Correlations Between The Microstructures And Properties Of Cemented Carbide Substrates Of Diamond Film-coated Tools

Diamond film-coated tools with cemented carbide substrates have the incomparableadvantages with other machining tools in machining efficaciously non-ferrous materialssuch as Al-Si alloys, ceramics and various composite materials because of their highhardness, good toughness, long lifetime, free shape and low price. Because the propertiesof diamond film-coated tools are strongly dependent of cemented carbide substrates, theresearch of cemented carbide substrates has become much more important.This thesis chooses different categories of extra-fine and ultra-fine cemented carbidesubstrates as the subject of research. The microstructural parameters of cemented carbidesubstrates, like WC grain size, carbide contiguity, mean binder free path and cobalt contentare characterized and the properties including densities, Vickers hardness (HV10) andfracture toughness are measured. By formula deducing, the quantitative correlationsbetween the microstructural parameters and the properties are created. The predictedresults show good consistence with the experimental dataThe results show that densities and hardness of WC/Co cemented carbides decreasewith the increase of the cobalt binder phase content, and at the fixed cobalt binder phasecontent, the hardness of cemented carbides increase with finer WC grains and proportionalto the microstructural parameters dWC-1/2and LCo-1/2. The fracture toughness KIcof cementedcarbides increases with the increase of cobalt binder phase content, and at the fixed cobaltcontent, it improves with the increase of WC grain size and has a defined functionalrelation with dWC-1/2and LCo-1/2. The analysis shows that there are only four independent slipsystems in WC. With the increase of WC grain size, its crack deflecting and branchingeffect increases, which elevates toughness by increasing the area of fracture surface.