Microstructural characteristics of oxides in 5083 Al synthesized byreactive atomization and deposition
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A detailed study of the size, distribution, and morphology of oxide particles in as-sprayed deposited 5083 Al synthesized by reactive atomization and deposition was reported. The results indicated that the oxides exhibit thin-plate morphology and are distributed at prior droplet boundaries, grain boundaries, and grain interiors with a dimensional scale on the order of tenths of micrometers up to a few micrometers. The mechanisms involved in the formation of the observed oxide distribution were analyzed in detail. I. INTRODUCTION
Reactive atomization and deposition (RAD) is a relatively novel processing technique, which effectively modifies conventional spray forming by substituting a reactive gas mixture for an inert atomization gas to introduce reinforcements from the gas/metal chemical reactions.1–3 Among the possible reactive gases, oxygencontaining gas mixtures are of particular interest given the affinity for oxygen of most metal systems in combination with inherent stability of oxides. Due to the existence of porosity in the as-sprayed deposited materials, thermomechanical processing (e.g., extrusion, rolling, forging, and hot isostatic pressing) is typically performed to achieve full density.4,5 Thermomechanical processing also fragments oxides into fine dispersoids and uniformly distributes them in the matrix. It has been documented that, the fragmented oxide dispersoids are on the order of tens of nanometers in size,6,7 which is the required size scale for an effective grain growth retardation and dispersion strengthening. Inspection of the available literature reveals, however, that microstructural characterization of oxides in as-sprayed deposited RAD materials has received only limited attention. As a consequence, relatively few reports results are available. In related work2 involving transmission electron microscopy (TEM) analysis, Zeng et al. indicate that in as-deposited RAD Ni3Al, Y2O3 and Y3Al5O12 are distributed both intergranularly and intragranularly with width of 0.1–0.2 m and length of 0.2–0.6 m. However, Dai et al. argued that in as-deposited RAD 5083 Al, ␥–Al2O3 particles exhibit a size of less than 20 nm and are distributed as stringers along grain boundaries.8 a)
Please address all correspondence to this author: e-mail: [email protected] DOI: 10.1557/JMR.2004.0393 3090
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 10, Oct 2004 Downloaded: 23 Apr 2015
Recently, the potential of implementing spray forming and RAD as a single-step manufacturing technique has attracted considerable attention.4,5 As a result, progress in controlling and minimizing porosity has been accomplished via considerable experimental9–12 and numerical studies.13–15 In cases where the objective is to manufacture a net-shaped product via a single-step RAD operation, the as-sprayed deposited state represents the final one. Thus, it is essential to provide insight into the microstructural characterization (i.e., size, morphology and distribution) of oxides in as-deposited RAD materials, to understand the
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