Engine components in aircraft need to be built tough. Not only must these parts withstand soaring temperatures of around 650°C, but they must also contend with mechanical forces that can lead to wear and tear over time. But regularly scrapping and replacing gas turbine components is an expensive and laborious process, especially when replacement parts are not readily available.
Consequently, technologies to repair metal components are in high demand by the aerospace industry. One of the most widely used materials used to manufacture these components is Inconel 718, an easy-to-fabricate nickel-based superalloy with exceptional strength. Conventional methods to repair worn-out parts involve depositing a fine spray of Inconel powders onto their surface and melting them within the intense heat of plasma in a technique known as atmospheric plasma spray (APS).
The problem, however, is that Inconel powders are often warped under plasma’s extreme temperatures of around 15,000°C, prompting materials scientists to seek alternative repair methodologies. Among these is the relatively new technique known as cold spray (CS), where Inconel powders are propelled onto the surface of a material to be repaired at a fraction of the temperatures required by APS.
Jisheng Pan from A*STAR’s Institute of Materials Research and Engineering (IMRE), in collaboration with researchers at the Institute of High Performance Computing (IHPC) and the Singapore Institute of Manufacturing Technology (SIMTech) led a study on the performance of CS relative to the current gold standard, APS. “As Inconel 718 powders can be deposited by both techniques, this study can help the research community and industry players compare them directly,” said Pan.
The team first applied Inconel powders to superalloy surfaces using both CS and APS, then examined the physical characteristics of the resulting coatings, including their porosity, microstructure, hardness and tensile strength.
From a structural perspective, CS preserved the architecture of deposited Inconel powders, while APS altered it due to heating. Promisingly, like APS, Inconel powders were shown to adhere strongly to the surface of the metal using CS. Further characterization revealed that APS coatings were stronger and were more malleable than those applied with CS, which was harder but displayed residual post-coating stresses that made it more brittle. With further tweaks, the researchers conclude that CS could potentially enhance a wide range of applications, from mending aircraft carrier parts to fixing submarines.
“Through these research efforts, we hope to promote the interests in adopting CS in local industries, both for aesthetic purposes and structural repair,” Pan concluded. The researchers plan to accelerate the technique’s entry into industrial manufacturing practices by identifying the optimal process parameters for effective surface coatings.
The A*STAR-affiliated researchers contributing to this study are from the Institute of Materials Research and Engineering (IMRE), Institute of High Performance Computing (IHPC), and Singapore Institute of Manufacturing Technology (SIMTech).