Original HCI surface treatment for diffusion bonding of nickel superalloy specimens

Abstract

Nickel superalloys containing Ti and Chave shown considerable precipitation of TiC at bond interfaces during solid-state bonding operations, i.e. diffusion bonding and hot isotatic pressing (HIP). To enhance surface bond ability a new surface treatment has been developed which completely depletes the Ti (and Al) at the metal surface to a controllable depth by the use of a H²-HCI atmosphere. It has been shown that the draining rate of the alloying elements is controlled by the degree of material surface reactivity with HCI. A detailed examination of HIP and cast IN 100 andforged Waspaloy after H²-HCI treatment is presented and an extension of the treatment to HIP and forged René 95 and forged INCO 718 is also included. In general, a treated depth from 25 to 30 μm was found to be beneficial in subsequent bonding operations. Metallographical observations on control and pretreated specimens showedgreatly improved recrystallization and the absence of precipitated TiC in the, bonding zone.