Kinetics of the reactive spreading of molten aluminum on ceramic surfaces

Abstract

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.

Ceramic-metal interfaces and the spreading of reactive liquids

“…Coatings of nickel, silver, copper, and chromium have been applied to the surface of ceramics to enhance wettability, while the sodium process is used to prepare Al 2 O 3 for wetting by metallic liquids. [44][45][46][47][48][49][50][51][52][53] Chemical vapor deposition titanium coatings have been shown to enhance the wettability of alumina through the formation of intermetallic species at the ceramic surface. 54 Commercially available alloys include TiCuSil™ and InCuSil™.…”

“…Additions of calcium, lithium, and magnesium improve the wettability of aluminum by reducing the oxide film, thus allowing intimate contact. 29,[47][48][49][50]57 The addition of oxygen and other surface-active elements to liquid metals has been shown to lower the solid-liquid, γ sl , and the liquid-vapor, γ lv , surface energies, thus improving wettability in certain instances. 58 This process is also known as direct bonding or gas-metal eutectic bonding.…”

Reactions Between Ti2AlC, B4C, and Al and Phase Equilibria at 1000 °C in the Al-Ti-B-C Quaternary System

“…[22] Typically temperatures greater than 1000°C are necessary for Al to wet TiC and/or B 4 C preforms in MI experiments. [3,4] However, it has been previously reported that Ti additions to B 4 C porous preforms enhance the infiltration kinetics of Al into the latter, [3] which coincides with the finding that Ti-B interactions aid in the reactive wetting of Al on ceramic surfaces, [23] though the reaction mechanisms and phase equilibria remain largely un-investigated. [3] Nevertheless, this interest in manufacturing Al matrix composites with both borides and carbides [24] would be greatly aided by an understanding of the reaction mechanisms and especially the equilibrium phase relations of these systems.…”

Direct Observation of Wetting and Spreading of Molten Aluminum on TiB2 in the Presence of a Molten Flux from the Aluminum Melting Point up to 1033 K (760 °C)

“…Although the contact angle is higher with alumina-saturated bath compared with those obtained with low alumina fluxes, it is considerably lower than fluxless wetting in this range of temperatures. [1][2][3][4][5] Differences in the wetting and spreading of the TiB 2 substrate by molten aluminum at low temperatures in this work can be attributed to the ability of the flux to melt at a relatively low temperature and to its ability to dissolve the alumina skin on the droplet surface. The oxide film prevents the molten aluminum from achieving intimate contact with the ceramic, and its dissolution in the molten flux is vital to achieve wetting.…”

“…It has been reported in most cases that the wettability of TiB 2 by molten aluminum occurs well above the aluminum melting point. [1][2][3][4][5] For example, Rhee [2] obtained a contact angle of 57 deg after a 30-minute hold at 1107 K (834°C) under vacuum. Bardal et al [5] obtained a contact angle of 10 to 20 deg after a 100-minute hold at 1263 K (990°C) under vacuum.…”