状不同．由于马氏体开始转变温度的不同．CuZnAl形状记忆合金的骨架曲线模型与滞回曲线模型的参数稍有区别,因此,不同相变温度的CuZnAl形状记忆合金的模型需要作修正．另外,马氏体状态记忆合金的力学曲线模型为双线性模型．     

新形式超弹性形状记忆合金线材力学性能试验研究

超弹性是形状记忆合金(SMA)的重要特性之一.鉴于钢绞线在力学性能上的优势,提出一种新形式的SMA线材--SMA绞线,其目的在于将其埋设到土木工程领域的混凝土构件中.通过试验,主要研究了应变幅值和加卸载循环次数对普通圆截面SMA丝材和SMA绞线的应力诱发马氏体相变应力、残余应变、最大相变应变和耗能能力的影响.研究结果表明,SMA绞线比SMA丝具有更好的力学性能.建议在工程应用中将SMA的线材形式作为一项影响其超弹性力学性能的因素.     

Microstructural evolution and mechanical properties of a low-carbon quenching and partitioning steel after partial and full austenitization

In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected.     

TiNi形状记忆合金回复力模型

通过修正Clausius Clapeyron方程 ,使之在马氏体分数不断变化的条件下仍然适用 ,并在此基础上建立了TiNi形状记忆合金的回复力模型 ,模型中的参数均可通过实验确定 .利用此模型 ,使用典型的TiNi形状记忆合金性能参数 ,计算得到了TiNi形状记忆合金回复力与温度的关系曲线 ;与实验测试曲线的对比表明 ,本模型在大的预应变条件下与实验结果是吻合的     

形状记忆合金的抗穴蚀能力试验研究

桨叶多发生穴蚀，而有关形状记忆合金抗穴蚀方面的研究较少，为此选用CuZnAl、TiNi涂层、热处理TiNi涂层等几种形状记忆合金材料制作的试件，利用磁致伸缩激振穴蚀装置研究其抗穴蚀性能．试验结果表明TiNi涂层的抗穴蚀能力优于CuZnAl合金，热处理TiNi涂层的抗穴蚀能力优于未经热处理的TiNi涂层．     

NiTi形状记忆合金动力阻尼特性的研究

应用相位法测量阻尼，系统研究了ＮｉＴｉ形状记忆合母相状态下动力阻尼特性，研究结果表明：ＮｉＴｉ形状记忆合金银邓使在母相状态下，其阻尼Ｑ＾－１也可达到１０＾－１量级，阻尼Ｑ＾－１随振动频率的增大而显著减小；当频率高于某一临界值时，其阻尼较小且趋于稳定，在一范围内，阻尼Ｑ＾－１随振幅的增大而增大，随预应力的增大而增大。     

Low-cost (ZrCu)50-xTax high temperature shape memory alloys showing excellent shape memory effect

ZrCu-based alloys, as one of the most potential high-temperature shape memory alloys, show quite high martensitic transformation temperature, relatively low price for the raw materials, and good casting fluidity. In this work, the martensitic transformation (MT) and shape memory effect of (ZrCu)_50-xTa_x high-temperature shape memory alloys were systematically investigated. Both X ray diffraction and SEM backscattered electron image demonstrated the coexistence of the main phase monoclinic martensite phase and the second phase Ta₂Cu. SEM results also revealed that increasing Ta content resulted in a larger volume fraction of Ta₂Cu phase. Differential scanning calorimetry results showed that the MT temperatures remarkably increased with Ta addition. The ductility of the (ZrCu)_50-xTa_x alloys was reduced to some degree with increasing Ta content. The shape memory effect was improved significantly, in which (ZrCu)₉₈Ta₂ alloy showed the 6.19% maximum recovery strain during 8% pre-strain under compression at 25 ?°C.     

Mg-Al-RE系镁合金组织与性能

通过铸造和挤压变形工艺,研究了AE(Mg-Al-RE)系合金的显微组织及稀土和铝含量的变化对AE系合金显微组织和力学性能的影响.实验结果表明:AE系合金的铸态显微组织由α-Mg基体相和沿晶界分布的Al.4RE,Mg17Al12相组成.随着稀土含量的增加,Mg17Al12相逐渐消失,Al4RE相的体积分数增加,并逐渐沿晶界处形成连续网状结构.挤压实验结果显示:AE系合金具有良好的形交加工性能,挤压后合金的强度和塑性均比铸态合金大幅度提高.稀土元素的加入对合金形变过程中的动态再结晶有一定的抑制作用.在AE系稀土镁合金中增加Al含量,可以使合金的综合力学性能上升到一个较高的水平.