Fabrication,Microstructure And Properties Of Laminated High Nb-TiAl Composite Sheets

TiAl-based alloys are considered to be ideal for high temperature applications due to high modulus of elasticity,high creep and oxidation resistance.However,It is also difficult to process TiAl-based alloy sheets using conventional manufacturing processes,such as forging,rolling,etc.due to the inherent brittleness of intermetallic compound.people are inspired by the high-strength and tough shell nacre composed of layered hard phase and organic matter.In this paper,pure Ti foil,pure Al foil and pure Nb foil are used as raw materials to prepare layered high Nb-TiAl composite board by hot pressing sintering process and subsequent heat treatment.The layered high Nb-TiAl composite sheets are formed by alternating a unique fully-lamellar?₂/?layer and an equiaxed?-TiAl layer.The preparation process of layered high Nb-TiAl composite sheets were optimized,and the microstructure change,reaction synthesis mechanism and mechanical properties of the composite sheets were studied.A multi-layer Ti/Al/Nb composite board with good interface bonding was prepared by hot pressing at 580°C/2h/90MPa.The composite sheets were subjected to low temperature heat treatment at different holding times at 600⁷00°C to determine the best low temperature heat treatment process.In the low-temperature heat treatment process,the solid-liquid reaction is used to accelerate the diffusion between the elements,and a new?Ti,Nb?Al₃ reaction layer is formed at the interface between the Al layer and the Ti?Nb?layer.As the reaction layer thickens,the gap due to the Kendall effect also becomes wider and wider.At 660?for 10h,the Al layer of the multilayer Ti/Al/Nb composite sheet is almost completely consumed,forming?Ti,Nb?Al₃.In the high temperature heat treatment stage,the?Ti,Nb?Al₃ and the unreacted Ti layer and the remaining Nb layer continue to undergo diffusion reaction to form high Nb-TiAl,and the layered high Nb-TiAl composite sheets are formed by alternating a unique fully-lamellar?₂/?layer and an equiaxed?-TiAl layer.A special Blackburn orientation relationship between the?phase and the?₂ phase in the fully-lamellar?₂/?layer is{0001}?₂?{111}??<11^-20>?₂?<11^-0>?.There are also?-TiAl twins crystals in this region.The prepared layered high Nb-TiAl composite sheets was tested for room temperature fracture toughness in two different directions.The fracture toughness of the loading side parallel to the normal direction was 25%higher than the fracture toughness of the loading mode parallel to the rolling direction,reaching 14.5MPa·m^1/2.The fracture surface of layered high Nb-TiAl composite sheets has obviously characteristic of cleavage fracture.The composite sheets was subjected to tensile tests at 800? and 900?.At900?,the tensile strength of the material was 400MPa and the elongation was 5.5%.The cleavage fracture in the equiaxed gamma region is brittle,and the interlamellar layer is interposed and interspersed along the lamellar layer.At 900?,the layered high Nb-TiAl composite sheet has a tensile strength of 400MPa and an elongation of5.5%.The cleavage fracture in the equiaxed?region is brittle,and the interlamellar layer is interposed and intercalated along the lamellar layer.