The Effect of Processing Variables on Powder Interlayer Bonding in Nickel-Based Superalloys

Abstract

Powder Interlayer Bonding (PIB) has been considered as a lower-energy joining technology for nickel-based superalloys compared to conventional methods; such as friction welding. Typically; nickel-based superalloys exhibit high energy requirements for joining due to their high operating temperatures. However; PIB utilizes a localized temperature gradient created by an induction current; reducing the energy requirements for the process. PIB is a solid-state joining method that compresses and heats a powder interlayer between two faying surfaces to produce one joined workpiece. It has been successfully used to bond titanium alloys; and the objectives of this work were to explore its application as a joining method for nickel-based superalloys. Initial results showed that joining nickel-based superalloys via PIB is possible; and bondlines with very little porosity were observed. Further analysis showed that these bonded areas had lower porosity than the base material; suggesting PIB could be a successful joining method for difficult-to-join nickel-based superalloys.

Powder Interlayer Bonding of Nickel-Based Superalloys with Dissimilar Chemistries

“…It is evident that during bonds 1 and 2 the NGSA has maintained its much coarser grain size which was observed in the base material before bonding. The fine grain bondline compared to the surrounding base material has also been observed in other PIB trials involving the NGSA [7].…”

“…From Figure 4 it is possible to observe the variation in grain size between the different alloys. The RR1000 has a much smaller grain size (4–11 µm [ 24 ]) than Inconel 718 (58 µm [ 25 ]) and the NGSA (23 µm [ 7 ]). Interestingly, a large variation of grain size within the microstructure of the NGSA is present with grains as small as 5.5 µm and as large as 76 µm being found during analysis.…”

“…Once the interlayer region was heated to the desired temperature, a compressive force of 5–6 kN was applied via the electric screw rig. The desired temperatures were determined from results of previous studies involving nickel-based superalloys [ 7 ]. All PIB bonds were performed in an argon environment to prevent oxidation during the bonding process.…”

“…Diffusion bonding is a solid-state bonding process that involves the joining of two components without the use of any filler material and pressure and an elevated temperature are used to produce the joint [ 7 , 8 , 9 ]. The elevated temperatures the materials are subjected to are below the melting point of the materials and this ensures that the process remains solid-state.…”

The fatigue performance of titanium alloys joined via the powder interlayer bonding method

“…Powder interlayer bonding (PIB) was originally conceived as a repair method for the joining of aerospace alloys. The method has already proved successful at delivering high integrity bonds in titanium alloys [15,16] gamma titanium aluminides and nickel alloys [17]. The PIB process is a solidstate joining process that utilises a metallic powder interlayer between the two surfaces being joined.…”