Glass Forming Ability And Mechanical Properties Of Zr(Co,Cu)Al-based Amorphous Alloys

Amorphous alloys have attracted widespread attention in basic scientific research and practical applications due to their excellent properties,such as,high strength,high hardness,good corrosion resistance and oxidation resistance.However,the glass forming ability(GFA)and room temperature brittleness of amorphous alloys severely limit their application as structural materials.Therefore,it is an important research goal for researchers to improve the GFA of amorphous alloys and improve their room temperature plasticity.Among the many methods for improving GFA and room temperature plasticity of amorphous alloys,the microalloying method is still one of the most simple and effective methods,and the rare-earth element microalloying is the most concerned.In this paper,the effect of Y/Sc alloying on the GFA and mechanical properties of Zr(Co,Cu)Al-based amorphous alloys were systematically studied.The main work and results obtained include the following three aspects:(1)In this study,a amorphous alloy with a diameter of 14 mm was obtained,which were alloyed with high Y element(7-10 at.%),and their GFA was analyzed from the thermodynamic point of view.The results show that the origin of the high GFA of Zr46Co28Al16Y10 alloy was attributed to the smaller Gibbs free energy difference between the supercooled liquid state and crystalline state of the Zr46Co28Al16Y10 than that of Y-free alloy.Meanwhile,four amorphous alloys amorphous alloys with two phases(Zr-rich and Y-rich amorphous)were obtained in alloys with higher Y content(15-36 at.%).The formation process of ZrCoAlY two-glassy-phases amorphous alloys was explained by the solubility gap curve of Zr-Y binary phase diagram and the nature of the liquid phase separation.In addition,the fracture mode of all ZrCoAlY amorphous alloys prepared in this study is brittle fracture,and the fracture strength is higher than 1400 MPa and decreases with increasing Y content.(2)In this study,a series of ZrCoAlSc bulk amorphous alloys were prepared by copper mold casting method.The relationship between glass forming ability,thermal stability,mechanical properties and Sc contents were studied.The experimental results show that the addition of trace element of Sc(?3at.%)has little effect on the GFA and fracture strength of ZrCoAl amorphous alloy,but has a significant improvement on its room temperature ductility.Among them,Zr49Co28Al16Sc2amorphous alloy has the highest fracture strength(1812±20MPa)and room temperature compressive plasticity(?10%)compared with other alloys.By analyzing the fracture morphology,free volume and relaxation characteristics of the prepared amorphous alloys,it is found that the indirect cause of high plasticity of Zr49Co28Al16Sc2 amorphous alloy is the large number of shear bands formation,which was induced by the more free volume compared with other alloys.In addition,the first-principles molecular dynamics calculation results show that the high plasticity of Zr49Co28Al16Sc2 alloy is due to the segregation Sc atoms and unevenly distributed on the matrix.The inhomogeneous distribution of this Sc atom leads to an increase in structural non-uniformity in the entire alloy,which provides more nucleation sites for the formation of shear bands,and ultimately improves the plasticity of the alloy.(3)In this study,ZrCuFeAl and ZrCuNiAlTi amorphous alloys were selected as the research objects,and the effects of Sc microalloying on GFA and mechanical properties were systematically studied.The experimental results show that the GFA of ZrCuFeAl alloys can be significantly improved by small amount of Sc addition,but has little effect of ZrCuNiAlTi alloys.Meanwhile,ZrCuFeAlSc and ZrCuNiAlTiSc amorphous alloys show higher fracture strength than 1790 MPa and 1750 MPa,respectively.In addition,small amount of Sc elements addition can improve the room temperature plasticity of the two ZrCuAl-based amorphous alloys.The two amorphous alloys with the best plasticity are Zr58Cu25Al10Fe5Sc2 and Zr61Cu12.5Ni10A17.5Ti6Sc3,and their plasticities are 6.1%and 8.9%respectively.By analyzing the morphology of the shear band on the side of the fracture,fracture morphology and the residual free volume of the prepared amorphous alloys,it is found that Zr58Cu25Al10Fe5Sc2 and Zr61Cu12.5Ni10Al7.5Ti6Sc3 amorphous alloys have higher room temperature compression plasticity because of their higher residual free volume.These residual free volumes promote the increase of shear band number.crossover and proliferation during compression,and ultimately increase their plasticity.