Seminar on High-temperature fracture behavior of an α/β Titanium alloy manufactured using laser powder bed fusion

20 Aug 2024 04.30 PM - 06.00 PM MAE Meeting Room D (Blk N3.2-02-59) Current Students, Public

Dr Sheng Huang

Massachusetts Institute of Technology, US

This seminar will be chaired by Prof Upadrasta Ramamurty.

Seminar Abstract

In this talk, the room and high temperature (up to 600°C) mechanical properties, with an emphasis on the fracture toughness and fatigue resistance, of an α/β titanium alloy that was additively manufactured using the laser powder bed fusion (LPBF) technique will be presented. The study focused on the as-printed (α’ lath martensite with negligible β phase content) and heat-treated (α/β structure with a significant volume fraction of the β phase) states to critically examine the β phase's role in fracture and fatigue behavior, considering the significantly higher diffusion rates of various species in β compared to α. Experimental results reveal that the heat-treated sample exhibits superior ductility and fracture initiation toughness at elevated temperatures, compared to the as-printed sample, due to the presence of β ligaments in the former. While the fatigue crack growth (FCG) rates in both the as-printed and heat-treated samples deteriorated with increasing temperature, the threshold for FCG generally increased, attributed to creep-induced crack tip blunting. Moreover, a double Paris exponent phenomenon is observed for the heat-treated sample at 300°C, attributed to hydrogen-assisted crack growth, with the β phase providing an accelerated diffusion pathway. Overall, there is an intricate relationship between creep, hydrogen diffusion, and the β phase in dictating the fracture behavior of LPBF α/β titanium at elevated temperatures.

    Speaker's Biography 

    Huang obtained his Ph.D. degree from Nanyang Technological University (Singapore) in February 2022, where his thesis work introduced a novel laser scanning strategy to address the porosity-segregation trade-off commonly associated with in-situ alloying, effectively tripling the part's build rate through innovative melt pool engineering. This achievement stemmed from a synergy of modeling and experimentation, unveiling that microstructural inhomogeneity is essential for imparting extrinsic toughening mechanisms in Ti41Nb (wt%). Throughout his Ph.D. and subsequent postdoctoral research, Huang has set up several testing capabilities for the lab, including fracture and fatigue testing, stress corrosion cracking, and X-ray computational tomography. He expanded his research to encompass a wide array of materials such as PH 15-5 stainless steel, dispersion-strengthened AA8009, Ti matrix composites, and CoCrFeNi-based high entropy alloys (HEA). Currently, he is a postdoctoral associate in the Department of Materials Science and Engineering at the Massachusetts Institute of Technology, developing an advanced laser setup from scratch. Alongside his core research, Huang has actively engaged in decarbonization efforts, focusing on the hydrogen embrittlement characteristics of Ti alloys and investigating hydrogen coating technologies. To date, Dr. Huang has published 18 research papers, secured 5 patents, and contributed to 2 conference articles and 1 book chapter. His scholarly contributions appear in prestigious journals like "Acta Materialia," "Nature Communications," and "Progress in Material Science."

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