Study On Thermoplastic Forming Properties And Mechanism Of Lightweight Ti-Be Based Amorphous Alloys

Amorphous alloys have good room-temperature properties,a large elastic limit and a high breaking strength,but their room-temperature plasticity is poor,so they cannot be manufactured by traditional room-temperature plastic working.However,they have an excellent thermoplastic forming ability in the supercooled liquid region and a relatively good molding accuracy.The use of amorphous alloys is promising in micro–nanocomponents and Micro-Electro-Mechanical Systems.Most research on the thermoplastic properties of amorphous alloys has focused on precious-metal bases?Pd-,Pt-,and Au-based?,which are limited by their high price and cannot be applied on a large scale.The titanium-based amorphous alloy has a small density and a high specific strength.In recent years,many large-scale Ti-based amorphous alloys have been researched by many scholars,which has reduced the preparation difficulty of titanium-based amorphous alloys significantly compared with Pd-,Pt-,and Au-based amorphous alloys.Limited research exists on the thermoplastic molding properties and thermoplastic forming properties of titanium-based amorphous alloys,and most of the focus has been on micron-scale research.Research at the nanoscale has not been reported,so we focused on titanium-based amorphous alloys with the following objectives:First,parent alloy Ti₄₅Zr₂₀Be₃₅ was designed to form a Ti–Zr–Be–M alloy system and included 17 alloy compositions of the master alloy.A 3-mm rod-shaped sample of titanium-based amorphous alloy was prepared by vacuum arc melting and copper die casting.The physical properties of the amorphous alloy were characterized by X-ray diffractometry and differential scanning calorimetry to obtain the thermodynamic parameters of the amorphous alloy.The thermoplastic molding properties of the amorphous alloys were evaluated by static thermomechanical analysis.When Fe was doped in the Ti₄₅Zr₂₀Be_35-xFe_x and(Ti₄₅Zr₂₀Be₃₅)_100-xFe_x systems at 4 at.%–6 at.%,the amorphous alloy thermoplastic molding performance was improved significantly compared with the master alloy.The thermoplastic forming property of the best-performing alloy Ti₄₅Zr₂₀Be₃₀Fe₅ was more than 2.5 times that of the parent alloy Ti₄₅Zr₂₀Be₃₅.The relationship between the thermoplastic forming properties and thermodynamic parameters of each alloy was investigated.There was a clear linear relationship between the thermal formability of the amorphous alloys and the normalized parameter S.The S-parameter needs to be calculated from the thermodynamic parameters obtained by differential scanning calorimetry,which is time-consuming and labor-intensive for the development of a new alloy.In this study,MATLAB was used to establish a back-propagation neural network,and its weight threshold was optimized by using a genetic algorithm.A large amount of data were used as a training sample.The physical,chemical,and thermodynamic parameters of the alloy were used as an input to the network to reflect the thermoplastic forming properties of the alloy.The parameters were used as the network output.Eight types of titanium-based amorphous alloys were selected to verify the generalization ability of the neural networks.The output results show that the S-parameters that were calculated from the thermodynamic parameters of the titanium-based amorphous alloys agreed well with the S-parameters that were predicted by neural networks.Eight data sets provided a consistent trend,the error between the S values was less than 15%,and the S values of the individual alloys tended to be consistent,which verifies the practicability and generalization of the BP neural network that was established in this study.Because of the limited thermoplastic deformation ability of titanium-based amorphous alloys,existing research on titanium-based amorphous alloys focused mostly on the micrometer scale.Because of the active nature of the elemental Ti,it was oxidized easily under high-temperature conditions,and the research was carried out under vacuum.In this study,an amorphous alloy Ti₄₅Zr₂₀Be₃₀Fe₅ with an excellent thermoplastic deformation ability was obtained by using a composition design.By using thermomechanical analysis to study the viscosity change during heating,The time-temperature-transformation curve of Ti₄₅Zr₂₀Be₃₀Fe₅ was established by an isothermal crystallization experiment.Combined with the viscosity–temperature curve,a suitable temperature was selected to provide the amorphous alloy with a low viscosity and a sufficient time window at this temperature.Combined with the improved Hagen–Poiseuille's equation and Karman's nonlinear equation in the cylindrical coordinate system,the thermoplastic forming of the Ti₄₅Zr₂₀Be₃₀Fe₅ amorphous alloy was used to guide the selection of nanomolding process parameters.At 694 K and 1/60 s^-1,the amorphous alloy filled the 400-nm pore size anodic aluminum oxide Template in air to form a nanometer column with a 400-nm diameter and a height-to-diameter ratio higher than 3.Through correspondence between the height–diameter ratio of the formed nanopillars and the force,the rationality of the thermoplastic forming map of the amorphous alloy was also verified.