Although its confirmed technological revolution, Additive Manufacturing is constantly evolving, offering new challenges and opportunities. In this context, Graded Multi-Material production is one of the most attractive and un-explored topics. This work is focused on demonstrating the feasibility of producing such a graded multi-material with SLM technique, starting from AISI 316L and Fe35Mn. The peculiarity of the chosen system permits to interpret the gradient transition as a compositional variation of manganese content in the stainless steel, thus continuously generating new alloys. Preliminary printing campaigns were performed on pure AISI 316L, Fe35Mn and on two pre-mixed blends, AISI 316L + 33 wt% Fe35Mn and AISI 316L + 66 wt% Fe35Mn, aiming at a clear understanding of the optimal printing parameters, scanning strategy and laser mode, necessary to realize fully-dense and geometrically accurate specimens. These objectives could be reached through a proper variation of laser parameters and system settings. Only then, a multi-material design could be approached. The graded multi-material printing was designed with six different compositional steps constituted by the two pure materials and four in-situ mixed blends with different wt% of Fe35Mn, respectively 20, 40, 60 and 80 wt%. The printing of each layer was performed thanks to a prototype SLM machine equipped with a novel delivery system, able to release and mix on-demand specific amounts of the two feedstock powders. A complete gradient compositional transition was successfully printed from AISI 316L to Fe35Mn along the building direction. The printed samples, excluding the very bottom and very top parts, result fully-dense and with high geometrical accuracy. Not only a compositional gradient was detected but also hardness showed a gradual variation from higher to lower values when increasing the manganese content. Microstructural investigation confirmed a great compatibility between the two starting materials, highlighting the presence of the only austenitic phase and showing a homogeneous microstructure along the building direction. EBSD analysis confirmed the presence of the typical macro-texture of an SLM product, characterized by highly orientated and elongated grains, and a micro-texture with lattices orientated along the building direction.
Nonostante l’ormai affermata rivoluzione tecnologica portata dalla Manifattura Additiva, questa è in continua evoluzione, offrendo nuove sfide ed opportunità. In questo contesto, la produzione di componenti Multi-Materiale a gradiente composizionale risulta uno degli argomenti più interessanti ed inesplorati. Per tanto, questo progetto si focalizza sul dimostrare la fattibilità di realizzare tale componente tramite la tecnica SLM, ottenendo una completa transizione tra due materiali di partenza, AISI 316L e Fe35Mn. La peculiarità del sistema scelto consente di interpretare la transizione del gradiente come una variazione compositiva del contenuto di manganese nell'acciaio inossidabile, dando origine a nuove leghe. Campagne di stampa preliminari sono state eseguite su AISI 316L puro, Fe35Mn e su due pre-miscele, AISI 316L + 33% in peso di Fe35Mn e AISI 316L + 66% in peso di Fe35Mn, con l'obiettivo di definire i parametri di stampa ottimali, la strategia di scansione e la modalità di emissione laser, necessarie alla realizzazione di campioni densi e geometricamente accurati. Solo successivamente è stato possibile approcciarsi al design di campioni multi-materiale. La variazione in composizione è stata progettata attraverso sei step costituiti dalle due polveri di materiali puri e da quattro miscele, prodotte in-situ, a diverso contenuto di Fe35Mn, rispettivamente 20, 40, 60 e 80%. La stampa di ogni strato è stata eseguita grazie a un prototipo SLM dotato di un nuovo sistema di erogazione, in grado di miscelare e di rilasciare su richiesta determinate quantità delle due polveri di partenza. In questo modo, è stato quindi realizzato con successo un gradiente di composizione. I campioni multi-materiale stampati, escludendo le estremità inferiori e superiori, sono risultati densi e geometricamente accurati. Non solo è stato rilevato un gradiente composizionale, ma anche la durezza è risultata variare in modo graduale, decrescendo all’aumentare del contenuto di manganese. Un’indagine microstrutturale ha quindi confermato una grande compatibilità tra i due materiali di partenza, evidenziando la presenza di un’unica fase austenitica e mostrando una microstruttura omogenea lungo la direzione di stampa. Un’analisi EBSD ha poi rivelato la presenza di una macrostruttura tipica di un prodotto SLM, caratterizzata da grani altamente orientati ed allungati, ed una microstruttura con reticoli cristallini orientati lungo la direzione di stampa.
Opportunities and challenges of multi-material 3D printing via selective laser melting : design, development and characterization of an AISI 316L and Fe35Mn graded component
LUCCHINI, FEDERICO;ROSSI, RICCARDO
2017/2018
Abstract
Although its confirmed technological revolution, Additive Manufacturing is constantly evolving, offering new challenges and opportunities. In this context, Graded Multi-Material production is one of the most attractive and un-explored topics. This work is focused on demonstrating the feasibility of producing such a graded multi-material with SLM technique, starting from AISI 316L and Fe35Mn. The peculiarity of the chosen system permits to interpret the gradient transition as a compositional variation of manganese content in the stainless steel, thus continuously generating new alloys. Preliminary printing campaigns were performed on pure AISI 316L, Fe35Mn and on two pre-mixed blends, AISI 316L + 33 wt% Fe35Mn and AISI 316L + 66 wt% Fe35Mn, aiming at a clear understanding of the optimal printing parameters, scanning strategy and laser mode, necessary to realize fully-dense and geometrically accurate specimens. These objectives could be reached through a proper variation of laser parameters and system settings. Only then, a multi-material design could be approached. The graded multi-material printing was designed with six different compositional steps constituted by the two pure materials and four in-situ mixed blends with different wt% of Fe35Mn, respectively 20, 40, 60 and 80 wt%. The printing of each layer was performed thanks to a prototype SLM machine equipped with a novel delivery system, able to release and mix on-demand specific amounts of the two feedstock powders. A complete gradient compositional transition was successfully printed from AISI 316L to Fe35Mn along the building direction. The printed samples, excluding the very bottom and very top parts, result fully-dense and with high geometrical accuracy. Not only a compositional gradient was detected but also hardness showed a gradual variation from higher to lower values when increasing the manganese content. Microstructural investigation confirmed a great compatibility between the two starting materials, highlighting the presence of the only austenitic phase and showing a homogeneous microstructure along the building direction. EBSD analysis confirmed the presence of the typical macro-texture of an SLM product, characterized by highly orientated and elongated grains, and a micro-texture with lattices orientated along the building direction.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/147868