The sintering of nickel/aluminium spheres to nickel plates

Abstract

Spheres of nickel, and of nickel containing 0.5,1.0, 2.0, and 10.0 wt % aluminium, all of approximately 100μm diameter, were sintered under vacuum to nickel plates for various times within the temperature range 1000 to 1300° C. Neck growth was determined as a function of time. Values for the exponent of time in the neck growth equation,x/a = At ⁿ of 0.19, 0.18, 0.15, and 0.16 were found for the above compositions, respectively. An activation energy of 33 kcal/mole was found for sintering nickel spheres to nickel plates. An activation energy of 69 kcal/mole was found for sintering Ni/1.0% Al spheres to nickel plates.

Assuming a surface-diffusion mechanism of material transport, as suggested by Nichols and Mullins, the difference in activation energies is explained on the basis of a difference in surface energy, as reflected in the ease with which vacancies are formed at the surface. Similar reasoning is employed to explain the difference in activation energies found between sintering nickel spheres to nickel plates under vacuum in this research, and sintering nickel wire compacts under a hydrogen atmosphere in work reported by Pranatis and Siegle.