Details

Autor(en) / Beteiligte

• Fleißner-Rieger, Christian
• Tunes, Matheus Araujo
• Gammer, Christoph
• Jörg, Tanja
• Pfeifer, Tanja
• Musi, Michael
• Mendez-Martin, Francisca
• Clemens, Helmut

Titel

On the existence of orthorhombic martensite in a near-α titanium base alloy used for additive manufacturing

Ist Teil von

• Journal of alloys and compounds, 2022-03, Vol.897, p.163155, Article 163155

Ort / Verlag

Lausanne: Elsevier B.V

Erscheinungsjahr

2022

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• •A second type of martensite was found in a Ti6242S alloy used for additive manufacturing.•Appearance of the martensitic variant can be controlled via processing parameters.•Orthorhombic martensite is softer; Softening indicates a gain in ductility.•Nanometer-sized lattice defects affect precipitate morphology. Inspired by a novel orthorhombic phase transformation in the powder material, the adaption of cooling rates during the additive manufacturing process originates a new martensite variant with beneficial material specifics for this cutting-edge production technique. [Display omitted] Additive manufacturing is a state-of-the-art production technology to produce tailor-made and highly complex parts. Among various other alloys, Ti base alloys are frequently used in this manufacturing technique due to their well-balanced properties and their wide range of applications. Allotropic phases and the occurrence of athermal phase transformations are the main reasons why these alloys hold a great development potential and are the basis of extensive use. High cooling rates during manufacturing lead to martensitic phases and the formation of nanometer-sized microstructures resulting in extraordinary strength. Simultaneously, such high cooling rates cause a high amount of lattice defects and the occurrence of residual stresses, which finally may result in delamination effects and cracks. Usually, a common approach to reduce residual stresses during additive manufacturing is to decrease thermal gradients by increasing the heat input or preheating the building platform. Instead of applying the typical approaches to lower thermal gradients, this study deals with the origin of the ‘softer’ orthorhombic martensite by accelerating the solidification process. The implementation of the orthorhombic phase in bulk components was inspired by a new phase transformation herein reported for the first time in the powder material, which also validates the possible occurrence of two martensitic phases in the same alloy. Various sophisticated characterization techniques like high energy and high-temperature X-ray diffraction, high-resolution transmission electron microscopy as well as atom probe tomography were applied to characterize this softer orthorhombic martensitic phase in detail aiming to highlight the opportunities accompanied by this new approach for additive manufacturing of titanium alloys.