Synthesis Of The Al-based Amorphous Alloy And Composites By Spark Plasma Sintering

Al-based amorphous alloy exhibits fantastic potential application due to the high specific strength.However,low glass forming ability?critical size is only 1mm?and almost no macroscopic plasticity restrain the application of the materials.Due to the super plasticity of the amorphous alloy within the supercooled liquid region,powder metallurgy?PM?offers an effective solution to break the size limitation of Al-based amorphous alloy.In the present research,Al-Cu-Ti amorphous alloy was prepared through mechanical alloying?MA?and spark plasma sintering?SPS?.The effect of preparation on the structure and properties of the sintered alloy were investigated.In order to improve the properties of the sintered alloy,different second phase particles?such as the high entropy alloy?HEA?particles and Al particles?were added as the reinforcement.The main research results are as follows,Al₆₅Cu_16.5Ti_18.5 amorphous powder was prepared by MA.The amorphization of amorphous powder was mainly controlled by the amorphization of the solid solution and intermetallics.The amorphization of solid solution resulted from the solid solution diffusion reaction.The grain boundary energy,defects energy,and anti-order energy induced the amorphization of the intermetallics.Al-based amorphous alloy was prepared by SPS.The sintered alloy which was sintered within the supercooled liquid region showed almost no crystallization but low relative density and poor mechanical properties.While the strength of the sintered alloy increased dramatically when sintering above the crystallization temperature.And the strength of the sintered alloy increased firstly and then decreased with the increasing temperature.This could be attributed to the increasing particles bonding strength and the crystallization of the amorphous phase.When the inner part of the particle was amorphous/nanocrystalline and there was nearly no defects at the contact region of the particles,the sintered alloy exhibited the maximum strength.However,high temperature also induced the almost crystallization and grain coarsening of the particles,therefore,the strength of the alloy decreased.Due to the high strength of the HEA,Al-based amorphous-HEA composite was prepared by SPS.The strength of the composite?with 50%volume fraction of HEA?was twice as high as the Al-based amorphous alloy.This could be attributed to the existence of the interdiffusion?ID?layers between the HEA particle and matrix.Micro-crack could propagate stable within the ID layer and the fracture energy increased dramatically,which induced the high strength of the composite.However,the composite showed low plasticity because the HEA particle cannot deform coordinated with the ID layer,fracture occurred within the brittle matrix and ID layer.Due to the high plasticity of Al,Al particles embedding with Al-based amorphous powder could be obtained through MA,the particles were consolidated by SPS to prepare Al-based amorphous-Al alloy composite.The composite showed high strength and good plasticity.This could be attributed to that the composite containing large grain size nanocrystalline,micron grains,and amorphous/nanocrystalline region.The strength difference between the large grain size nanocrystalline?low strength high work hardening ability?and amorphous/nanocrystalline region?high strength low work hardening ability?reduced during deformation,which balanced the distribution of the stress and restrained the plastic instability of the composite,therefore,the composite exhibited high strength and good plasticity.