| Spheroidal nickel powder was treated with a fine dispersion of alumina by reaction with aqueous aluminum nitrate. Compacts of pure and dispersoid-treated powder were sintered in 5%{dollar}rm Hsb2/Nsb2{dollar} using both dilatometry and quenching to investigate densification and microstructural evolution. Isothermal and constant heating rate sintering were studied.; The sintering data were analyzed using the combined stage sintering model derived by Hansen, Rusin, Teng, and Johnson (1992). A method was outlined for predicting densification behavior based on a minimal number of trial experiments. The model was modified to include the effect of a dispersion of inert particles on sintering.; Densification was predominantly by grain boundary diffusion. The sintering activation energy of pure metal compacts was 174 kJ/mole, in excellent agreement with tracer values of grain boundary diffusivity.; Values of the microstructural geometry parameter of the sintering model, {dollar}Gammasb{lcub}rm b{rcub},{dollar} rose sharply between 80-85%, coincident with the onset of grain growth; this was attributed to a measured rise in the number of pores per grain, which decreased the diffusion distance. {dollar}Gammasb{lcub}rm b{rcub}{dollar} was much lower in magnitude and had a different dependence on density than predicted by the traditional intermediate stage sintering models. However, {dollar}Gammasb{lcub}rm b{rcub}{dollar} calculated from the present data coincided remarkably well with values calculated from data of other studies of nickel and alumina, suggesting that the grossly idealized geometry assumed by the traditional intermediate stage models accounts for these differences.; Computer simulations of sintering based on the combined stage model and using measured values of {dollar}Gammasb{lcub}rm b{rcub}{dollar} and grain size from isothermal sintering agreed well with constant heating rate sintering experiments.; Dispersed alumina particles at 100 ppm concentration inhibited the sintering of nickel powder at lower temperatures. The extent of inhibition increased with alumina concentration, but disappeared at high temperatures. The apparent activation energy for dispersoid-treated compacts at high temperatures agreed with those of the pure metal. The data were interpreted in terms of an interface reaction mechanism. |
