Kinetics of the reactive spreading of molten aluminum on ceramic surfaces
- PDF / 3,378,153 Bytes
- 11 Pages / 587 x 795 pts Page_size
- 86 Downloads / 199 Views
The spreading kinetics of molten aluminum on ceramic surfaces bearing reactive coatings has been studied through the direct observation of sessile drops, either formed in situ or emplaced at temperature. Analysis of videotapes permitted the assessment of the rate of advance of rapidly spreading droplets. Experimental conditions in this study were chosen to avoid the severe retarding effect of the aluminum oxide film which is typically encountered in aluminum wetting experiments. A variety of reactive coating systems were examined (B, Cu, Ni, Ti, and Ti + B), and the effect of coating amount was assessed. Based upon the experiments of this study, the main effect of the coatings is to drive spreading due to strong exothermic interfacial reactions. The intensity of the interfacial reaction causes the change in free energy per unit area of interface to dominate the rate of movement of the triple line.
I. INTRODUCTION The challenge in processing carbon-reinforced aluminum composites is to promote wetting and interface formation between the carbon fibers and the aluminum matrix without significant attack of the fiber or formation of an intermediate compound—either of which degrades composite performance. Avenues to prevent such reactions by passivating the carbon substrates were presented in an earlier study.1 Since aluminum carbide is thermodynamically favored at temperatures above the melting point of aluminum, a knowledge of interfacial kinetics is essential. The application of coatings which promote aluminum wetting is one of the approaches that has been used to reduce the exposure to elevated temperatures during composite fabrication. The mechanism by which reactive coatings promote wetting and infiltration is addressed in this study. Significant reductions in process temperature, pressure, and hold times have been achieved by the use of reactive coatings. Some phenomenological studies of wetting enhancements have been reported, but there is still little understanding of the interfacial processes which are operative. Oxide film effects have not been examined separately from spreading kinetics. The objective of this study was to examine the spreading kinetics of aluminum on ceramic surfaces bearing reactive coatings. Of particular interest were those coating systems (B, Cu, Ni, Ti, and Ti + B) where strong exothermic reactions with aluminum were involved. Experimental conditions in this study were chosen to avoid the severe retarding effects of the aluminum oxide film which are generally known to affect sessile drop experiments.2"11 640
J. Mater. Res., Vol. 10, No. 3, Mar 1995
Summary of previous aluminum-matrix composite studies using coatings Ignatowitz12 summarized 10 years of research which had centered on the reinforcement of aluminum with carbon fibers. The problem, which persists today, was to promote wetting and Al-C interface formation without the formation of A14C3, which degrades composite strength. Pressure infiltration, precoating fibers with Al, or fiber coatings were all tried in an attempt to contr
Data Loading...
