Nucleation control of diamond synthesized by microwave plasma CVD on cemented carbide substrate

Abstract

Diamond was coated on to cemented carbide substrate by microwave plasma CVD, in which nucleation control of diamond crystals was investigated under constant deposition conditions; total pressure 30 torr, CH4 flow rate 1 ml min−1, H2 flow rate 199 ml min−1 and microwave power 550 W. Nucleation tends to occur selectively on the edge part of WC grains of the cemented carbide substrate with coarse WC grain size of about 1 μm, where the nucleation density was 9×106 cm−2. The density increased to about 5×107 cm−2 when using a finegrained substrate (WC grain size ∼0.5 μm). A considerably enhanced nucleation was observed by introducing a number of fine microflaws on to the substrate surface. Microflawing treatment with diamond fine powder (grain size 0–1/4 μm) suspended in an ultrasonic cleaner bath was effective for increasing the diamond nucleation density up to 5×108 cm−2. The grain size of grown diamond crystals decreased with increasing microflawing time.