The Research On Thermal Processing Properties In Supercooled Liquid Region And Room Temperature Mechanical Stability Of Zr-based Amorphous Alloys

Zr-based amorphous alloys have received extensive attention due to their excellent mechanical properties and amorphous forming ability.This article continued the previous research work of the research group and studied the relaxation,thermophysical properties,deformation behavior in supercooled liquid region and the stability of mechanical properties at room temperature of(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂bulk amorphous alloy.The following conclusions can be obtained:?1?The relaxation behavior of five different amorphous alloys including(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂2 was investigated by dynamic thermomechanical analysis.The results illustrate that(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂2 amorphous alloy does not possess significant?relaxation due to its strong glass liquid properties compared to La-based and other weak glass liquid.The loss modulus of the(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂2 3mm rod specimen is slightly higher than that of the plate specimen of the same composition in the theoretical?relaxation temperature range.Although the composition is the same,the rod specimen has a more non-uniform microstructure.?2?The glass transition thermodynamic parameters of(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂amorphous alloy were determined by the continuous heating-up specific heat curve,and the specific heat step of the glass transition,the enthalpy change and the entropy change in the supercooled liquid region were calculated.?3?The thermal conductivity and the thermal diffusivity in the supercooled liquid region of the(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂2 amorphous alloy were studied by a laser thermal conductivity meter combined with specific heat data.The results demonstrate that the thermal diffusion coefficient of(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂2 amorphous alloy in the supercooled liquid region upgrades with increasing temperature,and the thermal conductivity increases firstly and then decreases.In the range of 355.9?to 456.0°C,the thermal diffusivity range varies from 4.744mm²/s to 5.299mm²/s,and the thermal conductivity varies from 16.31W/?m?K?to 20.44W/?m?K?.The as-cast amorphous alloy possesses a relatively high thermal diffusivity and thermal conductivity and has significant advantages in the hot processing of the supercooled liquid region.?4?Using Gleeble-3500 thermal simulation compressor,the rheological behavior and superplastic forming process of(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂2 amorphous alloy in supercooled liquid region at different temperatures and strain rates were studied.The results show that the rheological behavior of the amorphous alloy changes from non-Newtonian rheology to Newtonian rheology in the supercooled liquid region with the decrease of strain rate and the increase of temperature,which leads to good fluidity and suitable for carrying out superplastic forming and other thermal processing methods.During the superplastic processing in supercooled liquid region,the compression rate should be set as 5×10^-3s^-1,and the temperature range is390°C-400°C.?5?Thestabilityandreproducibilityofthemechanicalpropertiesof(Zr_0.72Cu_0.165Ni_0.115)₈₈Al₁₂2 amorphous alloy at room temperature were investigated.The results show that the elastic modulus is basically stable at 23³2GPa,and the numerical distribution of yield strength is relatively concentrated and stable.The compressive strength,yield strength and plastic deformation all exhibited different degrees of size effect that the performance decreased with the increase of the diameter,especially the plastic deformation was the most significant.Overlap of multiple shear bands is observed both in 2mm and 3mm amorphous samples.With the increase of the diameter,the fracture patterns of 4mm and 6mm amorphous samples become sparse gradually,and the number of shear bands decreases.