We have been studying diamond coatings on cemented carbide for cutting
tool applications. To improve the adhesion strength of diamond film,
a cemented carbide insert which contains a metal belonging to group 4a
or 5a was heat treated before coating. A thin solid solution layer, w
hich contains a large amount of this metal but no cobalt, was formed o
n the surface of the heat-treated carbide insert. The diamond film dep
osited onto the heat-treated insert showed a high adhesion strength, b
ecause the surface of the solid solution layer was very rough. The cut
ting performance of the diamond-coated insert was almost the same as t
hat of a sintered diamond insert.