Thermal properties of lattice structures by laser powder bed fusion for aerospace systems

SÉLO, Richard Roger Joachim (2022) Thermal properties of lattice structures by laser powder bed fusion for aerospace systems. PhD thesis, University of Nottingham.

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In the aerospace industry, thermal management concerns numerous components but is bounded to the limitations of traditional manufacturing processes which results in inefficient and inadequately large equipment. Consequently, a change in how heat exchangers are manufactured and designed is needed. Additive manufacturing (AM) techniques such as laser powder bed fusion (LPBF) are capable of alleviating conventional design drawbacks. Among new complex structures, triply periodic minimal surface (TPMS) lattice structures are of particular interest with their high surface area to volume ratios that are ideal to increase surface-based interactions such as heat transfer. However, the adoption of LPBF for thermal applications is impeded by the lack of available material for LPBF and insufficient knowledge on how AM material thermal properties are affected by the LPBF process and of the thermal properties of lattice structures.

The first part of this thesis focused on the characterisation of the thermal conductivity of materials and lattice structures manufactured by LPBF using an in-house developed testing apparatus based on the guarded comparative longitudinal heat flow technique. AlSi10Mg is the most applied aluminium alloy in LPBF, however, there is an incomplete body of knowledge surrounding its thermal conductivity. In this thesis, AlSi10Mg specimens were manufactured by LPBF and tested to characterise the effect of the unique LPBF microstructure and heat treatments on the thermal conductivity. In addition, the effect of lattice parameters on their apparent thermal conductivity was investigated by manufacturing and testing lattice structures made by LPBF in several alloys of interest for aerospace (Ti6Al4V, AlSi10Mg, and Hastelloy-X). Models were proposed to predict the thermal conductivity of lattices and specimens with tailored conductivity were manufactured.

Forced convection heat transfer of AlSi10Mg lattice structures manufactured by LPBF was evaluated by measuring pressure drop and heat transfer of the structures using an in-house developed testing apparatus. A metric based on the maximum variation of the cross-sectional area was proposed as a quick estimate of the lattice structures pressure drop. It was demonstrated that the thermal performance of lattice structures can be up to 6 times higher than that of pin-fin geometry.

The last part of this thesis focused on the extension of LPBF material library with the high-strength aluminium alloy EN AW 2618. Despite a wide range of parameter optimisation and high relative density (>99 %), crack-free EN AW 2618 has not been manufactured due to its crack sensitivity and high cooling rates in LPBF. Subsequently, A20X, a newly developed high-strength aluminium alloy specifically designed for LPBF was investigated. Crack-free material with high relative density (>99 %) was achieved. It was demonstrated that its thermal and mechanical properties can compete with those of conventional EN AW 2618.

The results from this thesis presented lattice structures made by LPBF as a route through which enhanced heat exchangers could be designed. Through these improvements, heat exchangers can potentially become more efficient and compact with possible multifunctional properties that could be generated as part of the design process.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Tuck, Christopher
Ashcroft, Ian
Maskery, Ian
Keywords: Lattice structures; Laser fusion; Additive manufacturing; Thermal conductivity; Alloys, Thermal properties; Aluminum alloys
Subjects: T Technology > TJ Mechanical engineering and machinery
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 68716
Depositing User: SELO, Richard
Date Deposited: 31 Jul 2022 04:41
Last Modified: 31 Jul 2022 04:41

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