Study On Preparation And Magnetic Properties Of Fe-Co-B-P-C Amorphous Nanocrystals Alloys

In this thesis,a series of Fe Co BPC amorphous and nanocrystalline alloys are prepared by single-roller melt spinning method and subsequent crystallization using industrial raw materials.With using differential scanning calorimetry(DSC)and X-ray Diffraction(XRD),the thermal stability,crystallization activation energy and structure are investigated for amorphous and nanocrystalline alloys.In addition,the magnetic properties and nanoindentation mechanical behaviors of amorphous and nanocrystalline alloys are studied.The effects of composition and heat treatment on the microstructure and properties of amorphous and nanocrystalline soft magnetic alloys are systematically investigated in order to obtain excellent magnetic materials with high Ms and low coercivity.The relevant experimental results show that:(1)Fe_85-xCo_xB₁₁P₂C₂(x=11,13,15,17,19,21)alloy system has a strong ability to form amorphous,and a completely amorphous structure can be prepared under the condition of a copper roller speed of 35 m/s.Thermal analysis results show that when the Co content is 15 at.%and 19 at.%,The two amorphous alloys have larger crystallization activation energy.The quenched Fe₇₀Co₁₅B₁₁P₂C₂ amorphous ribbon has the highest saturation magnetization of 202 emu/g.Compared with the quenched Finemet amorphous ribbon saturation magnetization of 135 emu/g,the saturation magnetization is increased by about 1/3.However,the intrinsic coercive force of the two types of amorphous ribbons are 26.5 Oe and 28.1 Oe,respectively,the difference is not obvious.(2)The heat treatment results show that during the annealing process,both Fe₇₀Co₁₅B₁₁P₂C₂ amorphous ribbon and Finemet amorphous ribbon precipitated nanocrystalline?-Fe phase.The best annealing process for Fe₇₀Co₁₅B₁₁P₂C₂ amorphous ribbon is:the annealing temperature is 703 K and the holding time is 30 minutes.The nano-grain size is 18.3 nm,the saturation magnetization is 221 emu/g,and the coercive force is reduced to 14.9 Oe.Compared with the annealed Finemet alloy,the saturation magnetization is 68 emu/g,which has a broader application prospect.(3)The test results of nano-indentation indicate that the quenched Fe₇₀Co₁₅B₁₁P₂C₂amorphous ribbon has the lowest hardness and elastic modulus and exhibits good toughness.Due to the precipitation of nanocrystals in the annealed ribbon,the hardness and elastic modulus of the ribbon are significantly improved,and the brittleness of the material is increased.There is a creep platform in the holding zone of the indentation of the quenched and annealed alloy ribbons.the quenched creep rate and creep depth are greater than the annealed amorphous ribbon.