Corrosion And Wear Behaviors Of A ZrCuNiAl Bulk Metallic Glass Of The As-cast And Heat Treatment States

In the present dissertation, a Zr_50.7Cu₂₈Ni₉Al_12.3（at %） bulk metallic glass（BMG） and the alloys with different crystallization volume fraction（Vf） were selected as the model materials. The microstructure of the ZrCuNiAl alloys with different crystallization Vf has been systematically characterized. The corrosion and wear behaviors of the as-cast sample and the samples after heat treatment（HT） in simulated groundwater and simulated seawater and simulated sweat, have been studied. The interaction between the corrosion reaction and wear behaviors of the alloys of different states has been explored.The microstructural observations of the as-cast and the HTed samples have been performed by using transmission electron microscopy（TEM）. With prolonging the annealing time in 463 ℃, the crystalline morphology of alloys transform from massive shape to complicated needle-like shape, yielding a critical transition point at 40 % Vf.The corrosion behaviors of the as-cast and HTed ZrCuNiAl alloy samples have been examined in simulated groundwater and simulated seawater and simulated sweat using potentiodynamic polarization curves and impedance spectroscopy. Polarization results show that the corrosion resistance of alloys in three simulated solutions firstly increased and then decreased with increasing the Vf, yielding the best corrosion resistance at 14 % Vf. Impedance test results indicated that, the corrosion resistance in three simulated solutions, including capacitive arc diameter, the impedance value and the charge transfer resistance of the studied alloy samples follow a sequence as 14 % alloy >as-cast ZrCuNiAl BMG> 40 % alloy > 100 % alloy. Both polarization curves and impedance spectroscopy indicated that, 14 % Vf alloy sample possesses the best corrosion resistance in three simulated solutions, and is better than 316 L stainless steel in simulated groundwater and simulated sweat, and better than Ti-6Al-4V alloy in simulated seawater.Scanning electron microscope（SEM） observations suggest that the alloy with 14 % Vf exhibit the lowest level of pitting corrosion. Energy disperse spectroscopy（EDS） analysis results demonstrated that there exist partial dissolution of Zr, Ni, and Al elements, and the enrichment of Cu element. The immersion test results of the as-cast and HTed ZrCuNiAl alloy samples in simulated groundwater for 3 and 12 days also show that, among the studied alloy sample with different Vf, the 14 % sample exihibits the lowest the corrosion rate and corrosion extent. X-ray photoelectron spectrometer（XPS） results indicated that, after immersing 12 days, the sample surface of 14 % Vf alloy formed dense oxidation film enriched in Zr4+, Al³⁺, Ni²⁺ and deficient in Cu²⁺.The Vickers hardness of the as-cast and HTed ZrCuNiAl alloy samples were measured. With the increase in the Vf value, the hardness of the alloys firstly increases and then decreases, yielding a maximum value in the 14 % Vf alloy sample.The wear behaviors of the as-cast and HTed ZrCuNiAl alloy samples were examined in air and in three simulated solutions. As Vf increases, the coefficient of friction and the mass loss and surface roughous firstly decrease and then increase, yielding a minimum value in the 14 % Vf alloy sample. The above results demonstrated that the 14 % Vf alloy sample has the best wear resistance, among the studied samples of different states. For all the samples of different states, the coefficient of friction in three simulated solutions is smaller than that in air, which can be attributed to the formation of lubrication film in the sample surface. The mass loss of the samples in three simulated solutions is greater than that in air while the wear morphology of the samples in three simulated solutions is swallower than in air as evidenced in SEM observations because of the positive interaction between corrosion reaction and wear process.