Pulsed Laser Mixing of Ni-Au Surface Films on Nickel Substrates
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PULSED LASER MIXING OF Ni-Au SURFACE FILMS ON NICKEL SUBSTRATES
P.P. PRONKO, H. WIEDERSICH, K. SESHAN9 A.L. HELLING, T.A. AN'DP.M. BALDO Materials Science Division, Argonne National Lab, Argonne,
LOGRASSO, Illinois 60439 USA
ABSTRACT
The melt phase alloying of Ni-Au films on Ni substrates has been studied for rapid quenches following 35 nano-second Q switched ruby laser pulses (0.69p wavelength) in the energy 2 reginme of 0.5 to 3.0 j/cm . The Ni and Au films were each 200 A in thickness having been deposited on a polished Ni substrate by standard hot ribbon vapor deposition methods. Data was obtained on pre and post alloyed surface layers using Rutherford backscattering, transmission electron microscopy, and STEIM energy dispersive X-ray analysis. The melting and resolidification dynamics of the liquid-solid interface was monitored through finite difference integration of the non-linear heat conduction equation to give temperature profiles, depth of melting and melt front velocities associated with the liquid-solid phase change. Resolidification velocities were typically 15 meters/second with melt depths extending to a few thousand angstroms depending on pulse energy. RBS data confirms that liquid phase diffusion of gold in nickel has occured. TEM analysis reveals the presence of a two phase mixture being composed of nickel rich and gold rich material. Microbeam energy dispersive X-ray analysis indicates the presence of a relatively uniform mixing of these two Phases. Pronounced one dimensional solute segregation was not observed in these specimens, however, overall penetration depths of the gold was somewhat larger for the lower energy densities than for the larger ones. Also, unusual circular cell patterns were observed in the resolidified material, their contrast being enhanced by preferential etching during the TEM specimen polishing procedure.
INTRODUCTION
Fundamental studies of Q switched (nano-second) laser pulse alloying of metallic systems has received much less attention than similar techniques applied to semiconductor annealing phenomena. In the past there has been some reluctance in attempting to apply such nulsed mixing to metallic layers on the grounds that the high initial reflectance in metals coupled with an abrupt increase in absorption during the melting phase change would combine in such a way as to produce spontaneous vaporization at the surface. Such an effect would obviously make high speed, controlled, pulse melt alloying very difficult to apply and unpredictable in its outcome. * Present Address:
Universal Energy Systems, Inc. 3195 Plainfield Road, Dayton, Ohio 45432 ± Visiting Faculty Member: University of Arizona, Metallurgy Department, Tuscon, Arizona 85721 #+ Participants in Argonne Visiting Student Programs
600 Examination of reflectives for various types of metallic surfaces [1] indicates that nickel would be an attractive candidate for testing these ideas under the ruby wavelength of 0.69p meters since its reflectance is calculated to be only 65% for bulk material. Con
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