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Published online by Cambridge University Press: 15 February 2011
We have investigated the generation of point defects and dislocations, and the formation of dislocation loops as a function of pulse energy density in laser annealed Al, Ni, and MgO containing nickel precipitates. In the case of Al where vacancies are mobile above 200 K, mostly vacancy loops were observed at room temperature in laser melted layers. Dislocations are formed below the laser-melted layers as well as in specimens treated with pulses below the melting threshold, due to thermal stresses. In the case of Ni (where vacancies are mobile above 373 K) the microstructure in room temperature laser annealed specimens consists of primarily dislocations and their tangles. In MgO:Ni crystals, enough laser energy was absorbed to melt nickel precipitates. The dislocation structure around the precipitates and the transformation of nickel precipitates from coherent into incoherent, provided information on melting and crystal growth of these precipitates.
Research sponsored by the Division of Materials Sciences, U. S. Department of Energy under contract W–7405–eng–26 with the Union Carbide Corporation.