Surface re-orientation caused on metals by abrasion—its nature, origin and relation to friction and wear

Abstract

No adequate study of the surface structure of abraded poly crystalline metals has been made hitherto. The present electron-diffraction investigation of unidirectionally abraded beryllium and magnesium elucidates for the first time the characteristic nature and the origin of the fibre texture caused by abrasion, particularly its relation to the friction coefficient and the wear. The effects of a wide variety of conditions of load, speed, temperature and abrasive-particle size are determined. The main fibre orientation developed is of [001] type, the axis being inclined by an angle δ away from the outward normal, towards the direction from which the abrasive particles came. For beryllium δ is about 21°, the fibre axis being then along the resultant of the normal load W and the tangential frictional force F , at tan-1 μ = tan -1 0.38 to the normal. For magnesium δ= 22° and μ = 0*40. This main oblique fibre orientation is clearly a compres­sion texture, the (0001) slip lamellae becoming oriented normal to the compression axis. A very weak tendency of azimuthal preference round this axis, with <100> normal to the abrasion direction, was also observed in a few cases. With increasing load (above 1 Kg/cm 2 , using 0000 emery paper) on beryllium, in addition to the above main oblique texture the surface regions showed an increasing proportion of metal having a [001] fibre orientation with its axis normal to the surface, associated with the progressively greater amount of metal removed by shearing. Similar oblique and normal [001] fibre textures are developed by abrasion on single-crystal beryllium surfaces, showing clearly the extent of the lattice fragmentation. The region of transition to the underlying undisturbed crystal lattice indicates by its form that the deformation process involves flexural rotational slip on (0001), i. e. rotational slip on (0001) with simultaneous flexure of the slip lamellae about an axis parallel to (0001) not limited to the usual <210> direction.