A Machinability Assessment of the Novel Application of Field-Assisted Sintering Technology to Diffusion Bond (FAST-DB) and Functionally Grade Dissimilar Nickel-Based Superalloys

Abstract

This work presents an alternative processing route to the conventional powder HIP—forge route for Nickel-based superalloys. Demonstrating how the field-assisted sintering technology (FAST) process can be exploited to successfully diffusion bond or functionally grade two or more Nickel-based superalloys from powder feedstock. The robustness of the process has been further demonstrated by the successful bonding of one alloy in powder form to another in the solid form. Chemical and microstructural analysis of the diffusion bond between the alloys is characterised, in both cases, with a short diffusion zone—in agreement with thermodynamic model predictions. A gradual transition in microhardness across the bond region was measured in all samples. A machinability assessment was also carried out through a simple face turning operation. Analysis of the cutting forces and machined surface shows signs of a directionality when machining across the bond region between two alloys, indicating that care must be taken when machining multi-alloy FAST-DB components.

Processing, Microstructure, and Properties of Bimetallic Steel-Ni Alloy Powder HIP

“…The powder-to-powder route was considered to be optimal due to the possibility of forming mechanical locks at the interface and local deformation of the particles at the interface for a better diffusion. Dissimilar powder bonding using spark plasma sintering (SPS) was studied for Inconel 718 and RR 1000 that resulted in no defects, intermetallic phases, and prior particle boundaries (PPB) at the bonding interface [21]. Despite the advantage of a shorter heating cycle in SPS to control kinetics of phase formation and grain coarsening, SPS does not have the scalability for large components with complex shapes, as the powder HIP approach has proven.…”