Infiltration Processing of Tungsten-Reinforced Bulk-Amorphous Metal Matrix Composites

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MM8.6.1

Infiltration Processing of Tungsten-Reinforced Bulk-Amorphous Metal Matrix Composites Laszlo J. Kecskes and Steven T. Szewczyk U.S. Army Research Laboratory Weapons and Materials Research Directorate Aberdeen Proving Ground, MD, 21005-5069, USA ABSTRACT High-density tungsten (W)-reinforced bulk amorphous metal (BAM) matrix composites have been fabricated by a pressure infiltration methodology. A hafnium (Hf)-based BAM with a density of 11 g/cm3, glass transition temperature, Tg, of 495 ˚C, and liquidus temperature, Tliq, of 1,050 ˚C has been used to infiltrate open-porosity W-wire preforms to create W-Hf-BAM composites. Because of the considerably higher Tliq of Hf-based BAM alloys than those based on Zr, the interaction of the BAM with the fixture components, reaction with the W perform, and the formation of undesirable intermetallic phases in the composite were of primary interest. The roles of infiltration pressure, soak temperature, and time at temperature on the composite structure were examined. The structure and quality of the composites were determined with simple fracture tests, scanning electron microscopy, X-ray diffraction, and differential thermal analysis. The fabrication procedure steps and the characteristics of the composites are described.

INTRODUCTION Over the past few years, there has been a growing interest in developing a range of fabrication methodologies for W-BAM composites [1]. Seminal work on these materials, done at the California Institute of Technology, identified process conditions for W wire- or powderreinforced, Vitreloy-1-, Vitreloy-105-, or Vitreloy-106-BAM matrix composites [2-4]. Vitreloy 105, (Zr-BAM), one of the non-beryllium containing, zirconium (Zr)-based BAMs, with a nominal composition of Zr52.5Ti5Ni14.6Cu17.9Al10 has density, ρ, of 6.7 gcm-3, Tg of 410 ˚C, and Tliq of 850 ˚C. As was shown by Dandliker et al. [2], such composites can be fabricated with relative ease using a pressure infiltration technique. At the U. S. Army Research Laboratory, we have decided to apply this technique to fabricate higher-density composites. Experiments were undertaken to fabricate composites wherein the BAM matrix was a Hf-based equivalent of Vitreloy 105, (Hf-BAM). Hf52.5Ti5Ni14.6Cu17.9Al10 has ρ = 11.0 gcm-3, Tg = 495 ˚C, and Tliq = 1,050 ˚C. Because of the considerably higher Tg and Tliq of the Hf-BAM, its enhanced interaction with the fixture components and the W preform, as well as its devitrification into undesirable intermetallic phases in the composite were of primary interest. The roles of infiltration pressure, soak temperature, and time at temperature on the composite structure were also examined. For comparison, samples of Zr-BAM and W-Zr-BAM were prepared also. The structure and quality of the composites were determined with simple mechanical tests, scanning electron microscopy (SEM), x-ray diffraction (XRD), and differential thermal analyses (DTA). The fabrication procedure steps and the characteristics of the resultant composites are described.

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