NaCl造孔剂添加量对多孔NiTi合金孔结构和力学性能的影响

选用Na Cl作为造孔剂,采用压制+烧结法制备孔结构和弹性模量可控的多孔Ni Ti形状记忆合金,采用SEM,XRD和形状回复率检测等测试手段研究造孔剂添加量对Ni Ti形状记忆合金的孔结构和力学性能的影响。结果表明:随Na Cl添加量增加,多孔体孔隙率从39%上升到72%,孔径大于50μm的孔隙数量明显增加;多孔体主要由Ni Ti奥氏体相(B2)和马氏体相(B19′)组成,并存在少量Ni Ti2,Ni3Ti和Ni4Ti3等相;合金的弹性模量随造孔剂的添加从30%时的10.8 GPa下降到70%时的1.5 GPa;当添加量为50%时,多孔体孔隙分布均匀,大于50μm的孔隙占45%,弹性模量为4.8 GPa,形状回复率达到最高值83%,最适合多孔植入体的要求。     

热爆法制备多孔NiTi形状记忆合金

Porous NiTi shape memory alloys (SMAs) havebeen widely used in medical fields such as hard tis-sue implant and medical instrument because of itsspecial pseudoelasticty, which can accommodate thedeformation of hard tissue, and its attractive combi-nation of properties such as excellent mechanicalproperties, good corrosion resistance, biocompati-bility and unique shape memory effect[1,2]. Moreo-ver, its porous structure allows the ingrowths of newtissue along with the transport of body fluids, …     

Electrochemical and surface characterization of a nickel-titanium alloy

For clinical implantation purposes of shape memory metals the nearly equiatomic nickel-titanium (NiTi) alloy is generally used. In this study, the corrosion properties and surface characteristics of this alloy were investigated and compared with two reference controls, AISI 316 LVM stainless steel and Ti6A14V. The anodic polarization curves, performed in Hanks' solution at 37 degrees C, demonstrated a passive behaviour for the NiTi alloy. A more pronounced difference between the corrosion and breakdown potential, i.e. a better resistance to chemical breakdown of passivity was found for the NiTi alloy compared to AISI 316 LVM. X-ray electron spectroscopy (XPS) and scanning electron microscopy (SEM) were undertaken to study the elemental composition and structure of the surface films prior to, and after immersion in Hanks' solution. The passive film on the NiTi alloy consists of a mainly TiO2-based oxide with minimal amounts of nickel in the outermost surface layers. After immersion in Hanks' solution the growth of a calcium-phosphate layer was observed. The passive diffusion of nickel from the NiTi alloy, measured by atomic absorption spectrophotometry reduced significantly in time from an initial release rate of 14.5 x 10(-7) microg cm(-2) s(-1) to a nickel release that could not detect anymore after 10 days. It is suggested that the good corrosion properties of the NiTi alloy and the related promising biological response, as reported in literature, may be ascribed to the presence of mainly a TiO2-based surface layer and its specific properties, including the formation of a calcium-phosphate layer after exposure to a bioenvironment.     

Fabrication of porous NiTi alloy via powder metallurgy and its mechanical characterization by shear punch method

In this study, Porous NiTi shape memory alloy has been produced by mechanical alloying of the elemental Ni and Ti powders. The compacting process was done at two temperatures (warm and cold press) and then sintering at 980 and 1050°C was performed on the specimens. Microstructure and mechanical prop-erties of the samples were investigated by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction. Moreover, shear punch test (SPT) employed to investigate the effect of compaction pressure and sintering temperature on the mechanical properties of the fabricated samples. It was revealed that warm compaction/sintering resulted in 15% yield stress improvement and 20% ultimate tensile strength (UTS) enhancement with respect to conventionally produced specimens. The proposed approach in this paper seems a step forward towards fulfillment of the demand for heavy load-bearing artificial bone.     

Ni55Mn25Ga18Ti2高温形状记忆合金的热循环稳定性

选择双相韧化的Ni?Mn?Ga?Ti高温形状记忆合金为研究对象。制备了淬火态Ni₅₅Mn₂₅Ga₁₈Ti₂高温形状记忆合金,并对其在室温至480 ℃之间进行高达500次的相变热循环,获得了5, 10, 50, 100和500次热循环态样品。采用X射线衍射、扫描电镜、能谱仪、同步热分析仪及室温压缩等实验方法,研究了淬火态和热循环态合金样品的微观组织、相变行为、力学及记忆性能,进而分析其热循环稳定性。研究结果表明:经500次循环后,Ni₅₅Mn₂₅Ga₁₈Ti₂合金相结构和显微组织未发生明显变化,均为由非调制四方结构的板条马氏体相和面心立方富Ni的γ相组成的双相结构;随着循环次数增加,马氏体相变温度几乎不变,逆马氏体相变温度和相变滞后在循环5次后趋于稳定;抗压强度及压缩变形率波动幅度较小;形状记忆性能下降,但形状记忆应变仍保持在1.4%以上;Ni₅₅Mn₂₅Ga₁₈Ti₂高温形状记忆合金显示出良好的热循环稳定性。      

Effect of solution treatment under load on microstructure and fabrication of porous NiTi shape memory alloy by self-propagating high temperature synthesis

Abstract

Porous NiTi shape memory alloy was fabricated by self-propagating high temperature synthesis. Effects of solution treatment under load applied on the microstructure were investigated. The densities of the phases changed insignificantly with solution treatment but the intermetallic phases such as Ti₂Ni, Ni₄Ti₃ and Ni₃Ti₂ disappeared and the density of B2(NiTi) phase increased with the load applied during solution treatment. Consequently, porous NiTi SMA with ideal pore characteristics, high chemical homogeneity and high strength for hard tissue implants was obtained.     

Effects of Process Parameters upon the Shape Memory and Pseudo-Elastic Behaviors of Laser-Welded NiTi Thin Foil

This article discusses the effects of laser welding parameters such as power, welding speed, and focus position on the weld bead profile, microstructure, pseudo-elasticity (PE), and shape memory effect (SME) of NiTi foil with thickness of 250 μm using 100W CW fiber laser. The parameter settings to produce the NiTi welds for analysis in this article were chosen from a fractional factorial design to ensure the welds produced were free of any apparent defect. The welds obtained were mainly of cellular dendrites with grain sizes ranging from 2.5 to 4.8 μm at the weld centerline. A small amount of Ni₃Ti was found in the welds. The onset of transformation temperatures (A _s and M _s ) of the NiTi welds shifted to the negative side as compared to the as-received NiTi alloy. Ultimate tensile stress of the NiTi welds was comparable to the as-received NiTi alloy, but a little reduction in the pseudo-elastic property was noted. Full penetration welds with desirable weld bead profiles and mechanical properties were successfully obtained in this study.     

重熔镍钛合金的形状记忆效应分析

采用不同的工艺及设备对近等原子比的形状记忆合金进行重熔,获得铸态组织形状记忆合金,对采用不同坩埚所制备出的NiTi合金进行对比分析,采用金属坩埚所得到的形状记忆合金的成分满足医疗器械及外科植入物用NiTi形状记忆合金的成分要求,且具有良好的形状记忆效应。     

The effect of aging temperature on transformation parameters of porous NiTi shape memory alloy fabricated by SHS

This study reports some different and efficient approaches for the aging temperatures which cause changes in the transformation parameters of porous NiTi (Ti-50.5 at % Ni) shape memory alloy (SMA) with porosity of 55.3% fabricated by self propagating high temperature synthesis (SHS). Changes which occurred in phase transformations due to the effects of various thermal procedures have been investigated by using X-ray diffraction. The micro structure was investigated using a scattering electron microscope and a light optical microscope. The shape memory behavior and transformation temperatures were studied through the differential scanning calorimetry (DSC). During the compression tests, it was observed that the compressive strength of the specimens was higher than the compact human bone, and that it increased with increasing aging temperature.     

Stress-strain behavior and shape memory effect in powder metallurgy TiNi alloys

The shape memory properties of the TiNi alloy produced by a powder metallurgical method have been evaluated from tensile stress-strain curves. The contamination of the powders during atomization can be suppressed by applying the Plasma Rotating Electrode Process (P-REP), so that the compact made by Hot Isostatic Pressing (HIP) is expected to exhibit the shape memory effect identical to the typical alloy grown from melt. The fracture behavior of the P/M alloy is also studied, and the improvement of fracture strength of the P/M alloy is attempted.     

形状记忆合金在航空航天领域的应用与进展

叙述了形状记忆合金的功能特性,并介绍了NiTi形状记忆合金在航空航天领域的应用及其进展。     

Zr离子注入对NiTi形状记忆合金表面硬度和耐磨性影响

研究了Zr离子注入参数（注入剂量和注入电流）对NiTi形状记忆合金表面成分、形貌、硬度和耐磨性的影响.发现Zr离子注入后,Zr离子浓度在NiTi合金表面呈高斯分布,同时降低了合金表面的Ni含量.Zr离子注入后合金表面形貌出现沟槽结构,合金外表层纳米硬度、杨氏模量和显微硬度明显提高.摩擦磨损实验结果表明,Zr离子注入降低了NiTi合金初始摩擦因数,显著延长了维持初始低摩擦因数的时间,同时使磨痕的宽度和深度分别减小了30%~50%和28%~50%.因此,选择适当的注入参数可以使NiTi合金获得最佳的耐摩擦磨损性能.     

Corrosion resistance improvement of NiTi osteosynthesis staples by plasma polymerized tetrafluoroethylene coating

NiTi shape Memory Alloys (SMA) are potential biomaterial candidates for medical devices such as osteosynthesis staples. However, Ni dissolution induced by uniform or localized corrosion could lead to toxicity. In this work, plasma polymerized tetrafluoroethylene (PPFTE) coating is used to improve the corrosion resistance of NiTi plates and corresponding NiTi stables. The scratch test indicates a good surface adhesion of the film but that it lacks cohesiveness. Potentiodynamic tests in physiological Hank's solution show that PPTFE coating improved the pitting corrosion resistance. The passivation range is increased from 35% to 96% compared to the untreated sample and the pit diameter is decreased from 100 microns to 10 microns. The uniformity of the deposited film is a very important parameter. When the film is damaged, the corrosion seems to increase in comparison to the untreated samples. Otherwise, if the staple is carefully manipulated, the coating follows the large deformations induced by the memory effect of the alloy without cracking, and then, protects efficiently the staple from pitting.     

NiTi形状记忆合金超弹性的研究现状

综述了NiTi形状记忆合金在有关超弹性性能方面的基础研究、应用研究、力学行为、磨损性能以及数学建模等问题。     

硼对Ni-46Ti-4Al合金微观组织和力学性能的影响

采用电子探针、透射电镜和X射线衍射方法研究了添加微量B元素(0～1%)(质量分数)对Ni-46Ti-4Al合金微观组织的影响,并采用力学压缩试验测试了合金的室温和高温力学性能.结果表明,Ni-46Ti-4Al合金由NiTi基体和(Ti,Al)<,2>Ni两相组成.添加微量B元素(0.02%)可以促使Ni-46Ti-4Al合金中出现TiB<,2>化合物,且与(Ti,Al)<,2>Ni相都在晶界上析出.随着B含量增加,(Ti,Al)<,2>Ni相逐渐减少,TiB<,2>相逐渐增多.这两相的硬度均高于NiTi基体相,是合金中的强化相.添加适量的B可以显著提高Ni-46Ti-4Al合金的室温和高温屈服强度,例如:添加l%B合金的室温屈服强度达到2553 MPa,比Ni-46Ti-4Al合金提高了128%.添加0.02%B和1%B合金在600℃时的屈服强度分别为382和498 MPa,比Ni-46Ti-4Al合金提高了35%和70%.合金屈服强度和两个强化相((Ti,Al)<,2>Ni和TiB<,2>相)的总体积分数成正比.B加入后一方面使Ni-46Ti-4Al合金得到固溶强化,另一方面,还促使生成具有强化作用的TiB<,2>相,这是合金室温和高温屈服强度提高的主要原因.     

Ag-28Cu钎焊TiNiSMA接头的微观组织特征

为充分发挥SMA的高阻尼特性,制作高性能的新型阻尼器,本文开展了TiNiSMA的钎焊制备及其性能研究。研究结果表明:焊接接头的界面组织主要为a-Ti+Ti2Cu(TiCu2及Ti(Ni,Cu))+Ag一次固溶体+Ag-Cu共晶。随着钎焊温度的不断升高,焊缝尺寸不断减小。钎焊温度为870℃时,连接层与母材界面以小型锯齿状结合,而生成的Ti2Cu相对形状记忆效应有利,组织致密。     

Investigation on the fracture behavior of shape memory alloy NiTi

This work investigates the fracture behavior of shape memory alloy NiTi (50.7 at. pct Ni) at room temperature. Macroscopic mechanical tests, microscopic in situ observations of tensile fracture processes by scanning electron microscopy (SEM), and detailed analyses of fracture surfaces were carried out. The results reveal that specimens with different thicknesses show various shape memory effects and superelasticities. The main crack with a quasi-cleavage mode that combines cleavage with ductile tearing is initiated at the notch tip and is stress-control-propagated in line with the direction of the maximum normal stress. The microstructure has little effect on the direction of crack propagation, but coarser substructures show lower resistance to the crack propagation. In specimens with various types of notches, various notch acuities present different effects on the crack initiation and propagation and result in different fracture behaviors.     

镍钛形状记忆合金线坯连续定向凝固温度场的数值模拟

连续定向凝固过程中结晶器的温度分布对固-液界面位置和形状具有重要影响.在建立三维物理模型以及确定材料热物性参数、边界条件与冷却水对流换热系数计算方法的基础上,采用ANSYS有限元软件对不同参数组合条件下镍钛形状记忆合金线坯连续定向凝固的稳态温度场进行了数值模拟.研究结果表明,在所给定的模型及各种参数条件下,镍钛形状记忆合金在结晶器内可以完成凝固过程,且固-液界面呈平直状,具备了进行连续定向凝固制备的基本条件.

     

TiNiZr形状记忆合金的性能研究

系统地研究了锆对TiNiZr形状记忆合金性能的影响，对Ti49.4-xNi50.6Zrx(x=0,1,2,3)三元合金的相变温度进行了研究，表明合金相变温度随锆含量的增加先降后升；对合金系进行了机械性能及记忆性能研究，发现加锆后合金的机械性能和记忆性能都获得提高；此外还对Ti46.4Ni50.6Zr3的脆性根源进行了初步探讨。