Glass Forming Ability And Deformation Behavior Of New Al-Ni-Er Based Metallic Glasses

Al based metallic glasses have atteacted widely attention due to their high specific strength,high elastic limit,and nice corrosion resistance,which make them be the light metallic glass material with well application prospect.However,the applied range of Al-based metallic glasses is limited because of their poor glass forming ability and non-ductile fracture at room temperature.Therefore,in the thesis,the main research contents are carried out around these two key questions.By mean of the stable clusters line model and microalloying,we successfully synthesized Al-Ni-Er based metallic glass ribbons and bulk metallic glass（BMG）rod with 1 mm diameter with good glass forming ability and large plasticity.We analyzed shear deformation behavior for Al-Ni-Er based metallic glass by means of nanoindentation,focused ion beam,quasi-static compression test and in-situ TEM tension.The main results are summarized as follows:Based on the stable clusters line model,the prediction of the Al-Ni-Er alloy glass forming ability was achieved.A series of Al-Ni-Er-La and Al-Ni-Er-Co-La metallic glass compositions were successfully fabricated by adding trace rare earth element La and transitional elements Co to micro alloying,by means of conventional melt spinning quenching method.The results show that the values of T_rg were raised from 0.44 up to 0.47,and the values of T_g and T_x eventually promoted 29.7 K and 33.7 K respectively,with the additive La and Co elements,which significantly improved the glass forming ability and thermal stability.In addition,critical millimeter scale of the sample dimension was found in Al85Ni5Er4Co2La4,Al85Ni4Er4Co3La4,and Al86Ni7Er5Co2La1.The results of the nanoindentation test showed that the serrated plastic flow phenomenon occurring in the nanoindentation load curve of Al-Ni-Er metallic glass at room temperature.The indentation deformation characteristics indicated that the surface around the indentation of most samples had pile-up by pressing upward and outward,showing that Al-Ni-Er based metallic glass had larger plastic deformation capacity.The TEM results shows that the nanocrystals precipitate under the indentation.The isothermal annealing test on Al₈₅Ni₇Er₈ metallic glass showed that a large number of fcc-Al nanocrystalline precipitated from the metallic glass matrix when the annealing time was 60 and 90 minutes,and the alloy nano hardness increased from 3.43 GPa to 5.55 and 5.7GPa,which suggested that the fcc-Al nanocrystalline has a significant reinforcement to the metallic glass matrix.The grain size of the nanocrystalline had not significantly grown after the annealing process,whereas,the quantity of nanocrystals are obviously increased.Therefore,the effect of nanocrystalline quantity on the mechanical properties of Al-based metallic glass was greater than the nanocrystalline grain size.The quasi-static experimental results of Al-Ni-Er-Co-La bulk metallic glass showed that the plastic strain was larger than 11%,and obvious work hardening effect and serrated plastic flow phenomenon could be observed.SEM results showed that multiple shear bands with high density were produced in compression.The multiple shear bands interaction could inhibit the failure of bulk metallic glass,eventually improved the material flow stress and plasticity.For further revealing the mechanism during the deformation process for metallic glass,nanoscale tensile samples were fabricated on the Al-Ni-Er based metallic glass ribbons using by focused ion beam processing technology,and the In-situ tensile experiment was proceeded in the transmission electron microscopy.The results suggested that the metallic glass nanowires showed obvious size effect.The strain reached to 14.6%,and keep the amorphous state after fracture.The metallic glass nanowires plasticity and fracture pattern are closely related to the thickness of the nanowires.