Effects of heating history on sintering properties of nickel powder compacts

Abstract

The effects of heating history on the sinterability of nickel powder compacts as a model material are examined from a view point of driving force and flow resistance, that is, the sintering stress and viscosity. Sinter-compression tests were conducted at different constant temperatures for cylindrical specimens, which underwent one-step or two-step heating. In the two-step heating, the specimens were heated up to a higher temperature and cooled down to the test temperatures. After the tests, the microstructure of each specimen was examined and compared with the change in sintering stress and viscosity. For the whole range of test temperatures, viscosity was increased by the two-step heating, which can be explained by the effects of time-hardening. On the other hand, for the lower range of test temperatures, the sintering stress was decreased by the two-step heating. This may be a result of the formation of large pores due to inhomogeneous shrinkage in the unstable state of the powder with small contact in the initial stage of sintering.