Laser-Pulse Melting of Hafnium-Implanted Nickel Studied with TDPAC and RBS/Channeling Techniques
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Nuclear and Electron Resonance Spectroscopies Applied to Materials Science
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LASER-PULSE MELTING OF HAFNIUM-IMPLANTED NICKEL STUDIED WITH TDPAC AND RBS/CHANNELING TECHNIQUES
L. BUENE*, E. N. KAUFMANN**, M. L. McDONALD Bell Laboratories, Murray Hill, New Jersey 07974 J. KOTHAUS, R. VIANDEN, K. FREITAG Institut fiir Strahlen-und Kernphysik, University of Bonn, West Germany C. W. DRAPER Western Electric Engineering Research Center, Princeton, New Jersey 08540
ABSTRACT The perturbed angular correlation technique has been applied to study the local environment of tantalum in nickel after ion implantation of hafnium and after laser-pulse melting. The magnetic hyperfine interaction at the daughter nucleus tantalum in nickel is used to determine the uniqueness of the tantalum lattice site. Several hafnium concentrations were employed and auxiliary measurements using ion-beam channeling, Rutherford backscattering and Auger electron spectroscopy were performed.
INTRODUCTION Recently it has been demonstrated that impurities implanted into various metal substrates, in particular nickel, can be incorporated in the substrate lattice to concentrations exceeding the equilibrium solubility of the system by laser-pulse melting of a surface layer followed by rapid resolidification. The resolidification process is epitaxial and the impurity concentration redistributes according to an effective distribution coefficient applying to the moving solid-liquid interface [1]. The question arises as to how, at the microscopic level, the solute atoms incorporate into the solid as the interface moves past them. For example, one might imagine that as the impurities incorporate into the lattice beyond their normal solubility, defects must also be incorporated during the solidification process in order to minimize total strain energy. Such a question can be examined using the hyperfine interaction which sees the solid from the viewpoint of the impurity atom. The nickel lattice is an excellent choice for this experiment for several reasons. It is magnetic thus providing a convenient hyperfine interaction. It has been studied with respect to laser pulse melting more extensively than any other pure metal [1]. It shows no high temperature allotropic transition thus insuring the simplest possible metallurgical picture. In addition, it is a sufficiently light element to permit Rutherford backscattering experiments as well. The appropriateness of a hafnium probe arises from the following considerations. The binary phase diagram for the hafnium-nickel system shows no liquid phase miscibility gap and shows a finite (0.5%) but limited solid solubility [2]. Thus one expects to easily exceed the equilibrium solubility but at the same time not generate second phase precipitates. The relative atomic radius of hafnium to that of nickel is quite large and therefore might be expected to enhance any defect (for example, vacancy) trapping at the resolidification interface. Hafnium has an isotope, viz., 181-Hf, which is highly appropriate for perturbed angular
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