Preparation,Microstructure And Properties Of AlLa₃/La-Based Amorphous Composite

The room temperature plasticity of the La-based amorphous composites was effectively improved by the synergic effect of intermetallic compound AlLa₃ andα-La spherulites.However,the strengthening and toughening mechanisms of the AlLa₃ on amorphous composites and its intrinsic mechanisms still need to be explored.In this present study,two series of La-based endogenous amorphous composite systems based on the composition design were prepared.The microstructure and mechanical behaviors of those two composites were studied respectively.Furthermore,the effects of the volume fraction,size of the AlLa₃ as well as the proportion of different phases on the mechanical performance,and then the strengthening and toughening mechanisms of the AlLa₃ on amorphous composites were investigated.The main conclusions of this work are given as follows:（1）A series of amorphous composite systems of composition（AlLa₃）_x（La₆M₅）_100-x（x=80,85,88,93,95）were obtained on the connection line between AlLa₃ and eutectic point（AlLa₃）₁₄（La₆M₅）₄,which based on the La-Al-M（M is Cu,Ni,Co,and other metal elements）pseudo-ternary phase diagram.The endogenous crystal phases in the structure are AlLa₃ andα-La phases.The AlLa₃ content exhibited an increasing trend with the increase of x content,and the highest AlLa₃ content（～75%）was obtained in M85 and M95.The content and the size of the AlLa₃ phase have a great influence on mechanical performance of the amorphous composite materials.The（AlLa₃）₉₃（La₆M₅）₇ composite displayed the best mechanical properties with the AlLa₃ content of 63.7%and AlLa₃ size of 10μm,which had a compressive strength of 687MPa and a fracture elongation of 14.5%.（2）The La_yAl_90-y（Cu,Ni）₁₀（y=66,68,70,72,75）amorphous composite material system was developed by tuning the La/Al ratio.As the La content increases,the transformation of the endogenous crystal phase occurs:AlLa₂-AlLa₂+La-AlLa₃-AlLa₃+La.The La₇₀Al₂₀（Cu,Ni）₁₀amorphous composite exhibited that all the endogenous crystal phase is AlLa₃,and it contained a high content of the AlLa₃ phase.The volume fraction and size of the AlLa₃ phase is about 62.3%and 12μm respectively.The La₇₀Al₂₀（Cu,Ni）₁₀ amorphous composite showed a superior mechanical performance,which had a compressive strength of 621 MPa and a compressive ductility of 9%.It is confirmed that the La-based amorphous composite material could be strengthened and toughed by single AlLa₃ phase.（3）The AlLa₃ alloy was prepared by quenching and homogenization annealing.The microstructure of the alloy after quenching showed that it consists of AlLa₃ and eutectic structure（α-La+metastable AlLa₂）.After homogenization annealing treatment,the alloy showed an enhanced mechanical performance by improving the microstructure morphologies.The microstructure of the alloy after annealing is:AlLa₃+α-La+AlLa_2.The sample displayed a almost all AlLa₃ microstructure after quenched at 800℃and subsequently homogenization annealed at 500℃.The mechanical properties of the AlLa₃ alloy were effectively improved and it had a compressive strength of 570 MPa and a compressive ductility of 9.5%.In the present section,the prepared AlLa₃ alloy and the AlLa₃ phase in the amorphous composite material have hexagonal close-packed（HCP）structure,a=b=7.195?,c=5.503?,α=β=90°,γ=120°.The AlLa₃ alloy with HCP structure produced a large amount of plastic deformation during the compression process,and there are a large number of dislocation entanglements between the crystals.Due to the superior ductility of the AlLa₃ alloy,it can effectively hinder the expansion of the shear band and promoted its proliferation in the amorphous composite material.Thus,the room temperature plasticity of the amorphous composite material was effectively improved.The adiabatic shear of amorphous matrix and dislocation deformation of AlLa₃ are the main mechanisms of plastic deformation of the La-based amorphous composites.