Surface Modification Of TiAlN Coating By High Current Pulsed Electron Beam

The application of High Current Pulsed Electron Beam?HCPEB?technology in TiAlN coating treatment has attracted much attention,but there was seldom attention has been paid to the effects of composition,crystal structure and stress state on the post-treated TiAlN coating.In this study,theinfluences of coating composition,crystal structure and residual stress on the mechanical properties of TiAlN coating werecarried out,accompanying withfirst-principles calculations based on Density Functional Theory?DFT?.TiAlN coatings were treated with different parametersof HCPEB treatment.The top and crosssection morphology of TiAlN coatings were investigated by SEM,and the surface composition was analyzed by EDS.The lattice constant of TiAlN coating were measured by XRD,and the residual stress of TiAlN coatings was measured by 2?-sin2? method for the original and post-HCPEB treated coatings.The mechanical properties of TiAlN coatings were tested by using the nano-indentation.The results showed that the grain boundary of the TiAlN was obscured or even disappeared after HCPEB treatment.The atomic ratios of Ti and Al in the coating were almost unchanged before and after HCPEB treatment,and there was no new phase occurring in post-treated coatings.Compared with the lattice constant?4.1780 ??of the originalTiAlN coating,the lattice constant of post-treated coatings showed obvious downtrend,fluctuating from 4.1627 to 4.1749 ?.The residual compressive stress of the untreated coating was 243.77 Mpa,whereas the residual compressive stress of the post-treated TiAlN coatings changed from 90.98 to 532.65 Mpa.The residual compressive stress of the TiAlN coating showed a rise-lower-rise-lower-rise trend with the increasing of the total deposition energy.The nano-hardness of original TiAlN coating was 28.174 GPa.With electron beam deposition energy increased,the optimal mechanical properties of the post-coating was obtained when the process parameters was 11.6KV-80A-20 times.The results of the first-principles calculations showed that the Ti₄Al₄N₈ type could exist stably when the lattice constant changed from 4.1627 to 4.1749 ?.The mechanical properties calculation results showed that the Young's modulus of Ti₄Al₄N₈ with different lattice constants was consistent with the experimental results.The variationof mechanical properties of post-TiAlN coatings was attributed to the change of lattice constant which caused by HCPEB treatment.The Ti₃AlN₄ calculation results showed that the elastic modulus of Ti₃AlN₄ was 421.77 GPa.The Ti and Al atoms vacant have a very small impacton Elastic Modulus,but the N atom vacancy played a key role in the elastic modulus of Ti₃AlN₄,even decrease to 82.92 GPa.