Zero Thermal Expansion And Environmental Stability In ThMn₁₂- And Laves-based Compounds

Zero thermal expansion(ZTE)materials possess unique dimensional stabilities.These materials are much desired in many applications where the thermal stress can be relieved and even avoided.Therefore,ZTE materials play essential roles in engineering applications such as spacecraft,optical instruinstruments,and the container of liquid natural gas ships.However,ZTE materials easily undergo functionality or structural-integrity degradations involving multiple instabilities,for example,the expansion of carbon fibers due to moisture.the aging of MOFs under X-ray radiation,the chalking of ceramics,and the corrosion of alloys,etc.This thesis focuses on the(near)ZTE behavior of alloys,and designed the(near)ZTE alloys with corrosion resistance or mechanical stability.The research tries to extend the potential applications of(near)ZTE materials.In Laves-based compounds,Zr0.8Ta0.2Fe1.7Co0.3 with ZTE behavior was obtained through optimizing the composition of elements with anticorrosion property such as Zr and Ta.The compound shows an isotropic ZTE behavior from 5 K to 360 K as the widest temperature range among all isotropic ZTE alloys.Besides,the compound shows anti-corrosion property.The corrosion rate of Zr0.8Ta0.2Fe1.7Co0.3 is one order lower than that of the classic Invar alloy in the immersion test.Temperature-dependent neutron diffraction,macro-magnetism,and first-principles calculations show the relationship between its ZTE behavior and magnetism,i.e.the magnetovolume effect.Scanning transmission electron microscopy,absorption spectroscopy,and first-principles calculations show that its anticorrosion behavior attributes to its passive film covering the bulk,which provides an extra protection during the corrosion.Such ZTE alloy with anticorrosion property has the potential to broaden the robust applications.especially in marine services.In ThMn12-based compounds,ErFe10V1.4Mo0.6 was obtained by optimizing the composition of V and Mo elements,and it shows a wide-temperature-range 2D near zero thermal expansion behavior.Temperature-dependent neutron diffraction,macroscopic magnetism,and absorption spectrum show that the magnetic moment of Fe element is modified by the non-magnetic elements of V and Mo,which influences the thermal behavior of the compounds.The difference between the thermal expansion behaviors obtained from the dilatometer and the X-ray diffraction shows the compound is highly textured.Based on the study of ErFe10V1.4Mo0.6,which shows anisotropic near ZTE behavior in a wide temperature range,we developed a 2D low thermal expansion alloy as Er0.9Fe10V1.7Mo0.3.The non-stoichiometric design leads to a dual-phase phase alloy with a ductility positive thermal expansion α-Fe phase and a hard 2D zero thermal expansion ThMn12 phase.The mechanism of its abnormal thermal expansion behavior is similar as the ErFe10V1.4Mo0.6.In situ neutron diffraction.scanning transmission electron microscopy and EBSD show the high mechanical strength attributes to the synergy effect of the dual phase,especially the coherent interface between the α-Fe and the ThMn12 phase.The 2D low thermal expansion alloy with high mechanical strength has the potential to face a wide-temperaturerange thermal shock and high stress environment.