LaSPAM - Novel postprocessing for fatigue and hydrogen resistance of Additive Manufacturing aircraft materials

In last two decades, Additive Manufacturing (AM) technologies have offered new opportunities to aircraft system designers and component manufacturers. The unpreceded design capacities of AM lead to a significant reduction of the buy-to-fly ratio, which makes an impact on production costs, raw material efficiency and engine consumption - with a consequent reduction in greenhouse emissions. However, the certification of the structural components for aircraft application, for both airframe and engine components, is hampered by the underperformance of as-build AM materials under dynamic loads. The required post-processing of AM in form of machining and diverse heat/pressure treatments to improve this performance significantly increase production time, cost, and energy consumption. Recent studies are showing that the Laser Shock Peening (LSP) technology, as a surface treatment and post-processing technology, can exert a significant influence on AM material properties, by for example increasing the fatigue behave of AM-made Ti-6Al-4V up to 100 times. LSP imprints a structural modification of the sample, from the surface up to a determined depth (up to 10mm), which causes a relevant change in the material properties. LSP induces a high-energy short-interval shock wave up to certain depth of the material, reducing significantly the residual tensile stresses, surface roughness, sealing the pores and modifying the superficial microstructure. In this way, LSP increases resistance of AM as-built materials to fatigue and further on may reduce hydrogen infiltration. Both effects are very relevant for aircraft applications since the behaviour under dynamic loads represents the main present challenge in the uptake of AM parts in aircraft systems, while hydrogen infiltration will bring significant challenge in a future hydrogen-powered climate-neutral aircraft engine. LaSPAM is planning to conduct a comprehensive study of the LSP effect on AM-made materials of relevance for the aircraft applications: - Aluminium alloy for airframe structural components and - Titanium alloy for airframe and engine components The aim of this study is evaluation of LSP as post-processing technology in AM parts by the quantification of: - the improvement in terms of the fatigue -performance in aluminium - the resistance to hydrogen embrittlement effect in titanium In line with that, the following two specific goals or milestones are foreseen: - Analysis of the requirements for aircraft components and definition of the Key Performance Indicators (KPI) to quantify the improvement brought by LSP. This will allow selection of particular applications within the scope of aircraft systems, where AM has already proven the huge potential, where the combined use of LSP and AM can bring significant benefit. - Definition and conduction of the specific test procedures to validate the LSP influence on the previously defined KPI. This will be oriented to demonstrate the improvement introduced by the LSP treatment in comparison to the untreated material samples. It will define the typology of the sample, development of testing protocols and expected results in accordance with the aeronautical standards.