Shuyang’s nanoindentation study on SrNi2P2 and its Rhodium doped structure has been published at Journal of Materials Research! Congratulations! Two UConn undergraduate students (Kiera Burns and Aurora Buswell) participated in this research.

Shuyang Xiao, Sarshad Rommel, Kiera A. Burns, Aurora A. Buswell, Vladislav Borisov, Juan Schmidt, Roser Valentí, Paul C. Canfield, Mark Aindow, Seok-Woo Lee, “Effects of Rhodium doping on dislocation nucleation in a [001] SrNi2P2 single crystals under spherical nanoindentaiton,” Journal of Materials Research (2023) [PDF][web] – DOI: https://doi.org/10.1557/s43578-023-01073-y

Abstract: Nanoindentation was performed on SrNi₂P₂ single crystals and their dilute solid solutions, Sr(Ni_1−xRh_x)₂P₂ (x = 0 ~ 0.055), under [001] loading to investigate the effects of elemental doping on Young’s modulus and dislocation nucleation stress. The results show that Young’s modulus and the dislocation nucleation stress decrease as the Rh content increases, and their Rh content dependence also varies with the Rh content. Electron diffraction analysis and the anisotropic lattice distortion calculations revealed that a local structural transition from the orthorhombic superstructure to the tetragonal structure and local compressive residual stresses could be the main reasons for the decrease in Young’s modulus and dislocation nucleation stress, respectively. The overlap of stress–strain fields between Rh atoms and the associated local structural transition contribute to their Rh content dependence. The results also indicate that elemental doping does not necessarily strengthen materials if the incipient plasticity is controlled by dislocation nucleation, unlike conventional solid solution strengthening.

 

Farewell lunch with Shuyang and Jay. We wish both a great success in their next endeavor! Congratulations again on their graduation!

Tyler’s work at EAG Lab in Silicon Valley (CA) is highlighted at the MSE Department webpage! Excellent article!

EAG Laboratories Scientist Shares Insight into Nanotechnology Research

 

Many congratulations on Shuyang’s graduation. Shuyang received PhD degree, and his study focused on fundamental understanding of mechanical behavior of SrNi2P2 intermetallic compound. This material exhibits superplasticity via double lattice collapse and expansion process, and this discovery was published at Nano Letters. Shuyang also studied the temperature effect, the cyclic loading effect, and the solute effect on superplasticity. He also discovered the tension-compression asymmetry in superplasticity mechanism. Due to this asymmetry, SrNi2P2 exhibits relatively large temperature changes during cyclic loading and demonstrates a strong potential as an elastocaloric material!

Shuyang will come back to China and start to work on SiEn integrated circuit Co., Ltd. We hope he makes a great contribution to developing a future semiconductor technology. Many congratulations on all your outstanding achievements at UConn!!!

Congratulations on Jay’s graduation! Jay received M.S degree and made a significant contribution to fundamental understanding of mechanical behavior of wire-arc-additive-manufactured (WAAM) material. Jay discovered the high solute concentration at dendrite boundaries, and this periodic distribution of solutes lead to the Hall-Petch type behavior. This result is very important for the development of strong WAAM materials. Jay starts their next journey at Collins Aerospace! Good luck!

 

Zhongyuan’s research is highlighted at the UConn MSE webpage!

Discovering the Power of Materials Science at UConn: “Material is the foundation of everything.”

 

 

Shuyang finished his PhD defense successfully. Many congratulations!

He gave a wonderful presentation on mechanical properties of SrNi2P2 single crystals, which show unusual superplastic behavior via lattice collapse and expansion. He has investigated tension-compression asymmetry, temperature effect, and composition effect.

Title: Mechanical behavior of SrNi₂P₂ single crystals at small length scales

Committee:

Prof. Seok-Woo Lee (major advisor)

Prof. Mark Aindow

Prof. George Rossetti Jr.

Prof. Rainer Hebert

Prof. Jasna Jankic

Date/Time: Wednesday, April 5, 2023. 10:00 AM

Location: Science One 1002

 Abstract: Elastic strain limit, which is the measure of the maximum allowed fractional change in material length before a permanent shape change occurs, is the quantity used to describe the elastic deformability of materials. Superelasticity is the recoverable deformation associated with the reversible structural transition, which often leads to the large maximum recoverable strain. Achieving superelasticity is important for various engineering applications, which require a reliable impact protection, strain engineering, elastocaloric effect, and shape memory effect. In 1985, Hoffmann and Zhang postulated the possibility of forming and breaking Si-type bonds in ThCr₂Si₂-structured intermetallic compounds under uniaxial deformation along their c-axis, which could lead to superelasticity via the unique reversible structural transition, lattice collapse and expansion, respectively. By reviewing crystallographic data of a wide variety of known ThCr₂Si₂-structured compounds, SrNi₂P₂ has been identified as one of the most likely candidates to have a relatively small critical stress of structural transition, which would allow us to observe the structural transition and superelasticity before fracture occurs.

In this study, micro-compression test, micro-tensile test, and nanoindentation were conducted on SrNi₂P₂ single crystals along c-axis direction and confirmed that superelasticity indeed occurs through the lattice collapse and expansion process that Hoffman and Zhang suggested. This unique structural process enables excellent fatigue resistance and the efficient elastocaloric cooling. The phase diagram in stress-temperature space was also constructed with cryogenic mechanical data. In addition, the critical role of anisotropic residual stress, which could be developed by a doped element, in superelasticity and plasticity has been identified. It is noteworthy to mention that theoretical calculation predicts the presence of ~2500 ThCr₂Si₂-type intermetallic compounds. Therefore, all the results not only provide a fundamental insight into the understanding of the structure and mechanical properties of SrNi₂P₂ but also suggest a strong possibility to discover another superelastic ThCr₂Si₂-type intermetallic compounds. This new class of superelastic materials could be useful for the development of impact-resistant materials for structural applications, cryogenic linear actuators for space engineering, and elastocaloric cooling systems for refrigeration.

Zhongyuan receives the summer doctoral dissertation fellowship! Congratulations!

Jessica’s study on mechanical properties of nanocrystalline MgAl2O4 is published at Acta Materialia! Many congratulations! This works used nanoindentation, microvillar compression, and micro-cantilever bending extensively to investigate the grain size effect on hardenss, yield strength, and fracture toughness. The significant improvement in fracture toughness when the grain size becomes smaller than 10.5nm provides a great promise to develop a high toughness ceramic! Wonderful works!

Jessica M. Maita, Sarshad Rommel, Jacob R. Davis, James A. Wollmershauser, Edward P. Gorzkowski, Boris N. Feigelson, Mark Aindow, Seok-Woo Lee, “Grain size dependence of mechanical properties of nanocrystalline magnesium aluminate MgAl2O4,” Acta Materialia, in press (2023) [PDF][web]

 

 

Shuyang and Zhongyuan gave a presentation at the TMS 2023 at San Diego, CA!

• Zhongyuan Li: Micro-mechanical characterization on amorphous carbon and its nanoporous structures (Poster Presentation)
• Shuyang Xiao: Multi-stage superelasticity in SrNi2P2 intermetallic compound via lattice collapse and expansion and the influence of cryogenic temperature (Oral presentation)