| In recently, a series of titanium alloy of ultra-high strength has been developed. Similar to other alloys, titanium alloys acquiring ultra-high strength tend to sacrifice the part of the plastic. Therefore, It is a hot issue that to obtain titanium alloys with ultra high strength and high plasticity. In this academic paper,we selected the Ti-Fe based alloy containing Nb and C as the object and investigated the microstructure and mechanical properties of this alloys in as-cast, hot rolling and hot forging state conditions.First of all, we have investigated the effect of C addition on the microstructure and mechanical properties of the Ti95-xFexNb5(x=25,20,15,10) alloys. The research findings reveal that TiC phase, the change of preferred orientation of primary β-Ti phase and a uniform distribution of spherical β-Ti phase dendrites were observed in the hypoeutectic Ti70Fe25Nb5(T70), Ti75Fe20Nb5(T75) alloys with addition of C. The maximum compression strength and the fracture strain of this alloys are 3050 MPa and 3268 MPa, 17.6% and 27.3%, respectively. The research findings reveal that evenly distributed, small strips TiFe precipitated phase in the β-Ti phase were observed in the nearly eutectoid Ti80Fe15Nb5(T80), Ti85Fe10Nb5(T85) alloys with addition of C. The maximum compression strength and the fracture strain of this alloys are 3046 MPa and 3070 MPa, 30.7% and 38.1%, respectively.Secondly, it have been studied that the microstructure and mechanical properties of the as-cast hypoeutectic Ti95-x(Fe97.45C2.55)xNb5(x=25,22,20,18) alloys that have been optimized. The results indicated that in the as-cast alloys the content of eutectic microstructure, primary β-Ti phase and TiC phase and the distribution of each phase significantly influenced the compressive mechanical properties of this alloys. Among them, a small amount of TiC phase, a large number of nearly spherical primary β-Ti phase and a small amount of(β-Ti+TiFe) eutectic distributed at interface of primary β-Ti phase were observed in the Ti75(Fe97.45C2.55)20Nb5(T75C) alloy. The T75 C alloy shows ultra high strength(3268 MPa) and good plasticity(27%).Finally, we investigated the microstructure and mechanical properties of the as-cast nearly eutectoid Ti95-x(Fe97.45C2.55)xNb5(x=15,13,10,8) alloy that were optimized, studied microstructure and mechanical properties of hot rolling(water quench/air cooling) Ti85(Fe97.45C2.55)10Nb5(T85C) and Ti87(Fe97.45C2.55)8Nb5(T87C) alloy and hot forging state T85 C. The results indicated that the precipitated TiFe phase was observed in grain of β-Ti phase of this alloys, the content of the precipitated phase and morphology and size of the precipitated phase apparently influenced the mechanical properties of this alloys. The β-Ti phase with relatively low degree of solid solution strengthening and the TiFe phase distributed in the β-Ti phase with the size approximately is 0.5-9 and 0.5-7 um, respectively,were observed in the as-cast T85 C and T87 C alloys. The as-cast T85 C and T87 C alloys display high strength(3070 MPa, 3024 MPa) and excellent plasticity(38.3%, 39.3%). The grain size of β-Ti phase of the hot rolling alloys and the content of TiFe phase uniformly distributed in the β-Ti phase apparently influenced the mechanical properties of this alloys. Among this alloys, the β-Ti phase with larger grain size and the more content TiFe phase were observed in the T85 C alloy with water quenching after hot rolling. Its tensile strength and elongation are 1063 MPa and 14.4%, and it showed good tensile mechanical properties. The microstructure similar to the microstructure of the T85 C alloy with water quenching after hot rolling was observed in the T85 C alloy with hot forging. The maximum compression strength and compression fracture strain of the alloy are 3192 MPa and 38.3%, and the ultimate tensile strength and tensile fracture elongation of the alloy are 1074 MPa and 14.4%. It shows good comprehensive mechanical properties. |
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