Effect Of Strain Rate On The Mechanical Behavior Of Amorphous Alloys And Their Composites

Amorphous alloys and their composites have received extensive attention due to their excellent performance and numerous characteristics.The deformation behavior of such materials at different strain rates is of great significance in engineering applications and fundamental theoretical research,and many researchers have conducted a lot of research on them.However,due to the limitations of experimental methods,many issues cannot be thoroughly and comprehensively studied.In this paper,the main characterization method of material dynamic deformation,that is,the traditional split Hopkinson pressure bar technology(SHPB),has been greatly improved,mainly including the establishment of a full SHPB model,and a new method of medium strain rate loading and dynamic deformation interruption.On this basis,the effect of strain rate on the mechanical behavior of amorphous alloys is studied in detail,including the influencing factors of the dynamic mechanical behavior of amorphous alloys,the correlation between dynamic compressive strength and fracture behavior,mechanical behavior under a wide range of strain rates,the fracture fractal behavior under high strain rates and dynamic interruption experiments of amorphous alloys.Finally,the mechanical behaviors of three types of amorphous composites with different structures under different strain rates are studied in detail,including a series of CuZr-based amorphous composites,high-stability ?-dendritic phase-reinforced TiZr-based amorphous composites and TiZr-based amorphous composite with stress-induced martensite transformation.Due to the complexity of the split Hopkinson pressure bar technique,the required constant strain rate can only be approached through reverse experiments,that is,multiple incident wave shaping experiments.The workload is huge,but the efficiency is incredibly low.The best experimental method is to calculate various experimental parameters based on the required strain rate and only perform a few dynamic loading experiments to achieve the required strain rate.This requires the establishment of a full model SHPB for simulation experiments.The three main modules of SHPB,bullets,shapers and sample loading were independently modeled,and SHPB simulation equations were proposed.The theoretical predictions and experimental results are in good agreement.A new medium strain rate loading method is proposed.Different shapers can be used to control the duration of the incident wave and realize the medium strain rate loading of amorphous alloys and their composites.Several new SHPB interruption experiment methods are proposed.Among them,single pulse loading expansion,changing bullet length and special shaper design can realize interruption experiment for different strains.The effect of preparation method and sample size on the mechanical properties of Ti32.8Zr30.2Ni5.3Cu9Be22.7(ZT3)amorphous alloy was studied.The results showed that the mechanical properties of ZT3 prepared by flip casting at different strain rates were better than those of injection casting and drawing rod casting.It was also found that ZT3 alloy has a significant size effect,the smaller diameter ZT3 performs better than the large size at a lower strain rate,while the large diameter ZT3 performs better than the small size at a higher strain rate.The effect of Zr/Cu ratio on the mechanical behavior of(ZrxCu)87Ni4Al8Nb1(x=1?3,CZX1-G-CZX3-G)series of amorphous alloys under different strain rates was studied.It was found that with the increase of Cu/Zr ratio,the quasi-static yield strength gradually decreases,while the dynamic yield strength first decreases and then increases.A large number of tests were performed on CZX1-G,CZX175-G and ZT3 amorphous alloys at different strain rates.The results showed that the dynamic compressive strength and the fracture surface area showed a large dispersion,but the dynamic compressive strength has a good correlation with the fracture surface area.The dispersion is mainly attributed to the difference of the average initial free volume concentration of different samples,the stress concentration caused by the SHPB experiment and the high sensitivity to defects under dynamic compression.The mechanical behavior of CZX3-G amorphous alloy at room temperature under a wide range of strain rates was characterized,and it was found that when the strain rate is less than the critical strain rate,the yield strength of the alloy decreases slowly with the strain rate,and when the strain rate is greater than the critical strain rate,the yield strength decreases rapidly.An improved collaborative shear model is proposed,which is in good agreement with the experiment under a wide range of strain rate.The mechanical behavior of CZX175-G and ZT3 amorphous alloys at very high strain rates was characterized,and it was found that the fracture behavior showed obvious fractal characteristics.As the strain rate increases,the fractal dimensions of the two alloys increase with the strain rate,and the proportion of small sizes in the broken pieces gradually increases.Two methods were used to try dynamic loading interruption experiments on ZT3,and the results found that the SHPB control accuracy is not enough and the dynamic plasticity of amorphous alloys is too low,which makes it impossible to conduct dynamic interruption experiments on amorphous alloys.For the(ZrxCu)87Ni4Al8Nb1(x=1?3,CZX1-C?CZX3-C),CZX-C series of amorphous composites,when a single B2-CuZr phase or CuZr2 phase is precipitated on the amorphous matrix,the quasi-static strength of the composite material is higher than that of the amorphous alloy of the same composition,and the CuZr2 phase makes the composite The dynamic strength of the material is significantly lower than that of the amorphous alloy with the same alloy composition.The strength of the composite material with the appropriate size and volume fraction of the B2-CuZr phase at different strain rates is nearly 10%higher than that of the amorphous alloy with the same composition.For the Ti50.32Zr27.92Cu4.56Ni2.12Be9.08MO6(M10)alloy with high ?-phase stability,the dynamic compressive plasticity of M10 alloy is as high as 18%.The compressive plasticity decreases with the increase of strain rate.The number of shear bands increases with the increase of strain rate.The microstructure of the alloy before and after deformation does not change at different strain rates.The main deformation mode of the dendrite is dislocation slip.The dislocation density after quasi-static compression deformation is significantly higher than that of dynamic deformation.The higher dynamic compression plasticity is attributed to the good matching of modulus of amorphous matrix and dendritic phase.For the Ti50.32Zr33.92Cu4.56Ni2.12Be9.08(MO)alloy with stress-induced martensite transformation,the compressive plasticity of MO alloy also decreases with the increase of strain rate.The microstructure of the as-cast dendritic phase is ? phase plus a small amount of co phase.During the quasi-static deformation process,the content of ?)phase gradually decrease as strain increases,the proportion of ? phase transformed into ?" phase through martensite gradually increases,and during dynamic deformation,adiabatic shear temperature increase induces the transformation of ? phase to ? phase due to high-speed deformation with the increase of strain,and the content of co phase decreases first and then increases.The decrease of deformation causes the ratio of ? phase to transform from martensite to ?" phase not as much as at quasi-static strain rates.