Surface energy absorbing layers produced by ion implantation

Abstract

Single crystals of magnesia have been ion implanted with 80 keV Si − and Cr + ions at variable doses and then subjected to testing in a shock plasma. The peak surface temperature has been calibrated by measuring the size and temperature deformation of the fragments formed by multiple microcracking during thermal shock. The crack density curves for MgO crystals demonstrate that in a wide range of thermal shock intensity the ion implanted crystals develop a system of microcracks of a considerably higher density than the unimplanted ones. The high density of cracks nucleated in the ion implanted samples results in the formation of a surface energy absorbing layer which effectively absorbs elastic strain energy induced by thermal shock. As a consequence the depth of crack penetration in the layer and hence the degree of fracture damage are decreased. The results indicate that a Si implant decreases the temperature threshold of cracking and simultaneously increases the crack density in MgO crystals. However, in MgO crystals implanted with Cr a substantial increase in the crack density is achieved without a noticable decrease in the temperatutre threshold of fracture. This effect is interpreted in terms of different Cr and Si implantation conditions and damage. The mechanical properties of the energy-absorbing layer and the relation to implantation-induced lattice damage are discussed.