Application of chemical transformation induced fracture for cutting of superhard materials

A hybrid CO2 laser/waterjet machining system is used to cut superhard materials – polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (pCBN) through a “score and snap” mechanism – laser heating leads to localized damage and chemical transformation of surface layers, and subsequently, stress fields developed due to constrained expansion of transformed material and waterjet quenching act on the laser-made “score” to propagate crack through the thickness. During the localized laser heating and subsequent waterjet quenching, PCD and pCBN materials near the top surface underwent chemical transitions. Build up of tensile stresses in the surrounding material resulted due to (i) volumetric expansion of transformed material creating an asperity/wedge effect and (ii) thermal gradients associated with rapid quenching. These tensile stresses in the surface layers lead to crack formation and caused separation of PCD and pCBN wafers along the laser path.