Anomalous Thermal Expansion Behaviors Of La(Fe,Si)₁₃-based Compounds And Ti Alloys At Low Temperatures

Anomalous thermal expansion(ATE)materials have become a research hotspot in new materials fields with their unique physical properties and potential applications in space technology,applied superconductivity,cryogenic engineering,and precision electronic instruments,etc.In this thesis,the ATE properties of La(Fe,Si)₁₃-based compounds and TiNbZrO alloys were studied by controlling the chemical elements and heat treatment processes.Various materials with negative temperature expansion(NTE)and zero thermal expansion(ZTE)were prepared.Main research work was carried out as follows:(1)The thermal expansion test instrument was built and can measure the thermal expansion and magnetostrictive properties of solid materials at temperatures ranging from 1.8 K to 400 K and magnetic field up to 14T.Using this measurement system,we also studied the NTE and magnetostrictive properties of LaFe_13-xAl_x compounds.(2)La(Fe,Si)₁₃ compounds were prepared by arc melting.By optimizing the composition,the NTE operation temperature window was broadened,and the ZTE material in the wide temperature region(?=-0.8×10^-6K^-1,15-150 K,?T=135 K)was found.The ATE property of LaFe_13-xSi_x material is mainly related to the magnetic exchange coupling between Fe atoms and the magnetic phase transition.(3)LaFe_10.0Si_3.0C_x material modified by doping C atoms was studied.The effect of C content on the ATE property of La(Fe,Si)₁₃ material was studied.Finally,the ZTE material in the wide temperature zone(?=-0.4×10^-6K^-1,120-229 K,?T=109 K)was obtained.(4)La(Fe,Co,Si)₁₃/Cu composites were prepared by high pressure synthesis.The composite material combines the ajustable thermal expansion of La(Fe,Co,Si)₁₃ and the high thermal conductivity of Cu.It was found that the high pressure synthesis enhanced the controllability of the coefficient of thermal expansion(CTE)of the composites and broadened the NTE temperature range of the composites.Even when the Cu content is 75 wt.%,the composite still has a negative thermal expansion effect(?=-3.7×10^-6K^-1)in a relative wide temperature range(274-304 K,?T=30 K).(5)The?-type TiNbZrO alloy was designed by using d-electron alloy theory.Through the optimization of cold rolling process and the heat treatment process,TiNbZrO alloy with enhanced mechanical properties,controllable CTE and the ZTE property in the wide temperature range(?=-0.04×10^-6K^-1,100-623 K,?T=523 K)was prepared.