Mechanical Behavior Of In-situ La-based Metallic Glass Matrix Composites Upon Dynamic Tension At Room And Cryogenic Temperature

The short-range ordered and long-range disordered structures in bulk metallic glasses?BMGs?contribute to their excellent mechanical properties.These superior performances make BMGs as potential candidates of novel structural materials.However,BMGs usually lack plasticity and exhibit catastrophic failure upon uniaxial tension at room temperature due to rapid propagation of highly-localized shear bands.This greatly restricts their further development in the engineering field.In order to overcome this shortcoming,a serious of in-situ dendrite-reinforced metallic glass matrix composites?MGMCs?have developed as a new class of metallic materials.These MGMCs exhibit pronounced tensile ductility at room temperature,such as Ti-based,Zr-based,and La-based MGMCs.The ductile dendrites can effectively impede the rapid propagation of shear bands and promote the multiplication of shear bands.Modern engineering requires that materials have excellent mechanical properties in many extreme conditions,such as low temperature and high strain rate,etc.However,only a few studies have been focused on mechanical performances upon extreme conditions.It is important to explore the mechanical performances of MGMCs upon dynamic tension at room and cryogenic temperatures.In this study,La₇₄Al₁₄Cu₆Ni₆?La74?MGMCs are developed.The deformation mechanism is investigated upon high-speed dynamic tension at room and cryogenic temperatures.?1?At room temperature,the current composites display a yielding strength of 420 MPa and ultimate tensile strength of 540 MPa upon quasi-static tension.Apparently,a large work-hardening capacity is obtained during plastic deformation,accompanied by considerable tensile ductility?4%?.The large work-hardening capacity together with a homogeneous elongation is attributed to the formation of deformed twins within dendrites.The deformed twins become the dominant mechanism accommodating plasticity.Upon dynamic tension,the tensile ductility of the current MGMCs is about 2%.The yielding strength is decreased from 400 to 320 MPa with an increase of strain rates from1.2×10³ to 4.0×10³ s^-1,exhibiting negative strain rate sensitivity?SRS?.This negative SRS is highly dependent on thermal softening within the glass matrix upon dynamic tension.?2?At cryogenic temperature,the present composites display a yielding strength of 550 MPa and a homogeneous elongation of 2%upon quasi-static tension.Ductile-to-brittle transition occurs in current La-based MGMCs upon dynamic tension.Shear-band toughness of the glass matrix and dendrites are calculated,respectively.With the increase of strain rates,shear-band toughness of dendrites decreases increasingly,and high strain rate causes deteriorated ductility of dendrite.Shear bands within the glass matrix will be vulnerable to pass through dendrites,which leads to the occurrence of ductile-to-brittle transition.?3?A modified Cooperative-Shear?C-S?model is employed to establish the relationship between the yielding strength and strain rate.Johnson-Cook?J-C?model faithfully predicts the plastic flow behavior of La74 MGMCs upon dynamic tension.