Low-Energy Deposition of High-Strength AI(O) Alloys From an ECR Plasma
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JC. Barbour*, D.M. Follstaedt*, J.A. Knapp*, DA. Marshall", S.M. Myers*, and R.J. Lad** *Sandia National Laboratories, Albuquerque, NM 87185, "University of Maine, Orono, ME 04469 ABSTRACT Low-energy deposition of AI(O) alloys from an electron cyclotron resonance (ECR) plasma offers a scaleable method for the synthesis of thick, high-strength Al layers. This work compares alloy layers formed by an ECR-0 2 plasma inconjunction with Al evaporation to O-implanted Al (ion energies 25-200 keV), and it examines the effects of volume fraction of A1 20 3 phase and deposition temperature on the yield stress of the material. TEM showed the AI(O) alloys contain a dense dispersion of small y-A1203 precipitates (-1 nm) ina fine-grain (10-100 nm) fcc Al matrix when deposited at a temperature of -100'C, similar to the microstructure for gigapascal-strength O-implanted Al. Nanoindentation gave hardnesses for ECR films from 1.1 to 3.2 GPa, and finite-element modeling gave yield stresses up to 1.3 ± 0.2 GPa with an elastic modulus of 66 GPa ± 6 GPa (similar to pure bulk Al). The yield stress of a polycrystalline pure Al layer was only 0.19+0.02 GPa, which was increased to 0.87+0.15 GPa by implantation with 5 at.% 0. INTRODUCTION The formation of thick, high-strength aluminum alloys is important for providing strong wear-resistant coatings on low-weight Al components and possibly for surface coatings on Al interconnects. Previously [1], the surface (up to 0.5 rim) of bulk Al disks was shown to be strengthened by a dense dispersion of 1-3 nm sized particles which were created through 25-200 keV 0 ion implantation. These particles are disordered y-A1203 precipitates which were coherent with the fcc Al matrix. Recently, this work has been extended to compare O-implanted layers to AI(O) alloy layers formed using an 02 electron cyclotron resonance (ECR) plasma inconjunction with electron beam evaporation of Al. Our first paper on this topic [2] examined the hardness of an ECR A10.800.2 layer deposited on both Al and Si substrates. This paper reports on the work inprogress to form these materials and determine their microstructure and mechanical properties as a function of deposition conditions. Specifically, finite element (FE) modeling is performed using the computer code ABAQUS/Explicit [3] inorder to extract the yield stress (ay) and the modulus of elasticity (E)from the hardness data. Also, the variation incry with increasing volume fraction of the A1 203 phase and increasing deposition temperature are examined. The introduction of hard particles into a metal matrix can strengthen the material through several mechanisms which inhibit dislocation motion: dislocations restricted to bowing around particles, work hardening from pile-up of dislocation loops around the particles, and an increase in yield stress due to coherency strain. Inaddition, the metal matrix may also exhibit an increase inay as a result of grain-size strengthening. The effectiveness of dispersion strengthening depends on the particle spacing, the particle size, and th
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