Basic Research Of CVD Diamond Coated High Speed Steel Tool Using Borided Transition Interlayer

High speed steel is one of the most widely used tool materials, mainly used in the manufacture ofcomplex shaped tools (such as a milling cutter, drilling bit etc.) and forming tools (such as a hobbingcutter, broach etc.). However the Fe dissolves carbon in a high level, creates graphite intensively andhas a high coefficient of thermal expansion, the Fe in high speed steel (HSS) has many disadvantagefor deposition of chemical vapour deposition (CVD) diamond. It is very difficult to deposite CVDdiamond on a HSS directly. The surface modification to form a transition layer is an effective methodto reduce the negative effects of Fe during diamond deposition. The thesis is focused on the boridingtreatment to the high speed steel surface and CVD diamond coating deposition technology on themodified high speed steel tool. The main research work and achievements are as follows:1.The thermal stress in CVD diamond coating on high speed steel was studied. The relationshipbetween the deposition temperature, cooling rate, the thickness of the coating, borided interlayer andthe thermal stress in CVD diamond coating was studied. It shows that low deposition temperature,small cooling rate, thick coating and thin borided interlayer are good for decreasing the stress in CVDdiamond coating.2. A borided transition interlayer of Fe-B compound with FeB and Fe2B was prepared. The CVDdiamond deposition experiment results show the borided transition interlayer can reduce the adverseeffects of Fe on the growth of diamond. The influences of different deposition temperatures, methaneconcentrations, pressures, borided temperatures on CVD diamond coating deposited on the boridedhigh speed steel surface using HFCVD method was investigated. Better deposition parameters fordepositing CVD diamond coating with good adhesion stress between the coating and HSS substrateare obtained, which provides a technology to deposite CVD diamond coating on high speed steelmilling cutter.3. CVD diamond coated high speed steel milling cutters were produced. The cutting experimentproves that diamond coated high speed steel can be used for machining of high silicon aluminumalloy.