Sicignano, Nicola (2025) Development of an innovative and sustainable SLM-based manufacturing process for Invar36 components. [Tesi di dottorato]

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Abstract

This PhD thesis presents a comprehensive investigation into the development of a sustainable and innovative Selective Laser Melting (SLM) process for manufacturing high-performance Invar 36 components. As a critical Fe–Ni alloy, Invar 36 is prized for its exceptionally low coefficient of thermal expansion (CTE) and outstanding dimensional stability, making it indispensable for precision applications in fields such as aerospace, cryogenics, and optics. Traditional manufacturing techniques often face limitations in design freedom, material efficiency, and energy consumption. This research addresses these challenges by employing Additive Manufacturing (AM), specifically SLM, to enable the production of lightweight, complex, and customized Invar 36 parts. The study follows an integrated experimental and analytical approach. Initially, the work focuses on process optimization: a systematic Design of Experiments (DoE) is utilized to define optimal SLM parameters (laser power, scanning speed, hatch spacing) that ensure high-density, defect-free parts with microstructural uniformity and superior mechanical reliability. Subsequently, the research examines the crucial role of post-processing heat treatments in relieving residual stresses, enhancing phase stability, and preserving the alloy's functional properties. Dedicated analyses of mechanical performance and thermal expansion behaviour validate the full potential of the optimized SLM + heat treatment route for high-precision, thermally stable applications. Finally, the thesis incorporates a crucial sustainability dimension. The work explores powder recycling strategies and demonstrates their effectiveness in maintaining material integrity, enabling a circular production model. This is reinforced by a Life Cycle Assessment (LCA) study, which quantitatively compares the environmental performance of the optimized SLM process against conventional investment casting. The LCA highlights the significant potential of SLM to reduce the carbon footprint and overall resource consumption, especially when integrated with effective material reuse practices. In conclusion, this research establishes a robust, repeatable, and environmentally conscious SLM-based manufacturing route for Invar 36, contributing significantly to the adoption of sustainable AM in the high-precision components industry.

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