A Basic Study of Cold Welding in Ultrahigh Vacuum

Abstract

The cohesion of the FCC metals Ag, Al, Cu, and Ni under ultrahigh -11 -9vacuum in the range of 10 to 10 torr was investigated using the technique of cold welding specimens previously fractured in the vacuum.The cohesion strength of the weld increased with compression load for all metals; all data fell on one curve of slight positive curvature when the cohesion load (stress) and the compression load (stress) were divided by the initial fracture load (stress) of the virgin specimen.The effect of compression load on the cohesion coefficient a for all metals could be described bywhere LC is the compression load and L is the initial fracture load. Ultra-F 0 sonic measurements on Cu indicated that the contact area was proportional to the ratio L F / Optical microscopy observations on the weld interface were 0 in accord with this; they also indicated the excellent matching of the two fractured surfaces possible with the present apparatus.The cohesion results are explained on the basis that the rupture of the weld occurs at a constant value of the "true" fracture stress.Limited studies were conducted with Cu to determine the effects of: (1) a subsequent heat treatment on the weld strength, (2) alloying with 30% Zn and (3) exposure of the freshly fractured surfaces to the gases N 2 , 02, CO, CO and air.The heat treatments reduced the strength of the weld; the 70-30 2 brass alloy exhibited a lower cohesion coefficient than unalloyed Cu; prolonged exposure to the gases 02, CO, CO and air caused an appreciable reduction in P 2 the cohesion coefficient, whereas no effectwas observed for N 2 . The adverse effects noted for the first two variables are not clearly understood at this time.The results for the exposure to the gases are in good agreement with predictions based on absorption theory and LEED observations reported in the I literature.

Cold Welding in Hold Down Points of Space Mechanisms Due to Fretting When Omitting Grease

“…It showed among other things that the level of adhesion in vacuum is strongly dependent on "size". Experiments ranged from microscopic level (contact loads of a few mN, [8,9]), to medium scale (loads in range of N, [7]) up to very high loads (linked to the use of rotation welding machines, thereby exceeding elastic regimes in the specimen [10]). It had to be concluded that the level of adhesion cannot be reliably transferred between "levels of dimension".…”