Combustion synthesis in the Ti-C-Ni-Mo system: Part I. Micromechanisms
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I.
INTRODUCTION
THE synthesis of ceramics, intermetallics, and composites by combustion synthesis has been the subject of a considerable amount of recent research; this has encompassed both macrokinetics and micromechanisms,v-221 The combustion synthesis in the Ti-C-Ni system has been studied by the combustion-wave arresting technique,t19,20] synchrotron X-ray radiation,tIll and thermal analysisY2] The objective of this investigation is the elucidation of the physical processes occurring in the propagation of stable combustion waves in Ti-C-Ni and Ti-C-Ni-Mo powder mixtures using the wave arresting technique developed by Rogachev et al. v9,2~ The results of this first part will be presented in this article, while analysis and further discussion will be presented in the companion articleY 3j II.
EXPERIMENTAL PROCEDURES
High-purity (>99 pct) powders of elemental Ti, C, Ni, and Mo were used in this investigation. The particle sizes for the Ti, C, Ni, and Mo were 44 /zm (-325 mesh), 2
J.C. LaSALVIA, Postdoctoral Fellow, Institute for Mechanics and Materials, and M.A. MEYERS, Professor, Department of Applied Mechanics and Engineering Sciences, are with the University of California, San Diego, CA 92093. D.K. KIM, formerly Materials Research Scientist with the Department of Applied Mechanics and Engineering Sciences, University of California, is Professor of Materials Science with the Department of Ceramic Science and Engineering, Korea Advanced Institute of Science and Technology, Taejon 205-701, Korea. R.A. LIPSETT, formerly Undergraduate Research Associate with the Department of Applied Mechanics and Engineering Sciences, University of California, is Graduate Student, Dept. of Engineering, University of Southern California, Los Angeles, CA 90007. Manuscript submitted October 24, 1994. METALLURGICALAND MATERIALSTRANSACTIONSA
/xm, 3 /xm, and 2 to 4 /xm, respectively. The Ti powder consisted of particles with an irregular shape, as well as agglomerates. Particle sizes range from approximately 5 to 100/xm. Because of their irregular morphology, particles larger than 44/zm are able to pass through the 325 mesh powder sieve. The C powders exhibit a flakelike morphology and form large agglomerates with sizes on the order of 50/xm. The Ni powders exhibit a "filament" morphology in which the powders agglomerate to form long chains. The Mo powders consist of agglomerated particles with a spheroidal morphology. Three powder mixtures were used in this investigation corresponding to the final product compositions (weight percent): (1) 70TIC, 30Ni; (2) 66TIC, 30Ni, and 4Mo; and (3) 62TIC, 30Ni, and 8Mo. Powders were dry mixed in a ceramic grinding jar with grinding media (2:1) under an Ar atmosphere for approximately 24 hours. The powders were then removed from the ceramic grinding jar and placed within a vacuum oven for a minimum of 24 hours. Combustion wave velocity and temperature measurements were conducted on the compositions listed previously, using cylindrical specimens 3 cm in height and diameter with green densities a
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