Effect of cryodeformation by high-pressure torsion on the fracture surface of Au-Co alloys

Abstract

Au-Co alloys with limited solubility were synthesized by the high-pressure torsion in boiling nitrogen at various anvil revolutions. Au and Co were initially in the state of a powder mixture in an equiatomic ratio. The obtained alloys were subjected to SEM fractography and XRD analysis in transmission X-ray synchrotron radiation, depending on the amount of strain. It is shown that the morphology of the fracture surfaces of the synthesized alloy depends significantly on strain. It is revealed that the mutual mixing of the components increases with strain. The images of the fracture surfaces of the Au-Co alloys testify that, as the strain and the number of anvil revolutions increase, a transition from ductile fracture, with inclusions of brittle intergranular fracture, to uniformly ductile fracture is observed over the entire thickness of the sample. A further increase in the strain and the number of anvil revolutions corresponds to the transition from the ductile type of the fracture surface to the brittle one. In addition, the fractography of the Au-Co alloys has revealed that the relief of the fracture surface becomes more homogeneous and that the size of the structural elements of the fracture surface decreases with increasing strain.