The Glass-forming Ability And Spin-glass Behavior Of Fe-based Bulk Metallic Glasses

Fe-based bulk metallic glasses?BMG?exhibit numerous compelling physical properties,such as ultra-high strength,high wear resistance,excellent soft magnetic properties,unique magnetocaloric effects,etc.In addition,it has the advantages of energy saving and low cost,which make them have great application value in the industrial field and have high scientific importance in understanding condensed matter related physics.The development of Fe-based BMGs in recent years is gradually confirming this assertion.During the research process,the development of new materials with excellent performance and functional characteristics,and the understanding of the relationship between structural and physical properties are constant themes.In this context,the glass forming ability?GFA?and unique spin glass behavior of Fe-based BMGs have been systematically studied in this work.Firstly,based on the Fe-Co-Cr-Mo-C-B-Tm alloy system,by changing the C/B atomic content ratio,Fe₄₂Co₆Cr₁₅Mo₁₄C_xB_21-xTm₂?x=9,11,13,15,17?amorphous alloys were obtained.The C/B atomic content ratio effectively increases the GFA of the alloys to the centimeter level.An amorphous alloy ingot having a diameter of up to 16.52 mm under near-natural cooling is obtained by an improved casting method.While improving the GFA,the mechanical properties of the alloys are also improved,and the maximum fracture toughness can reach 4882 MPa.Changing the C/B content ratio also affects the thermal stability and fragility of their supercooled liquid.The fragility parameter m of the supercooled liquid is between 44 and 51.The decrease of the m value indicates that the supercooled liquid is closer to the Arrhenius behavior,corresponding to greater GFA and mechanical properties.The Avrami index obtained from the isothermal crystallization process decreases with the increase of C content,indicated that the crystallization process gradually changes from being governed by three-dimensional growth at increasing nucleation rate to growth at decreasing nucleation rate.The XPS analysis shows that even small changes in the electronic structure significantly affect GFA.Alloys with greater GFA corresponding to a minimum binding energy of B 1s and C 1s,indicating that the atomic arrangement is more dense,and the density test also confirms this result.The study found that the above metallic glasses show obvious spin-glass behavior.In order to further study this phenomenon,the systematic magnetic test of the above alloys was carried out.Results show that the alloys are paramagnetic at room temperature,and the DC magnetic susceptibility under ZFC and FC process separates at low temperature.As the C content increases,the Curie temperature rises and the frozen temperature stabilizes at 8 K.The peaks of AC susceptibility curves move toward high temperatures with increasing frequency,and the relaxation time parameters are in good agreement with other reported spin-glass systems.In the isothermal magnetization study,the alloys in the low field also exhibits the characteristics of spin-glass.The Arrot curves show that the spin-glass-ferromagnetic transition is a first-order magnetic phase transition,and the ferromagnetic-paramagnetic transition is a second-order magnetic phase transition.The amorphous alloy has a significant magnetocaloric effect during magnetic phase transition and the magnetic entropy change peak shifts toward the high temperature as the applied field increases.In order to study the effect of rare earth elements on the properties of Fe-based BMGs,Fe_44-xCo₆Cr₁₅Mo₁₄C₁₅B₆Tm_x?x=0,2,4,6?alloys was designed based on the previous study.Studies have shown that the alloy maintains a great GFA with the increase of Tm in a relatively wide range,and the mechanical properties of the alloy are degraded due to the non-uniformity of the alloy clusters which leads by the presence of positive mixed heat in the system.The thermal stability of the supercooled liquid of the alloys are affected by Tm addition.The alloys are paramagnetic at room temperature,and also exhibit obvious spin-glass behavior at low temperature.As the Tm content increases,the magnetization and Curie temperature gradually decrease,the frozen temperature increases,which related to the antiferromagnetic coupling and exchange integral.