Hydrogen embrittlement of Ti-6al-4v alloy with surface modification by TiN coating

Ti-6Al-4V alloy is widely used in industry due to its excellent properties. However, hydrogen embrittlement may affect the mechanical properties of the alloy if the preventive precautions are not taken into account. Moreover, TiN coating of the substrate may reduce the diffusion rate of hydrogen in corrosive environments. Consequently, the present study is conducted to investigate the hydrogen diffusion into Ti-6Al-4V alloy when subjected to TiN coating. To achieve this physical vapor deposition (PVD) TiN coating of the alloy is realized and electrochemical testing of both workpieces, one coated and the other untreated, is carried out. This provided hydrogen diffusion into both workpieces, which in turn provides the comparison basis for the effect of TiN coating on the hydrogen embrittlement process. To measure the relative hydrogen concentration, the elastic recoil detection analysis (ERDA) technique is used while elemental analysis of the workpiece surfaces after the electrochemical treatment is carried out using the EDS technique. SEM microphotography is conducted to examine the hydrogen embrittlement in the vicinity of the substrate surface. The study is extended to include tensile testing of both TiN-coated and untreated workpieces before and after the electrochemical treatment. It is found that hydrogen diffusion reduces considerably for TiN-coated workpieces and local pitting occurs, which in turn initiates the hydrogen diffusion into the substrate. Tensile strength is slightly affected due to hydrogen embrittlement.