Deformation Behaviour of Cu-Cr in-situ Composite

With the increasing requirements for higher strength materials with high electrical conductivity, a lot of interest has been paid to develop Cu-based composites in the last 25 years. These composites have superior tensile strength, combined with good electrical conductivity, to that exhibited by pure Cu and conventional Cu alloys. To date, much of the research carried out on this composite has focused on the mechanical and electrical properties of the as processed material. However, there is a basic lack of understanding of the way in which the properties may change or degrade during service. Without this knowledge, these composites cannot be fully and safely exploited. Thus the objective of this study was to investigate the thermo-mechanical behaviour of a Cu-Cr composite, and the nature and extent of any damage mechanisms occurring within the composite over a wide range of experimental conditions. Neutron diffraction was used to investigate the deformation behaviour of the individual phases in the composite and their interaction through elastic and plastic loading at room temperature. For the composite, a fairly good agreement was observed in the phase strains predicted by the Eshelby theory and measured by neutron diffraction. In-situ tensile tests in the SEM were also performed to study the damage mechanism of the composite. Tensile and creep tests were carried out in air and in vacuum over a wide range of temperatures. To provide data for comparison with the composite material, pure Cu specimens were tested whenever possible. Creep resistance increases significantly with the introduction of Cr fibres into Cu. The higher creep rate of the composite in air than in vacuum is due to the gradual decrease of the cross-sectional area of the matrix due to increasing thickness of the oxide layer. Damage characteristics and distributions were found to be similar during tensile and creep testing.