Comparison of Cu Strengthened by Ionic Bonded Particles and Cu Strengthened by Metallic Bonded Particles.

Abstract

Cu matrix composites, because of their high mechanical strength, are often used as conductors in high-performance electrical applications. These composites are manufactured through thermomechanical processing, which introduces a high density of particles that act as obstacles to dislocation motion. Increasing the density of these particles enhances the mechanical strength of the conductors, which we tested under static loading. Under cyclic loading, especially pulsed electrical mechanical loading, conductors may soften, harden, or even fail. Failure is likely to occur whenever the applied stress exceeds the flow stress of the conductors. Understanding and predicting the performance of conductors under cyclic loading can help researchers estimate the lifespan of any apparatus made from these conductors. The performance of conductors depends on whether the strengthening particles are characterized by ionic interatomic bonding or metallic bonding. During fabrication, we observed both the accumulation of dislocations and the dissolution of particles (which added more solute atoms to the matrix). Because both dislocations and solute atoms tend to migrate at room temperature or higher, the complexity of microstructure changes increases in composites under cyclic loading. To minimize such complexity, we designed our test to determine fatigue properties at 77 K. We subjected the conductors to cyclic fatigue tests using a load-controlled mode (the mode most commonly used in applications). This work sheds light on the correlation between tensile properties and fatigue properties in our composite conductors. We found that the correlation varied, depending on whether the conductors had been strengthened by ionic bond or metallic bond particles.