In Search of the Optimal Conditions to Process Shape Memory Alloys (NiTi) Using Fused Filament Fabrication (FFF)

Abstract

This research was performed so as to investigate the additive manufacturing of NiTi shape memory alloys, which is associated with direct processes, such as selective laser melting. In addition to its expensive production costs, NiTi readily undergoes chemical and phase modifications, mainly as a result of Ni loss during processing as a result of high temperatures. This research explores the potential usefulness of NiTi as well as its limitations using indirect additive processes, such as fused filament fabrication (FFF). The first step was to evaluate the NiTi critical powder volume content (CPVC) needed to process high-quality filaments (via extrusion). A typical 3D printer can build a selected part/system/device layer-by-layer from the filaments, followed by debinding and sintering (SDS), in order to generate a near-net-shape object. The mixing, extruding (filament), printing (shaping), debinding, and sintering steps were extensively studied in order to optimize their parameters. Moreover, for the sintering step, two main targets should be met, namely: the reduction of contamination during the process in order to avoid the formation of secondary phases, and the decrease in sintering temperature, which also contributes to reducing the production costs. This study aims to demonstrate the possibility of using FFF as an additive manufacturing technology for processing NiTi.

Fused Filament Fabrication of NiTi Components and Hybridization with Laser Powder Bed Fusion for Filigree Structures

“…The most evident phases in this system are presented in the work of Carreira et al [6]. This assumption is based on the fact that hydrocarbons (polymers) are also used and The most evident phases in this system are presented in the work of Carreira et al [6]. This assumption is based on the fact that hydrocarbons (polymers) are also used and identified as the main source of impurities in this reference.…”

“…The most evident phases in this system are presented in the work of Carreira et al [6]. This assumption is based on the fact that hydrocarbons (polymers) are also used and The most evident phases in this system are presented in the work of Carreira et al [6].…”

“…Another major advantage of filament-based AM compared to powder bed fusion is the potential for multi-material use via switching between several filament feedstocks during manufacturing. Further advantages of FFF over LPBF AM for NiTi have been previously considered, such as difficulties in LPBF processing, Ni content and transformation temperature volatility and the formation of undesirable phases during melting and solidification [ 6 ].…”

Optimization of metallic powder filaments for additive manufacturing extrusion (MEX)

“…The set material for this study was austenitic stainless steel 316L (SS 316L) since it is one of the most studied materials in AM. This material can be a good standard for the methodology to be established by the present work and extrapolated to other metallic alloys [29]. The characteristics of the selected powders were studied using the 4S's methodology (size and size distribution, shape, and structure).…”

Optimization of Metallic Powder Filaments for Additive Manufacturing Extrusion (MEX)

“…The set material for this study was austenitic stainless steel 316L (SS 316L) since it is one of the most studied materials in AM. This material can be a good standard for the methodology to be established by the present work and extrapolated to other metallic alloys [30].…”