26th August 2024

Compressive mechanical response and microstructures in low strain rate plastic deformation of stainless steel 316L fabricated by selective laser melting

Y. Yang, Y. Bai, Y. Wang, Y. Zhang, C. Weng, W.F. Lu, H. Wang
Journal of Materials Research and Technology 29 (2024) 4327–4344

Abstract. Characterization of the mechanical properties plays an essential role in the post-processing and evaluation of the functionality of the additively manufactured metallic parts. A number of studies have been focused on the tensile properties of additively manufactured metals. However, the quasi-static compression test of the additively manufactured 316L blocks with different heat-treatment conditions and scanning strategies seems to be overlooked in the literature. This paper aims to provide a comprehensive study of compressive mechanical response in plastic deformation of SS316L fabricated by selective laser melting (SLM). The mechanical response and microstructures in compressive deformation is analyzed for three printing strategies with 0°-, 90°- and 67.5°- scanning and three heat treatment conditions (450 °C for 3 h, 1100 °C for 1 h with furnace cool and 1100 °C for 1 h with water quenching) for selective laser melted (SLMed) stainless steel 316L in comparison with wrought stainless steel 316L in this work. Alteration of mechanical properties, microstructure evolution and compressive deformation mechanism is studied. Melt pool features are not significantly affected by low-temperature heat treatment (450 °C for 3 h) but fully dissolved through high-temperature heat treatment (1100 °C for 1 h). High-temperature heat treatment provides a higher resistance to compressive plastic deformation for SLMed 316L compared with the low-temperature heat-treated and as-built samples where more twinnings are observed. The compressive plastic deformation mechanism of 90°- and 67.5°-scanning samples is similar, which mainly results from twinning-induced plasticity. For 0°-scanning samples, the strong crystallographic texture is the main cause of anisotropic deformation. Modelling and simulation have been conducted to explain the anisotropic deformation mechanism of the 0°-scanning strategy. Simulation results suggest that the morphology difference of laser-scanning tracks and melt pools, which leads to material flow along the laser scanning direction, explains the anisotropic deformation mechanism.

Read the full article here!

Supported by Singapore Ministry of Education (Project Nos.: MOE-T2EP50120-0010, MOE-T2EP50220-0010, and A-8001225-00-00), and the National Natural Science Foundation of China, China (Grant No.: 51775562).
26th August 2024

New insights into the deformation mechanism of orientation-dependent nanoindentation behaviours

Z. Zhang, Q. Yan, Y. Zhang, H. Wang, Z. Tong, X. Jiang
Tribology International 200 (2024) 110112

Abstract. Nanoindentation has been widely used to access the micro-/nanomechanical properties of materials. However, the contribution of micro-texture evolution to the anisotropic surface topography, the correlation of dislocation density characteristics with the orientation-dependent plastic volume, and the specifics of inherent slip activities, are still not fully elucidated up to now.Herein, nanoindentation simulations were performed on (001)-, (101)- and (111)-oriented single-crystal aluminium. Dominant slip systems are exactly determined for each surface pile-up for the first time. Moreover, lattice rotation facilitates the formation of pile-ups. The anisotropic plastic volume is controlled by the preference of intrinsic dislocation movement. In (001) sample, dislocations prefer to propagate along the free surface instead of into the depth of the sample, causing its most obvious pile-ups.

Read the full article here!

Supported by UK’s EPSRC Future Metrology Hub [grant number: EP/P006930/1], the UK’s STFC Innovation Partnership Scheme (STFC-IPS) project [grant number: ST/V001280/1], the European Union’s Horizon 2020 research and innovation programme [grant number: 767589], the China Scholarship Council (CSC) [grant number: 201806220092], and Singapore Ministry of Education Academic Research Funds [grant numbers: A8001225–00-00 and MOE-T2EP50220–0010].

15th August 2024

ME4101A Penultimate Year Students for AY24/25

This year, we proposed ME4101 Dissertation Project Topics tailored to our current and future research directions. We are glad to announce that we have 04 students joining our research team.

 

Ryan Lim Chi Huang
Ryan is a final-year engineering student with a keen interest in the hands-on aspects of engineering. He is passionate about manufacturing and aims to create innovative products with enhanced quality with versatile technological capabilities and know-hows. Outside of academics, he enjoys building and collecting mechanical keyboards, curating vinyl records, and exploring the intricacies of watches. His goal is to leverage his engineering skills to develop products that bridge the gap between functionality and user experience. He will embark on his final year project titled Experimental study on the ductile-to-brittle transition during repeated micro-scratching of brittle materials under the mentorship of Dr. Lionel Lee.

 

Shannon Tan
Shannon is an undergraduate student majoring in Mechanical Engineering at the National University of Singapore. Prior to his undergraduate studies, he has shown aptitude in his machining operations in his diploma studies. With an interest in design and manufacturing process, he has since read a technical elective on Additive Manufacturing processes while on a local exchange at Nanyang Technological University, which has evoked interest in the area of powder metallurgy. This has led him to pursue a final-year project involving both subtractive and additive manufacturing processes through his dissertation project titled Micro-texturing of biomedical grade additively manufactured metal under the mentorship of Ms. Hoe Lay Min. 

 

Vaishnavi Harihara Venkatesan
Vaishnavi is a Year 4 undergraduate in the Department of Mechanical Engineering at National University of Singapore. She have worked in AEM holdings as part of my internship and has experience in finite element analysis (FEA) simulations and web development. Outside the classroom, her hobbies include playing the keyboard. For her final year, she will be studying the Investigation of ultra-precision machining of brittle materials under light irradiation under the mentorship of Mr. Guo Yunfa. 

 

 

 

Ye Ximin
Ximin is currently an undergraduate student in the 3+1+1 NUS Partner Chinese Universities Education Framework between Southern University of Science and Technology (SUSTech) and NUS. His interests are focused on atomic and close-to-atomic scale manufacturing and nature-inspired engineering. Since February 2023, he has been leading a project that investigates the machining sciences of ultrasonic-assisted tip-based nanofabrication under the supervision of Prof. Yongbo Wu at SUSTech. Ximin has also co-authored several peer-reviewed journal articles, including publications in the Chinese Journal of Aeronautics and the Lubricants. He has been recognized with several honors, including the Merit Student Scholarship (First Class) and the Outstanding Student Award in SUSTech. Ximin enjoys sports and excels at tennis having secured second place in the men’s team event at the 27th China University Tennis Championship (South China Division). His final year project titled Atomic-scale investigation of enhanced machinability in CaF2 through ion implantation will be studied under the mentorship of Dr. Zhan Jiaming.