Comparative study of martensitic transformation behavior of NiAlMn and NiAlMnFe high temperature shape memory alloys

A comparative study of microstructure and martensitic transformation (MT) behavior of Ni₅₉Al₁₁Mn₃₀ and Ni₆₀Al₁₉Mn₁₆Fe₅ high temperature shape memory alloys (SMAs) has been performed by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS), optical microscopy, and micro-hardness testing. The MT temperature (MTT) of Ni₅₉Al₁₁Mn₃₀ alloy is higher than that of Ni₆₀Al₁₉Mn₁₆Fe₅ alloy, and both alloys’ MTT increases with increasing annealing temperature. The temperature hysteresis and hardness of Ni₅₉Al₁₁Mn₃₀ alloy are smaller than that of Ni₆₀Al₁₉Mn₁₆Fe₅ alloy. The MT behavior of Ni₆₀Al₁₉Mn₁₆Fe₅ is sensitive to aging temperature and its MTT and hysteresis decrease with increasing aging temperature. However, the MT behavior of Ni₅₉Al₁₁Mn₃₀ alloy is not sensitive to aging temperature. The MT stabilization effects appear in both alloys during thermal cycles. This stabilization effect vanishes from the second thermal cycle. The quenched microstructure of Ni₅₉Al₁₁Mn₃₀ and Ni₆₀Al₁₉Mn₁₆Fe₅ alloys is M plus gamma phase, in which the volume fraction of gamma phase is about 40 and 20%, respectively, and the microhardness of M is higher than that of gamma phase. No aging effects were found in both alloys after aging at 400 °C.     

Characterization of intermetallic phases and oxides formed in annealed Ni/Al multilayer structures

Two different multilayer structures composed of ten alternating Ni and Al thin films were sputter deposited on Si (111) substrates. These multilayers with individual Ni and Al thin film thicknesses of about 25 nm and 38 nm and of 25 nm and 13 nm, respectively, have the average compositions of Ni_0.50Al_0.50 and Ni_0.75Al_0.25. The samples were heat treated in a differential scanning calorimeter instrument with a constant heating rate of 40 °C min ⁻¹ in Ar from room temperature to 550 °C. The compositions of as-deposited and heat-treated samples were studied with high-resolution Auger electron spectroscopy (AES) rotational depth profiling. X-ray photoelectron spectroscopy (XPS) analyses show an excess of Ni in both annealed samples. X-ray diffraction measurements of annealed multilayers show the formation of Ni₂Al₃ and NiAl₃ phases in the Ni_0.50Al_0.50 sample and the presence of Ni₃Al and Ni A1₃ phases with some excess of Ni in the Ni_0.75Al_0.75 sample. AES and XPS investigations of the reacted layers after 15 min annealing in air at 500 °C disclose considerably different surface oxide thin films: on the Ni_0.50Al_0.50 layer the oxide thin film consists of Al₂O₃ with a small amount of NiO, whereas that on the top of the Ni_0.75Al_0.25 layer is thicker and consists of NiO on top and some Al₂O₃ below.     

Nickel Enriched Diffusion Layers on a NiAl Alloy

The intermetallic phase NiAl is a perspective material for high-temperature and shape memory effect applications. Formation of Ni₅Al₃, Ni₂Al, Ni₃Al phases which influence the extent of martensitic transformation in NiAl have been studied up to now with controversial results. We have investigated (using SEM and local elemental analyses) the microstructure of nickel enriched surface layers on a Al-79 wt.% Ni alloy. The layers were prepared by diffusion annealing and subsequently given two different heat treatments: at 930°C outside the Ni₅Al₃ region and at 500°C within the Ni₅Al₃ region of the phase diagram. In the specimen which was only diffusion annealed separate islands of Ni₅Al₃ phase elongated in the direction of the concentration gradient could be recognized within the nickel enriched surface layer. In the samples additionally annealed at 500°C, a well defined continuous layer of the Ni₅Al₃ phase situated 0.4 mm below the specimen surface was found. In the samples annealed at 930°C, isolated Ni₃Al precipitates were observed. Their number and size gradually increased with increasing nickel content.     

Formation of intermetallic compounds in the Cr–Al–Si ternary system

The microstructure and composition of binary and ternary intermetallics have been studied in ternary diffusion couples of Cr and an Al–Si eutectic alloy. The ternary intermetallic always formed in the liquid part of the diffusion couple as a dendritic structure. Two intermetallics compounds, CrSi₂ and Cr₅Si₃, of the Cr–Si binary system have been observed. The CrSi₂ intermetallic has a high solubility of up to 20 at.% Al and forms as faceted plates. A number of intermetallics, namely, CrAl₇, Cr₂Al₁₁, CrAl₄, Cr₄Al₉, Cr₅Al₈ and Cr₂Al, of the Cr–Al system have been observed. The solubility of Si varies from as low as 0.8 at.% in Cr₂Al to as high as 9 at.% in Cr₄Al₉. A schematic of the reaction scheme of the Cr–Al–Si system is presented. This has been based on the observed microstructure and composition of phases.     

The production of high purity metal alloys by surface segregation

The synthesis of high purity liquid metal alloys has been accomplished by exploitation of surface segregation phenomena. The process consists of remelting the alloy in an ultra high vacuum chamber. At the melting temperature, low-level bulk impurities segregate to the surface of the liquid alloy to form an elastic solid skin enclosing the liquid which may be skimmed off to form an impurity-free alloy. In some cases, the segregated impurities prevent wetting and the alloy forms a spherical droplet of material. The pure alloy in the droplet interior may then be released by fracture of the impurity surface shell. Details of the melting arrangement and surface analysis of the alloy before and after segregation will be discussed. Applications of the technique to produce high purity eutectic alloys of transition metal borides (Pt₇₂B₂₈, Ni₅₅B₄₅,Pd₇₂B₂₈) and arsenides (Pd₂As) will be discussed.     

On the Ni5Al3 phase and related phenomena in a NiAlFe alloy

The Ni₅Al₃ Phase and related phenomena have been systematically studied using a Ni-25Al-15Fe alloy, with conventional and in situ optical microscopy and electrical resistance measurements. The present experimental results are comprehensively discussed in comparison with previous reports in order to clarify the complex characteristics of the Ni₅Al₃ phase and its formation mechanism.     

Al/Mo-C中间层对锆合金表面Zr2Al3C4涂层界面性能影响

锆合金表面涂层研究作为提高核燃料包壳事故容错能力的重要技术手段之一, 能够有效解决失水事故下锆水反应的问题。Zr₂Al₃C₄以其优异的抗氧化性能和适用于核环境的化学组分而成为锆合金包壳的候选涂层材料之一。由于Zr₂Al₃C₄涂层与锆合金基底之间的元素扩散以及热膨胀系数不匹配等问题, 在其上制备Zr₂Al₃C₄涂层的相关研究较少。本研究通过磁控溅射结合后续热处理工艺, 以Al/Mo-C作为扩散屏障层, 在锆合金基底上制备Zr₂Al₃C₄涂层。结合X射线衍射仪、扫描电子显微镜和透射电子显微镜等分析手段, 研究了Al/Mo-C中间层对涂层的相和微观结构的影响。结果表明, 在800 ℃退火3 h后, 未添加中间层的涂层开裂, 同时由于Zr-Al-C涂层与基底之间存在明显的元素扩散, 导致Zr₂Al₃C₄无法成相。Al/Mo-C中间层作为扩散屏障, 能够有效阻止退火过程中Zr-Al-C涂层和基底之间的元素扩散, 从而大大降低Zr-Al-C涂层与标准化学量比的偏差, 有利于最终涂层中Zr₂Al₃C₄相的形成。此外, 该扩散屏障层能够抑制Zr₂Al₃C₄涂层在退火过程中产生裂纹, 同时将退火态涂层与锆合金基底的结合力提高30 N。     

Investigation of thermal stability, phase formation, electrical, and microstructural properties of sputter-deposited titanium aluminide thin films

Titanium aluminide thin films are being considered as coating materials for high temperature applications due to their high melting points and high oxidation resistance. In this study, Ti₃₇Al₆₃ and Ti₅₃Al₄₇ thin films are deposited onto SiO₂ substrates by RF magnetron sputtering using compound targets and then annealed in vacuum to investigate the properties of the films. Rutherford backscattering spectrometry, X-ray diffractometry, transmission electron microscopy, and four-point probe measurements are used to analyze the characteristics of Ti₃₇Al₆₃ and Ti₅₃Al₄₇ thin films for high temperature electronics applications. The films show good thermal stability up to 700 °C for 1 h in vacuum. Reasonable resistivity is obtained when appropriate compositions and anneal conditions are used.     

Characterization, Processing, and Alloy Design of NiAl-Based Shape Memory Alloys

The microstructures and phase transformations in binary Ni-al, ternary Ni-Al-Fe, and quaternary Ni-Al-Fe-Mn shape memory alloys (SMAs) were investigated by light and electron microscopy, electron and X-ray diffraction, and differential scanning calorimetry. The effects of alloying additions (B, Fe, and Mn) on martensite stability, shape recovery, and tensile ductility were also studied. NiAl-based SMAs can be made ductile by alloying with B for enhanced grain boundary cohesion and Fe for improved bulk properties. Iron has the undesirable effect that it decreases the martensite → austenite transformation temperatures (A_p). Fortunately, A_p can be increased by decreasing the “equivalent” Al content of the alloy. In this way, a high A_p temperature of 190°C has been obtained without sacrificing ductility. Recoverable strains of 0.7% have been obtained in a Ni-Al-Fe alloy with A_p temperature of 140°C. Manganese additions (2–10%) lower A_p, degrade hot workability, and decrease room temperature ductility. Good-quality, ductile SMA ribbons have been produced by melt spinning. However, additional alloy design is required to suppress the aging-induced embrittlement caused by Ni₅Al₃ formation.     

Chemical stability, microstructure and mechanical behavior of LaPO4-containing ceramics

The use of LaPO₄ as a weak interface in composites for high temperature applications was investigated using tape-cast laminates and fiber model systems. Three laminates were fabricated with LaPO₄ as one component and Al₂O₃, Y₃Al₅O₁₂ or LaAl₁₁O₁₈ as the other. The chemical compatibility between the different components of the laminates, as well as the mechanical responses to flexural deformation and the propagation of indentation cracks, were examined. Two fiber model systems (Al₂O₃ fiber/LaPO₄ coating/Al₂O₃ matrix and Y₃Al₅O₁₂ fiber/LaPO₄ coating/Al₂O₃ matrix) were studied by fiber pushout tests to measure the interfacial shear strengths. The interfacial shear strengths were calculated by the linear and shear-lag approaches for different embedded fiber lengths. The results suggest that Y₃Al₅O₁₂ fiber-reinforced composites with LaPO₄ coatings have potential as high temperature materials in oxidizing environments.     

热处理对Ni-P-A12O3化学复合镀层摩擦磨损性能的影响

热处理可显著提高镀层的硬度和耐磨性能。采用化学镀的方法在45钢表面制备了Ni-P-纳米A12O3复合镀层,并以不同温度对其热处理,研究了镀层热处理前后的物相、硬度和耐磨性能。结果表明：400℃热处理后,Ni-P-A12O3复合镀层达到稳态,稳定相是Ni＋Ni3P＋NiO＋A12O3;镀层的显微硬度随热处理温度的升高而先...     

Black Nickel Coatings for Solar Collectors

Black nickel alloy coatings suitable for solar collectors were produced by electrodeposition from baths containing Ni and Zn sulfates and thiocynate. Variables having the greatest influence on optical properties of the black deposits are: pH-value, temperature, zinc and thiocyanate concentration. Of particular importance is the plating current which is related to the cathode potential that controls the composition, and alternatively, the optical properties of the deposited coatings.

The mechanism of blackening of the Ni coatings was attributed to the deposition of sulfide particles with Ni-Zn alloy. It was shown that, in absence of thiocyanate, co-deposited Zn causes a degree of blackening to Ni coatings due to the deposition of Ni₃Zn₂₂ as identified by x-ray phase analysis. Considerable blackening can be achieved by sulfur, which is deposited as Ni₃S₂. In a modified composition it was possible to replace sulfur by phosphorous supplied to the coating by the addition of sodium hypophosphite to the plating solution.

The coatings were of optimum optical properties as far as maximum absorptance and minimum emittance. Absorptance values as high as 0.93 could be obtained for selective coatings (2-3 microns thick) deposited under optimized conditions. Performance tests for coated solar water heater panels showed that the coatings are well qualified. The endurance of the coatings was evaluated in actual service conditions with regard to thermal degradation and corrosion resistance.     

锂离子电池正极材料LiNi0.8Co0.15Al0.05O2的制备与性能

采用共沉淀法制备粒径10 μm左右的前驱体Ni_0.8Co_0.15Al_0.05（CO₃）_x（OH）_y,然后采用该前驱体和LiOH·H₂O成功制备了锂离子电池正极材料LiNi_0.8Co_0.15Al_0.05O₂（LiNCA）,并详细研究了煅烧氛围、煅烧温度和煅烧方式等条件对LiNCA电化学性能的影响。研究表明,在O₂中煅烧获得的LiNCA放电容量达到170 mAh·g^-1,50次循环后容量保持率达到95%,性能明显优于空气氛围中煅烧得到的LiNCA。在O₂氛围下,700~750℃温度范围煅烧得到的LiNCA性能最好,煅烧温度过高或过低,LiNCA性能均明显下降。将前驱体在O₂氛围中450℃条件预煅烧,然后与LiOH·H₂O在700~750℃混合煅烧的煅烧方式,得到的LiNCA放电容量明显提高,可达190 mAh·g^-1。     

碳钢坩埚表面渗铝复合涂层

以碳钢板为基板材料, 通过表面渗铝和高温化学反应在其表面形成复合保护涂层。研究了反应层厚度与反应温度、时间之间的关系, 并用光学显微镜、XRD对涂层形貌、相组成进行了表征。实验结果表明: 反应产物层厚度随反应温度、时间的增加而增加; 复合涂层由过渡层和反应产物层组成, 过渡层组成为Fe₃Al及少量Fe₂Al₅、Fe₁₄Al₈₆、Al₂O₃, 反应产物层组成为TiB₂、MgO和少量的Mg₂TiO₄、Mg₂B₂O₅、Fe₃Al、FeAl、Ti₂B₅。      

Some nonlinear and linear elastic properties of Ni40Ti50Cu10 near the martensitic transformation

Linear and nonlinear elastic effects occuring in a single crystal of the ternary alloy Ni₄₀Ti₅₀Cu₁₀ were determined with a modified ultrasonic pulse echo-overlap technique at different temperatures. All linear elastic coefficients could be measured above and below the martensitic transformation supplementing the results of [A. Alippi (Ed.), Proceedings of the International Conference on Acoustics, Rome, 2001]. A large jump of the elastic stiffness c₄₄ could be detected. First nonlinear elastic measurements were performed. No substantial increase of anharmonicity could be found. The maximum stress amplitude was held far below the yield stress of the material.     

FABRICATION OF A Ni3Al/Al2O3UNIDIRECTIONAL COMPOSITE BY PRESSURE CASTING

A gas pressure liquid metal infiltration technique for producing fiber reinforced Ni₃Al/Al₂O₃ and Ni₃Al/Al₂O₃ composites has been described. Composite bars of 9.5 mm diameter, 150 mm long were produced. It was found necessary to add 0.5 at.%Ti to both Ni₃Al and NiAl alloys to obtain adequate wetting. There was a strong tendency for liquid metal infiltration along one side of the fibers causing a shift of the fibers to the opposite side. No interface reaction zone was observed at optical magnifications up to 1000X. A composite of Ni₃Al containing 33 volume percent of FP fibers fractured at 890 MPa which is approximately 3 times the yield strength of the matrix IC-50(21.73A1-0.34Zr-0.IB-Balance Ni at.%) + 0.5 at. %Ti.     

包埋渗铝法制备Fe-Al渗层及其扩散机制

包埋渗铝法可在钢基体表面制备出一层致密、坚固、连续的Fe-Al渗层，以改善基体性能。本文在不同温度和不同时间下对Q235低碳钢进行包埋渗铝，形成Fe-Al渗层，采用X射线衍射、扫描电镜及能谱分析等方法研究了渗铝层的物相结构、表面及截面形貌和成分，采用显微硬度仪测量了截面硬度。结果表明，不同渗铝温度下获得的渗铝层，主要含有Fe₂Al₅和FeAl₃两相，且750℃得到的渗层存在较多Fe₂Al₅相；随着渗铝温度升高，Fe-Al渗层厚度增加，Al原子扩散系数增大，但显微硬度降低；不同渗铝时间下制备的渗铝层，物相仍以Fe₂Al₅和FeAl₃为主，但随着渗铝时间延长，FeAl₃含量减少，且Al原子扩散系数变大，渗层显微硬度略有降低。在进一步分析Fe-Al渗层形成的热力学与动力学基础上，总结了渗铝层形成的扩散机制。     

三元陶瓷Pb(In1/2Nb1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3准同型相界附近组分的介电、铁电和压电性能

铅基复合钙钛矿铁电材料广泛应用于机电传感器、致动器和换能器。二元铁电固溶体Pb(Ni_1/3Nb_2/3)O₃- PbTiO₃(PNN-PT)由于其在准同型相界(MPB)区域具有优异的压电、介电性能而备受关注。然而较大的介电损耗和较低的居里温度限制了其在高温高功率器件方面的应用。本研究通过引入Pb(In_1/2Nb_1/2)O₃ (PIN)作为第三组元改善PNN-PT的电学性能, 提高其居里温度; 通过两步法合成了MPB区域的三元铁电陶瓷Pb(In_1/2Nb_1/2)O₃- Pb(Ni_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PNN-PT), 研究了其结构、介电、铁电和压电性能。制备的所有组分陶瓷具有纯的钙钛矿结构。随着PT含量的增加, 陶瓷结构从三方相转变为四方相。通过XRD分析得到了室温下PIN-PNN-PT体系的MPB相图。体系的居里温度由于PIN的加入得到了很大的提高, 更重要的是PIN的引入降低了PNN-PT体系的介电损耗和电导。MPB处的组分展现出了优异的电学性能, 室温下, 性能最优组分为0.30PIN-0.33PNN-0.37PT: d₃₃=417 pC/N, T_C=200 ℃, ε′= 3206, tanδ=0.033, P_r=33.5 μC/cm², E_C=14.1 kV/cm。引入PNN-PT的PIN第三组元使得体系的居里温度和压电性得到提高的同时降低了的介电损耗和电导率, 因此, PIN-PNN-PT三元铁电陶瓷在高温高功率换能器等方面具备一定的应用潜力。     

Microstructural studies of NiAl-based model alloys and commercial coatings after isothermal oxidation

Abstract

Four commercial aluminide diffusion coatings (one Pt-free) and four polycrystalline NiAl model materials, isothermally oxidised in laboratory air at 1050°C for 1 hour, have been investigated. The coatings were deposited on a single crystal Ni-based superalloy, CMSX-4. Two of the model materials are binary alloys containing different Al amounts. The two other have the same Ni/Al ratio as the binary alloys but were alloyed with 4 at% Pt. In order to control the surface roughness, all materials were polished prior to oxidation. Microstructural studies have been conducted using X-ray diffraction and scanning electron microscopy. To get a deeper insight on the platinum influence on the oxide structure, two commercial coatings (one Pt free and the other modified with Pt) were also investigated using transmission electron microscopy. The results obtained are discussed according to the influence of Al and Pt contents in the materials.     

直接热分解法制备单相Pd-Fe合金催化剂及电催化氧还原活性

以醋酸钯和醋酸亚铁为前驱体, 采用直接热分解法制备了碳载Pd₃-Fe₁(Pd₃-Fe₁/C)催化剂。用X射线衍射(XRD)、透射电镜(TEM)和X射线光电子能谱(XPS)等技术对催化剂进行了表征, 用循环伏安法和线性扫描伏安法研究了催化剂对氧的电催化还原性能。结果表明, 制备的Pd₃-Fe₁/C复合催化剂具有单相均一的合金结构, Fe进入Pd晶格改变了Pd电子结构和结构常数。电化学数据表明, Pd₃-Fe₁/C对氧还原比Pd/C催化剂有更高的电催化性能。