Preparation And Analysis Of The Thermophysical Properties Of Al-Cu-Fe Ternary Quasicrystals

As early as the 1940s,the concept of thermal barrier coating was put forward.Thermal barrier coating provides thermal insulation and anti-corrosion protection for metal hot end parts of turbine engine and gas turbine,ensures the service life and reliability of hot end parts,and improves the overall efficiency and service life of engine.Now it has been widely used in aircraft and automobile engines and other hot end parts vulnerable to corrosion.Quasicrystal is different from crystal and amorphous materials.It has special lattice structure and unique atomic arrangement rules.Quasicrystal shows the unique thermal and mechanical properties that traditional metal and non-metal materials do not have.It has high heat,corrosion and friction resistance,low surface energy,high hardness,good wettability with metals and so on.Quasicrystals are widely used in surface modification materials and composites because they show the characteristics of high hardness,wear resistance and corrosion resistance similar to ceramics,make up for the problem that it is difficult to recycle the combination of ceramics and metals,and have strong interface bonding ability with the metal matrix.However,the research on the structure and physical properties of quasicrystals are still in the primary stage,which leads to the relative lag of the research on quasicrystal thermal barrier coatings.To explore the effect of cooling rate on the microstructure and properties of Al-Cu-Fe quasicrystal materials,the as-cast and rapid solidification solid strip rejection Al₆₃Cu₂₅Fe₁₂quasicrystal materials with different cooling rates were prepared by the metal mold casting method and single roll spin quenching method respectively.The cooling rates of metal mold copper mold casting and strip rejection quasicrystal materials prepared at different speeds were estimated by Pro CAST simulation software and the Fourier heat conduction formula.The microstructure and phase composition of as-cast and rapidly solidified quasicrystal materials with different cooling rates were analyzed through optical microscope,scanning electron microscope,energy spectrometer,transmission electron microscope and X-ray diffraction,The as-cast Al-Cu-Fe quasicrystal materials were heat treated at（700℃/750℃/800℃）/4h and700℃/（2h/4h/6h）respectively.The effects of cooling rate and heat treatment process on the specific heat capacity,thermal diffusion coefficient,thermal conductivity,elastic modulus and nano hardness of quasicrystal alloys were studied.The results show that:The cooling rate of as-cast quasicrystal sample is about 1×10~2K/s,and the corresponding cooling speeds of strip throwing thin strip samples prepared at different rotating speeds（500/2000/4000）r/min are 6.37×10~5K/s,1.77×10~6K/s and 3.98×10~6K/s respectively.The as-cast Al-Cu-Fe quasicrystal sample mainly contains four phases:λphase(Al₁₃Fe),I phase(Al₆₃Cu₂₅Fe₁₂),βphase（AlFe（Cu））andτphase（AlCu（Fe））,in which I phase is mainly distributed aroundλphase.In the rapid solidification strip rejection sample,due to the rapid rotation speed of the copper rod,and the short contact time between the metal melt and the copper rod,the cooling rate reaches（10~5～10~6）K/s,the melt undercooling degree of the metal is large,and the quasicrystal I phase is formed directly from the undercooled melt without the formation of primaryλphase.Therefore,the strip rejection sample is only composed of quasicrystal I phase with icosahedral structure andβphase with a small amount of Cscl simple cubic structure.The nano hardness and elastic modulus of each phase of the rapid solidification strip throwing material increase with the rotating speed of the copper roller.When the rotating speed of the copper rod reaches 4000 r/min,the nano hardness of quasicrystal phase I reaches the maximum value,19.6 GPa（HV1999.2 GPa）approximately.After DSC thermal analysis of the as-cast Al-Cu-Fe quasicrystal materials cooled at 20℃/min and 50℃/min respectively,it can be obtained that the first precipitatedλphase will not precipitate when cooled at 50℃/min,and only quasicrystal I phase andβphase precipitate,that is,heat treatment can promote the formation of quasicrystal I phase,which plays a positive role in the preparation of single-phase quasicrystal materials.β+τ→I transformation will occur during the heat treatment of Al-Cu-Fe quasicrystals.After heat treatment,the thermal conductivity of Al-Cu-Fe quasicrystals is significantly lower than that of as cast quasicrystals.When the temperature is lower than 150℃,the thermal conductivity of quasicrystal is relatively stable.At this time,the thermal conductivity of as cast Al-Cu-Fe quasicrystal sample is about 5W·m^-1·K^-1and that after heat treatment is about 1.5W·m^-1·K^-1.Comprehensive analysis shows that increasing the cooling rate mainly plays two roles in refining grains and inhibiting the precipitation ofβphase andτphase.When the cooling rate is higher than 4×10~6K/s,the quasicrystal material with almost single phase can be obtained.The quasicrystal and its similar phase can be transformed into quasicrystal phase by annealing at a temperature close to the melting point of quasicrystal,to obtain the single-phase quasicrystal material.