Preparation And Mechanical Properties Of ?Ti₅Si₃-TiAl?/TiAl And Tial Layered Materials

With the development the modern aerospace industry,the design requirements for high-temperature structural materials are also increasing.TiAl-based alloys have become one of the most promising materials in the aerospace industry due to their high specific strength and specific modulus,excellent high temperature oxidation resistance and creep resistance.However,TiAl intrinsic brittleness and poor fracture toughness have become the biggest obstacles on the road to practical use.In recent years,it has been demonstrated that structural design of materials can improve their overall performance and even increase strength and plasticity.Therefore,our group obtained the layered TiAl alloy with equiaxed crystal??-TiAl?and lamellar??₂-Ti₃Al/?-TiAl?layer distribution by elemental foil annealing method,and the comprehensive performance is better.Based on the previous results,the content of the lamellar structure in the layered TiAl alloy was further adjusted by optimizing the heat treatment process to control the layer thickness ratio,and the high temperature mechanical properties and fracture behavior were studied.In this paper,pure Ti foil and Al-Si foil were used as raw materials to prepare?Ti₅Si₃-TiAl?/TiAl layered composites with equiaxed crystal and lamellar layer distribution by vacuum hot pressing sintering and reaction annealing heat treatment.The Al-Si foil was replaced with a pure Al foil,and a TiAl layered composites was prepared by the same process as a control system.The thickness of the sheet layer was controlled by controlling the heat treatment process,and the influence of the heat treatment process on the content of the lamellar layer was analyzed.The effects of Ti₅Si₃ particles and layered structure on the high temperature mechanical properties and fracture behavior of the materials were analyzed by high temperature tensile test.First,the metal foils are alternately arranged and subjected to hot pressing treatment to obtain a composite panel having a good interface.The composites were subjected to low-temperature heat treatment to obtain a Ti/TiAl₃ layered composite plate.During the low temperature annealing process,the temperature not only affects the reaction rate,but also affects the diffusion behavior.Too high or too low is not conducive to subsequent heat treatment.The optimized low temperature annealing process was finally determined to be 660°C/3h-680°C/7h.The composite plate is subjected to high-temperature heat treatment to obtain a?Ti₅Si₃-TiAl?/TiAl layered composite plate in which equiaxed crystals and lamellar crystals are alternately arranged.The TiAl layered composites were obtained by the same heat treatment method.The temperature affects the thickness of the lamellar layer by affecting the diffusion rate of the element.The higher the temperature,the thicker the sheet structure.The degree of uniformity of the interlayer components affects the formation of the lamellar structure by affecting the distribution of the components.When the content of Al is too high,the more uniform the composition,the thinner the layer;when the content of Al is moderate,the more uniform the composition,the thicker the layer.Compared with furnace cooling,air cooling results in a reduced lamellar content,but the lamellar spacing is small.The high temperature tensile test shows that the tensile strength of?Ti₅Si₃-TiAl?/TiAl layered composite plate is 294MPa at 800°C,the plasticity is poor,and the low temperature tensile properties are related to the high content of Al.The fracture characterization of the material reveals that the interlaminar layer is dominated by intergranular fracture,while the main fracture mode of the coarse crystal in the TiAl layer is transgranular fracture.The main fracture mode of fine crystal is intergranular fracture.The tensile strength of the TiAl layered composites at 880°C is 408MPa and the elongation is 4.24%.The fracture characterization of the material shows that the fracture mode of the lamellar+Ti₃Al layer is mainly quasi-dissociation fracture,while the intergranular fracture and quasi-dissociation fracture exist simultaneously in the TiAl layer.