Microstructure/hardness relationship in a dual composite

Abstract

Double cemented (DC) carbide [1–3] is a novel dual composite composed of granules of conventional cemented carbide (WC + Co) dispersed in a metal matrix, typically cobalt (see Fig. 1). This concept of a “composite-within-a-composite” facilitates microstructural design to optimize properties for different applications. Properties of the overall composite are variable through control of granule and matrix properties, granule size and volume fraction, typically 70 to 90%. Granule properties are controlled by the grade of cemented carbide granules, i.e., Co content and WC particle size. Matrix properties are controlled by the matrix metal employed, modifiable through alloying or heat treatment. Studies to date have shown that this microstructural flexibility can achieve unusual combinations of properties, such as improved toughness and wear resistance compared to conventional cemented carbide, due to the larger metal matrix mean free path [2]. The particulate nature of the granules enables fairly conventional powder processing. DC carbide is currently being introduced in oil well drill bit inserts and should have use in many other applications requiring combined wear resistance and toughness. This material is also an ideal model for systematically investigating the microstructure/property relationships of a particulate reinforced dual composite, a design concept readily extendable to other metal and ceramic systems. Prior studies by others have investigated particulate dual composites containing lower volume fractions of cemented carbide granules in steel matrices [3–7] to improve wear and thermal shock resistance. Several