A rotary friction welding process is provided. The process includes: providing a first axisymmetric workpiece (11) having a first annular weld surface (13), and a second axisymmetric workpiece (21) having a second annular weld surface (23), aligning the workpieces (11, 21) on a common axis with the weld surfaces facing each other, rotating one workpiece (11) about the axis relative to the other workpiece (21), and engaging the workpieces (11, 21) at the first and second weld surfaces (13, 23) such that the rotation raises the temperature at the weld surfaces (13, 23) to create a weld interface, and ceasing the rotation and allowing the weld interface to cool to weld the workpieces (11, 21) together at the interface. The first annular weld surface (13) is at a radially inward extent of the first workpiece (11), and the second annular weld surface (23) is at a radially outward extent of the second workpiece (21). On a longitudinal section through the aligned workpieces (11, 21), the first and second annular wel
