Research On Preparation Of Oxide Dispersion Strengthened Iron-based Materials And Their Properties

Oxide dispersion-strengthened iron-based materials have been widely applied in the aerospace,automotive,and nuclear industries,etc.,due to their excellent mechanical properties and creep resistance.The ultrafine and uniformly distributed dispersoids in the metal matrix can act as effective obstacles to dislocation motion and grain boundary migration,further improving mechanical properties of the ODS alloys.In this study,Fe-Y2O3 nanocomposites with different Y2O3 content were prepared through solution combustion synthesis(SCS)involving liquid-liquid mixing,then consolidated by pressureless sintering and SPS,and a high-performance oxide dispersion-strengthened iron alloy was successfully prepared.The main research contents are listed as follows:(1)Fe-Y2O3 nanocomposites with uniformly dispersed Y2O3 nanoparticles were prepared via SCS followed by hydrogen reduction using ferric nitrate and yttrium nitrate as the oxidizer and the sources of Fe and Y,and glycine as the fuel.The influences of the reduction temperature on phase constituents,grain size and magnetic properties of Fe-Y2O3 nanocomposites were discussed.The optimum reduction process,Fe-Y2O3 nanocomposites were prepared at 400? for 2h When the Y2O3 content was 1wt%,with the reduction temperature increasing,the average grain size and saturation magnetization of the Fe-Y2O3 nanocomposites gradually increase,while the coercivity and specific surface area decrease.The saturation magnetization and coercivity value of the Fe-Y2O3 nanocomposite reduced at 600?reaches 190.3emu/g and 233.60e,respectively,with an average crystalline size of-64nm and specific surface area(SSA)of 10m2/g.The effect of different Y2O3 content on the preparation of nanocomposites was studied.With the increase of Y2O3 content,the particle morphology of the product obtained by the same reduction temperature was basically unchanged,the grain size of the product decreases,and the specific surface area increases.The grain size of the Fe-Y2O3 nanocomposites with different Y2O3 content obtained at 400? is less than 50nm,and the Y2O3 particles are uniformly dispersed.(2)The Fe-Y2O3 nanocomposites with different Y2O3 content were consolidated by pressureless sintering.The effects of different Y2O3 content and sintering temperature on the relative density,microstructure,mechanical properties and magnetic properties of sintered alloys and densification behavior were studied.As the content of Y2O3 increases,the sintering activation energy of the nanocomposites increases,and the sintering densification process slows down.The relative density of the nanocomposites with the Y2O3 content of 0wt%,0.2wt%and 0.5wt%after sintering at 700?,700? and 900? exceeds 95%,reaching 97.3%,95.6%and 95.3%,respectively.And the average grain sizes of the obtained alloys are 0.45?m,0.43?m,and 0.96?m,respectively.But,the nanocomposites with Y2O3 content of 1 wt%and 2wt%is still less than 95%even after sintering at 1 300?.The Y2O3 nanoparticles was uniformly dispersed in the Fe-0.5wt%Y2O3 alloy obtained at 900? and the particle size was less than 100 nm.Fe and Fe-0.2wt%Y2O3 obtained at 700? reach the maximum microhardness and tensile strength values,whicih are 211.9HV0.2,170.9HV0.2,and 510.05MPa,496.91 MPa respectively,while Fe-0.5wt%Y2O3 reaches the maximum microhardness and tensile strength values of 206.2 HV0.2 and 520.60MPa,when the sintered temperature is 900?.Fe,Fe-0.2wt%Y2O3 and Fe-0.5wt%Y2O3 sintered at 1300? reach the saturation magnetization(B6000)of 1.78T,1.76T and 1.74T,the maximum magnetic permeability of 2.92mH/m,2.38mH/m and 1.79mH/m,the coercive force values of 186.7A/m,203.9A/m and 225.7A/m,respectively.(3)The Fe-Y2O3 nanocomposites with different Y2O3 content were consolidated by SPS.The ODS iron alloys with high strength and ductility were successfully prepared.The effects of sintering temperature on the relative density,microstructure and mechanical properties of sintered alloys were investigated,and the strengthening mechanism was revealed.The relative density of Fe,Fe-0.2wt%Y2O3,Fe-0.5wt%Y2O3,Fe-1 wt%Y2O3 and Fe-2wt%Y2O3 sintered at 700?reaches or exceeds 95%,which are 96.8%,96.5%,96.3%,95.8%and 95%respectively.And the microhardness reaches maximum values of 298.0HV0.2,373.5HV0.2,391.9HV0.2,529.4HV0.2 and 570.2HV0.2,respectively.The ultimate compressive strength and total true strain of Fe-2wt%Y2O3 alloys sintered at 600?,650? and 700? reach 2.12GPa,1.86GPa and 1.52GPa with total true strain of 8%,29%and 54%respectively.The grain sizes of Fe-2wt%Y2O3 alloys are 119.6 nm,147.5 nm,and 178.5 nm,respectively,and the Y2O3 nanoparticles are 11.6 nm,15.5 nm,and 19.3 nm,respectively,and the Y2O3 particles are uniformly dispersed in the grains interior.Through experimental and computational analysis,the grain boundary strengthening and intragranular second phase particle dispersion strengthening are the dominant strengthening mechanisms of sintered alloys.