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.
Highlights
Titanium has historically been a key material in the development of the gas turbine industry over the last 75 years and is extensively used in gas turbine applications [1]
One of the largest factors to the success of titanium for gas turbine applications is its high strength to weight ratio when compared to other materials
Due to the acceptable combination of low-density and high-strength fatigue performance at ambient temperatures, α + β-alloys such as Ti 6-4 are typically used in the low-pressure compressor and fan blade assemblies of gas turbine engines, with highertemperature capability alloys such as Ti-6246 being used in hotter sections such as the high-pressure compressor [6]
Summary
Titanium has historically been a key material in the development of the gas turbine industry over the last 75 years and is extensively used in gas turbine applications [1]. Both the large size and geometric complexity of these components mean that repair is far more difficult than in multiple-component assemblies, especially when you consider the need to retain the microstructure and limit heat damage in the region surrounding the repair For this reason, liquid-state welding processes such as tungsten inert gas (TIG), plasma arc (PA) and laser beam (LB) welding [13] would not be suitable for safety critical repairs in components such as blisks. Very reasonable mechanical properties are attainable, and fatigue testing has often resulted in fractures in the parent material rather than interlayer region [28] This demonstrates the importance of careful control of interlayer application and bonding process itself in order to prevent contamination, while the need to minimise defects in the interlayer region suggests that thinner and more refined powders may be more applicable in the bonding of similar metals. HIPing appears to give more uniform microstructures and mechanical properties in components, but at a higher processing cost than diffusional bonding processes, this trade-off could be considered one of quality vs cost
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