STRUCTURE-PHASE STATES OF THE METAL-SURFACE AND UNDERSURFACE LAYERS AFTER THE TREATMENT BY POWERFUL ION-BEAMS

The structural phase state and strength properties of the surface laye r and bulk were studied for metals and alloys with different melting t emperatures exposed to high-power ion beams (HPIBs). It has been estab lished that, irrespective of the ion beam specific power (Q approximat e to 12-50 MW cm(-2)) and in the absence of surface melting, a charact eristic feature of the surface morphology is crater formation. The dis clination and microtwin-type rotation defects, microcracks, the surfac e layer amorphization and dislocation substructures of different dislo cation density were observed inside and in the vicinity of craters. It has been shown that changes in the element and phase states of the su rface layer are due to vapor-plasma cloud deposition and adsorption of the gas medium of the accelerator working vacuum. A physical concept of the formation of high local gradients (moments) of stresses with th eir relaxation through disclination-type rotation effects under the HP IB action has been developed. A high-energy substructure with a high c ontinuum disclination density was found experimentally. The evolution of the defect substructure was examined, depending on the distance fro m the surface under irradiation. Physical models of the crater formati on and mechanisms for the formation of the dislocation-disclination su bstructures under the HPIB irradiation are proposed. (C) 1998 Publishe d by Elsevier Science S.A.