Preparation And Investigation On Microstructure And Properties Of La-based Mtallic Glass Composites

La-based metallic glass alloy has a strong glass forming ability,wide composition range,peculiar physical properties and low glass transition temperature,thus it has a potential application value.However,it always exhibite brittle fracture at room temperature.At present,introducing a crystalline phase into amorphous matrix is an effective method to improve its plasticity at room temperature.In this paper,the effects of the preparation technology on the microstructure and mechanical properties of W_f/La-based amorphous composites and the effects of quenching temperature,isothermal treatment and cooling rate in the solid-liquid region on the microstructure and mechanical properties of the in-situ La-based metallic glass composites are systematically studied from the perspectives of ex-situ method and in-suit method.The results show that:(1)W_f/La₆₂Al₁₄Cu₁₂Ni₁₂ bulk metallic glass composites(BMGCs)were successfully prepared by a new forward melt infiltrating method.Compared with W_f/Zr(Vit1)-based BMGCs,the preparation of W_f/La₆₂Al₁₄Cu₁₂Ni₁₂ BMGCs is simpler and more convenient.The optimal temperature for the preparation of W_f/La-based amorphous composites is 640?.The volume fraction of the tungsten fiber was found to have remarkable influence on compressive properties and fracture mode of the composites.With the increasing of the volume fraction of tungsten fibers,the compressive strength of the composite increases linearly,and its compressive strength satisfies the principle of summation,while the plasticity of the composite shows a trend of increases first and then goes down.The introduction of tungsten fiber can significantly improve the strength of composite,strikingly,the composite with fiber volume fraction of 60%shows a significant plastic strain of 11.7%as well as a high fracture strength of 1600 MPa.The results show that after the heat treatment of the tungsten fiber,the splitting of tungsten fiber during the deformation of composite can be significantly reduced.When the heat treatment temperature of the tungsten fiber is 1000?,the composite had the best performance,with a compressive strength of 1573 MPa and a compressive plasticity of 14.4%.(2)The microstructure and mechanical properties of the in-situ La-based BMGCs can be controlled by the overheating treatment,and the number and size of?-La dendrites in the amorphous matrix greatly reduced with the increasing of quenching temperature.The change of the cooling rate in the solid-liquid region can significantly affect the phase composition and microstructure characteristics of the in-situ La-based BMGCs.As the cooling rate decreases,the number of?-La phases gradually decreases,but the number and size of Al La₃phases increased continuously.When the cooling rate is 5?/min,the composite is composed of amorphous,23.5±3.6?m?-La phase(23.1 vol.%),2.7±0.7?m Al La₃ phase(33.7 vol.%),and the composite shows a compressive strength of 524 MPa and a compression plasticity of8.8%.(3)The comprehensive mechanical properties of in-situ La-based BMGCs can be greatly improved after isothermal treatment in the solid-liquid region.After 5 minutes of isothermal treatment at 430?,The composite is composed of three phases:amorphous,17.2±4.0?m?-La phase(21.7 vol.%),4.5±1.6?m Al La₃ phase(37.2 vol.%),and the composite exhibits a significant plastic strain of 17%,together with a high fracture strength of 564 MPa.The results show that the simultaneous improvement of composite's strength and plasticity can be attributed to two aspects:one is that a large number of Al La₃ phases with higher hardness can effectively improve the strength of the in-situ La-based BMGCs;the other is the synergistic toughening between Al La₃ phase and?-La phase.During the deformation process of the composites,the micron-sized and slightly ductile intermetallic Al La₃ phase and spherical?-La dendrites can effectively block the propagation of the shear bands,resulting in branch and deflection of shear bands,and the deformation of composite shows a localized tendency,which greatly delays the occurrence of catastrophic brittle fracture.At the same time,the phases of?-La and Al La₃ can also participate in the deformation of composite by dislocation slip,which effectively improved the plasticity of the in-situ La-based BMGCs.