Beryllium Single Crystals Research Articles

Twinning caused by abrasion on single crystals of beryllium

Results concerning the lattice re-orientation caused bv abrasion on single crvstals of beryllium have been obtained by electron diffraction. The occurrence of twinning found in certain cases in sub-surface regions of abraded singlecrystal beryllium surfaces was dependent upon the initial crystal orientation with relaiion to the direction of the applied compressive stresses. The operative {101-bar2} set of twinning planes was found to be the one which most facilitated development of the characteristic oblique STA001! compression fibre texture produced by the abrasion in the outermost surface layers by rotational slip or flexural rotational slip of the sub-surface twin. (auth)

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

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.

Early Aging Effects in Copper - 1.76% Beryllium Single Crystals

AbstractA technique is described for the study of the early stages of precipitation hardening in single-crystalline and poly crystalline copperberyllium alloys. Since no trace of the equilibrium precipitate responsible for hardening can be detected by ordinary X-ray or metallographic techniques prior to the onset of overaging, the described method is based on the changes produced in the matrix as the result of the formation of aggregates along preferred lattice planes. Such formations produce accommodation strains in the matrix lattice which, can be detected as a change in the intensity and angular range of matrix reflection.An interpretation of the age hardening sequence in a copper - beryllium, alloy after isothermal annealing is presented in terms of fundamental transformations.