Powder interlayer bonding of geometrically complex Ti-6Al-4V parts

Abstract

Powder interlayer bonding (PIB) is a novel joining technique, which has been developed to facilitate high-integrity repairs of aerospace components, manufactured from commonly used titanium alloys. The PIB technique utilises an interlayer between complex geometric components which are mated under pressure and a highly localised heating source. In this study, induction heating enabled bonding in an inert fusion zone by use of an oxygen-displacing shielding gas, with particular attention to the initial heating and pressure application. These early stages proved crucial to the elimination of pores and consolidation of the alloy powder, with porosity volume fraction reduced to just 0.5% after just 20 sec at the bonding force. The technique has produced high-integrity bonds in alloys such as Ti-6Al-4V, retaining approximately 90% of the alloy strength in previous studies, offering advantages over established joining methods such as tungsten inert gas (TIG) and plasma arc (PA) welding due to a more highly localised heating and fusion zone. It is believed that powder interlayer bonding can compete against these techniques, providing a more time and cost-effective repair route for net shape components manufactured from a range of alloys with minimal post-processing.

Powder Interlayer Bonding of Nickel-Based Superalloys with Dissimilar Chemistries

“…However, new generation nickel-based superalloys have been specifically designed with increased volume fraction of the second phase strengthening precipitate gamma prime (γ′) (>40%) to meet the high temperature requirements of the engine [ 5 ]. This increased γ′ increases the strength of the alloy but also hinders weldability by making the material prone to microcracking during weld solidification [ 6 ].…”

The joining of gamma titanium aluminides via the powder interlayer bonding method

“…Continued growth of the necks requires material to be transported to this region via diffusion mechanisms such as volume and surface diffusion, where vacancies move from the neck region through the powder or along the surface of the powder respectively [33]. As bonding through the intermediate phase progresses, continued plastic deformation densifies the powder interlayer before slowing as the total surface area of the powders reduces until finally ceasing as previously illustrated [32]. Final densification and pore elimination occurs during the final phase where recrystallisation is facilitated by the stored energy introduced during the earlier deformation.…”

“…It has already been shown that PIB can be used to provide high-integrity bonds between aerospace alloys [27,[30][31][32]; so, it is no surprise to see high-integrity bonds being produced in the TiAl alloy. The joint is formed through a solid-state sintering process, where the combination of thermal energy and applied load act to consolidate and densify the powder.…”

“…As described in previous work [27], the bonding process can be viewed as three associated phases: the initial, intermediate and final phases. Localised bonding occurs between adjacent powders through the formation of necks during the initial phase, resulting in a small amount of plastic deformation as illustrated in the Ti-6Al-4 V alloy [32]. Continued growth of the necks requires material to be transported to this region via diffusion mechanisms such as volume and surface diffusion, where vacancies move from the neck region through the powder or along the surface of the powder respectively [33].…”

“…Hence, bond 2 was produced at the higher temperature of 1120°C, putting it in the α + γ region of the phase diagram. Previous PIB work [32] has highlighted that increasing the bonding temperature can refine porosity through the powder interlayer. As illustrated in Fig.…”