Infiltration and wetting of alumina participate preforms by aluminum and aluminum-magnesium alloys
- PDF / 786,753 Bytes
- 7 Pages / 613 x 788.28 pts Page_size
- 23 Downloads / 230 Views
I.
INTRODUCTION
THE pressure
infiltration process for making metal matrix composites uses an applied pressure difference to force liquid metal into a preform of reinforcement material. The pressure required for a given degree of infiltration is expected to depend in part on the extent to which the liquid metal wets the preform material. One approach to reducing the pressures required in the process, thus making it more economical, is to consider using alloys that better wet the preform material. The details of the infiltration process affect the relationship between the applied pressure difference and the wetting. The pressure difference across the liquidvapor interface in a pore is known as the capillary pressure. Unless vacuum is present in the preform, liquid metal will displace gas from the preform during the infiltration process. If this gas is not trapped in the preform, then an increase in the applied pressure difference will increase the capillary pressure and fill more of the pore space with fluid. In this case, the capillary pressure or applied pressure difference required for a given degree of infiltration can be related to the changes in interfacial energy occurring during infiltration and thus to more standard measures of wetting. In this work, the infiltration and wetting of alumina particulates by A1 and A1-Mg alloys was investigated. A1-Mg alloys were selected because Mg has been observed to improve the wetting between liquid aluminum and alumina in sessile-drop experiments, in some stirring processes, and in the LANXIDE* processJ x-4J The *LANXIDE is a trademark of LANXIDE Corp., Newark, DE.
TAMALA R. JONAS, Research Engineer, is with American National Can Beverage Technical Center, Elk Grove Village, IL 60007. JAMES A. CORNIE, Visiting Scientist, Department of Mechanical Engineering, and KENNETH C. RUSSELL, Professor, Department of Materials Science and Engineering and Department of Nuclear Engineering, are with Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted July 18, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS A
infiltration was studied by tracking the position of the infiltration front as a function of time with a capacitance technique. A fluid flow model was used to interpret these results and determine capillary pressures characteristic of the infiltration process. Contact angles were obtained from the characteristic capillary pressures using a thermodynamic energy balance both with and without terms correcting for irreversibility and incomplete filling of the pore space. Although determination of the wetting from the capillary pressure is less direct than conventional measurement methods, it provides information about the wetting under actual process conditions. These conditions typically differ from those present in conventional sessile-drop wetting experiments because the solid surfaces are rough and because the liquid metal is flowing, rather than stationary, which could disturb its surface oxide layer and limit the effect of reaction.
II.
THEORY
Data Loading...
