Powder Injection Moulding of High performance Carbides
This project focuses on the Powder Injection Moulding (PIM) and characterisations of cemented tungsten carbide with less than 3wt% Cobalt. The effects of lower Cobalt concentrations on the sinterability and properties of the composites are characterised. The mechanism of abnormal grain growth, which is found being affected by the amount of Co, is discussed. The possibility of in-situ-toughening tungsten carbide, making use of abnormal grain growth of tungsten grains to reinforce tungsten carbide-cobalt composites, is also investigated. To apply this concept, the self-reinforced tungsten carbide and functionally graded tungsten carbide will be synthesised using PIM process.
Contact PersonChua Beng Wah(bwchua@SIMTech.a-star.edu.sg)
SolutionRecently, several reports have been published on in-situ-toughened (or self reinforced) ceramics, such as silicon carbide and silicon nitride. Rather than foreign substances addition, the reinforcing agents in these in-situ-toughened composites are formed during the fabrication process, making use of abnormal grain growth (AGG) of some silicon carbide or silicon nitride grains. Abnormal grain growth is also discovered in the cemented tungsten carbide and can be controlled by the composite compositions and processing conditions. Therefore, the tungsten carbide could be in-situ-toughened by tailoring the abnormal grains in the composite.
BenefitsIn this project, a self-pressure generating sintering has been developed. The process enables the fabrication of different materials properties with reduced voids using the pressure produced due to difference in shrinkage during sintering. Also, the conditions for AGG are also found which could be used to fabricate in-situ formed composites with better toughness, compared to brittleness of the conventional materials.
ApplicationsThe materials and process developed could be used for some of the nozzles used in electronics and cutting tools. Some of the materials and process could also be used in the stamping industries as a punch tool.
Cemented tungsten carbide with lower cobalt concentrations shows high hardness but poor toughness. The problem for conventional functionally graded cemented carbide is the cobalt homogeneity during high temperature sintering process. Furthermore, the metal binder phase lowers the hardness and corrosion resistance of the composite and limits its applications. Other approaches to improve the fracture toughness of tungsten carbide seem to be of necessity.