Sol-gel prepared Ni-alumina composite materials - Part II Structure and hot-pressing temperature

The microstructure of sol-gel prepared Ni-alumina ceramic-metal composites containing up to 50% Ni has been studied with X-ray diffraction, the scanning electron microscope and the transmission electron microscope. The influence of processing temperature upon the size distribution of Ni was established. It was found that increasing the total amount of Ni increases only the number of micrometre-size Ni inclusions in the alumina, whereas the hot-pressing temperature determines the size distribution of Ni. When temperatures much higher than the melting temperature of Ni are used, a large number of Ni inclusions of the order of 10 nm can be found mainly within alumina grains; only a few are formed in grain boundaries and in triple points. When a temperature close to the melting point is used, there are fewer nanometre-size Ni inclusions and a larger number of Ni inclusions of the order of ∼ 100 nm to 1 μm. In this case, the large (∼ 100 nm) and small (∼ 10 nm) Ni inclusions are found in grain boundaries and triple points.