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Additive Manufacturing of Silicon Nitride Additive Manufacturing of Silicon Nitride Céline Montanari Materials Engineering, masters level 2017 Luleå University of Technology Department of Engineering Sciences and Mathematics Student : Céline Montanari École Européenne d’Ingénieurs en Génie des Matériaux (EEIGM) Université de Lorraine, Nancy, France Luleå University of Technology (LTU), Luleå, Sweden Department of Engineering Sciences and Mathematics Division Material Science Examiner: Professor Marta-Lena Antti Luleå University of Technology (LTU), Luleå, Sweden Department of Engineering Sciences and Mathematics Division Materials Science Supervisors: Erik Adolfsson Ceramics division, Swerea IVF, Mölndal, Sweden Emil Johansson Additive Manufacturing division, Swerea IVF, Mölndal, Sweden i Additive Manufacturing of Silicon Nitride This work was performed at Swerea IVF AB, Mölndal, Sweden Department of Engineering Sciences and Mathematics Division Material Science Luleå University of Technology Gothenburg, Sweden 2017 ii Cover page: Additive manufactured silicon nitride ceramic components iii Acknowledgments I would like to express my sincere gratitude to my supervisors, Dr. Erik Adolfsson and Emil Johansson, for their guidance and continuous support throughout my Master’s thesis studies. Thank you for your advice, encouragement, and giving me the opportunity to perform my Master thesis at Swerea IVF. I would also like to express my deep appreciations to my examiner Prof. Marta-Lena Antti, for the supervision of my thesis work and her helpful advice and discussions. I am grateful to all the members at Swerea IVF for the help and assistance they provided with the analysis of my results and their valuable time to teach the use of the equipment. Special thanks to the master thesis students sharing my office, Ida Marklung, Julia Aronsson and Maria Peshkova, for their support, friendship, along with our fika times. To my family, and Yunus, I want to thank you for loving and encouraging me during all my studies, for this I am eternally thankful. Céline Montanari iv v Abstract This study aims to investigate the fabrication of silicon nitride ceramics via additive manufacturing method. Silicon nitride exhibits excellent thermo-mechanical properties and it is one of the main structural ceramics. The excellent properties of silicon nitride are obtained through densification via liquid phase sintering. The shaping limitations engendered by conventional manufacturing method of ceramics, such as those in powder pressing, give additive manufacturing a promising potential for fabrication of complex geometrical shapes and small-scale production. Three-dimensional ceramic components can be produced via lithography-based additive manufacturing technique. Due to issues associated with light absorption, lithography-based additive manufacturing has mainly been focused on oxide ceramics, known for their low light-absorption properties. On the other hand, silicon nitride exhibits very high light absorption level. In this study, the possibility to additively manufacture silicon nitride ceramics via the lithography-based ceramic manufacturing technique was presented. Photocurable suspensions with dispersed silicon nitride powder were formulated. The influence of the powder composition was investigated by varying the sintering additives content and silicon nitride powder grade. The suspensions were characterized, and the photo-reactivity effects on the printability were investigating by measuring the cure depth, while also considering the rheological behavior and thermal decomposition of the various photocurable suspensions. Additive manufacturing of silicon nitride ceramic components was successfully achieved. By formulating various suspension compositions, suitable viscosity and cure depth were achieved with 43 vol.% solids loading. Cure depth of 40 µm was found to be sufficient to allow the shaping process, and complex geometrical shapes were fabricated at small-scale. The microstructure and physical properties of additive manufactured parts were similar to those of conventionally made parts. These results suggest that new possibilities with respect to the fabrication of complex geometrical shapes and small-scale series silicon nitride ceramics can be accomplished via lithography-based additive manufacturing. vi I. Table of contents Acknowledgments .................................................................................................................... iv I. Table of contents .............................................................................................. vii II. List of figures .................................................................................................... ix III. List of tables ..................................................................................................... xii IV. Abbreviations .................................................................................................. xiv 1. Introduction .................................................................................................................. 1 1.1 General introduction ........................................................................................... 1 1.2 Background to the project .................................................................................. 2 1.3 Project aim .......................................................................................................... 3 1.4 Scope .................................................................................................................. 3 1.5 Thesis report outline ........................................................................................... 3 2. Literature Review ......................................................................................................... 5 2.1 Overview of silicon nitride ................................................................................. 5 2.1.1 Silicon nitride compound .................................................................................. 5 2.1.2 Crystal structure and transformations ................................................................ 6 2.1.3 Densification and microstructural development ................................................ 8 2.2 Silicon nitride powders ..................................................................................... 10 2.2.1 Powder characteristics ..................................................................................... 10 2.2.2 Nitridation mechanisms ................................................................................... 10 2.3 Manufacturing of silicon nitride ceramics........................................................ 12 2.3.1 Processing steps of Si3N4 ceramics ................................................................. 12 2.3.2 Challenges ....................................................................................................... 15 2.3.3 Additive manufacturing technologies.............................................................. 16 2.4 Additive manufacturing of ceramics via stereolithography ............................. 16 2.4.1 Perspectives on stereolithography ................................................................... 16 2.4.2 Stereolithography of ceramic suspensions ...................................................... 18 2.5 Photocurable ceramic suspensions ................................................................... 21 2.5.1 Components of photopolymerizable ceramic suspensions .............................. 21 2.5.2 Polymerization of acrylate monomers ............................................................. 22 2.6 Lithography-based ceramic manufacturing of silicon nitride .......................... 24 2.7 Summary of literature review ........................................................................... 27 3. Experimental Procedure ............................................................................................ 29 3.1 Raw materials ................................................................................................... 29 3.1.1 Ceramic powders and dispersant ..................................................................... 29 3.1.2 Photopolymerizable resins and photoinitiator ................................................. 30 vii 3.2 Experimental methods ...................................................................................... 31 3.2.1 Preparation of starting ceramic powders ......................................................... 31 3.2.2 Preparation of ceramic suspensions ................................................................ 33 3.2.3 Additive manufacturing of silicon nitride parts via stereolithography ............ 34 3.2.4 Thermal debinding and sintering procedures .................................................. 35 3.2.5 Fabrication of ceramic parts by conventional method: powder pressing ........ 36 3.2.6 Characterization of the ceramic suspensions ................................................... 37 3.2.7 Characterization of the sintered parts .............................................................. 37 3.2.8 Process validation methodology ...................................................................... 38 4. Results and Discussion ............................................................................................... 40 4.1 Characterization of photocurable ceramic suspensions ................................... 40 4.1.1 Influence of silicon nitride powder grade and resin composition
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