Cohesion of Copper and Steel Repeatedly Fractured and Rejoined in Vacuum
The cohesion of copper and soft steel repeatedly ruptured and rejoined in vacuum at room temperature initially decreases with each successive fracture-rejoin cycle even when exposure is too low to permit formation of a monolayer of gas on the fractured surfaces and even when the joining stress is too low to cause measurable plastic strain.
At 500 C the cohesive stress for steel is nearly constant for at least four cycles with time in contact ranging from 1–6 minutes. For copper at 400 C cohesion was only 70% after 2 hr in contact on the first cycle due to excessive exposure but was time dependent and reached 75% in 12 hr.
Comparison of the results with published data on roll cladding indicates that less deformation is required for good bonding if surfaces are not exposed to air after fracturing or wire brushing.