This proposal seeks to apply the "Graded Structures" concept to engineering components, required to perform in environments which no single material is capable of satisfying.
The three cornerstones of the work involved the development of technologies for the fabrication of 2 and 3-Dimensional bodies in graded form, the assessment of microstructure and testing of laboratory specimens and prototype tools, and the interaction with industry to advise and exploit the findings.
The work mainly involved the WC/Co system used in the fabrication of mining tools and tooling for beverage cans.
The fabrication technologies exploited in this programme for the construction of 2 and 3-Dimensional structures have been Powder Injection Moulding (PIM), warm rolling, pressureless sintering and HIP'ing. The first two have been developed to produce flat sandwich structures and complex 3-Dimensional shells in a range of WC/Co compositions. Pressureless sintering in the solid and liquid state have been utilised with and without post HIP'ing and the conditions necessary for full densification have been established.
Finite Element techniques were applied to determine residual stresses at 2 and 3-Dimensional interfaces and they have illustrated the effects of compositional changes and geometries on internal stresses developed upon cooling from the fabrication temperature.
Prototype mining tools fabricated by sintering and HIP'ing and incorporating flat and conical interfaces have been successfully produced and tested under simulated conditions. Although direct comparisons between tools incorporating graded structures and those commercially available cannot at this stage be made with any degree of certainty, these initial tests have demonstrated the importance of developing the geometry of such tools to reduce the cost of rock machining and the potential for the construction of smaller machines for tunnelling. This was shown to be possible with the introduction of graded structures and more work is required to determine the cost savings and environmental effects of the new tools.
Collaboration throughout the project with the industrial endorsers has demonstrated the importance of making full use of current technologies and fully appreciating the specific needs from tools. It also demonstrates that any further work on these tools should take into account the total engineering needs of the suppliers, users and machine manufacturers since it is apparent that the benefit of such development could only be meaningful if seen from the perspective of industry across the supply chain.
Specifically, it involves the engineering of composite multi-layer structures to enable the utilization of the wear and/or heat resistance of ceramics and cermets and the toughness of metallic alloys. Combination of carbide carmets with tool steels and oxides or borides with nickel base alloys will initially be investigated. Along with the applied technological aspects of the research a fundamental approach will be adopted to facilitate the engineering of interfaces in order to overcome joining problems associated with the physical and chemical incompatibilities between dissimilar materials. Powder metallurgical techniques will be applied to fabricate "graded" components, including hot isostatic pressing, uniaxial hot pressing, injection moulding and tape casting. The structures produced will be assessed metallographically and the microstructure and physical properties obtained will be correlated against the fabrication techniques employed.