Greater improvement of carbon and boron co-doping on the mechanical properties, wear resistance and cutting performance of AlTiN coating than that of doping alone

The effects of carbon and boron co-doping on the microstructure and properties of AlTiN coatings are still unclear. In this study, a comparative study on the effects of carbon and boron co-doping and doping alone on their microstructure and performance of the as-deposited AlTiN, AlTiCN, AlTiBN and AlTiBCN coatings was performed. The results showed that, typical columnar crystal structure changes, starting from undoped AlTiN coating, have been well demonstrated after doping. At the doping content is 5 at.% (relative to the non-N elements), carbon can induce a stronger [200]-preferred orientation, which is beneficial for enhancing the nanohardness and Young's modulus of the coating, while the grain refinement of boron plays a dominant role in the coating growing. When the actual doping content further increases to 10 at.%, carbon as well as boron supports the formation of the hexagonal structure (w-AlN). Due to the amorphous transformation, carbon and boron are present in the form of amorphous carbon and BN, respectively. The above microstructure evolution after doping can be inherited in the co-doped coating. The AlTiBCN coating exhibits the best adhesion between the coating and substrate because of the formed amorphous-nanocrystalline composite structure. Compared to doping alone, carbon and boron co-doping significantly reduces the wear rate, and AlTiB0.08C0.02N has the minimum value of 1.8 × 10−6 mm3/(N·m). The improving effect of carbon and/or boron on the cutting performance of the coated tools is in sequence as follows: carbon and boron co-doping > carbon doping > undoped > boron doping. The AlTiB0.02C0.005N coated tool exhibits the best cutting performance. •A low content of carbon can induce a stronger [200]-preferred orientation.•More than 2 at.%, carbon as well as boron supports the formation of the hexagonal structure (w-AlN).•Carbon and boron are present in the form of amorphous carbon and BN, respectively.•AlTiB0.08C0.02N has the minimum value of 1.8×10−6 mm3/(N·m), and AlTiB0.02C0.005N coated tool exhibits the best cutting performance.