Investigation On Erosion-Corrosion And Cavitation Erosion-Corrosion Behaviors Of Al Alloyed TaSi₂ Nanocrystaline Coating Under Acid Environment

To better clarify and understand the role of Al in the mechanical properties of the TaSi₂ compounds,the phase stability,elastic properties of the Ta(Si_1-xAl_x)₂ compounds with different Al content were investigated by using first-principles methods.Initially,First-Principles was employed to calculate some important parameters,include formation energy,mechanical properties?such as elastic constants,bulk modulus?B?,shear modulus?G?,Young's modulus?E?,hardness?H??.The binary and ternary TaSi₂ are thermodynamically and mechanically stable,while Al addition reduces their thermodynamic stability slightly.The results for the Ta(Si_1-xAl_x)₂ show that the values of elastic modulus and the hardness?H?decrease with increasing Al content,suggesting that the Al alloying weakens the hadness and shear deformation resistance of TaSi₂.The Pugh's index?B/G?,Cauchy pressures,and Poisson's ratio indicated that there was a threshold value for Al addition,below which the increase of Al content made the Ta(Si_1-xAl_x)₂ compounds more ductile and above which no obvious change occurred.To widen the scope of non-aerospace applications for titanium alloys,the two TaSi₂ and Al alloyed TaSi₂ nanocrystalline coatings prepared by a double cathode glow discharge technique were exploited to enhance the mechanical and corrosion resistance of Ti-6Al-4V alloy in acidic environments.Subsequently,the microstructure and phase composition of the two as-deposited TaSi₂ and Ta(Si_0.875Al_0.125)₂ coatings were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?.The XRD result shows that the coatings are consisted of only C40 TaSi₂ phase.Both the two coatings exhibited a uniform thickness of15?m and dense structure,and were mainly composed of spherically shaped nanocrystallites with an average diameter of about 5 nm.Nanoindentation measurements revealed that Al alloying reduced the hardness?H?and elastic modulus?E?values of the TaSi₂ coating,but enhanced plastic deformation capability.Scratch tests show the adhesion strength between the coatings and the substrate is enough for engineering application,and the addition of Al further enhance the adhesion strength.The wear experiment results indicate that both the two coating exhibit good wear resistance.Erosion-corrosion and ultrasonic cavitation-erosion tests were carried out by immersing samples in 5.0 wt.%HCl solution and 0.5 M HCl solution,respectively.The erosion-corrosion and cavitation-erosion analysis of the tested samples was fulfilled by various electrochemical techniques?such as the current response,open circuit potential,potentiodynamic polarization and electrochemical impedance?,mass loss weight and SEM observation.The results suggested that the two coated samples have proved to be a better protection against the erosion-corrosion and cavitation-erosion damage of Ti-6Al-4V in acidic environments and the corrosion resistance of the TaSi₂ coating is further improved by the addition of Al.