A method for manufacturing a turbine rotor assembly from dissimilar materials includes the step of preforming a turbine disc of powdered metal by direct hot isostatic pressing; machining the OD of the disc rim to an exact dimension; prefabricating a ring of airfoil elements having a circular rim with a machined ID therein fit to the OD of the turbine disc; sealing joint lines on side surfaces of the joined parts to create a vacuum at the interface with a high melt temperature sealant; thereafter diffusion bonding the joined and sealed parts by hot isostatically pressing them at temperatures in excess of 1500.degree. F. and under fluid pressure directly applied to the parts in excess of 1000 psi to press the ring ID into intimate contact with the OD of the disc until the dissimilar materials are diffusion bonded to form a high strength butt joint therebetween.