Grain morphology, texture, and microhardness gradients in aluminum diffusion-bonded to aluminum oxide

Abstract

The evolution of grain morphology, crystallographic texture, and microhardness in Al bonded to Al 2O 3 is dealt with. Specimens of a bilayer Al–Al 2O 3 and symmetric trilayer Al 2O 3–Al–Al 2O 3 were produced by solid-state diffusion bonding. Metallographic examination revealed the size and shape of grains in the Al layer, and the X-ray diffraction technique was used to measure the crystallographic texture at various through-thickness and in-plane locations. The results showed the existence of gradients in grain size, grain shape, texture, and microhardness through the thickness of the Al. Away from the interface, the aluminum grains were equiaxed, with a sharp cube recrystallization texture. Near the interface elongated and slanted grains, with a rotated cube texture, were observed. The microhardness was seen to correlate with the distribution of grain size. Finite element analyses employing crystal plasticity models were carried out to simulate the polygranular flow of Al during diffusion bonding. The interface constraint imposed by the Al 2O 3 layer was found responsible for the evolution of the observed gradients in microstructure in the Al layer. The predicted grain morphology trend was also in agreement with experimental observations.