Peculiarities of LiF single-crystal deformation in vaseline oil at elevated temperatures

Abstract

The influence of Vaseline oil on dislocation mobility and the microhardness under friction and indentation of lithium fluoride (LiF) single crystals was investigated. The experiments were carried out under a load of 0.1 N, at a temperature from 297 to 473 K, with an indentation time from 5 to 900 s and for a friction load of 0.45 N. The lengths of the screw and edge dislocation arms in air and Vaseline oil, as well as the width of the dislocation region (along the friction track), were estimated. It was established that at room temperature in oil, neither the dislocation arm lengths and dislocation region nor the microhardness changed in comparison with tests in air. The dual effect of Vaseline oil at elevated temperatures was revealed: the work-hardening in the impression region and the increase in screw dislocation mobility at the periphery of the dislocation rosette. Under friction, the essential increase in dislocation motion in {110} 45 sliding planes is observed. It was supposed that the increases in dislocation mobility and microhardness in Vaseline oil could be connected with the breaking of carbon-hydrogen bonds and hydrogen penetration and interaction with surface defects. It was suggested that the breaking of carbon-hydrogen bonds in mineral oil (as a basis of lubrication) may lead to a change in defect mobility in the surface layers of metals and alloys.