Study On Microstructure And Properties Of Transition Zone Of TC4/Inconel 718 Bimetal Structure Via Laser Additive Manufacturing

The rapid development of the aerospace industry has put forward higher requirements for the thrust-to-weight ratio of aircraft.Compared with nickel-based superalloy structure,the bimetal structure composed of titanium alloy with lightweight and high strength and nickel-based superalloy with excellent high-temperature properties could significantly reduce the weight of parts and increase the thrust weight ratio of the aircraft.In this work,the bimetallic structures composed of TC4 titanium alloy and Inconel 718 nickel-based superalloy fabricated by laser additive manufacturing technology.The effects of direct transition,Cu interlayer transition,and Ta/Cu composite interlayer transition on crack sensitivity,microstructure,and properties of LAM TC4/Inconel 718 bimetallic structure were studied by optical microscope,scanning electron microscope,X-ray diffractometer,element energy spectrum analyzer,electron backscattering diffraction analyzer,Vickers hardness tester and tensile tester.Due to the formation of many brittle intermetallic compounds in the transition zone between TC4 and Inconel 718(such as Ti Ni and Ti₂Ni),the bimetal structure fabricated via direct transition produced cracks,indicating it challenging to achieve high-quality bonding.The TC4/Inconel 718 bimetallic structure with Cu interlayer transition is mainly composed of a large amount of?-Cu and?-Ni solid solutions and a small amount of Ti₂Cu,Ti Cu,Ti Ni and Ti₂Ni intermetallic compounds.Compared with direct transition,the presence of a large amount of?-Cu solid solution in the transition region could improve the plasticity and reduce the crack sensitivity of the bimetal structure.Therefore,it is possible to realize the manufacture of TC4/Inconel 718 bimetal structure without metallurgical defects(such as cracks).However,due to the interdiffusion of elements,there are still a tiny amount of Ti-Ni and Ti-Cu intermetallic compounds in the transition zone.The Vickers hardness is as high as 592 HV,so that the bimetal structure is brittle.Based on the characteristic that the intermetallic compound would not form between Ti-Ta,Ta-Cu,and Cu-Ni,TC4/Inconel 718 bimetallic structures with one layer of Ta/Cu composite interlayer transition and two layers of Ta/Cu composite interlayer transition fabricated by LAM.The Ti-Ni compound phases in the bimetallic structure were effectively inhibited,the highest Vickers hardness is 444 HV,and the room temperature tensile property is 280 MPa.The fracture site occurs in the Ta/Cu transition zone,which is a quasi-cleavage fracture.The bimetal structure using two layers of Ta/Cu as the interlayer realized the effective control of intermetallic compounds in the transition zone.The phase evolution of the interlayer with the Ta/Cu bilayer in the bimetallic structure was as follows:?-Ti??-Ti+Ta?Ta?Ta+Cu?Cu?Cu+?-Ni+laves??-Ni+laves.The Vickers hardness distribution of each region and interface is uniform,the tensile strength at room temperature is 369 MPa,and the fracture occurs in the near Ta zone near the Ta/Cu interface.