Interfacial microstructures of HIP joined W and ferritic–martensitic steel with Ti interlayers

W and ferritic–martensitic steel (FMS) were joined successfully using a hot isostatic pressing (HIP) method. To minimize the difference in the thermal expansion between W and FMS, a Ti interlayer was applied. HIP was performed at 900 °C with 100 MPa for 1.5 h, and subsequently at 750 °C with 70 MPa for 2 h. The first HIP stage was aimed at forming diffusion joining interfaces between W and FMS. The second HIP stage corresponds to a tempering process to retain the mechanical properties of FMS. The joining interfaces were analyzed microscopically. A diffusion layer was formed continuously along the interface between the inserted Ti foil and FMS, whereas no diffusion layer was observed at the interface between the W and Ti interlayer. At the FMS side, α-ferrite was formed at the vicinity of the interface, amounting to ∼200 μm in thickness. The α-phase was gradually decreased as being apart from the joining interface, and a typical martensitic phase was then obtained in the bulk FMS.