Ti-Ni-Gd形状记忆合金的马氏体相变

采用电弧炉制备了添加不同Gd含量的Ti-Ni-Gd三元合金,利用DSC、X射线衍射仪研究了重稀土元素Gd对Ti-50.7Ni合金的马氏体相变的影响.结果表明添加重稀土元素Gd后,Gd含量不超过2%(原子分数)时,淬火态的Ti-Ni-Gd三元合金中分别发生两步马氏体相变,Gd含量为10%(原子分数)时,合金中发生了一步马氏体相变,同时稀土元素Gd的加入能明显提高Ti-Ni合金的相变温度.Ti-Ni-Gd合金中马氏体仍为B19'单斜结构,而且马氏体的点阵参数随Gd的加入发生明显变化,晶胞产生畸变.     

添加Co对Ti-Ni形状记忆合金组织和性能的影响

以400和600℃退火态Ti-49.8Ni和Ti-49.8Ni-1.0Co合金为对象,用示差扫描热分析仪、光学显微术、X射线衍射仪和拉伸试验研究了添加Co对退火态Ti-Ni形状记忆合金相变、组织和形状记忆行为的影响。结果表明,400℃退火态Ti-49.8Ni和Ti-49.8Ni-1.0Co合金冷却时皆发生A→R→M(A-母相,R-R相,M-马氏体)两阶段相变;加热时Ti-49.8Ni合金发生M→A一阶段相变,Ti-49.8Ni-1.0Co合金发生M→R→A两阶段相变;600℃退火态Ti-49.8Ni和Ti-49.8Ni-1.0Co合金冷却加热时皆发生一阶段AM相变。400℃退火态Ti-49.8Ni和Ti-49.8Ni-1.0Co合金的组织呈纤维状,塑性较差;600℃退火态合金的组织呈等轴状,塑性良好。Ti-49.8Ni合金室温组成相为马氏体,呈形状记忆效应;Ti-49.8Ni-1.0Co合金的室温组成相为母相B2,呈超弹性特性。退火时间对Ti-Ni合金的组织和性能影响不大,合金的相变温度随退火时间延长缓慢升高。形变温度显著影响Ti-Ni合金的超弹性特性,随形变温度升高合金的超弹性应力增加,超弹性滞回面积减小。     

窄热滞Ti-Ni-Cu-Cr合金的马氏体相变和形状记忆行为

为了开发性能稳定的窄热滞Ti-Ni基形状记忆合金,设计制作了Ti-45Ni-5Cu-0.3Cr(原子分数)形状记忆合金丝,用示差扫描热分析仪和微机控制电子万能试验机研究了退火态和时效态Ti-45Ni-5Cu-0.3Cr合金的马氏体相变和形状记忆行为,探讨了形变温度对该合金形状记忆行为的影响。结果表明,350～700℃/0.5 h退火态和300～600℃/1～50 h时效态Ti-45Ni-5Cu-0.3Cr合金冷却/加热时皆发生A→M/M→A(A-母相B2,CsCl型结构;M-马氏体B19′,单斜结构)一步马氏体可逆相变,马氏体相变温度比较稳定,在14～21℃之间变化;相变热滞较窄,在17～21℃之间变化。室温下,退火态和时效态Ti-45Ni-5Cu-0.3Cr合金皆呈形状记忆效应,且形状记忆行为稳定。随变形温度升高,Ti-45Ni-5Cu-0.3Cr合金的应力应变平台应力增加,残余应变减少,合金特性由形状记忆效应转变为超弹性,转变温度在50～60℃之间。     

Ti-Ni-Ce合金中稀土相的晶体结构及形成机理

利用高温X射线和透射电镜分析研究了Ti-Ni-Ce合金中富稀土相的形貌及晶体结构,发现稀土Ce在Ti-Ni合金中以正交结构的CeNi金属间化合物的形式存在.应用Miedema生成热模型对CeNi相的形成机理进行分析,结果表明Ce元素与Ni元素的亲和力远大于其与Ti之间的亲和力,因此,Ti-Ni-Ce合金中的富Ce相以CeNi的形式存在是必然的.     

真空电阻炉退火温度对电子设备用Ti-51Ni记忆合金相变和形状行为的影响

选择电子设备用Ti-51Ni形状记忆合金作为测试材料,分析不同退火条件下Ti-51Ni合金形成的显微结构、相变特征及其超弹性变化情况。研究结果表明:在退火态Ti-51Ni合金中包含了r相以及马氏体m相。较低退火温度下合金中形成了具有纤维特征组织,较高退火温度下在合金中存在众多的尺寸较小的等轴晶结构。合金中的马氏体组织发生正、逆相变过程的峰值温度先上升后下降,合金中的r相组织发生正、逆相变过程的峰值温度单调下降。为了提高Ti-51Ni合金的力学强度,应在300～400℃范围内对其进行退火处理;如果需要提高Ti-51Ni合金的塑性,需将退火温度设定在500～600℃之间。随着温度继续上升接近马氏体的相变温度时,MR发生快速减小,从而引起逆马氏体相变的过程。当退火温度上升后,残余应发生了先减小后增大的现象。     

Ni52 Mn23Ga24.5 Sm0.5合金的马氏体相变和磁致伸缩性能

研究了多晶Ni52 Mn23 Ga24．合金添加微量的稀土元素Sm后，对合金的马氏体相变和磁致伸缩性能的影响。结果发现，微量稀土元素Sm的掺入，降低了合金的马氏体相变温度和居里温度，但并未改变合金的晶体结构，同时由于晶粒细化作用，使合金室温时的磁致应变性能下降。     

稀土元素对Cu-Ag原位纤维复合材料的结构与性能影响

研究了稀土添加剂Ce、Y和Gd对Cu-Ag原位纤维复合材料结构和性能的影响,制备了具有高强度和高导电性相结合的Cu-Ag-Ce原位纤维复合材料.结果表明添加少量稀土元素Ce、Y或Gd,使Cu-Ag原位纤维复合材料铸态树枝晶状结构演化为胞状树枝晶、明显的胞状和不规则胞状晶结构,富Ag相有球化倾向.稀土Ce可提高材料的综合性能,Y和Gd对材料的综合性能没有提高作用.     

合金元素对Ni41Ti44Cu7Zr8合金相变及力学性能的影响

合金元素影响Ni41Ti44Cu7Zr8形状记忆合金的相变马氏体屈服应力,分析表明具有合适原子尺寸并且与Ti原子间具有合适的负混合焓的合金元素,能有效提高Ni41Ti44Cu7Zr8合金的马氏体屈服应力。少量的Fe元素添加能够显著降低该合金的相变温度,1%Fe元素的添加能使合金的相变温度降低约48℃,在室温时表现出超弹性行为;3%Fe元素的添加能使该合金的马氏体相变温度降低88℃以上,室温加载时不表现形状记忆特征。     

成分对多晶Ni-Mn-Ga磁性记忆合金相变行为的影响

研究了Ni50Mn25+xGa25-x和Ni50Mn29Ga21-xTbx两种成分系列磁性记忆合金的相变行为.保持Ni含量不变,增加Mn,降低Ga含量会使马氏体相变温度明显提高,同时相变滞后温区减小,居里温度基本不变.如果添加稀土元素铽、相变温度继续升高,居里温度仍然不变,材料继续保持强的铁磁性及热弹性马氏体相变的特征.     

Pd对多晶Ni56.5Fe17Ga26.5合金马氏体相变和力学性能的影响

通过电弧炉冶炼了在Ni56.5Fe17Ga26.5合金中添加Pd的合金试样,利用SEM,XRD,TEM,DSC,TG和万能材料试验机研究了Pd对Ni56.5Fe17Ga26.5合金马氏体相变和力学性能的影响.结果表明,添加Pd促使合金中形成较多的γ相,并且使其球化,提高了合金的塑性.通过DSC和TG测量了马氏体相变温度...     

Effect of Y addition on microstructure and martensitic transformation of a Ni-rich Ti–Ni shape memory alloy

In the present work, 1 at% Y was added to Ti-50.7at%Ni alloy to prepare Ti-50.2Ni-1Y alloy and the effects of rare earth Y addition on the microstructure and martensitic transformation behavior of Ti-50.7at%Ni alloy was investigated by optical microscope, scanning electronic microscope (SEM) X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show the microstructure of Ti-50.2Ni-1Y alloy is different with that of Ti-50.7at.%Ni alloy, and its microstructure consists of B19′martensite and the Y-rich phase, which may be YNi phase. One-step martensitic transformation occurs in Ti-50.2Ni-1Y ternary alloy. The phase transformation temperatures increase rapidly with Y addition, and the increase of Ms is about 85°C.     

Effect of low temperature ageing on the transformation behaviour of near-equiatomic NiTi

A unique three-stage transformation behaviour on cooling has been observed in a Ti-50.2 at% Ni alloy after a low temperature ageing treatment. The cooling transformation in the aged alloy occurred as a three-stage process of austenite-to-R phase transition followed by two separate martensitic transformations. The R phase transition developed during ageing with a clear second order nature initially and gradually evolved into a predominantly first order process. The occurrence of the R transition is not associated with a decrease in the martensitic transformation temperature during ageing. The reverse transformation to austenite occurred in one step, regardless of the nature of the forward transformation on cooling. An all-round shape memory effect was observed in aged samples. These experimental observations suggest that precipitation induced by the ageing treatment is responsible for the unusual transformation behaviour. This revised version was published online in November 2006 with corrections to the Cover Date.     

Explaining texture weakening and improved formability in magnesium rare earth alloys

Wrought magnesium alloys are rarely used due to their poor formability which is caused by strong textures created during processing. Addition of rare earth (RE) elements including Y, Ce, La, Gd and Nd weakens these strong basal textures and significantly improves formability. Developing a mechanistic understanding of this effect is critical in leading alloy design towards a new class of highly formable magnesium alloys. This fall in texture intensity occurs during recrystallisation and only requires very low solute RE additions, 0·01 at.-% in the magnesium–Ce case. These additions retard dynamic recrystallisation and increase non-basal slip; however, a full understanding of the RE effect has yet to be obtained, with a variety of mechanisms proposed. Recent research in these areas is critically reviewed.     

稀土对Al-Zn-M g-Cu/Al2O3陶瓷界面润湿性的影响

采用真空座滴法和熔铸法研究了在Al-Zn-Mg-Cu 合金中加入稀土(Ce、Y) 对Al2Zn2M g2Cu/Al₂O₃陶瓷界面润湿性的影响。结果表明,Al-Zn-Mg-Cu 合金中加入稀土可有效降低铝合金/Al₂O₃界面的接触角, 改善界面结合状态; 稀土改善界面润湿性存在一最佳含量范围, 添加Ce 的最佳含量约为0. 5w t% , Y 约为0. 7w t%。稀土改善润湿性的作用主要是稀土与Al₂O₃膜、Al₂O₃陶瓷发生反应。Mg、Zn、Cu 等合金元素在界面富集并参与界面反应对润湿性有利; 稀土与Mg、Zn、Cu 等合金元素适当组合改善润湿性的效果比单一稀土明显。      

Effects of Composition and Thermal Cycle on Transformation Behaviors, Thermal Stability and Mechanical Properties of CuAlAg Alloy

The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La Ce) was added to improve the mechanical property of the studied alloy. It was found that Ag addition in the CuAl binary alloy can improve the stability of martensitic transformation and high Al content leads to the disappearing of martensitic transformation. The tensile strength and strain of the Cu-10.6Al-5.8Ag (wt pct) alloy were measured to be 383.5 MPa and 0.86%, respectively. With rare earth addition, the tensile strain increased from 0.86% to 1.47%. The CuAlAg alloy did not exhibit martensitic transformation on the second heating process. Its poor thermal stability still needs to be improved.     

The Purity and Thermal Stability in Air of Metal-Encapsulating Carbon Nanocapsules (MECNCs)

Rare earth elements (Y, La, Ce, Nd, Gd and Dy) encapsulated by carbon nanocapsules (CNCs) were synthesized and their purity and air oxidation stability were estimated. The purity was estimated as the rare earth carbide content. Gd- and Dy-encapsulating CNCs had higher than 30 wt% and others 15 to 20 wt%. Encapsulated rare earth carbide was oxidized by heating in air at 400°C or higher. This suggested oxidation damage to the graphene capsules of CNCs.     

The comparison of effects of four rare earth elements additions on structures and grain sizes of Ti-44Al alloy

By vacuum arc melting, four kinds of rare earth (RE) elements, Ce, La, Nd and Gd, were added in the range from 0.05% to 0.5% (mole fraction) to binary Ti-44% Al alloy to refine its grains of structures for high ductility. Effects of RE elements on structures and grain sizes of the alloy were investigated and compared. It was observed that Ce had the strongest effect on promoting growth of columnar colonies and Gd had the weakest one, while the other RE elements obviously promoted this growth in as-cast structures of the ingots. It was seen that the four RE elements initially reacted with oxygen to form oxides in the melt, the RE aluminides occur at boundaries during heat treatment, and sometimes the aluminide co-existed with oxide at boundaries or in grains. Results of measurement of grain sizes showed that the grains in the ingots heat-treated were effectively refined by properly adding the four RE elements, and the average grain size in the ingot with 0.15% Gd is finer and more uniform than that with Ce, La and Nd. The results of comparison verified that the sequence of effects of the four RE elements is Ce, La, Nd and Gd from strong to weak, which means that the alloy is sensitive to a small amount of Ce addition and is comparatively dull to a larger amount of Gd.     

载荷对Ti-Ni形状记忆合金丝振动响应特性的影响

针对形状记忆合金作为阻尼材料在机械、土木等工程领域中广阔的应用前景,选取 Ti 50.2%(原子分数)Ni 形状记忆合金作为研究对象。在弹簧、质量块和形状记忆合金丝组成的振动系统中,测定并分析了不同温度和弹簧刚度下,载荷对系统振动响应特性的影响规律。研究结果表明超弹性Ti 50.2%(原子分数)Ni合金具有优良的减振性能,且其减振性能的优劣与系统加载有着密切联系。     

Tensile properties and transformation temperatures of Pd added Ti-Ni alloy dental castings

The effect of palladium (Pd) addition to Ti-Ni alloy as the third element was investigated to improve the super-elasticity of the alloy castings at body temperature for dental application. Ti-50.8Ni (at %) alloy, which exhibited super-elasticity at 310 K in castings, was used for comparison. 5.0, 7.5, 10.0 and 15.0 at % Pd was added to Ti-50.0Ni alloy by the substitution for Ni. The change in the proportion of Ti and Ni was also examined at the fixed Pd addition of 7.5 at %. The properties of the alloys were investigated in tensile test and differential scanning calorimetry (DSC). Ti-42.5Ni-7.5Pd alloy castings showed good super-elasticity among the examined alloys from the viewpoint of residual strain and elongation. Moreover, apparent proof stress could be changeable by the proportion of Ti and Ni with residual strain being kept low. Ti-42.5Ni-7.5Pd alloy castings exhibited better super-elastic flexibility than Ti-50.8Ni alloy, which is proven by lower apparent proof stress and larger elongation. This flexibility appears to be caused by its relatively high martensitic transformation starting temperature point. It is suggested that this flexibility with super-elasticity could widen the clinical application of the alloy casting in dentistry. © 2000 Kluwer Academic Publishers