Method for joining SiC-diamond

#This application is a 371 of PCT/IB2008/052878 filed on Jul. 17, 2008, published on Jan. 22, 2009 under publication number WO 2009/010934 A and claims priority benefits of South African Patent Application No. 2007/05939 filed Jul. 17, 2007, the disclosure of which is incorporated herein by reference.

#This invention relates to a method for joining ceramic composite parts comprising at least one ceramic material and at least one superhard material to at least one other part. In particular, this invention relates to a method for joining silicon carbide diamond composites to other materials and to materials and tools including such joined materials.

#Ceramics, such as SiC, Si3N4, Al2O3, ZrO, for example, are materials that are typically hard, refractory and relatively chemically inert and are accordingly used in a range of applications such as wear-resistant parts, ballistic armour, cutting tools and electronics. The incorporation of superhard phases such as diamond and cubic boron nitride (cBN) into ceramic material can significantly increase the average hardness, abrasion resistance and thermal conductivity of the composite material. For example, U.S. Pat. No. 6,447,852 and U.S. Pat. No. 6,709,747 disclose a type of material comprising SiC and diamond as well as a small amount of silicon and other materials and a method for making same. Various forms of this material comprise different volume fractions and size distributions of diamond, with the formulation capable of being designed specifically for various applications. Applications of this material are as diverse as the thermal management of electronic devices, nozzles for water-jets and inserts for rock drilling bits. The shapes of the ceramic-diamond composite parts used in these and other applications can be complex, and almost always need to be joined to at least one other part to form an integrated component. The strength of such joins needs to be very high in certain applications, such as rock drilling, so that the ceramic-diamond composite part does not become detached from the component during operation.

#A SiC-diamond composite material part comprising 60 vol % diamond (ScD material 020902-C SNMN4404) is joined to a part comprising cemented tungsten carbide (5 mm×5 mm cubes cut from a plate of 8% Co in WC used as a wear surface).

#Surface Preparation

#The join surface of the SiC-diamond composite part was prepared by treating it with acid. This was done in two stages. Firstly, HCl/HF was used (other acids such as H2SO4 and HNO3 can also be used) to roughen or etch the non-diamond portion of the join surface (i.e. mostly the exposed SiC). This was followed by treatment with hot (20-150° C.) chromic acid in order to remove substantially any graphite that might be present at the join surface and at the exposed diamond surfaces, in particular.