Effects Of Pre-deformation On The Structure And Mechanical Properties Of Amorphous Alloy Composites With Deformation-induced Phase Transition

Amorphous composites with deformation-induced phase change behavior have been widely concerned by researchers because of their high strength of amorphous alloys,excellent plastic deformation capabilities of crystals,and good work hardening capabilities.However,it exhibits poor repeatability in mechanical properties due to the sporadic and uncontrolled expansion of the shear band in the amorphous matrix,which is similar with most amorphous composites and limits the practical application.Fortunately,the occurrence of phase transition in amorphous composites with stress-induced phase transition can effectively regulate the stress distribution in the composite,which is closely related to the initiation and expansion of the shear band.Therefore,trying to regulate the dynamic characteristics of martensite transformation through stress is of great significance to improve the plasticity and repeatability of properties of amorphous composites.In this paper,the Ti45.7Zr33Ni3Cu5.8Be12.5(ZT-M)amorphous composite with deformation-induced phase change behavior is taken as the research object.Axial pre-compression,lateral pre-compression,the methods of axial pre-tensioning,cyclic loading and stress retention have successfully adjusted the stress-induced phase transition behavior.The effects of different loading stresses and different loading methods on the microstructure,mechanical properties and deformation mechanism of the alloy have been systematically studied.The yield strength,compressive strength,and plastic strain of as-cast ZT-M amorphous composites were 1463 MPa,1896 MPa,and 5.9%.In the transverse preloading process,a single uniaxial pre-compression of 600 MPa to 1100 MPa and 10 cycles were performed in a direction perpendicular to the long axis of the sample.The results show that the single and multiple precompression treatments cannot effectively improve the mechanical properties and repeatability of the amorphous composite.The transverse pre-compressed prefabricated martensite is prone to reverse phase transformation during the performance test in the long axis direction,difficult to remain in the plastic deformation stage,and does not participate in the induced germination and controlled expansion of the shear band.The initiation and expansion of the shear band of the pretreated samples are similar to those of the as-cast state.In the axial pre-compression treatment process,a single uniaxial pre-compression of 600 MPa to 1100 MPa and a cycle of 10 uni-axial pre-compressions,a pre-compression of 900 MPa holding pressure(10 minutes,30 minutes),and a pre-compressed of 900 MPa cycles were performed in parallel to the long axis direction of the sample.The results show that the compressive strength and plastic deformation ability of the alloy after a single pre-compression treatment with different stresses are improved compared with the as-cast samples.After 10 cycles of pre-compression,the performance was further improved.As the treatment stress increased,the compressive strength and plastic strain increased first and then decreased.Among them,the 900 MPa cycle showed good comprehensive mechanical properties after 10 cycles.The results of holding pressure and cyclic preloading under this stress show that the strength,plasticity,and repeatability of the material increase simultaneously with the increase of the holding pressure time and the number of loading cycles.The mechanical property improvement at 900 MPa stress retention for 30 minutes is the most obvious.The yield strength,compressive strength,and plastic strain are 1628 MPa,2046 MPa,and 8.1%,which are 11.3%,8%,and 37.7%higher than those of the as-cast samples,respectively.The axial pre-compression treatment preferentially prefabricates the martensite in a specific orientation,which can promote the occurrence of martensite transformation during the compression test and play a role in adjusting the stress distribution in the sample.During the deformation process,the martensite phase further coordinates the plastic deformation of the alloy by forming deformed twins.Furthermore,the repeatability of the ZT-M alloy properties at a stress of 900 MPa for 30 minutes was further evaluated by the discrete coefficient.Compared with the original sample,the yield strength,compressive strength,and dispersion coefficient of plastic strain were reduced by 0.022,0.015,and 0.024,respectively,and the repeatability was improved by 102.9%,100.5%,and 15.7%,as 900 MPa is slightly higher than the critical stress of the stress-induced martensitic transformation.The prefabricated martensite lamellar spacing is small,which induces the initiation of high-density shear bands.The fracture surface shows a large amount of molten amorphous phase-coated in the crystalline state.In contrast,the "rope-like structure"produced by severe deformation can be observed in some areas.In the axial pre-tension treatment,a uniaxial pre-compression of 600 MPa to 1100 MPa and a single cycle of 10 uni-axial pre-tension,a pre-load of 1000 MPa holding pressure(10 min,30 min),and a pre-load of 1000 MPa cycles were performed in the direction parallel to the long axis of the sample.The results show that a single axial pre-stretching treatment can significantly improve the mechanical properties and repeatability of the material,and the difference between different stresses is not obvious.In the tensile stress state,the preferentially formed martensite orientation is[001]?"//[110]?//loading axis direction,the orientation ?" martensite phase,and metastable ? phase lattice distortion are smaller.Phase change easily occurs.After increasing the number of cycles to 10 times,it was found that as the pre-treatment stress increased,the compressive strength and plastic strain of the material showed a trend of the first decline and then increase.Among them,the compressive strength and plastic deformation amount increased after 1000 MPa treatment,showing excellent performance.Comprehensive performance.Further 1000 MPa pressure holding and cyclic preloading results show that the strength,plasticity,and repeatability of the material are positively related to the pressure holding time and loading cycle.The sample group with 1000 MPa pre-tension for 30 minutes has a compressive strength of 2019 MPa.It has better plastic deformation ability and repeatability.The plastic strain amount reaches 7.9%.The elastic modulus,compressive strength,and plastic repeatability are all improved by 302.9%,30.7%,74.4%as compared with the as-cast samples.From the side morphology of the sample,it was observed that the density of the shear band increased,the expansion path was curved,the multiple shear bands around the phase change grains were initiated,the amorphous melting area on the fracture of the sample increased,and the veins became shorter.