Study On Characteristics And Mechanical Properties Of Non-Equilibrium Solidification Microstructures In Al-Ni-Ru Alloy System

As an alloy system in which quasicrystal can be formed,its solidification structure is usually very complex.Especially with the change of solidification conditions,the alloy may have a highly complex non-equilibrium solidification structure.Investigating the distribution and structural characteristics of constituent phases involved in the formation of quenched non-equilibrium solidification microstructure is an effective way to explore new complex alloy phases and novel microstructure,which can provide important reference information for the microstructure design of complex alloy phase materials.The Al-Ni-Ru alloy system is a variety of high-quality quasicrystal forming system.In order to reveal the formation characteristics and properties of rapid cooling non-equilibrium microstructure in the alloy system,the structure,composition and mechanical properties of various non-equilibrium solidification microstructures in the Al₇₀Ni₂₀Ru₁₀ alloy rapid-solidified with different cooling rates were systematically characterized by scanning electron microscope,selected area electron diffraction（SAED）,high resolution imaging（HREM）,high angle annular dark field imaging（HAADF）and X-ray energy dispersion spectroscopy（EDS）,The main research results are summarized as follows:1.Al₇₀Ni₂₀Ru₁₀ alloy spheres with different solidification rates and diameters of about 0.7-3.4 mm were prepared by rapid solidification.The back scattering electron microscopic analysis of its cross section shows that the non-equilibrium solidification structure in the ball is highly complex.According to its solidification morphology and composition characteristics,it can be divided into:area A,the dendrite region with large grains and sparse structure,which is composed of Al Ni phase,Al-Ni-Ru decagonal quasicrystal phase with a period of 0.4 nm and a new cubic complex alloy phase W-Al-Ni-Ru;area B,a lamellar eutectic region composed of fine Al Ni and Al₂Ru phases;area C,a uniform and dense region composed of fine columnar crystals,composed of Al Ni and W phases;area D,the Ru-rich phase concentration area,is composed of Al Ni phase,W phase and Ru-rich phase Al₂Ru,in which the rich-Ru phase solidifies preferentially and aggregates to form different distribution pattern.2.HAADF observation at the atomic scale shows that the structure of 0.4 nm periodicity Al-Ni-Ru decagonal quasicrystal phase in non-equilibrium solidification structure is characterized by the quasiperiodic arrangement of smaller atomic clusters,which is obviously different from the reported structural characteristics of thermodynamic stable Al-Ni-Ru decagonal quasicrystal with the same periodicity.The rapid solidification of Al₇₀Ni₂₀Ru₁₀ alloy is not conducive to the formation of large atomic cluster structural units;higher solidification rate can change the formation type of quasi periodic structure,resulting in the formation of three-dimensional icosahedral quasicrystal.3.The non-equilibrium solidification structures in different alloy spheres were tested by nano indentation,and the induced deformation structures were examined by TEM.The results show that the constituent crystalline phases in regions A,B,C and D have good room temperature deformation ability,while the decagonal quasicrystal in region A have relatively poor room temperature plastic deformation ability.When the indenter is pressed into the crystal phase near the coexisting quasicrystal,cracks pointing to the quasicrystal will appear on the indentation surface,which intuitively reflects the brittle nature of the quasicrystal,while the quasicrystal phase embedded in the crystal phase below the indentation can be protected by the deformation strain coordination of the crystal phase and does not participate in the deformation.