Study into mechanical properties of TiN coating on Ti-6Al-4V alloy through three-point bending tests

Purpose – To examine the mechanical properties of TiN PVD coated Ti-6Al-4V alloy through three-point bending tests. Design/methodology/approach – Ti-6Al-4V alloy is cut in size and polished and cleaned chemically before TiN PVD coating process. Instron three-point bending equipment is used to conduct the bending tests for TiN coated and uncoated workpieces. During the tests, the load and displacement characteristics were recorded. The tests were terminated when the coating failed. Micrographs of surface and crack sites were obtained by scanning electron microscope. Findings – Coating failure occurs due to shearing effect on the tensile surface. The spalling and buckling of the coating on the compressive surface are observed. The compressive stress generated on the top surface (where the indent is in contact) did not cause adhesive failure of the coating. Moreover, cohesive cracks occur on the tensile surface of the coating. The crack ledge under the action of shear stress appears on the tensile surface of TiN coating and multi cracking of coating is resulted. The crack spacing is small indicating sliding and splitting separation between the adjacent columns in the coating. Research limitations/implications – The tests can be extended to include the duplex treated workpieces such as the heat treatment of surface prior to TiN coating. This enhances the interface properties of the coating and base alloy. Practical implications – The results can be used to assess the TiN coating applications in cutting tools, particularly drill bits and punches. Originality/value – This paper provides information on mechanical behavior of TiN coating when subjected to bending force and offers practical help for the researchers and scientists working in the coating area.