Study On The Microstructure And Mechanical Properties Of Ti-Fe-Y System Alloys

Titanium alloys have been widely applied due to their high specific strength and good ductility.Ti-Fe alloys have gradually attracted attention due to their high compressive strength exceeding 2 GPa and good ductility.In this paper,we first prepared(Ti_70.5Fe_29.5)_100-xY_x(x=0,1,2,3,4)alloys by vacuum arc melting followed by suction casting.(Ti_70.5Fe_29.5)₉₈Y₂ was selected to use solid solution elements Nb,Cr and interstitial elements O,C instead of a certain amount of Fe element.The microstructure of alloys was analyzed and the mechanical properties were tested.Researchs indicate that:(1)The microstructure exhibits hypoeutectic characteristics after adding rare earth element Y to the Ti-Fe eutectic alloy.The first precipitated phase is dendritic?-Ti,while the eutectic structure is lamellar Ti Fe and?-Ti.The thickness of lamellar Ti Fe phase in Ti_70.5Fe_29.5is about1?m,while the thickness of lamellar Ti Fe phase in(Ti_70.5Fe_29.5)₉₈Y₂ is only about 300 nm.The microstructure has achieved substantial refinement.(2)Due to the different extent of refinement,the compressive strength and plasticity of Ti-Fe-Y alloys increase and then decrease simultaneously with the increase of Y element,but overall improvement is significant compared with Ti_70.5Fe_29.5.(Ti_70.5Fe_29.5)₉₈Y₂ exhibits the best mechanical properties with high compressive strength exceeding 2447 MPa and large plastic strain of 14.2%,while Ti_70.5Fe_29.5 exhibits a compressive strength of 2058 MPa with limited plastic strain of 6.0%.(3)A small amount of Nb element can further refine the eutectic structure of Ti-Fe-Y alloys,while an excessive amount of Nb element can refine the first precipitated phase.(Ti_70.5Fe_24.5Nb₅)₉₈Y₂exhibits a compressive strength of 2472 MPa with large plastic strain of20.7%,while(Ti_70.5Fe_19.5Nb₁₀)₉₈Y₂ exhibits a compressive strength of 2337 MPa with larger plastic strain is 36.4%.Therefore,Nb element can significantly improve the plasticity of alloys and hardly affect the compressive strength.(4)The?-Ti matrix phase was coarsened to a large extent because of the large difference between Cr atom radius and Ti atom radius,which further reduces the solubility of Fe element in the matrix and precipitates along the grain boundaries eventually.The formation of reticular structure leads to the damage of machanical properties.The compressive strength of(Ti_70.5Fe_24.5Cr₅)₉₈Y₂ and(Ti_70.5Fe_19.5Cr₁₀)₉₈Y₂ was 1430 MPa and 1301 MPa respectively,and the plastic strains were 2.2%and 6.9%respectively.(5)The presence of trace O element has almost no effect on the morphology and size of Ti-Fe-Y alloys,but the Y-rich spherical phase is reduced.The analysis suggests that trace O atoms can be combined with surplus Y atoms in the matrix,thereby reducing the precipitation of brittle phases.The compressive strength of(Ti_70.5Fe_29.25O_0.25)₉₈Y₂ and(Ti_70.5Fe₂₉O_0.5)₉₈Y₂was 2477 MPa and 2310 MPa respectively,and the plastic strains were 13.4%and 18.0%respectively.Therefore,Ti-Fe-Y alloys are not sensitive to the O element.(6)C atoms can be combined with Ti atoms to form Ti C reinforcing phases and dispersed in the matrix,thereby improving the strength of alloys.The compressive strength of(Ti_70.5Fe_29.25C_0.25)₉₈Y₂ and(Ti_70.5Fe₂₉C_0.5)₉₈Y₂ was 2503 MPa and 2536 MPa respectively,and the plastic strains were 10.0%and 13.9%respectively.Therefore,C is an effective strengthening element of the Ti-Fe-Y alloys with little effect on plasticity.As the increase of C element,the strengthening effect is more obvious.