Microstructural Analysis of a Laser-Processed Zr-Based Bulk Metallic Glass
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TRODUCTION
BULK metallic glasses (BMGs) exhibit a number of exceptional physical, chemical, and mechanical properties, and thus have attracted tremendous attention as both coatings and structural materials.[1–4] The dimensions of as-cast BMG components are limited by the critical cooling rates necessary to produce fully amorphous structures, thus restricting their widespread use.[1,3] Laser additive manufacturing techniques present the novel opportunity for the production and repair of large-scale amorphous metallic components because of their inherently high cooling rates and small melt volumes.[5,6] However, the use of such techniques requires detailed understanding of the impact of rapid heating on glass structure, particularly in the heataffected zone (HAZ) where the glass may relax or devitrify. The present study examines the microstructure within the HAZ of a Zr-based glass after laser processing and contrasts it with the microstructure resulting from isothermal annealing conditions. Fe-, Ni-, and Zr-based metallic glass coatings have been produced by laser processing techniques with
H. SUN, Ph.D. Student, and K.M. FLORES, Associate Professor, are with the Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210. Contact e-mail: fl[email protected] This article is based on a presentation given in the symposium ‘‘Bulk Metallic Glasses VI,’’ which occurred during the TMS Annual Meeting, February 15–19, 2009, in San Francisco, CA, under the auspices of TMS, the TMS Structural Materials Division, TMS/ASM: Mechanical Behavior of Materials Committee. Article published online February 12, 2010 1752—VOLUME 41A, JULY 2010
varying degrees of success.[7–11] This prior research focuses on the deposition of amorphous layers on crystalline substrates, such as steel,[7] Ti,[10] and Mg,[11] in order to improve their wear or corrosion resistance. In these studies, amorphous structures were observed at the surface of the deposited layers; however, crystalline phases were usually observed near the interface of the deposited layers and the crystalline substrates. This crystallization was attributed to epitaxial growth from the substrate[10] or compositional mixing with the substrate material.[11] While these prior studies address the technologically relevant issue of glass-on-crystalline deposition, reports of laser deposition of glass forming powders on amorphous substrates, a necessary step for laser additive manufacturing of large-scale metallic glass components, are generally lacking. Our recent investigation of laser deposition of a Cu-based amorphous powder on a Zr-based metallic glass substrate indicated that laser deposition can be used to produce amorphous coatings with intermediate glass forming compositions.[12] However, residual heating effects result in crystallization of the underlying amorphous material. It is therefore of interest to investigate the development of the HAZ in the amorphous substrate in order to identify optimal processing parameters. In the present work, we invest
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