Formation of metastable structures and amorphous phases in Pu-based systems using the sputtering technique
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I.
INTRODUCTION
A L L O Y I N G through sputter deposition is an attractive technique that is being used increasingly for preparing wide ranges of both stable and metastable alloys in the form of coatings. When the triode or the magnetron systems are used for sputter deposition, the fabricated deposits can be quite thick t0.1 to 5 mm). In addition, a single deposit sputtered from a composite target can produce across the coated surface a wide range of continuously changing alloy compositions that can be subsequently examined at one time. Therefore. this approach greatly facilitates the studies of metastable alloys, especially in highly reactive systems such as those based on Pu, because it eases the problems associated with handling and characterization. Metastable and amorphous alloys of Pu with the elements Mn, Fe. Co, Ni, Cu, and Ru have been prepared previously at the Los Alamos National Laboratory with the use of the liquid quenching (LQ) technique, tl] The alloys were produced by the gun type cooling technique in quantities ranging in weight between 25 and 50 mg. An amorphous Pu-37.5 at. pct Ga alloy was also produced by a large dose of neutron irradiation. L2~ Earlier investigators have reported the occurrences of metastable structures in several alloys of Pu with Ti, Ga. and Ce following liquid quenching. [31 and in Pu with Ga, Ta. Ag, and Co following high-rate sputtering.t4,5.6] The convenience of a composite target with a triode sputtering system to produce extended compositional ranges of amorphous alloys was demonstrated for Pu-Fe, Pu-Si. and Pu-Ta systems, t71 Sputtering, being an atom-by-atom vapor deposition (VD) process, is sometimes claimed to be able to provide an effective quenching rate approaching 1012 ~
H.F. RIZZO. Staff Scientist. and A.W. ECHEVERRIA. Senior Technical Associate. are with the Lawrence Livermore National Laboratory, Livermore. CA 94550. T.B. MASSALSKI. Professor. is with Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted July 22. 1987. METALLURGICAL TRANSACTIONS A
second, which is substantially larger than the conventional LQ techniques ( 105 to 108 ~ Hence. observation of wide ranges of amorphous phase formation is c o m m o n with sputtering, t81 It has been shown t91 that sputtering also substantially increases the accessible composition ranges over which noncrystalline states can be formed. In this sense, it is not limited only to the eutectic regions m phase diagram. Figure 1 displays the compositional ranges of amorphous and metastable phase formation achieved in this study for the Pu-Pd and Pu-V systems. These results and others listed in Table I illustrate that the formation of glassy alloys by sputtering can occur in systems that have no eutectics, display no solid solubility, or involve compound formation. We report here on the application of the high-rate sputtering technique to the alloys rich in Pu with Si, A1. V. Fe, Co, Pd. Ta. Re, Os. and Ir. Samples of thicknesses exceeding 0.3 m m were obtained in the form of deposits with continuously
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