Formation of Lanxide TM a) ceramic composite materials
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E. Breval Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 23 December 1985; accepted 14 January 1986) An overview is given of a new process that has been used successfully to make numerous ceramic/metal composite materials by directed oxidation of molten metallic precursors. As an example, the formation of A12O3/A1 composites from Al is discussed in detail.
I. INTRODUCTION A. Background There has long been interest in the employment of ceramics beyond their traditional roles, in particular as replacements for metals in applications that can benefit from their superior hardness, their chemical stability, and their refractory character. Some early work focused on cermets,1 in the hope of obtaining composites combining the best attributes of ceramics with the ductility and toughness of metals. Unfortunately, cobalt-tungsten carbide is the only such material that has proven commercially successful on a large scale. More recently, development of methods of toughening brittle materials2'3 has stimulated interest in monolithic ceramics and ceramic/ceramic composites as replacements for metals. However, the present fabrication techniques often involve expensive raw materials and processing and impose limits to property engineerability and reproducibility, product reliability, and component size and shape. It is, therefore, processing breakthroughs that appear to hold the key to using ceramics in applications historically served by metals. This paper is intended to outline one such processing breakthrough, now identified by the tradename Lanxide. The characteristics of this process are discussed in general, and a specific application is discussed in detail.
B. The new process The Lanxide process involves formation of ceramic/metal composites by the oxidation of molten metal. In this context oxidation is used in its broadest sense, to mean one or more metals giving up electrons to, or sharing electrons with, another element or combination of elements to form a compound. Oxidation of metals has been considered only occasionally as a method of making ceramic bodies, a notable example being the nitridation of a silicon powder compact to form reaction-bond-
a)
Trademark of Lanxide Corporation, Newark, Delaware.
J. Mater. Res. 1 (1), Jan/Feb 1986
http://journals.cambridge.org
ed silicon nitride.4 The Lanxide process differs in that it involves the oxidation of a bulk molten metal by a gas to produce a solid ceramic body via a directed growth process that results from unusual oxidation behavior. The reaction product forms initially on the exposed surface of a pool of the molten metal and then grows outward, fed by transport of additional metal through the ceramic product of the oxidation reaction between the parent metal and the gas phase oxidant. The percentage of metal remaining in the monolithic composite thus produced depends upon the processing conditions and the starting materials. A typical feature of this process is the need to alloy one or more "dopants"
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