Metals In Ultrahigh Vacuum Research Articles

The cohesion of previously fractured Fcc metals in ultrahigh vacuum

The cohesion of clean surfaces of the fcc metals Ag, Al, Cu, and Ni was investigated using the technique of cold welding specimens previously fractured in an ultrahigh vacuum. The cohesive strength of the weld increased with compressive load, all data falling on a single curve with slight positive curvature when the cohesive strength and compression load were normalized through the initial fracture strength of each metal. The cohesion coefficients ranged from 0.62 to 1.15 and were in accord with those obtained using more elaborate techniques of surface preparation and testing. It is proposed that the essentially constant cohesion coefficient obtained for all the unalloyed fcc metals resides in the fact that the area of contact produced by a given compressive load is inversely proportional to the fracture stress of the metal and the cohesive strength is directly proportional to this fracture stress. A lowered cohesion coefficient was observed for copper specimens which had recrystallized in the vicinity of the interface either during the cold welding or as the result of a subsequent heat treatment.

Ultrahigh Vacuum Twist Compression Apparatus

A new apparatus is described which is used for bonding of metals in ultrahigh vacuum by the twist compression technique. It is shown that adhesion between hard metal specimens can be readily measured in ultrahigh vacuum after some initial mechanical abrasion of the surfaces, while adhesion tests in air at atmospheric pressure do not yield measurable adhesion coefficients. Experimental results are reported on the coefficients of adhesion and friction obtained for an atomically ordered platinum-cobalt alloy.

Cold welding tendencies and frictional studies of clean metals in ultra-high vacuum : C. E. Moeller and M. C. Noland, ASLE Trans., 10 (1967) 146–157

Cold welding tendencies and frictional studies of clean metals in ultra-high vacuum : C. E. Moeller and M. C. Noland, ASLE Trans., 10 (1967) 146–157

Investigation of the adhesion of metals in ultrahigh vacuum: M J Hordon and J R Roehring,Rep NASA-CR-66279, Dec 1966 ( National Research Corp, Cambridge, Massachusetts).

Investigation of the adhesion of metals in ultrahigh vacuum: M J Hordon and J R Roehring,Rep NASA-CR-66279, Dec 1966 ( National Research Corp, Cambridge, Massachusetts).

1426. Warm-welding of metals in ultrahigh vacuum: T H Batzer and R F Bunshah, J Vac Sci Technol, 4 (1), Jan–Feb 1967, 19–28

1426. Warm-welding of metals in ultrahigh vacuum: T H Batzer and R F Bunshah, J Vac Sci Technol, 4 (1), Jan–Feb 1967, 19–28

Warm-Welding of Metals in Ultrahigh Vacuum

Before metal surfaces can be welded, it is necessary to remove the contamination (oxide) layer on the surface and avoid recontamination of the clean surface by its environment prior to the welding operation. Mechanical abrasion is one way of removing the surface oxide layer used in such processes as friction-welding, roll-bonding, and diffusion-bonding. It would be desirable to have a technique for welding at low temperatures (0.1 to 0.4 Tm), with non-distorting, zero-shear type of leading. This paper describes such a process. In a uhv environment (to delay recontamination to very long times), two halves of a tensile specimen are cleaned by argon-ion bombardment, compressed at about 0.8–0.9 yield strength at 0.1 to 0.4 Tm, and held at temperature for finite times. The welded specimen is then tensile-tested in the uhv system to evaluate the process. The variables studied are temperature, time, loading, and the need for ion cleaning on various metals. Successful welds were produced in OFHC copper, Ti, and Be.

Cold Welding Tendencies and Frictional Studies of Clean Metals in Ultra-High Vacuum

The degree of cold welding in ultra-high vacuum (10−9 torr) was determined for 45 metal combinations. Static coefficients of friction were measured after stationary contact under 9.2-lb load for 300 hours at 200 C. Kinetic coefficients were measured at a velocity of 0.4 inch/second immediately after breakaway. Nearly all of the metal combinations tested exhibited maximum kinetic coefficients higher than the corresponding static coefficients. Metal transfer was from rider to ring when the rider was softer but followed no pattern when the ring was softer. Very little correlation was found between the friction characteristics of the metals and their physical properties.

Growth of Face-Centered-Cubic Metals on Sodium Chloride Substrates

Films of gold, silver, copper, nickel, palladium, and platinum were prepared by evaporation of the metals in ultrahigh vacuum onto hot, vacuum cleaved, sodium chloride substrates. Nickel, palladium, and platinum films that completely covered the surface were single crystals in the orientation of the substrate. Complete gold, silver, and copper films were polycrystals in which there was a tendency for the (111) metal plane to be parallel to the (001) salt surface. Later, it was found that single crystal foils of gold, silver, and copper were obtained if the salt substrate was exposed to air prior to the deposition of metal upon it. Careful comparison of the growth of gold on clean and on air-contaminated salt surfaces has shown that the effect of air is not to improve the alignment of the initial gold nuclei, but is to increase the number of nuclei generated per unit area. This increase causes nuclei to coalesce earlier in film growth. The stage in film growth at which coalescence occurs influences the orientation changes that accompany coalescence, and thereby influences the orientation of the complete film.