多孔NiTi形状记忆合金的制备及性能

采用球磨后的NiTi合金粉末为原料,添加尿素作为造孔剂,利用粉末烧结法制备多孔NiTi形状记忆合金.研究烧结温度、保温时间和预成型压力等条件对制备的多孔NiTi合金组织结构和力学性能的影响.结果表明:相对于传统的Ni粉和Ti粉近等原子比混合烧结方法,此方法制备的多孔NiTi合金的相组成更加纯净.且随烧结温度升高,多孔N...     

NiTi形状记忆合金基本驱动特性

研究了预应变ＮｉＴｉ形状记忆合金的基本驱动特性，结果表明，加热和冷却过程回复力存在滞后行为；卸载过程中应力与应变具有与加热、冷却过程相关的非线性关系；卸尖力随卸载应变速率增加而降低，此外研究了预应变ＮｉＴｉ合金丝产生回复力后对外应力的响应行为。     

三元Ni-Ti基形状记忆合金的研究现状

针对二元NiTi形状记忆合金在应用中所显示出的局限性,三元NiTi基形状记忆合金通过第三组元的加入,改善了二元NiTi形状记忆合金的某些性能,弥补了其在应用中的不足,降低了成本,进一步扩大了NiTi基形状记忆合金的应用范围,从而一直受到研究者的广泛关注.综述了三元NiTi基形状记忆合金的研究现状,总结了存在的不足:首先,对于合金体系还需要大量的量化研究,确定出不同应用条件下合金的有效成分范围是其实用化的基础;其次,合金制备过程熔炼介质对合金产生的影响等重视不够;同时,应用性能研究还有待加强,性能的长效性与稳定性是关键,这方面的研究还缺乏充分而有效的数据.     

热机械循环方法对训练NiTi合金双程形状记忆效应的影响

采用4种典型的热机械循环方法训练获取具有双程形状记忆效应的镍钛合金丝,从双程形状回复量、高温相形状、低温相形状和相变温度的变化等方面系统研究了训练方法对双程形状记忆效应训练效果的影响.结果表明,在不同训练方法中镍钛合金丝被加载应变时所处的物质相态的差异是造成不同训练效果的主要原因,其中在马氏体相变过程中因加栽引入的位错最有利于双程形状记忆效应的形成.     

NiTi形状记忆合金丝焊接性研究

采用Ｐ１０５－９Ａ精密时间控制交流点焊机进行了ＮｉＴｉ形状记忆合金细丝的十字搭接焊。通过焊接接头的力学性能测试和热影响区宽度与内部组织的结果表明，采用电阻点焊方法，焊接部分的抗拉强度可达母材抗拉强度的９０％以上，接头内部没有或只有少量的铸态组织，热影响区宽度为０．２８ｎｍ文中还对焊接接头进行了变形恢复试验，接头的形状恢复率可达９８％以上。     

热处理对NiTi形状记忆合金的相变的影响

对含Ti 50.8%的NiTi形状记忆合金在300℃、400℃、500℃保温不同时间进行时效处理,然后通过差示扫描量热仪DSC对其相变温度点进行测定,发现经时效处理调节后,Af最大可下降20~30℃左右,而Ms变化不大。通过不同时效温度和保温时间的DSC曲线比较,得出热处理对其相变温度点的影响规律,即在300~500℃时效处理时,保温时间越短,Af降低越明显,在相同保温时间时,保温温度越低,Af降低越明显。     

用 NiTi 形状记忆合金制造散热器感温感压活门

采用NiTi形状记忆合金作为散热器的驱动感温活门,利用该合金的热弹性马氏体相变原理,在不改变散热器感温感压活门功能、工作原理的前提下,实现散热功能,提高了空气滑油散热器的寿命及可靠性。     

NiTi形状记忆合金热变形行为及加工图

目的应用Gleeble 3500热模拟试验机,研究Ni Ti形状记忆合金在变形温度650~1000℃、应变速率0.001~10 s~(–1)条件下的热变形行为,并基于动态材料模型构建合金的加工图。方法采用包含Arrhenius项的Z参数法建立该合金的本构关系数学模型,计算变形激活能,构建应变量为0.7和1.2时的加工图,并结合微观组织观察验证加工图预测结果的准确性。结果 Ni Ti合金热变形激活能Q为227.9 k J/mol。根据加工图可知,所研究Ni Ti合金的失稳变形工艺参数范围分别为:650~930℃,0.1~10 s~(–1)和930~1000℃,0.3~10 s~(–1),对应的失稳变形机制分别为局部流动和机械失稳;适宜的变形参数工艺范围为:750~800℃,0.01~0.03 s~(–1)和850~900℃,0.01~0.03 s~(–1),对应的变形机制为动态再结晶。结论研究结果可为Ni Ti合金成形工艺制度的制定和优化提供理论依据。     

镍钛合金在医疗器械领域应用和表面改性研究进展

镍钛合金基于特有的超弹性、形状记忆效应,广泛应用于医疗器械领域。其中超弹性表现为大变形下的弹性应变,应用于血管和腔道介入器械、口腔正畸丝、根管器械等;形状记忆效应可实现低温下易变形、体温下自回复,应用于热激活正畸丝、骨科、矫形外科、缝线等。此外,可通过多样化的表面改性技术,提升镍钛合金的生物相容性、腐蚀抗性、摩擦磨损性能,优化产品性能,拓展其在医疗器械制品中的应用范围。     

Superelasticity of NiTi Shape Memory Alloy Thin Films

The superelastic properties of NiTi thin films prepared with sputtering were studied. To characterize their superelasticity, tensile and bulging and indentation tests were performed. The measured mechanisms using these three methods were compared, and the factors that influence superelasticity were described.     

NiTi形状记忆合金相变过程中的超声波声速特性

用超声脉冲反射法测试了NiTi形状记忆合金（SMA）在相变过程中的纵波声速,研究了合金声速随温度变化的规律。结果表明：在非相变温度范围内,NiTi合金声速随温度缓慢变化,但在发生相变的温度范围内,声速的变化趋势发生明显改变;测得NiTi合金的各相变温度与常规电阻法基本一致,与电阻法等其他测量相变温度的方法相比,纵波声速法具有简单易行、测量方便以及对工件无损伤等优点。     

多孔NiTi合金的化学氧化处理表面改性研究

在H2O2+HCl溶液中对多孔NiTi合金进行了化学氧化处理表面改性。利用EPMA、SEM、原子吸收光谱对合金表面氧化膜的组成、形貌及化学氧化处理前后的Ni离子释出进行了研究。结果表明,经过H2O2+HCl溶液化学氧化表面处理后合金表面Ni含量显著降低,在生理盐水中的Ni释放速率明显下降;H2O2+HCl溶液浓度和氧化时间均对合金表面氧化膜的生长有较大影响。     

表面氧化及离子注氮对NiTi形状记忆合金耐腐蚀性能的影响

采用电化学测试的方法，研究了表面氧化以及表面氧化-离子注氮两种表面改性方式对NiTi形状记忆合金在人体生理模拟液(Hank′s溶液)中腐蚀行为的影响。腐蚀电位和极化曲线的测量结果表明表面氧化-离子注氮的方法使NiTi合金材料的腐蚀电位正移。雏钝电流密度下降，钝化电位区间扩大，合金表面耐蚀性明显提高。尤其是NiTi合金在进行氮离子注入后，测得击穿电位显著上升．增强了表面膜的抗局部腐蚀能力。因而表面氧化-离子注氮的改性方法可使材料的耐蚀性达到最佳。通过XPS的分析发现，离子注氮后合金表面形成氮化钛相以及富含羟基的化学效应，使NiTi基体的电化学性能得到提高。     

Porous Metal Sheets of NiTi made by Wet Powder Spraying

As a promising method to produce thin porous NiTi sheets, Wet Powder Spraying (WPS) is applied for NiTi powders. Layers with a thickness of 150 μm are obtained from pre‐alloyed NiTi powders with a particle size of < 12 μm. Optimized process control for spraying and sintering was used. Microstructure and phase formation is characterized. The sheets with a porosity of 15 % show a high pseudoelastic flexibility at room temperature. Phase transformation temperatures are determined by Differential scanning calorimetry (DSC). The one way effect could be demonstrated.     

Powder Metallurgical Fabrication and Characterization of Nanostructured Porous NiTi Shape-Memory Alloy

Production of NiTi alloy from elemental powders was conducted by mechanical alloying (MA) and sintering of the raw materials. Effects of milling time and milling speed (RPM) on crystallite size, lattice strain, and XRD peak intensities were investigated by X-ray analysis of the alloy. Powder compaction and sintering time and temperature effects on pore percentage of the as-mixed and the mechanically alloyed samples were empirically evaluated. The crystallite size of the mechanically alloyed Ni₅₀Ti₅₀ samples decreased with MA duration and with the milling speed. Depending on the crystal structure of the raw materials, the lattice strain increases with the milling duration. Metallographic studies proved the existence of martensitic B19' after sintering of both the as-mixed and the mechanically alloyed samples. Its amount was, however, greater for the former. Sintering lowered the porosity of the samples; no matter what powder (as-mixed or mechanically alloyed) was used. The porosity was greater, however, for the MA powders. This difference seemed to be due to the sharper liquid phase sintering effect of the as-mixed samples.     

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。     

NiTi形状记忆合金化学镀CoNiWP薄膜及磁性研究

采用化学镀法在NiTi形状记忆合金基体上镀覆CoNiWP磁性薄膜。用振动磁强计测试了样品的磁性能，结果表明NiTi形状记忆合金外层镀覆的金属薄膜是无定形结构并具有较好的磁性，其矫顽力是随化学镀进程逐渐增大到一定值后再逐渐下降。用扫描电镜表征镀层的形貌，结果表明化学镀开始初期，镀层颗粒比较细致，后来逐渐长大成晶胞状，当镀层完全覆盖基材后，再增加厚度会导致矫顽力下降。     

NiTi形状记忆合金薄膜的制备及形变特性

研究了适用于微器件的溅射态NiTi形状记忆合金薄膜.讨论了溅射工艺及织构对薄膜结构和相变特征的影响.利用薄膜热相变特性制成了微驱动器,观察并分析了该器件的形变特性.结果表明:原位加热溅射可以获得具有织构的晶化薄膜;用该薄膜制备的驱动器回复率为0.76%.     

Mechanical response of nitrogen ion implanted NiTi shape memory alloy

In the paper a change of material (mechanical) parameters of NiTi shape memory alloy subjected to ion implantation treatment is investigated. The spherical indentation tests in micro- and nano-scale and tension test have been performed to study an evolution of local superelastic effect in different volumes of nonimplanted and nitrogen ion implanted NiTi alloy. The differential scanning calorimetry has been applied to measure the change of characteristic temperatures due to ion implantation treatment. The structure of implanted material has been investigated using electron microscopy technique. It has been found that the ion implantation process changes the properties not only in a thin surface layer but also in bulk material. In the layer the pseudoelastic effect is destroyed, and in the substrate is preserved, however its parameters are changed. The characteristic phase transformation temperatures in substrate are also modified.     

Effect of Laser Printing Mode on Surface Topography,Microstructure, and Corrosion Property of Additive-Manufactured NiTi Alloy

Laser powder bed fusion (LPBF) is an emerging metal additive manufacturing method that can pave a pathway for manufacturing NiTi shape memory alloys (SMAs) with high performance. Considering the unique characterizations of LPBF process, the position and sequence of laser irradiation are different under different laser scanning modes, which will affect the performance of as-built samples. Herein, four different chessboard sizes are utilized to fabricate NiTi parts. The surface quality and relative density first increase and then decrease with the increasing chessboard size, obtaining the optimal surface roughness of 9.95 μm and relative density of 99.7%, respectively, at a chessboard size of 5 mm. As the chessboard size increases, the more pronounced precipitation of Ni₄Ti₃ with a higher quantity induces a strengthening effect, leading to a higher microhardness value of ≈290 HV_0.2 at a chessboard size of 9 mm. The electrochemical test shows a better corrosion resistance with a corrosion potential of 0.101 V and a corrosion current density of 1.670 × 10⁻⁵ A cm⁻² at a chessboard size of 5 mm. The corrosion mechanism is further revealed. This work emphasizes the importance of chessboard size as a reference for optimizing the process of additive-manufactured NiTi SMAs.