Correlation of mechanical and ultrasonic properties of Al-SIC metal-matrix composite
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I.
INTRODUCTION
M E T A L - m a t r i x composites are emerging as candidate materials for special purpose uses in several industrial, space, and military applications. To a large degree, they can be considered to be still in an early trial stage even though manufacturing, albeit of small amounts, has been going on for the last ten years. For traditional metals, such as steel and aluminum, a large data base has been accumulated during the last century which provides the designer with a wealth of information concerning physical, metallurgical, corrosion, mechanical, and fracture properties, etc. To this has been added a correspondingly large data base of nondestructive testing that has been developed for quality control and in-service inspections during the last 30 to 40 years. Conversely, large data bases for metal-matrix composites are not yet available but are beginning to develop, and an increasing number of papers are appearing in the literature. 1~-351 Current metal composites are "mixture" materials, and because of the way they are made, they contain many discontinuities (faults) that are not commonly found in normal, traditional metals. These discontinuities are due to gas-filled pores (these may appear following casting or may often occur when the base materials have a powder form), clustering of a constituent of the mixture, misalignment of reinforced fibers, clustering of fibers, etc. In nondestructive examinations, a metal composite that has some, or many, of these "faults" exhibits comparatively high ultrasonic absorption together with large back-scatter which is not observed for small-grained steels and aluminum. Note that large-grained materials, such as centrifugally cast austenitic steel, exhibit large ultrasonic absorption and back-scatter due to randomly oriented, anisotropic grains. The material discontinuities mentioned above that exist in metal-matrix composites will lead to locally variable mechanical properties whose presence can be identified by well-chosen nondestructive tests. Material taken from re-
G. MOTT and E K. LIAW are with the Metals Technologies Department, Westinghouse R & D Center, Pittsburgh, PA 15235. Manuscript submitted October 23, 1986. METALLURGICAL TRANSACTIONS A
gions which are suspected, on the basis of nondestructive testing, of having defects can be tested to determine if variability in its mechanical properties exists. Initially, a forged disk of a SiC reinforced aluminum metal-matrix composite material was scanned ultrasonically, and measurements of overall ultrasonic absorption, back-scatter from layers at different depths within the disk, and longitudinal wave velocity variation through its thickness were made. Ill The disk was subsequently machined for use in an experimental application and remnants of it were used for the present study. One of the objectives of this paper is to contribute to data bases in the areas of nondestructive and mechanical testing of metal-matrix composites. In addition, the results of nondestructive and mechanical tests will be syst
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