Effect Of Ti Content On Microstructure And Mechanical Properties Of Fe-Cr-Ni-Al-Mn Ferritic Alloy

Precipitation strengthed ferrite alloys have good application prospects in aerospace,nuclear industry and other fields because of their excellent mechanical properties,low density and low cost.In view of the poor mechanical properties of ferrite alloy strengthened by single B2-Ni Al phase above 600^oC,it is a novel idea to introduce other kinds of precipitates to strengthen ferrite alloy.In this paper,Fe-Cr-Ni-Al-Mn ferritic based alloys were prepared by mechanical alloying?MA?and spark plasma sintering?SPS?using Ti H₂ powder,nano Y₂O₃ powder and prealloyed atomized powder as raw materials,Two kinds of powder metallurgy ferritic alloys Fe-5Ni-1Al-2Mn-10Cr-x Ti and Fe-5Ni-1Al-2Mn-10Cr-x Ti-0.6Y₂O₃?x=0,0.5,1,1.5,2??mass fraction,%?were prepared by SPS.The effects of Ti content and nano-Y₂O₃on the microstructure and mechanical properties of the ferrite alloys were investigated.The microstructure and properties of the powders and alloys were studied by means of optical microscopy?OM?,X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,microhardness test and tensile properties test.The hardness of the alloys with different Ti contents first increases and then decreases with the aging time.The hardness of the alloys with different Ti contents reaches the peak value at 0.5 h after solution solution at 900^oC and aging at 550^oC The higher the Ti content,the higher the peak aging hardness.The yield strength of2Ti sample is the highest,which is 1748 MPa.However,the toughness is poor and brittle fracture occurs during tensile test.The yield strength of 1.5Ti peak-aged sample is 1472 MPa and the elongation is about 1.4%.The strength and elongation can be adjusted by aging process.The strength of 1.5Ti peak-aged sample decreases with the increase of tensile temperature,but the elongation increases from 9.2%to53.6%.At 873 K,the yield strength of 1.5Ti peak-aged sample is 394 MPa and the elongation is about 25.0%.TEM results show that B2-Ni Al type precipitates and L2₁-Ni₂Al Ti type precipitates exist simultaneously in 1.5Ti peak-aged samples.The size of B2-Ni Al precipitate is 2-5 nm and the number density is high.The size of L2₁-Ni₂Al Ti precipitate is 5-10 nm,and the number density is small.The addition of nano-Y₂O₃ improves the mechanical properties of the alloy at room temperature,and the increase of Ti content can also improve the strength of the alloy.The peak aging hardness of 2Ti-0.6Y₂O₃ sample reaches 557 HV,but brittle fracture occurs during tensile test.The strength of 1.5Ti-0.6Y₂O₃ peak-aged sample aged for 0.5 h has the highest strength,the yield strength is 1719 MPa and the elongation is about 1.2%.High temperature tensile test results show that the strength of 1.5Ti-0.6Y₂O₃ peak-aged sample decreases with the increase of tensile test temperature,but the elongation increases from 5.8%to 86.0%.At 873 K,the yield strength of 1.5Ti-0.6Y₂O₃ peak-aged sample is 259 MPa and the elongation is about 52.0%.