Cooling dynamics of two titanium alloys during laser powder bed fusion probed with in situ X-ray imaging and diffraction

• Published in: Materials & design Vol. 195; no. C; p. 108987
• Main Authors: Calta, Nicholas P., Thampy, Vivek, Lee, Duncan R.C., Martin, Aiden A., Ganeriwala, Rishi, Wang, Jenny, Depond, Philip J., Roehling, Tien T., Fong, Anthony Y., Kiss, Andrew M., Tassone, Christopher J., Stone, Kevin H., Nelson Weker, Johanna, Toney, Michael F., Van Buuren, Anthony W., Matthews, Manyalibo J.
• Format: Journal Article
• Language: English
• Published: United Kingdom Elsevier Ltd 01.10.2020; Elsevier
• Subjects: Additive manufacturing; Laser powder bed fusion; MATERIALS SCIENCE; Rapid solidification; Titanium alloys; X-ray diffraction; X-ray imaging; X-ray diffraction; Titanium alloys; Laser powder bed fusion; Additive manufacturing; Rapid solidification; X-ray imaging
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2020.108987

Metal parts produced by laser powder bed fusion (LPBF) additive manufacturing exhibit characteristic microstructures comparable to those observed in laser welding. The primary cause of this characteristic microstructure is rapid, localized heating and cooling cycles, which result in extreme thermal gradients where material solidification is followed by fast cooling in the solid state. The final microstructure and mechanical performance are also influenced by pore formation caused by melt pool fluid dynamics. Here, we use high speed, in situ X-ray diffraction to probe the kinetics of cooling and solid-solid phase transitions after laser melting in two aerospace titanium alloys: Ti-6Al-4V, an α + β alloy; and Ti-5Al-5V-5Mo-3Cr, a near-β alloy. We complement these diffraction studies with in situ X-ray imaging to probe melt pool dynamics and pore formation. From these two complementary probes, we quantify pore formation during melting and the subsequent microstructural evolution as the material rapidly cools after solidification. These results are critical for understanding defect formation and residual stress development in different titanium alloys under LPBF conditions and can help inform process models to predict final part performance. [Display omitted] •Direct comparison of materials dynamics in two titanium alloys using in situ X-ray imaging and diffraction during additive manufacturing.•High speed X-ray imaging quantifies fluid dynamics and pore formation during laser melting for both alloys.•In situ X-ray diffraction quantifies cooling rates and residual stress evolution after solidification.•Comparison to thermomechanical modeling provides mechanistic insight into behavior observed by X-ray diffraction.