Influence of partial substitution of Ti for Al on microstructure, thermal stability and corrosion resistance of novel quaternary Ni33.3Y33.3Al33.4-Ti medium entropy metallic glasses

In this present study, the influence of partial substitution of Ti for Al on microstructure, thermal stability and corrosion resistance of novel quaternary low-density Ni _33.3Y _33.3Al _{33.4- x}Ti _x ( x = 3∼21 at.%) medium entropy metallic glass ribbons (ME-MG ribbons) was investigated. According to the rule of atomic radius similarity, by gradually replacing Al by Ti, we have synthesized a series of multi-component glassy alloy ribbons via using a single roller melt-spinning technique and also have examined their phase structure, thermal characteristics, microhardness and anti-corrosion properties. Besides, the phase composition of some representative annealed ribbon samples and the crystallization activation energy of these melt-spun ME-MG ribbons have been also determined and studied in detail. Results show that all of the rapidly solidified alloy ribbons can maintain completely amorphous nature. However, the thermal stability of ME-MG ribbons becomes reduced with the increasing Ti content. The maximum crystallization onset temperature at the heating rate of 20 K/min is around 706.65 K for Ni _33.3Y _33.3Al _30.4Ti ₃ alloy ribbons. The maximum apparent activation energy of crystallization by means of thermodynamic analysis can be up to ∼803 kJ/mol for Ni _33.3Y _33.3Al _21.4Ti ₁₂ alloy ribbons. The average microhardness value of these metallic ribbons can reach 455 HV _0.1 or more when Ti content is less than 15 at.%, which is approximately 1.5 times the hardness of the Al-based amorphous alloy ribbons. The microstructural characterization of each ME-MG ribbon surface in as-received state and after a period of 45-hour and 75-hour corrosion immersion in 0.6 M NaCl solution was applied by scanning electron microscopy as well. Substituting moderately Al with Ti can effectively improve the anti-corrosion ability; the most positive pitting corrosion potential and the smallest corrosion current density are approximately -0.145 V _SCE and 0.045 μA/cm ² for Ni _33.3Y _33.3Al _24.4Ti ₉ and Ni _33.3Y _33.3Al _27.4Ti ₆ ME-MG ribbons, respectively. Thus, it can be deduced that these new-fashioned ME-MG ribbons possess the superior anti-corrosion property, higher microhardness and acceptable thermal stability simultaneously, which may open momentous possibilities for the development and practical application of high-performance metal materials.