Spark Plasma Diffusion Bonding of TiAl/Ti2AlNb with Ti as Interlayer

Abstract

To solve the problem of poor weldability between TiAl-based and Ti2AlNb-based alloys, spark plasma diffusion bonding was employed to join a TiAl alloy and a Ti2AlNb alloy with a pure Ti foil as interlayer at 950 °C/10 KN/60 min. After welding, slow cooling was carried out at a rate of 5 °C/min, followed by homogenization at 800 °C for 24 h. The microstructural evolution and elemental migration of the joint were analyzed via a scanning electron microscope equipped with an energy dispersive spectrometer, while the mechanical properties of the joint were assessed via microhardness and tensile tests. The results show that the spark plasma diffusion bonding formed a joint of TiAl/Ti/Ti2AlNb without microcracks or microvoids, while also effectively protecting the base metal. Before heat treatment, the maximum hardness value (401 HV) appeared at the Ti2AlNb/Ti interface, while the minimum hardness value (281 HV) occurred in the TiAl base metal. The tensile strength of the heat-treated joint at room temperature was measured to be up to 454 MPa, with a brittle fracture occurring in the interlayer. The tensile strength of the joint at 650 °C was measured to be up to 538 MPa, with intergranular cracks occurring in the TiAl base metal.

The Relationship between Microstructure and Fracture Behavior of TiAl/Ti2AlNb SPDB Joint with High Temperature Titanium Alloy Interlayers

“…The microstructure of the as-welded TiAl/Ti 2 AlNb SPDB joint is shown in Figure 3 . Defect-free high-quality welded joints can be obtained by using high temperature titanium alloy as the interlayer alloy at 950 °C/60 min, the microstructure of the joint exhibits a distinct gradient distribution from TiAl side to Ti 2 AlNb side, which can be divided into six layers in accordance with the difference of microstructure and morphology, as shown in Figure 4 a, which is similar to the the TiAl/Ti 2 AlNb joint with pure Ti [ 30 ] interlayer. According to the positional relationship between the intermediate layer and the base materials on both sides, as shown in Figure 4 a, the first, second, third, and fourth layers of the joint interface are transition microstructures of TiAl and the intermediate layer.…”