Martensitic Transformation of TiNi Shape Memory Alloy Fiber Reinforced Ni Matrix Composites

In this paper, a TiNi shape memory alloy fiber Ni matrix composite was fabricated by an electroplating method using TiNi alloy as the cathode and Ni as the anode. The constrained martensitic transformation behaviors of the TiNi alloy were studied by differential scanning calorimeter (DSC), and the results showed that two endothermic peaks appear on the DSC heating curves and the reverse transformation temperatures increase with increasing prestrain levels. Moreover, comparing to the free transformation, the temperature window of the constrained reverse transformation is widely expanded due to the influence of recovery stress.     

Micromechanical Modelling of Shape Memory Alloy Composites

An isothermal finite element method (FEM) model has been applied to study the behavior of two kinds of shape memory alloy (SMA) composites. For SMA‐fiber reinforced normal metal composites, the FEM analysis shows that the mechanical behavior of the composites depends on the SMA volume fraction. For normal metal‐fiber reinforced SMA matrix composites, the SMA phase transformation is affected by the increasing Young’s modulus of the metal fiber. The phase transformation was also treated using a simple numerical analysis, which assumes that there are uniform stresses and strains distributions in the fiber and the matrix respectively. It is found that there is an obvious difference between the FEM analysis and the simple numerical assessment. Only FEM can provide reasonable predictions of phase transformations in SMA/normal metal composites.     

形状记忆合金内耗行为的研究进展

综述了形状记忆合金内耗特性的构成和产生机理，研制了利用Cu-Al-Ni-Mn-Ti记忆合金与铍青铜复合，研制成功了一种新型的弹性、减震、导电复合材料，并对其内耗性能进行了研究。     

Cast Pipe Joints of Fe‐15Mn‐5Si‐8Cr‐5Ni‐0.25C Shape Memory Alloy with High Carbon Content

Abstract: The cast pipe joint of the Fe‐15Mn‐5Si‐8Cr‐5Ni‐0.25C alloy was manufactured (the numbers in the composition denote the weight percentage of the elements while the weight percentage of Fe is the balance). The corresponding microstructure and shape memory effect are compared with those of a forged alloy. The results show that the cast joint has a good shape memory effect and may be industrially applied while the cast joint keeps jointing under a tensile force of 20 kN and a sealing pressure of 5 MPa. Moreover, it is found that the addition of nitrogen in the alloy doesn’t evidently improve the shape memory effect of the alloy.     

热型连铸CuAlNi形状记忆合金丝的性能研究

用热型连铸法制取φ1.5mm的柱晶CuAlNi合金丝,具有轴向排列的柱晶组织.经过900℃固溶处理,拉伸曲线与单晶的相似,具有两个阶段的马氏体转变,抗拉强度可达633MPa,延伸率14.95%.在4%的固定应变下,反复拉伸疲劳断裂次数高达38560次,形状回复率为100%.反复拉伸后在晶界上形成一种新相,有效地松弛了晶界上的应力集中,可能是疲劳寿命大幅度提高的原因.     

形状记忆合金混杂复合材料层板的有限元分析与强度研究

形状记忆合金(SMA)与复合材料层板结合后,构成可驱动材料。形状记忆合金的非线性及其与复合材料层板的结合界面的力学性能对整体材料的性能影响较大。通过对埋入形状记忆合金驱动器的复合材料层板进行有限元模拟分析与试验研究,用有限元模拟分析的方法可以比较准确地模拟埋入形状记忆合金后复合材料的应力分布情况,结果表明,形状记忆合金的埋入不会对材料的强度产生较大影响。     

Effect of Plasma Etched CNFs on Toughness and Mechanical Properties of Epoxy Composites

Carbon nanofibers (CNFs) are plasma etched by using cold plasma of air and helium for different time durations. Changes in surface functional groups of CNFs due to plasma treatment were estimated by using elemental analysis and temperature programmed decomposition in helium atmosphere. The influence of plasma etched CNFs on the toughness of epoxy and tensile and flexural strength of carbon–epoxy composites have been studied. Results indicate that, air plasma etched CNFs can improve the toughness of epoxy, while helium plasma etched CNFs could not impart improved toughness to epoxy composites. On the other hand, mechanical properties of carbon–epoxy made with air plasma etched CNFs improved significantly as compared to helium plasma etched CNFs as well as untreated CNFs.     

Microstructure, Compression Property and Shape Memory Effect of Equiatomic TaRu High Temperature Shape Memory Alloy

The microstructure, phase transformation, compression property and strain recovery characteristics of equiatomic TaRu super high temperature shape memory alloy have been studied by optical microscope, XRD, DTA, compression tests and TEM observations. When cooling the alloy specimen from high temperature to the room temperature,β(parent phase)→β′(interphase) →β"(martensite) two-step phase transformations occur. The microstructure at room temperature show regularly arranged band morphology, with the monoclinic crystal structure. The twinning relationship between the martensite bands is determined to be (101) of Type I. Reorientation and coalescence of the martensite bands inside the variant happened during compression at room temperature. The β′→β reversible transformation contributes mainly the shape memory effect, with the maximum completely recovery strain of 2%.     

镍钛记忆合金薄膜的制备与结构

采用射频溅射法成功地制备了NiTi形状记忆合金薄膜。研究了不同成分靶材对膜最终成分的影响。电子探针和俄歇能谱仪测定结果表明，在Ni（50at％）／Ti（50at％）的靶材上添入适量的Ti，可以获得Ni／Ti为1：1的薄膜。经晶化处理后，其结构为B2，用电阻法和差热分析确定TAs，TAf，TMs和TMf点分别为22，44，30，60℃。观察到了形状记忆现象。     

Fine-Grained Bulk NiTi Shape Memory Alloy Fabricated by Rapid Solidifcation Process and Its Mechanical Properties and Damping Performance

A near-equiatomic NiTi shape memory alloy was fabricated by rapid solidification process through vacuum arc melting followed by vacuum suction casting in water-cooled thick copper mold.The rapidly solidified(or suction cast) NiTi alloy shows much finer grains and homogenous microstructure,in particular a uniform distribution of various fine precipitates,compared to the conventional cast one.The resultant alloy also exhibits the homogenous Ni distribution in the matrix of the alloy,allowing the martensitic transformation to take place throughout the NiTi alloy matrix simultaneously and resulting in sharper transformation peaks compared to the conventional cast alloy.Moreover,the suction cast NiTi alloy shows a significant improvement over the conventional cast one,in terms of possessing higher deformation recovery rates and displaying the increased compressive strength and damping capacity by 4% and 20%,respectively.     

Influence of Stress‐Aging Processing on Precipitates and Mechanical Properties of a 7075 Aluminum Alloy

Two‐step stress‐aging tests, as well as pre‐treatment plus stress‐aging experiments, are performed on a 7075 aluminum (Al–Zn–Mg–Cu) alloy. Influences of stress‐aging parameters on mechanical behavior and fracture mechanism are investigated through uniaxial tensile test and fracture morphology analysis. It is revealed that the stress‐aging dramatically influences the mechanical properties and fracture characteristics of the studied alloy, which is contributed to the sensitivity of microstructures to stress‐aging. When the alloy undergoes two‐step stress‐aging, the ultimate tensile strength and yield strength first increase and then decrease with the increased first step stress‐aging temperature, while the elongation first decreases and then increases. For the retrogression pre‐treated plus stress‐aged alloy, the yield strength first increases and then drops with the increased retrogression pre‐treatment time, while the ultimate tensile strength almost remains stable. Furthermore, the elongation continuously increases with the increased retrogression pre‐treatment time. The observation of fracture morphology indicates that the dimple‐type intergranular fracture is the main fracture mechanism for the two‐step stress‐aged and retrogression pre‐treated plus stress‐aged alloys.     

含碳Fe-Mn-Si记忆合金的记忆性能研究

研究了含碳Fe－Mn－Si记忆合金Fe－18．1Mn－5．5Si－0．32C（wt％）的记忆性能，并与典型的Fe－Mn－Si三元记忆合金比较．结果表明：碳原子显著提高Fe－Mn－Si合金的回复率和回复应力，增加可回复应变，使合金的可回复应变大于5％，还极大延缓Fe－Mn－Si记忆合金回复率的表减趋势．碳原子提高Fe－Mn－Si合金记忆性能的原因是碳原子通过固溶强化提高奥氏体的强度，抑制不可逆塑性变形，促进应力诱发γ→ε马氏体相变及其逆转变．同时，含碳Fe－Mn－Si合金中应力诱发马氏体位向较单一，减少了相互交截，有利于形状记忆效应。     

TA15钛合金两类组织对疲劳性能和断裂韧度的影响

研究了TA15钛合金片状和双态两种典型组织对疲劳性能和断裂韧度的影响,结果表明:在S-N曲线的高应力区,双态组织的疲劳强度高于片状组织;在低应力区,情况则相反,且片状组织的疲劳极限(656MPa)高于双态组织(565MPa).片状组织的疲劳裂纹扩展速率低于双态组织,且断裂韧度K1C高于双态组织,即片状组织的损伤容限性能优于双态组织.     

TiNi Shape Memory Alloy Foams Synthesized by Spacer Sintering and their Properties

Titanium （Ti） and nickel （Ni） elemental powders were blended by ball milling and the ball milled powders were employed to fabricate TiNi shape memory alloy （SMA） foams by spacer sintering. Effect of ball milling time on phase constitutes of the sintered TiNi alloy foams was studied by X-ray diffraction （XRD） analysis. Scanning electron microscopy （SEM） was used to characterize the porous structure, and compressive tests were carried out to evaluate the mechanical properties of＇the foams. Results indicate that porosities of the TiNi alloy foams can be controlled by using the spacer sintering method, and the porosities show a significant effect on the mechanical properties and shape memory effect （SME）.     

Cu－Zn－Al－Mn－Ni－Ti合金的显微组织及力学行为

本文利用电子拉伸试验、扫描电镜、金相显微镜研究了Ｃｕ－Ｚｎ－Ａｌ－Ｍｎ－Ｎｉ－Ｔｉ合金的细化效果、断裂方式、记忆性能及伪弹性。结果表明：试验合金的铸态、轧态和淬火态组织得到明显细化。晶粒细化后合金室温拉伸断裂强度为７５０ＭＰａ，断裂应变为６．６％，同未细化的Ｃｕ基记忆合金相比强度大大提高，塑性也有所改善。低温拉伸时呈穿晶断裂，断口主要为准解理台阶；高温拉伸时呈微孔聚集型断裂。试验合金的室温完全可恢复应变为４．０％，完全伪弹性恢复应变为４．５％，均达到了多晶体材料的理论平均值。     

Properties of Reinforced Glass with Crystalline Particles

The brittle behavior of amorphous soda-lime glasses has been a major setback for the widespread use of this material in many industrial applications. Due to the low energy barrier of the matrix, the arrest of propagating cracks in such amorphous material is poor and often results in low energy toughness and strength. Glass is more susceptible to heat treatment and its hardness is slightly affected by use reinforcement. In the present work, the effects of reinforcing soda-lime glass with CuO and ZrO₂ particles were investigated. Fracture toughness was measured using the indentation technique. It was found that the fracture toughness increased by 17.4% and 29.5% for glass samples reinforced with CuO and ZrO₂, respectively. The distribution of the reinforcement particles was strongly affected by their average size and degree of wetting. In particular, ZrO₂ particles having sizes in the nano-range are more uniformly distributed when compared to micron-range particles, which have the tendency to form isolated clusters in the glass matrix. AFM analysis performed on some samples showed evidence of particle distribution in the surroundings of indentations.     

Damping and Mechanical Properties of Cocured Composite Laminates with Embedded Perforate Viscoelastic Layer

The composite laminates with embedded acrylonitrile butadiene rubber(NBR) layer were fabricated by cocuring process.The embedded layers were perforated with a series of small holes to allow resin to flow through the damping layer and completely couple the structure to improve bending stiffness and interlaminar shearing strength of these cocured composite laminates.The damping,bending stiffness and shearing strength of these composite laminates with different perforation diameters were investigated.The exper...     

Titanium Silicide Reinforced In Situ Synthesized TiAl Composites and Their Mechanical Properties

A processing route involving in situ development of reinforcements of titanium silicides in a series of TiAl-based matrices has been attempted. The main features of this processing route are: 1) mechanical alloying of 58Ti-21Al-21Si (at%) powder mixture for 20-h to form a predominantly Ti solid solution; 2) incorporating a small quantity of mechanically alloyed powders, referred to as precursors, into Ti-Al-X (X stands for Cr, Mn, Nb, or their combination) powder mixtures that act as the matrix; and 3) hot isostatic pressing (HIPing) of the cold compacted mixture at a temperature of 1100°C for 4-h. In the present study, a series of composites based on different Ti-Al-X matrices were synthesized. After annealing at 1150°C for 4-h, their microstructures and mechanical properties were characterized by scanning electron microscopy (SEM) and compression tests at room and elevated temperatures (600°C and 800°C). The influence of alloying elements in the matrix was evaluated from the stress-strain response curves.