| Description |
Diamond-Tungsten-Metal (DTM) matrix composites are a promising material for exploration of the earth's oil and gas, as well as other applications calling for very high abrasion resistance. This material is used for its unique combination of properties, including: abrasive cutting capability, flexural strength, fracture toughness, impact resistance, hardness, and wear resistance. The present work centered on the development of a process for producing this composite material. A pellet-making process was developed to fabricate DTM particles which could then be directly used for making DTM inserts. Diamond grit was coated with dry, premixed matrix powders (tungsten carbide, cobalt and/or copper) by using sprayed binder liquid and a vibratory machine. This process successfully solved the problem of achieving uniform diamond distribution. Subsequently, a modified rapid-heating omnidirectional compaction (mROC) process was employed to fully consolidate the the DTM inserts. After DTM pellets were cold pressed under a pressure of 243.71 MPa to create green parts, these samples were then transferred to the hot press machine to undergo the mROC process. The mROC process was initiated by a preheating step at 200-300 °C for debinding for 30 minutes., and then five minutes at elevated temperature to melt the glass by surpassing its melting temperature. After that, a high temperature (approximately 1200 °C), high pressure (560 MPa) compaction step was operated for another five minutes. Cooling and pressure releasing is the final step, then the DTM inserts were obtained. The process was shown to create matrices with uniform microstructure, although tiny holes caused by free carbon and vaporized wax could still be observed. In this study, other characteristics and variables with potential effects on mechanical properties and the microstructures of DTM composites were investigated, including diamond-volume percentage and compositional variation of matrices. It was found that both higher diamond-volume percentage (diamond being the primary abrasion particles) and larger tungsten carbide (WC)-content (hard phase and the skeleton of matrix) contributed to the higher hardness of the matrix. In terms of matrix composition, copper was added to the binder phase and was also seen to decrease the average hardness of the composite. The primary contribution of copper in this regard was to improve the diamond retention of the matrix. Further modifications to the process were made by shifting the debinding step to a separate unit process between the cold press and mROC process. The debinding step was performed in a furnace with a hydrogen atmosphere, and the adhesion between diamond and matrix was improved. |
