铁基合金粉末低温温压工艺研究

对铁基合金粉末低温温压工艺进行了较为系统的研究,考察了粉末温度、模具温度、润滑剂含量和压制压力对温压密度的影响。结果表明：较佳的模具、粉末温度分别为120℃和100℃;粉末中较佳的润滑剂含量为0．65％;当压力为686MPa时,Fe-1．5Cu-0．5C和Fe-1．5Ni-0．5Mo-0．5Cu-0．5C粉末压坯密度分别达到了7．42,7．41g／cm^3;两种粉末的温压坯件经过烧结后密度进一步提高,合金元素镍、钼等具有优良的烧结强化效果。     

一种形状记忆合金扭转驱动器的制备与测试

研究了一种以镍钛（NiTi）形状记忆合金带材为基本驱动材料的平面涡卷式扭转驱动器。该驱动器利用NiTi合金的单程形状记忆效应与回复弹簧的相互作用,实现驱动器在高低温状态下正反两向的扭矩输出。分析了驱动器的基本结构形式和驱动原理,探讨了NiTi合金驱动部件的设计方法和基本制备工艺。设计制作了驱动器原理样机,并测试了驱动器的输入输出特性。测试结果表明,该驱动器在给定的高低温环境(10~60℃）下能够在正反两个方向连续稳定地输出扭矩,最大行程范围为0~175°,最大输出扭矩达到0.33N·m。实测结果证明了驱动器设计方案与制备工艺的可行性。     

压制压力对合金产品的影响

选用不同粗细粒度的原材料,采用进口Dorst压机,研究了压力大小对压坯密度以及线收缩系数的影响,建立了压制曲线,并运用光学显微镜分析了压坯烧结后的金相孔隙。结果表明,压力小于100MPa时,压坯密度随压力增加而快速增加,继续加大压力,密度增加趋势减缓。若采用过小的压力压制压坯,正常烧结后产品不能完全致密化,而当压力过大时,压坯出现裂纹。     

工艺参数对热等静压法制备多孔 NiTi记忆合金孔隙特性的影响

采用不封装的热等静压法来制备多孔NiTi形状记忆合金,着重研究了不同工艺参数对孔隙特性的影响规律.结果表明:采用烧结时间3h制备出的多孔NiTi记忆合金能得到令人满意的孔隙特征,分别采用100 MPa和400 MPa的冷压压力能够制备出两种完全不同孔状结构的多孔NiTi记忆合金,一种是均匀分布的结构,另外一种则是层状结构(多孔层-致密层-多孔层);而且,随着热压压力的增加,孔隙特征参数减小.     

低压烧结制备多孔NiTi形状记忆合金的结构及性能

采用低压烧结法制备了多孔NiTi形状记忆合金;研究了在1050℃下烧结不同时间所制备合金的结构及性能,并与常规粉末烧结方法制备的合金进行了比较。结果表明:低压烧结法在短时间内制备合金的孔隙可控性好,孔径主要分布在50~200μm之间,孔隙相互连通,呈网状分布,无明显各向异性;同时表现出良好的力学性能和超弹性能。     

激光辐照参数对自蔓延合成铝-钛-硼中间合金组织和性能的影响

采用激光引燃自蔓延技术合成铝-钛-硼中间合金,利用此中间合金可对ZL108铝合金组织进行细化,研究了激光辐照参数对中间合金和铝合金显微组织的影响。结果表明:通过对激光器工作参数的调整,可制备出具有TiAl3和TiB2颗粒含量适中、弥散分布的中间合金;在本试验条件下,激光功率1 200 W、照射1.0 s时,生成粒径约为1μm、弥散分布的TiB2,长度约10μm、均匀分布的长条状TiAl3,此时中间合金的细化效果最佳,铝晶粒平均尺寸为55μm。     

第一性原理研究压力下NiTi合金B2相的结构、力学以及热力学性质

运用第一性原理研究0~40 GPa下B2相NiTi合金的机械性能、 电子性质以及热力学性能. 计算发现, 几何优化后NiTi晶体的晶格常数与实验值和其他文献提供的数值大体一致, 表明随着压力的增加该型合金力学稳定且没有相变产生. NiTi合金的体模量B、 剪切模量G和杨氏模量E以及B/G的值随压力增大呈线性增加, 表明压力使其抗体积变形能力、 抗剪变能力及塑性增强. 研究发现, 压力也会使NiTi合金的各向异性发生改变. 对NiTi合金态密度的研究表明, 该合金同时显现出共价性与离子性, 并且压力对其电子性质无明显影响. 此外, 本文还研究了不同温度和压力下NiTi合金的热力学性能, 包括德拜温度ΘD,热容Cv和Cp的变化, 为今后实验提供理论数据.     

第一性原理研究压力下NiTi合金B2相的结构、力学以及热力学性质（英文）

运用第一性原理研究0~40GPa下B2相NiTi合金的机械性能、电子性质以及热力学性能。计算发现,几何优化后NiTi晶体的晶格常数与实验值和其他文献提供的数值大体一致,表明随着压力的增加该型合金力学稳定且没有相变产生。NiTi合金的体模量B、剪切模量G和杨氏模量E以及B/G的值随压力增大呈线性增加,表明压力使其抗体积变形能力、抗剪变能力及塑性增强。研究发现,压力也会使NiTi合金的各向异性发生改变。对NiTi合金态密度的研究表明,该合金同时显现出共价性与离子性,并且压力对其电子性质无明显影响。此外,本文还研究了不同温度和压力下NiTi合金的热力学性能,包括德拜温度Θ_D,热容C_v和C_p的变化,为今后实验提供理论数据。     

保温时间对部分瞬间液相连接硬质合金/钢接头组织与性能的影响

以"三明治"结构的钛箔/镍箔/钛箔为中间层材料,采用部分瞬间液相(PTLP)连接方法在1 000℃保温不同时间(1~4h)制备了YG10硬质合金/40Cr钢异质金属接头,研究了保温时间对接头微观形貌、物相组成和剪切强度的影响。结果表明:接头为由YG10硬质合金/TiC+WC/Co-NiTi/Ni3Ti/镍层/Ni3Ti/NiTi/TiC/40Cr钢组成的多层结构,硬质合金和镍层以及钢和镍层之间均形成了宽35~50μm的过渡层;当保温时间从1h延长到4h时,接头过渡层中的微观缩孔数量减少,过渡层厚度增加,接头剪切强度先增大后减小;当保温时间为2h时,接头剪切强度最高,为153MPa。     

激光诱导自蔓延合成Mg-Ni合金

用40WCO2激光器点火，在氩气保护的容器中自蔓延合成Mg—Ni合金。细致观察了激光诱导自蔓延高温合成反应的燃烧过程，对合成的试样进行了X射线衍射分析(XRD)、扫描电镜分析(SEM)。结果表明，用激光自蔓延方法可以制备Mg2Ni金属间化合物，且产物中没有普通制备方法中易于出现的杂质MgNi2等，氧化也很少；获得的样品呈层状、孔隙多，这是由样品的制备及反应过程所决定的。     

Fretting wear behavior of superelastic nickel titanium shape memory alloy

The fretting behavior of superelastic nickel titanium (NiTi) shape memory alloy was studied at various displacement amplitudes on a serve-hydraulic dynamic test machine. The results showed that the superelastic properties of the material played a key role in the observed excellent fretting behavior of NiTi alloy. Due to the low phase transition stress (only 1/4 the value of its plastic yield stress) and the large recoverable phase transition strain (5%) of NiTi, the friction force of NiTi/GCr15 stainless steel pair is smaller than the value of GCr15/GCr15 pair and at the same time the Rabinowicz wear coefficient of NiTi plate is about 1/9 the value of GCr15 plate under the same fretting conditions. For NiTi/GCr15 pair, even NiTi has a much lower hardness than GCr15, the superelastic NiTi alloy exhibits superior fretting wear property than GCr15 steel. It was found that the weak ploughing was the main wear mechanism of NiTi alloy in the partial slip regime. While in the mixed regime and gross slip regime, the wear of NiTi was mainly caused by the abrasive wear of the GCr15 debris in the three-body wear mode.     

Experimental Investigations of the Superelastic Impact Performance of Nitinol 60

Nitinol 60 (NiTi60) is a nickel–titanium alloy that has a unique combination of properties such as high hardness, low elastic modulus, and superelasticity. Recent studies of static indentation tests on prestressed samples demonstrated a considerable load capacity increase, which led to the current experimental work. The coefficient of restitution (COR) is measured for two NiTi60 spheres of different diameters (0.635 and 1.270 cm). This work shows that mechanically stressing NiTi60 spheres enables them to achieve a normal COR greater than 0.9 when colliding with NiTi60 landing. This is one of the highest ever reported COR values for self-mated crystalline metal alloys at moderate impact velocities. Consequently, it is believed that this material may be a potential candidate for use in applications requiring highly resilient and wear-resistant metallic materials. A well-known analytical formulation for the coefficient of restitution is used to gain insight and to elucidate some of the COR results presented.     

表面活性剂对电子束制备纳米镍粉的影响

在水溶液中,于常温常压下分别使用聚乙烯醇（PVA）和十二烷基三甲基溴化胺（DTAB）为表面活性剂,用电子束辐照方法制备了纳米镍粉;用X射线衍射仪、透射电镜、紫外可见分光光度计和红外光谱对所得产物进行了表征。结果表明：以PVA作表面活性剂得到相对纯的纳米镍粉,平均粒径约为12．6nm;而以DTAB为表面活性剂得到镍和三氧化二镍的混合物,平均粒径约为25nm;采用PVA为表面活性剂在产品的纯度和粒度上都优于DTAB。     

Effects of irrigation solutions on the surface of protaper instruments: A microscopy study

The aim of this study was to evaluate the effects of sodium hypochlorite (NaOCl), chlorhexidine digluconate (CHX), and mixture of tetracycline, citric acid, and detergent (MTAD) solutions on the surfaces of nickel titanium (NiTi) rotary files with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Irrigation solutions including 2.5% NaOCl, 5% NaOCl, 2% CHX, and MTAD were used. Four new ProTaper rotary NiTi files (F3) were immersed in each four irrigation solutions for 10 min, separately. One untreated NiTi file was used as a control specimen. The surface analysis was performed with SEM and AFM. The surface analysis in AFM was performed on 12 different regions located between first and second millimeters from the tip. SEM images were taken with different magnifications. No surface alteration was recorded under SEM evaluation. AFM revealed that the root mean square (RMS) values of all treated specimens were statistically higher than the control sample (P < 0.05). The sample which was treated with CHX showed lowest RMS values in test groups. All tested solutions caused surface alterations. CHX demonstrated limited surface alterations when compared to the other tested solutions. Microsc. Res. Tech. © 2012 Wiley Periodicals, Inc.     

Application of ANN in the prediction of the pore concentration of aluminum metal foams manufactured by powder metallurgy methods

In this work, the effect of fabrication parameters on the pore concentration of aluminum metal foam, manufactured by the powder metallurgy process, has been studied. The artificial neural network (ANN) technique has been used to predict pore concentration as a function of some key fabrication parameters. Aluminum metal foam specimens were fabricated from a mixture of aluminum powders (mean particle size 60 μm) and NaCl at 10, 20, 30, 40(wt)% content under a pressure of 200, 250, and 300 MPa. All specimens were then sintered at 630°C for 2.5 h in argon atmosphere. For pore formation (foaming), sintered specimens were immersed into 70°C hot running water. Finally, the pore concentration of specimens was recorded to analyze the effect of fabrication parameters (namely, NaCl ratio, NaCl particle size, and compacting pressure) on the foaming behavior of compacted specimens. It has been recorded that the above-mentioned fabrication parameters are effective on pore concentration profile while pore diameters remain unchanged. In the ANN training module, NaCl content (wt)%, NaCl particle size (μm), and compacting pressure (MPA) were employed as inputs, while pore concentration % (volume) of compacts related to fabrication parameters was employed as output. The ANN program was successfully used to predict the pore concentration % (volume) of compacts related to fabrication parameters.     

Effects of the presence of probiotic bacteria in the aging medium on the surface roughness and chemical composition of two dental alloys

The aims of this study were: (a) to determine if the presence of probiotic bacteria in an aging medium, that is, artificial saliva in this study, has relevant effects on the surface roughness and the chemical composition of two main alloys used in dentistry (NiTi and stainless steel [SS]) and (b) in the case of NiTi, if these effects are influenced by the coating of the alloy (rhodium and titanium nitride). Atomic force microscopy and Raman spectroscopy were used to study the surface morphology and identify metal oxides formed on the surface of the alloys. Experiments demonstrated that the probiotic bacteria Lactobacillus reuteri can induce processes that alter some features of the surface such as roughness and chemical composition. The effect is dependent on the type of alloy and coating. The bacteria increased roughness in the case of uncoated NiTi more than saliva alone (pH = 4.8). Probiotic bacteria tend to decrease the corrosive influence of saliva on NiTi when the alloy is coated with rhodium or titanium nitride and this effect was also evidenced on SS. Raman spectroscopy confirmed that only SS samples are prone to oxidation processes, predominantly associated with exposure to saliva rather than probiotic bacteria.     

Role of phase transition in the unusual microwear behavior of superelastic NiTi shape memory alloy

The excellent microwear performance of nano-grained superelastic nickel titanium (NiTi) polycrystalline shape memory alloy (SMA) is reported in this paper. The microwear test was conducted at temperatures ranging from 22 to 120 °C by a Hysitron triboindenter. The results showed that the NiTi SMA has superior microwear resistance compared to traditional tribo-materials such as stainless steel AISI 304 and that the material exhibits unusual hardness dependence of wear within certain temperature regimes. With the increase in temperature from 22 to 120 °C, wear resistance was found to decrease anomalously with an increase in hardness. Further investigation and analysis confirmed that the stress-induced phase transition during contact and wear play an essential role in the material's high wear resistance. It is demonstrated through contact mechanics analysis that the increase of hardness with temperature was mainly due to the increase in the phase transition stress. The observed applied threshold load that corresponds to the onset of the plastic deformation in the contact area was strongly influenced by the phase transition process at the tip region. For the investigated superelastic NiTi, the temperature-dependent interplay between reversible phase transition and irreversible plastic yielding plays a key role in the temperature dependence of the wear performance and is responsible for the observed apparent unusual hardness–wear relationships.     

以粉末为原料制备NiTi薄膜涂层的研究进展

NiTi薄膜涂层具有形状记忆特性、散热能力好、耐蚀性能好、超弹性性等特点,在很多领域里都具有广泛的应用前景。以粉末为原料制备NiTi薄膜涂层材料的研究现状进行综述,并对其应用加以评述。     

Evaluation of surface alterations in different retreatment nickel‐titanium files: AFM and SEM study

The aim of this study was to evaluate the surface changes of nickel titanium (Ni‐Ti) rotary retreatment files after three and five uses. Furthermore, the effects of 2% sodium hypochlorite and chloroform solutions and sterilization procedures on the NiTi rotary retreatment surfaces were investigated. ProTaper Retreatment files, R‐endo files, and Mtwo retreatment files were used for this study. The palatinal roots of maxillary molar teeth were obturated with gutta percha and Ah26. Retreatment procedures were performed with these retreatment file systems. The surface changes of untreated NiTi rotary files that were used three and five times, immersed in NaOCl and chloroform and subjected to sterilization procedures were investigated with atomic force microscopy (AFM) and scanning electron microscopy (SEM). The RMS values, three dimensional images and SEM images at various magnifications were obtained. RMS values showed that all three NiTi rotary retreatment file systems showed significant deteriorations after three and five uses. Cracks, damages and spiral construction deteriorations were detected in the SEM images after three and five uses. Furthermore, the Mtwo 15 file was broken off after five uses. AFM data indicated that 2% NaOCl caused significant surface deteriorations on NiTi rotary files and both AFM and SEM evaluation showed that chloroform solution and sterilization procedures did not cause significant surface deteriorations. In conclusion, ProTaper retreatment, R‐endo, and Mtwo retreatment files showed surface damages depending on retreatment procedures. Clinicians have to consider that retreatment files always have a tendency to break off after the third time they have been used. Microsc. Res. Tech. 78:356–362, 2015. © 2015 Wiley Periodicals, Inc.     

On the compressive behavior of sintered porous coppers with low-to-medium porosities—Part II: Preparation and microstructure

A polymer space-holder method was used in this study to prepare porous coppers with low-to-medium porosity within the range 5–50%. This provides the possibility to control the pore size, distribution and structure. Optical microscopy and scanning electron microscopy (SEM) with energy dispersion spectrum (EDS) were utilized to characterize the porous samples. Two different sizes of copper powders, 5 and 45 μm, were used to investigate the effect of raw materials powder size. Microstructure results have shown that there exist two different types of pore in the sintered samples: round-shaped macro-pores left over by the burnout of the space holder and irregular micro-pores or the intervals among metal powders. No matter which size powder was used, the size of the macro-pore falls into a range 200–500 μm, but the pore structures are different in the two cases, interconnected or open pores for the 45 μm raw powders and closed pore for the 5 μm powders. The sizes of the micro-pores among the copper powders in the two cases are also different, several microns for the 5 μm powders and 10–20 μm for the 45 μm powders, though all micro-pores are interconnected for both powder sizes. From the viewpoint of pore structure, it is concluded that the 45 μm powder is more appropriate for use to prepare the porous metal. In addition, the effect of the binder was also investigated. It is suggested that a binder that can be easily and completely removed should be used in order to induce the residue. This paper, as Part II of the publication, focuses on the fabrication of the porous samples where Part I [Lemons JE, editor. Quantitative characterization and performance of porous implants for hard tissue application. ASTM STP 953; 1985] has been published earlier for the mechanical properties of the material.