A novel cBN composite coating design and machine testing: A case study in turning

A composite coating series based on nano- and micro-sized cubic born nitride particulates and choice of application-specific binders were developed for turning engineering materials. The coating series were produced via two sequential processes: electrostatic spray coating of cubic boron nitride particles with size less than 2 μm for a conformal porous coating preform of designed thickness; and chemical vapor infiltration of ceramic binder phase(s) at a temperature of around 1000 °C for a dense and well adherent composite coating. In this paper, the coating design for different applications is discussed. As a study case, cubic boron nitride–titanium nitride composite coating was characterized by use of different techniques for coating cross-section, elemental composition, crystal phases, and adhesion strength. Characterization results indicated a composite coating with uniform coating thickness and evenly distributed cubic boron nitride particles in a titanium nitride matrix. Additionally, the coating was tested for its machining performance in continuous turning of AISI 4340 hardened steels and AISI 4140 pre-hardened steels at representative application conditions, and compared to corresponding industrial benchmarks. Testing results showed that the composite coating outperforms its industrial counterparts, polycrystalline cubic boron nitride compacts, titanium aluminum nitride coating by physical vapor deposition, multi-layer coating by chemical vapor deposition, and aluminum oxide bulk tools, in their respective applications.