| The properties of discontinuous reinforced titanium matrix composites have widespread applications than that of continuous reinforced titanium matrix composites.In order to study the effect of microstructure on the mechanical properties of the composites,this paper prepared a Ti Bw/TA15 composite material with columnar distribution through a low-energy ball milling+pre-sintering+canned hot extrusion process,and analyzed the microstructure evolution by microstructure observation The effect of the reinforced structure on the material properties is studied.The relationship between the hot extrusion temperature(850℃-1100℃)and the matrix structure was clarified,and the microstructure of the Ti Bw/TA15 and TA15materials obtained by extrusion was compared therefore the effect of whiskers on the material structure was clarified.The results show that extrusion temperature higher than 1050℃,the matrixβphase undergoes significant dynamic recrystallization,and its recrystalliza tion ratio is about 74%at 1100℃.Correspondingly,its room temperature structure is dominated by lamellarβtransformation structure.The structure is composed of<0001>plane parallel extrusion direction and<10-11>plane parallel extrusion direction formed byβphase transformation.The dynamic recrystallization ofα-phase and high-temperatureβ-phase occurs simultaneously during extrusion in the nearβ-phase region(1000-1050°C).Its room-temperature structure is composed of a small amount of initial equiaxedα-phase andβ-transformed structure,which is affected by the deformation of high-temperatureβ-phase.<0001>α//ED texture component is the strongest,and this phenomenon becomes more obvious as the temperature decreases.When the extrusion temperature is lower than 975℃,the matrix mainly deformsαphase andβphase.The room-temperature structure is composed of the initial elongationαphase andβ_t.The room-temperature texture contains about 15%of the deformedαphase with<10-10>surface parallel extrusion direction and<101>β//ED cooling transition<0001>α//ED,<10-11>α//ED,<10-10>α//ED texture components.The addition of the reinforcement phase raises theβtransformation temperature,restricts the high temperatureβgrain growth and weakens the Burgers orientation relationship,thereby promoting the transformation of the matrix structure to the refined equiaxedαphase and the coarse lamellar structure,and increases with the extrusion temperature,the average aspect ratio of the reinforced phase increased.Subsequently,the tensile strength and high temperature tensile properties of Ti Bw/TA15 and TA15 materials were tested and the strengthening mechanism was analyzed.The results showed that,unlike the pure matrix,the yield strength of the composite material showed a decreasing trend.Specifically,the matrix grain boundary strengthening effect of theβphase region is strong,and the whisker strengthening effect is not obvious.The yield strength of the composite material and the TA15 material is not much different,both of which are about 1300MPa.The corresponding fractures are small and shallow,which is typical of brittle fracture.In comparison,the material obtained by extrusion in the nearβ-phase region is composed of a small amount of equiaxedα-phase andβ-transformed structures,and its strength has been greatly improved compared to pure TA15 material,with an increase of about 20%during extrusion at 1000°C.Extrusion in the dual phase area ofα+β,the length-diameter ratio of the whisker of the material is significantly improved and theαstructure is deformed more,and the whisker reinforcement effect is obvious.On this basis,based on the elastoplastic theory and considering the effect of the limit length-to-diameter ratio,the shear lag theory is used to establish a model to analyze the stress of the whiskers and then estimate the yield strength of Ti Bw/TA15.The deviation between the predicted value and the experimental result is less than 1%.It provides an important reference for the subsequent control design of non-uniform structure matrix structure and whisker characteristics. |
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