EFFECTS OF HEAT TREATMENT ON TENSILE PROPERTIES AND SHAPE MEMORY EFFECTS OF Ni-Ti-Nb ALLOY

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Recovery Stress in a Ni-Ti-Nb Shape Memory Alloy with Wide Transformation Hysteresis

The effect of deformation on recovery stress of Ni144.7Ti46.3Nb9 alloy has been studjed using tensile test at various temperatures and TEM observation. It ls shown that the recovery stress increases with jncreasing total strain ET and reaches a maximum value (max) as ET= 9% but the maximum recov erV strain of the alloy is only about 4.6%. This is different from that of Ti-Ni binary alloy in which is obtained usually at maximum recovery strain and the reason of the difference is dis Cussed. Deformation temperature Td has a little effect on recovery stress when Td is less than Ms However, recovery stress decreases sharply when Td is higher than M, and lowers approximately down to zero near Msσ

Wettability of CuNi-Ti Alloys on Si_3N_4 and Interfacial Reaction Products

Based on the alloy Cu55Ni45 (at pct), holding the proportion of Cu to Ni in constant and in the temperature range of 1233~1573 K, the wetting angles of CuNi-0~56 at pct Ti alloys on Si3N4 have been measured by the sessile drop method. With the increase of Ti content, the wetting angles decreased. The equilibrium wetting angle was 5° when Ti content ≥32 at pct.In the case of same Ti content, the activity of Ti in CuNiTi alloy was weaker than that in CuTi alloy The cross-section of the CuNiTi-Si3N4 interface and the elements distribution were examined by scanning electron microscope with X-ray wave-dispersion spectrometer, and the reaction products formed at the interface were determined by X-ray diffiaction analysis method.

FORMATION OF AMORPHOUS Ni-Ti ALLOY BY MECHANICAL ALLOYING

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REVERSIBLE TRANSFORMATION BETWEEN MATRIX AND MARTENSITE IN Ni-Ti SHAPE MEMORY ALLOYS

The reversible transformation between matrix and martensite in Ni-Ti shape memory alloys has been dynamically observed under TEM.The orientation relation between martensite and austenite as well as the structural change near the transition temperature has been also studied with the help of HREM SADP.The results show that the orientation relation between martensite and austenite is[11]_A//[10]_M,[110]_A//[001]_M,(110)_A//(001)_M and the angle between(110)_A and(010)_M is about 6.5°.The crystal defects of martensite are found to be twin and stacking fault,and the twin plane as(100).

Thermodynamics of martensite transformation hysteresis in Ni-Ti shape memory alloys

A thermodynamic calculation method on the temperature hysteresis of thermoelastic martensite transformation in Ni Ti shape memory alloys was developed. The thermodynamic analysis indicates that the irreversible consumed energy and the elastic energy are the important factors influencing transformation hysteresis. It is revealed that the wide inherent transformation hysteresis can be attributed to the higher irreversible consumed energy of martensite transformation in Ni Ti Nb based alloys than those of Ni Ti binary alloys.

Crystalline structure and morphology of X phase in Cu Al-Ni-Mn-Ti alloy

The composition, morphology, crystalline structure and formation and evolution of X phase in a Cu 12.3Al 2Ni 2Mn 1Ti alloy were studied. The results show that the X phase is a Ti rich phase with atomic ratio of (Cu+Ni)∶ Ti∶Al=2∶1∶1 and DO 3 or L2 1 structure; it is directly formed in the liquid phase by crystallization in the process of solidification of the alloy; there forms free particle X phase through the progressive dissolution and breakdown of the inter dendritic microstructure in the following homogenization process. The X phase has three different morphologies, i.e. X L, X LS and X S, whose contents in the matrix rely on the heat treatment conditions. [

Relationship between phase composition and corrosion resistance of Ni-Ti-Nb based shape memory alloys

The stability and microstructure of Ni Ti Nb based shape memory alloys were investigated after alloyed with elements Zr, Cr and V. In artificial seawater (3.5%NaCl) and physiological solution (5%NaCl+0.1%H 2O 2), the results show that the alloying elements influence the corrosion behavior of Ni Ti Nb alloys. Generally, Zr improves the corrosion resistance of Ni Ti Nb alloy, Cr reduces its corrosion resistance and V does not change the property. In order to investigate the reason of the difference,the relation of the phase components and corrosion resistance of Ni Ti Nb based shape memory alloys were studied by element analysis and SEM.

时效处理对Ni-Ti-La合金微结构、相变及力学性能的影响

时效处理是调节合金微结构,影响合金性能的有效方法。用实验的方法分析了Ni-Ti-La合金的微结构,研究了合金的相变行为,测定了合金的维氏硬度。实验结果表明,用La元素替代Ni元素形成的Ti_(50)Ni_(49.5)La_(0.5)合金,经时效处理后合金由NiTi基体、NiLa沉淀相和Ti_(2)Ni沉淀相组成,并且沉淀相的数量随着时效温度升高而减少,合金在加热和冷却的过程中均为一步相变B2↔B19',合金相变开始温度随时效温度的升高而增大,合金的硬度随时效温度的升高而增大。用La元素替代Ti元素形成的Ti_(49.5)Ni_(50)La_(0.5)合金,经时效处理后合金由NiTi基体、NiLa沉淀相组成,并且沉淀相的数量随时效温度的升高而增加,合金在加热和冷却的过程中呈现一步相变B2↔B19',相变开始温度随时效温度的升高而增大,合金的维氏硬度随时效温度的升高而减小。时效处理对Ti_(50)Ni_(49.5)La_(0.5)合金和Ti_(49.5)Ni_(50)La_(0.5)合金的微结构产生了影响,进而影响了合金的相变行为和力学性能。

Experimental investigation of the normal spectral emissivity and other thermophysical properties of pulse-heated Ni-Ti and Au-Ni alloys into the liquid phase

In a previous paper it was shown that the normal spectral emissivity at 684.5 nm of a binary alloy can be lower than that of the pure constituent components. For the actual probes it was found that the observed values of normal spectral emissivity of the alloys are in between or higher than those of the pure constituent components. Experiments were conducted on the alloy systems Ni-Ti and Au-Ni. Their emissivity as well as electrical resistivity and enthalpy as a function of temperature is presented.

Research on Phases of W-Ni-Fe-TiB_2 Alloy

A new tungsten heavy alloy, W-Ni-Fe-TiB_2 was studied. This ally has higher hardness than tradition-al tungsten heavy alloy. Sintering time was 30 min for producing the alloy. In the new tungsten heavy alloy, four phases were found to be W, γ (Ni, Fe), TiB_2 and complex haride compound. TiB_2 and complexboride compound were precipitated in the matrix. So TiB_2 could strengthen the tungsten heavy alloy.

CHARACTERIZATION OF MECHANICALLY ALLOYED Ni-Al-Ti COMPOUNDS

Based on the previous work on the mechanical alloying of Ni-Al-Ti compounds. the mechanically alloyed Ni-Al-Ti compounds was characterized. The results show that with the increase of Ti content. the microhardness of the final products decrease apparently. The thermal behavior of the resultant Ni-Al-Ti compounds shows significant difference, the as-milled powders with different Ti content transform into different products after healing.So the microstructure of the milled alloys could be determined through adequate control of composition and heat treatments.

INVESTIGATION OF PHASE SEPARATION OF THE Fe-Ni-Co-Al-Cu-Ti PERMANENT MAGNET ALLOY

Microstructure formed in the Fe-Ni-Co-Al-Cu-Ti permanent magnetic alloy with different treatments was studied by means of TEM observation, XRD method and SAXS technology. The results indicated that spinodal decomposition and orderiing transformation coexisted in the alloy and spinodal decomposition was completed in a short time. The ratio of component of spinodal and ordered microstructure was dependent on the cooling rate. The variation of gyration radius RG of the rod-like precipitates could be accounted for by the different growth modes of the precipitates related to strain energy and interface energy.

AN FCC METASTABLE PHASE IN A RS Ni-Ti ALLOY

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Microstructure and high temperature tribological behavior of laser cladding Ni60A alloys coatings on 45 steel substrate

The crack-free Ni60 A coating was fabricated on 45 steel substrate by laser cladding and the microstructure including solidification characteristics, phases constitution and phase distribution was systematically investigated. The high temperature friction and wear behavior of the cladding coating and substrate sliding against GCr15 ball under different loads was systematically evaluated. It was found that the coating has homogenous and fine microstructure consisting of γ（Ni） solid solution, a considerable amount of network Ni-Ni3 B eutectics, m^23C6 with the floret-shape structure and Cr B with the dark spot-shape structure uniformly distributing in interdendritic eutectics. The microhardness of the coating is about 2.6 times as much as that of the substrate. The coating produces higher friction values than the substrate under the same load condition, but the friction process on the coating keeps relatively stable. Wear rates of the coating are about 1/6.2 of that of the substrate under the higher load（300 g）. Wear mechanism of the substrate includes adhesion wear, abrasive wear, severe plastic deformation and oxidation wear, while that of the coating is merely a combination of mild abrasive wear and moderate oxidation wear.

Synthesis of Y_2O_3 particle enhanced Ni/TiC composite on TC4 Ti alloy by laser cladding

A Y2O3 particle enhanced Ni/TiC composite coating was fabricated in-situ on a TC4 Ti alloy by laser surface cladding. The phase component, microstructure, composition distribution and properties of the composite layer were investigated. The composite layer has graded microstructures and compositions, due to the fast melting followed by rapid solidification and cooling during laser cladding. The TiC powders are completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The size of TiC dendrites decreases with increasing depth. Y2O3 fine particles distribute in the whole clad layer. The Y2O3 particle enhanced Ni/TiC composite layer has a quite uniform hardness along depth with a maximum value of HV1380, which is 4 times higher than the initial hardness. The wear resistance of the Ti alloy is significantly improved after laser cladding due to the high hardness of the composite coating.

Enhanced hydrogen storage kinetics of nanocrystalline and amorphous Mg_2N-type alloy by substituting Ni with Co

In order to improve the hydrogen storage kinetics of the Mg2Ni-type alloys, Ni in the alloy was partially substituted with element Co. The Mg2Ni-type Mg2Ni1-xCox （x=0, 0.1, 0.2, 0.3, 0.4） alloys were fabricated by melt-spinning technique. The structures of the as-spun alloys were characterized by XRD and TEM. The gaseous and electrochemical hydrogen storage kinetics of the alloys was measured. The results show that the substitution of Co for Ni notably enhances the glass forming ability of the Mg2Ni-type alloy. The amorphization degree of the alloys visibly increases with rising of Co content. Furthermore, the substitution of Co for Ni significantly improves the hydrogen storage kinetics of the alloys. With an increase in the amount of Co substitution from 0 to 0.4, the hydrogen absorption saturation ratio of the as-spun （15 m/s） alloy increases from 81.2% to 84.9%, the hydrogen desorption ratio from 17.60% to 64.79%, the hydrogen diffusion coefficient increases from 1.07×10-11 to 2.79×10-11 cm2/s and the limiting current density increases from 46.7 to 191.7 mA/g, respectively.

Preparation of ultra-fine fibrous Fe-Ni alloy powder by coordinated co-precipitation-direct reduction process

The precursor prepared by coordinated co-precipitation was direct reduced by hydrogen to ultra-fine fibrous Fe-Ni alloy powder. The effects of concentrations of reactants, pH value, reaction temperature and additive on the preparation of precursor were systematically investigated. The structures, thermal decomposition processes and morphologies of the precursors were characterized by X-ray diffraction (XRD), thermal gravity-differential thermal analysis (TG-DTA) and scanning electron microscoy (SEM). The results show that using 2% polyvinylpyrrolidone (PVP) (in mass fraction) as additive, a well-dispersed precursor with a uniform morphology can be obtained in a solution with Fe2+ and Ni2+ total concentration (1:1) of 0.8 mol/L, pH value of 6.2 at 60 °C, and a pure and well dispersed fibrous iron-nickel powder can be prepared by direct reduction of this precursor in a mixed atmosphere of nitrogen and hydrogen at the temperature of 420 °C.

Electrochemical hydrogen storage characteristics of nanocrystalline and amorphous Mg_2Ni-type alloys prepared by melt-spinning

The nanocrystalline and amorphous Mg2Ni-type alloys with nominal compositions of Mg2Ni1-xMnx （x=0, 0.1, 0.2, 0.3, 0.4） were synthesized by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are obtained. The structures of the as-spun alloy ribbons were characterized by XRD and HRTEM. The electrochemical hydrogen storage characteristics of the as-spun alloy ribbons were measured by an automatic galvanostatic system. The electrochemical impedance spectrums （EIS） were plotted by an electrochemical workstation. The hydrogen diffusion coefficients （D） in the alloys were calculated by virtue of potential-step measurement. The results show that all the as-spun （x=0） alloys hold a typical nanocrystalline structure, whereas the as-spun （x=0.4） alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg2Ni-type alloy. The substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving the discharge capacity and the electrochemical cycle stability. With an increase in the amount of Mn substitution from 0 to 0.4, the discharge capacity of the as-spun （20 m/s） alloy increases from 96.5 to 265.3 mA·h/g, and its capacity retaining rate （S20） at the 20th cycle increases from 31.3% to 70.2%. Furthermore, the high rate dischargeability （HRD）, electrochemical impedance spectrum and potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with raising the amount of Mn substitution.

First-principles study of stacking fault energies in Ni_3Al intermetallic alloys

The first-principles method based on the projector augmented wave method within the generalized gradient approximation was employed to calculate the superlattice intrinsic stacking fault（SISF） and complex stacking fault（CSF） energies of the binary Ni3Al alloys with different Al contents and the ternary Ni3Al intermetallic alloys with addition of alloying elements,such as Pd,Pt,Ti,Mo,Ta,W and Re.The results show that the energies of SISF and CSF increase significantly with increase of Al contents in Ni3Al.Addition of Pd and Pt occupying the Ni sublattices does not change the SISF and CSF energies of Ni3Al markedly in comparison with the Ni-23.75Al alloy.While addition of alloying elements,such as Ti,Mo,Ta,W and Re,occupying the Al sublattices dramatically increases the SISF and CSF energies of Ni3Al.The results suggest that the energies of SISF and CSF are dependent both on the Al contents and on the site occupancy of the ternary alloying element in Ni3Al intermetallic alloys.