Diffusion and sintering activation in an alloy made of iron microparticle and nickel nanoparticle powders

Chemical-metallurgical method is used to fabricate a nickel nanopowder (“nanonickel”) and a powder made of iron microparticles clad by nanonickel. The diffusion coefficients in this iron-nickel system are 2–3 times lower and the activation energy of sintering is 2 times lower as compared to a nickel micropowder. The diffusion activation and shrinkage temperatures in this system differ by 200°C. Special features of the structure formation in the sintered powder materials are studied.     

Characterisation of nickel alloy powders processed by spark plasma sintering

Abstract

In this study, nickel alloy powders were consolidated by spark plasma sintering. Experiments were performed between 700 and 750°C temperature range under 50 MPa pressure with holding times from 5 to 10 min. In addition to these main spark plasma sintering parameters three different heating rates ranging from 100 to 235°C min^?1 and two different particle size ranges (75–106 μm narrow size distribution and ?45 μm wide size distribution) were used for the experiments. After sintering, the sliding wear behaviour of the samples was investigated. The results revealed that the density of the material increased with raising the sintering temperature and holding time. However, heating rate and particle size also played an important role in the densification and these parameters were investigated in detail.     

Device for electric-pulse sintering of powders under pressure

The construction and energy parameters of an experimental device for electric-pulse sintering of powder under pressure are described. The properties of material prepared from Nibon-20 powder by electric-pulse sintering technology are given. Translated from Poroshkovaya Metallurgiya. Nos. 1–2(411), pp. 125–128. January–February, 2000.     

超细球形镍粉的制备

在不使用分散剂和表面活性剂的条件下,以水溶液为反应体系,水合肼为还原剂,采用液相还原法制备超细镍粉.通过扫描电子显微镜、X射线衍射仪、激光粒度分析仪、能谱分析仪等测试仪器对粉体进行表征,研究了反应温度和[N2H4]/[Ni2+]浓度比对镍粉平均粒径、形貌、分散性、还原率以及纯度的影响,探讨了镍粉从刺球形向球形转变过程中...     

The sintering of compacts from powders with particles in different conditions

Conclusions When data on shrinkage in the sintering of powders and x-ray diffraction data are compared with results of optical measurements [12], a correlation is found to exist between the characteristics of surface and volume defectiveness of powders and their shrinkage.In the shrinkage of calcium-hydride grade titanium powder, the surface condition of its particles plays a decisive role.Translated from Poroshkovaya Metallurgiya, No. 11(83), pp. 26–30, November, 1969.     

Dynamics of interparticle reactions in spherical metal powders during electric sintering

Conclusions The dynamic characteristics of the process of interparticle neck formation depend not only on current density (raising the current density by 1.7 times increases interaction rates by an order) but also on the positions of the particles relative to the direction of passage of current (particles lying in a plane parallel to the direction of passage of current interact 3.4–5 times more rapidly than particles lying in a plane perpendicular to this direction). The kinetics of powder particle sintering by an electric current is due to the most intense sintering mechanisms, such as viscous flow, transport through the gaseous phase, and spreading of liquid metal over the solid surfaces of particles. The strongest influence on the kinetics of mutual particle sintering is exerted by a transport mechanism with n< 0.5. Such a mechanism may be provided by electroerosion transport in the interparticle gap.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 25–29, September, 1987.     

Study of the sintering of nickel powders produced by different methods

Conclusions It was established in this investigation that, in the temperature range 500–700°C, carbonyl nickel powder is subject to more intensive sintering than electrolytic nickel powder. The theory of diffusional viscous flow is unsuitable for this case, and needs revision.It is shown that crystal lattice distortions, as determined by x-ray diffraction methods, do not cause an increase in the rate of sintering. Hypotheses are put forward for the possible mechanism by which diffusional mobility is increased in the case of carbonyl nickel.     

An analysis of the capillary forces in liquid-phase sintering of spherical particles

The interparticle force due to capillary action of a liquid contact between two solid spheres is shown rigorously to have two contributions, one the surface tension force itself and the other due to the pressure difference caused by surface curvature. Numerical means are used to solve for the shape of the liquid surface and to evaluate this interparticle force as a function of contact angle, volume of liquid, size of sphere, and surface tension. The rigorous solution is then compared to the often-used circle approximation. We also evaluate the effect of neglecting one of the terms in the force equation, as is sometimes done in the literature. The general force relations are then used to draw several practical conclusions concerning liquid-phase sintering of spherical powders.