Investigation On Erosion-corrosion Behaviors And Cavitation Erosion-Corrosion Behaviors Of Al Alloying ?-Ta₅Si₃ Nanocrystaline Coating

In this work,to obtain the optimized Al addition,the structural stability,mechanical properties and electronic structure of?-Ta₅Si₃ with different Al additions are systematically investigated by first-principles density functional calculations.The binary and ternary?-Ta₅Si₃ are thermodynamically and mechanically stable,while Al addition reduces their thermodynamic stability slightly.The elastic constants,bulk modulus?B?,shear modulus?G?and Young's modulus?E?of?-Ta₅(Si_1-xAl_x)₃ are calculated.The results for the?-Ta₅(Si_1-xAl_x)₃ show that the values of bulk modulus?B?,shear modulus?G?and Young's modulus?E?decrease with increasing Al content,suggesting that the Al alloying weakens the hadness and shear deformation resistance of?-Ta₅Si₃.Meanwhile,the toughness of?-Ta₅Si₃ after Al addition has been evaluated according to the bulk/shear modulus?ratio B/G ratio?and Poisson's ratio criteria,indicating Al alloying improves the toughness of?-Ta₅Si₃.In general,the D8m-structured ternary?-Ta₅Si₃,where two Si^4a atoms are replaced by two Al atoms,shows the better ductility compared to other Al alloyed?-Ta₅Si₃.To further explore the toughening mechanism,the density of states for?-Ta₅(Si_1-xAl_x)₃ have been calculated,demonstrating that the form of Al-Ta metallic bonds and the reduction of covalent property for the?-Ta₅Si₃ should be accounted for the improvement of ductility.Depending on on the optimal amount of Al addition,the?-Ta₅Si₃ and?-Ta₅(Si_0.83Al_0.17)₃nanocrystalline coatings are deposited onto mirror-polished 316L stainless steel substrates by a double cathode glow discharge plasma method.The phase identification,microstructural characteristic and composition of the coatings are analyzed using X-ray diffraction?XRD?,scanning electron microscopy?SEM?incorporating an X-ray energy dispersive spectroscopy?EDS?analyser attachment and transmission electron microscopy?TEM?.The XRD result shows that both coatings are consisted of only tetragonal?-Ta₅Si₃ phase.The cross-sectional SEM morphology indicates that the two coatings with a thickness of²0?m exhibit a dense and homogeneous microstructure along the thickness and well-attached coating/substrate interface.The as-deposited?-Ta₅(Si_0.83Al_0.17)₃ coating is composed of nearly rounded D8_m-?-Ta₅Si₃ grains with an average size of⁴ nm and exhibited the intense?002?and?400?preferred orientation.After Al alloying,the hardness and the residual stress of the?-Ta₅Si₃decreased by nanoindentation tests,but the contact damage resistance and adhesion strength are increased.The electrochemical tests in 3.5 wt.%NaCl solution show that the Al alloying improves the corrosion resistance of the?-Ta₅Si₃.The behavior of erosion-corrosion and cavitation erosion-corrosion for the?-Ta₅Si₃ and Al-alloyed?-Ta₅(Si_0.83Al_0.17)₃ coatings are investigated with the assistance of electrochemical measurements in laboratory.Based on the test results and the analysis of the materials failure,?-Ta₅(Si_0.83Al_0.17)₃ coating is found to possess the best resistance against erosion-corrosion and cavitation erosion-corrosion in 3.5 wt.%NaCl solution among the tested materials.