Wetting of ceramic materials by liquid silicon, aluminium and metallic melts containing titanium and other reactive elements: A review

An improved sessile drop technique which prevented the oxidation of aluminum was used to measure the changes in contact angle between boron nitride and molten aluminum in a purified He-3% H 2 between 1173 and 1373 K. The contact angle progressed through the four wetting phases similar to other ceramics when the results were plotted on a logarithmic time scale. However, at and above 1273 K the equilibrium contact angle was 0° which is much less than those of typical ceramics. Using the value in phase II, the original contact angle between boron nitride and aluminum (contact angle between non-reacted boron nitride and aluminum) was estimated to be 133° at 1373 K. The wetting progressed by producing another non-wetting material, AIN, in this non-wetting system. The detailed mechanism of the solid/liquid/vapor interfacial advance during wetting in such a system was also explained using Cassie's equation.

http://www.jwri.osaka-u.ac.jp/~dpt9/Acta(1993)BNAl.pdf

Interfacial reaction wetting in the boron nitride/molten aluminum system

The sessile drop technique was used to study the wetting behavior of Al-Si alloys on SiC sintered ceramic substrates under vacuum in the 700--1,100 C temperature interval. Al-Si alloys with Si concentrations up to 50% were tested. An expected non-wetting/wetting transition was observed at 900--1,000 C due to the presence of an alumina film surrounding the molten alloy. At higher temperatures wetting was observed and the Si concentration of the alloy has a marked effect on the measured contact angles, {theta}. At 1,100 C {theta} decreases from 55 to 25{degree} when instead of pure Al an Al12.3%Si or an Al16.6%Si alloy is used. The suppression of the formation of a continuous Al{sub 4}C{sub 3} layer at the interface and a process of dissolution and reconstruction of the SiC surface, due to the increased Si concentration of the Al-Si alloys, are the key factors to explain the observed behavior.

Wetting behaviour in the Al-Si/SiC system: interface reactions and solubility effects

The wetting behavior and strength at aluminum/alumina interfaces has been an active subject of research. Al/alumina applications include ceramic-metal composites and several applications for electronic industries. In this paper the interface strength and microstructure of Al/alpha-alumina was investigated. We discovered that in a solid-state joining, the strength of the joint increases with increasing joining temperature. In a liquid-state joining, the strength of the joint gradually decreases due to the formation of unbonded areas. The strength, sigma sub b, is expressed by the following equation as a function of unbonded area, A: sigma sub b = 2.22 A + 143 (70 percent {le} A {le} 100 percent). The highest strength reached 400 MPa when the interface was formed at around the melting temperature of aluminum. An aluminum layer close to the interface became a single crystal when it was bonded to a sapphire. The following crystallographic orientation relationship is established: (1{bar 1}1){sub Al}//(001){sub {alpha}}-Al{sub 2} O{sub 3}, (110){sub Al}// {sub {alpha}}-Al{sub 2}O{sub 3}. Amorphous alumina islands were formed at the interface. In the amorphous alumina, gamma-alumina nanocrystals grew from the sapphire, with the same orientation relationship to sapphire as above.

https://digital.library.unt.edu/ark:/67531/metadc784787/m2/1/high_res_d/827082.pdf

Wetting and strength issues at Al/α–alumina interfaces

The surface tension of liquid aluminium in high vacuum: The role of surface condition

Several series of experiments have been conducted to gain information about the wettability of AlN, BN, Si3N4 and two sialon ceramics by potential braze materials. It was possible to achieve wetting of all five ceramics using aluminium, copper-titanium alloys, and a Ag-28Cu-2Ti alloy. Wetting by aluminium and the Ag-28Cu-2Ti alloy was usually good. Both wetting and non-wetting alloys containing titanium reacted to form TiN and it is argued that the achievement of wettability is associated with a certain degree of hypostoichiometry. While aluminium should also have reacted, no clear evidence was obtained. In supplementary experiments it was found that bonds formed by brazing with aluminium at 1000 °C could have shear strengths as great as 60MPa. Although the experimental work was preliminary in nature, it suggested that good brazing systems could be developed.

L. M. Jones

Papers

Some observations on the wetting and bonding of nitride ceramics