Precipitation of an ordered intermetallic phase in WC-10% Ni

The cause of the variability of the intensity of magnetization of the nickel binder phase in cemented carbides was sought by electron diffraction and dark-field microscopy studies of fractured specimens, one of which was partially magnetic and the other almost non-magnetic. A coherent phase in the nickel binder having either a b c c or a CsCI-type structure was found on the boundaries of crack paths. A coherent non-randomly arranged CsCI-type phase was found in an epitaxial relationship with (12.0) planes of WC. The lattice parametera=0.295 nm for both coherent phases. This phase or phases occurs more frequently in non-magnetic than in magnetic nickel binders of hardmetals. When seen near WC grains the ordered phase is often accompanied by randomly arranged tungsten trioxide particles. The implication is that the ordered phase occurs more readily in carbon-deficient surroundings. The phase is postulated to be NiW because large quantities of tungsten are known to form solid solutions with nickel.     

Microstructure development during dissimilar welding: Case of laser welding of Ti with Ni involving intermetallic phase formation

Development of solidification microstructure in a laser welded Ti/Ni dissimilar binary couple is presented. At the fusion interfaces in both Ti and Ni, growth of the base metal grains into the weld pool is inhibited by the presence of composition gradients in the melt. Ti₂Ni dendrites grow toward the base metal at the Ti fusion interface. In the Ni side, appearance of a nickel solid solution phase is followed by layers of Ni₃Ti, Ni₃Ti+NiTi eutectic, and NiTi. NiTi dendrites and Ti₂Ni constitute the microstructure in the middle of the weld. Isolated titanium dendrites are observed throughout the weld, but their preferential occurrence toward the top surface of the weld is more prominent. Results are rationalised on the basis of interplay of the transport processes in the weld with the thermodynamics of the Ti-Ni system.     

采用机械合金化方法制备Ti3Ni2合金的结构及电化学储氢性能

采用机械合金化方法用Ni粉和Ti粉得到了Ti3Ni2非晶合金。晶态Ti3Ni2合金初始容量比非晶合金要高。晶态合金初始容量可以达到240mAh／g。而非晶合金容量为173mAh／g。随着循环次数的增加，晶态合金放电容量呈线性下降趋势。而对于非晶电极材料来说，随着循环的进行，初始容量下降，但是达到一定循环次数以后，电极的放电容量达到基本稳定。     

Combustion Synthesis of Ti—2B—Cu／Ni and 3Ti—2BN—Cu／Ni Bilayered Cermets

The effects of Cu and Ni (x=0, 10, 20 and 40 wt pct) and compaction pressures (12, 24, 84 and 108 MPa)on combustion wave velocity and wave front shape for Ti-2B-Cu/Ni and 3Ti-2BN-Cu/Ni bilayered cermets were investigated by a video camera. Since the boiling point of Cu is lower, the wave velocities of specimens are slower.Due to the higher specific heat of Ni than that of Cu, the wave velocities of specimens was slowed down a lot with increasing the Ni diluent. The wave velocity differences of the specimens containing Ni are more than that of the bilayered specimens containing Cu. Wave velocities of the specimens containing Ni increased more than that of the specimens containing Cu when higher pressure was employed for green mixture. The more the wave velocity difference of the bilayer, the more curved the specimen.     

Joining Ti-47Al-2Cr-2Nb with a Ti/(Cu,Ni)/Ti clad-laminated braze alloy

The joining of Ti-47Al-2Cr-2Nb using Ti-15Cu-15Ni (wt%) as braze alloy was investigated. Experiments were conducted at 980 and 1000°C for 10 min. The microstructure and the chemical composition of the interfaces were studied by scanning electron microscopy (SEM) and by energy dispersive X-ray spectroscopy (EDS), respectively. For both processing conditions the reaction between the -TiAl alloy and the braze alloy produced layered interfaces, which are essentially composed of ₂-Ti₃Al and of Ti-Ni-Cu-Al and Ti-Ni-Cu intermetallic compounds. Microhardness tests showed that all reaction layers are harder than either the or the (₂ + ) lamellar grains of the intermetallic alloy.     

Al2O3 reinforced Al/Ni intermetallic matrix composite by reactive sintering

An aluminium-nickel reinforced Al₂O₃ particulate composite was fabricated by a powder metallurgy route, where 35wt% aluminium and 30wt% nickel powders were mixed with 35wt% Al₂O₃ particles and compacted at 548 MPa. Sintering was carried out at 850 °C, where the synthesis reaction was sustained by the transient liquid phase resulting from the exothermic reaction associated with the formation of intermetallic compounds, i.e. reactive sintering. The resultant microstructure was studied using X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). It was found that the initial distribution of individual constituent powders affect the outcome of the reactive sintering and that the inward diffusion of aluminium in nickel was responsible for nickel aluminide formation.     

Aluminization of nickel-formation of intermetallic phases and Ni2Al3 coatings

The occurrence and growth mechanisms of the various intermetallic phases of the Al-Ni system formed during pack aluminization of unalloyed nickel have been investigated with respect to the aluminium activity in the pack. Several types of coatings were obtained: (1) a Ni₂Al₃ coating formed by inward aluminium diffusion in a high activity cement of pure aluminium; (2) a Ni-rich NiAl coating formed by outward nickel diffusion in a low activity pack constituted by an Al-Ni alloy; (3) a mixed type of coating exhibiting the phases Ni₂Al₃, Al-rich NiAl, Ni-rich NiAl and Ni₃Al in four superposed layers, formed in a pack containing an Al-Cr alloy; (4) a high temperature, high activity type of coating formed above 950° C with an outer layer exhibiting a hypereutectic structure of NiAl₃ grains in a eutectic matrix due to precipitation from the liquid state. The optimum cementation conditions, for the production of maximum thickness and quality Ni₂Al₃ coatings were determined. The influence of surface reactivity and pack activity on the coating quality parameters was investigated.     

High-temperature deformation characteristics of Ti-15at.% Al alloy

The deformation characteristics of Ti-15 at.% Al alloy have been investigated by compression tests in the temperature range 873 to 1273 K (0.44 to 0.64T _m) and by extensive transmission electron microscopy. Two types of deformation patterns were identified depending on the temperature: at lower temperatures below about 1073 K, the yield stress of the sample showed inverse temperature dependence, and serrations were found on the flow curves, whereas the normal dependences of the yield stress on temperature and strain rate were found at higher temperatures above about 1073 K. Corresponding dislocation substructures were composed of coarse bands of localized slip at 1023 K, and of rather uniformly distributed dislocations at 1123 K, and sub-boundaries as well as free dislocations at 1273 K. The main operating mechanisms in these temperature regimes were assumed to be the co-operative movement of numerous dislocations under the condition of the dynamic strain ageing, viscous glide of dislocations and dynamic recovery, respectively.     

Disordering of the Ni3Si intermetallic compound by mechanical milling

The ordered f c c intermetallic compound Ni₃Si was mechanically milled in a high-energy ball mill. The severe plastic deformation produced by milling induced transformations with increasing milling time as follows: ordered f c c disordered f c c nanocrystalline f c c. The structural and microstructural evolution with milling time was followed by X-ray diffraction, TEM, hardness tests, and differential scanning calorimetry (DSC). Complete disordering occurred at milling times of 2 h and kept the saturated H of the DSC peak in the range of estimated enthalpy even after 60 h milling. The structural development during milling of the f c c solid solution for Ni₃Si was presumably dominated by the formation and refinement of a dislocation cell structure into microcrystallites which eventually reached nanometre dimensions.     

原位自生Ti3 Al金属间化合物基复合材料的微观结构

采用原位自生（XD）法制备Ti3Al金属间化合物基复合材料,对复合材料的XRD,OM和SEM的分析结果表明,Ti-17Al-0.5C复合材料的基体为Ti3Al,增强相为Ti3AlC,且增强相在基体中按一定的方位排列,Ti-17Al-1.5(2.0)C复合材料的基体为Ti3Al,增强相由心部TiC矣包覆层Ti3AlC双层组成,随着含C量的增加,增强相由不发达的树脂晶变为等轴晶,对合金进行微力学探针测试表明,增强相TiC和Ti3AlC的显微硬度和弹性模量均大于基体Ti3Al,随着C含量的增加,合金中增强相和基体的显微硬度和弹性模量无明显变化。     

Superconductivity of heat-treated Nb-65 at.% Ti alloy

Brief reviews are given of the effect of heat-treatment on the microstructure of cold-worked bcc metals and the superconducting properties of niobium alloys. Particular attention is paid to the influence of interstitial impurities in these processes. The annealing effects in microstructure and superconducting properties of a cold-worked Nb-65 at.% Ti alloy, containing oxygen as a major impurity, have been studied. The precipitation process takes the form TiNb + O₂ various Ti oxides Ti + TiO. Differences in precipitation sequence are described for vacuum-annealing and annealing in impure argon. Flux-pinning is related to the microstructural observations. At least three pinning mechanisms appear to operate; dislocation pinning and two types of precipitate pinning. These observations are in accord with previously proposed pinning models.     

On the phase diagram of the Ga-Te system in the composition range 55 at % Te

Monoclinic Ga-Te was heated in the electron microscope. At about 800° C decomposition was observed and after cooling down to room temperature, two compounds were identified: the fcc Ga₂Te₃ and the Ga₃Te₄, for which a trigonal structure was identified. A relation between the three structures of Ga-Te, Ga₃Te₄ and Ga₂Te₃ is put forward.