Material and Process Characterization of Non-weldable Nickel Superalloys in Additive Manufacturing
Kupi, Kristiina (2016)
2016
Master's Degree Programme in Materials Science
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2016-06-08
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201605123969
https://urn.fi/URN:NBN:fi:tty-201605123969
Tiivistelmä
Over the last few years additive manufacturing industry has grown its significance in markets. Especially the possibility to make components from advanced metal materials, such as nickel superalloys, has increased the interest in for instance aviation industry. Furthermore, the increasing advantages of additive manufacturing technologies together with design complexity and customization needs is attractive. The aim of this thesis is to investigate current possibilities to manufacture advanced non-weldable nickel superalloys with available additive manufacturing methods. The main problem of processing these alloys is their susceptibility for cracking. The cracking behavior is first investigated in the literature review and the possibilities to solve the problem with process parameter designs are studied in the experimental part.
The nickel superalloys are determined to be non-weldable when a certain weight percentage of titanium and aluminum is exceeded. These elements form also the hardening precipitates to the alloy so their presence in the composition is also necessary. In the literature part of the work the cracking behavior is studied. Additionally the compositional effects are investigated and the basics of additive manufacturing are presented. Finally other possibilities to solve the cracking problem, which are not throughout examined in this study, are introduced. In the experimental part the alloy behavior is studied in EOS M-series machines and the processability is strived to improve by changing the process parameters and by modifying the nickel superalloy composition. The success of the experiments is primarily evaluated from the sample microstructure which reveals the possible cracks in the structure. Scanning electron microscopy with energy dispersive spectroscopy is used to gain more detailed information about the cracks and elemental distribution.
The main goal of the thesis was to study the behavior of non-weldable nickel superalloys in additive manufacturing and to find possible solutions to reduce cracking. One of the investigated nickel superalloys shows good results and the cracking was able to be limited by the suitable design of process parameters. The other alloy and the blends prove to be more challenging. The results suggest that smaller melt pool is favorable and reduces the cracking. Other findings concern the suitable process parameters which affect the heat input and power intensity and thus the amount of defects in microstructure. The development of additive manufacturing machines and the possibility to modify the alloy chemistry gives a wide variety of new possibilities to minimize the cracking. Moreover a lot more interesting and rewarding research can be done with the hardware and additionally with pre- and post-heat treatments.
The nickel superalloys are determined to be non-weldable when a certain weight percentage of titanium and aluminum is exceeded. These elements form also the hardening precipitates to the alloy so their presence in the composition is also necessary. In the literature part of the work the cracking behavior is studied. Additionally the compositional effects are investigated and the basics of additive manufacturing are presented. Finally other possibilities to solve the cracking problem, which are not throughout examined in this study, are introduced. In the experimental part the alloy behavior is studied in EOS M-series machines and the processability is strived to improve by changing the process parameters and by modifying the nickel superalloy composition. The success of the experiments is primarily evaluated from the sample microstructure which reveals the possible cracks in the structure. Scanning electron microscopy with energy dispersive spectroscopy is used to gain more detailed information about the cracks and elemental distribution.
The main goal of the thesis was to study the behavior of non-weldable nickel superalloys in additive manufacturing and to find possible solutions to reduce cracking. One of the investigated nickel superalloys shows good results and the cracking was able to be limited by the suitable design of process parameters. The other alloy and the blends prove to be more challenging. The results suggest that smaller melt pool is favorable and reduces the cracking. Other findings concern the suitable process parameters which affect the heat input and power intensity and thus the amount of defects in microstructure. The development of additive manufacturing machines and the possibility to modify the alloy chemistry gives a wide variety of new possibilities to minimize the cracking. Moreover a lot more interesting and rewarding research can be done with the hardware and additionally with pre- and post-heat treatments.