Fracture strength of two-step pretreated and diamond coated cemented carbide microdrills

Experiments were undertaken to evaluate effects of conventional two-step pretreatment process and diamond coatings on fracture strength of cemented carbide microdrills. For the pretreatment of the samples, the often used Murakami solution (10 g KOH + 10 g K3[Fe(CN)6] + 100 gH2O) and an acid solution of hydrogen peroxide (10 ml 98 wt% H2SO4 + 100 ml 38%H2O2) were used. Diamond coatings were deposited using a coaxial excited microwave plasma system. The experimental results reveal that for small sized tools, the pretreatment will bring about negative effect on the fracture strength of the microdrills and among the two steps in the etching process, the acid etching is more harmful because it will create a porous surface layer to the tools. Therefore, the conventional pretreatment process is not suitable for the treatment of small sized tools; even it could improve effectively adhesion of diamond coatings to the cemented carbide substrates.