The effect of heat treatments on microstructure of DMLS Ti-6Al-4V
Antikainen, Atte Juhani (2017)
Antikainen, Atte Juhani
2017
Materiaalitekniikan koulutusohjelma
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2017-02-08
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201701251073
https://urn.fi/URN:NBN:fi:tty-201701251073
Tiivistelmä
In this thesis the effect of heat treatments on microstructural evolution of additively manufactured Ti-6Al-4V was studied. The purpose is to promote further understanding of the metallurgy and phase transformation kinetics during heat treating of direct metal laser sintered Ti-6Al-4V. Particular interest is in the factors that affect fatigue performance.
In the theoretical section, laser sintering as a manufacturing method and its effect on microstructure and defect formation are briefly covered. Basic material physics, such as diffusion, phases and phase morphologies in Ti-6Al-4V are dealt with in more detail. Conventional processing methods, heat treatments, and resulting microstructures are presented. Factors that affect the mechanical properties are discussed in general.
In the experimental section, several standardized heat treatments were conducted. These heat treatments were done to find out if the heat treating standards can be applied to DMLS Ti-6Al-4V. Based on the results, another set of samples was heat treated differently. The samples were then examined under optical- and electron microscopes. EDS-analysis was utilized in investigating the diffusion of alloying elements.
Based on the research, the conclusion was that standard heat treatments do not lead to desired microstructures. Standard heat treatments resulted in expected phases, but their morphologies remained lamellar independent of the heat treatment. Annealing done in the single-phase region was the only one to result in disappearance of the columnar structures. Phase transformation kinetics was noted to differ between sample quenched from the two-phase region and DMLS sample. No notable difference was seen in the phase transformation kinetics between DMLS sample and a sample quenched from the single phase region, but high temperature annealing led to the formation of grain boundary alpha in the quenched sample.
In the theoretical section, laser sintering as a manufacturing method and its effect on microstructure and defect formation are briefly covered. Basic material physics, such as diffusion, phases and phase morphologies in Ti-6Al-4V are dealt with in more detail. Conventional processing methods, heat treatments, and resulting microstructures are presented. Factors that affect the mechanical properties are discussed in general.
In the experimental section, several standardized heat treatments were conducted. These heat treatments were done to find out if the heat treating standards can be applied to DMLS Ti-6Al-4V. Based on the results, another set of samples was heat treated differently. The samples were then examined under optical- and electron microscopes. EDS-analysis was utilized in investigating the diffusion of alloying elements.
Based on the research, the conclusion was that standard heat treatments do not lead to desired microstructures. Standard heat treatments resulted in expected phases, but their morphologies remained lamellar independent of the heat treatment. Annealing done in the single-phase region was the only one to result in disappearance of the columnar structures. Phase transformation kinetics was noted to differ between sample quenched from the two-phase region and DMLS sample. No notable difference was seen in the phase transformation kinetics between DMLS sample and a sample quenched from the single phase region, but high temperature annealing led to the formation of grain boundary alpha in the quenched sample.