ADVANCED MATERIALS & PROCESSES | MARCH 2024 18 DEVELOPING EHLA FOR INDUSTRY Established over 75 years ago, TWI is an international research and technology organization that provides advanced contract research and development solutions to its 700+ industrial members. With over 20 years working in laser metal deposition, TWI competes on the global stage and is a recognized leader in EHLA technology, developing solutions for corrosion, wear, and temperature protection (Fig. 2). Additionally, TWI has core activities in component repair, dissimilar material joining, refractory fusion, novel coatings such as those for hydrogen embrittlement protection, and emission-reducing brake rotor coatings. Dedicated research and development is underway, using EHLA for aerospace applications, specifically including: REACH compliant coatings aligned to hard chrome plating replacement and cobalt hardfacing replacement, advanced repair of safety critical components, dissimilar material joining, and high-speed additive manufacturing of components, including research into space applications such as rocket nozzle components. TWI has developed brake rotor coatings that have passed ISO hot and cold performance testing, while reducing brake emissions by around 10-fold, enabling industry to transition in confidence toward meeting Euro 7 emission regulations. The ceiling of throughput is still being explored and is often down to the application in question and the available machine system technology. Some higher fidelity applications utilize laser powers of just several kW, and some higher throughput applications develop >10-25 kW with deposition rates of 5-15 kg/hr, reaching surface coverage rates of 5 m2/hr. AEROSPACE DEVELOPMENTS TWI has recently developed EHLA solutions for the application of nickel super alloys to repair critical aerospace components, achieving significantly reduced heat input, less distortion, and reduced microstructure transformation to the original component substrate when compared to LMD and other fusion bonding deposition techniques, while also achieving a 15-fold increase in manufacturing speed for a particular repair application. Research has also been conducted on the application of titanium alloys. Where in the as-built (non-heat treated) condition of Ti-6Al-4V, material was produced with high density, measured via a sample of cross sections to 99.99%, while tensile results presented promising properties with an average of 1250 MPa yield strength but only 4% elongation (Fig. 3). From previous work in additive manufacturing of titanium alloys and based on various literature, it is anticipated that the elongation can be significantly improved by selecting appropriate heat treatment cycles. The final impact of heat treatment is still being investigated but is expected to result in better homogeneity of the microstructure and an improvement in elongation performance of the EHLA deposited Ti-6Al-4V material is currently being investigated. Additionally, fatigue performance is also planned for evaluation. THE HORIZON TWI has successfully demonstrated EHLA’s potential for its future role in aerospace manufacturing, proving many positive traits that support the transformative goals of the industry. The main opportunities for EHLA lie in the efficient deposition of high- performance materials, which currently make the quickest route to market and strongest business case in surface engineering and repair applications, while opportunities in dissimilar material joining and additive manufacturing are still being explored. Linear and freeform deposition, which make up a large portion of the application market for conventional laser cladding/DED, is initially more challenging for EHLA, and requires high- dynamic machines, that can meet the speed, very high-acceleration rates, Fig. 1 — EHLA process characteristics shown from a frame captured by an in-process highspeed camera and illumination laser. Fig. 2 — Thin 100 µm nickel superalloy EHLA coating applied to a shaft for corrosion protection.
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