About

Tim Rupert is a professor of materials science and engineering and the director of the Hopkins Extreme Materials Institute (HEMI) at Johns Hopkins University. His research focuses on nanostructured materials and defect engineering, with the goal of leveraging materials to enable new structural and energy technologies. He aims to increase the reliability and lifetime of materials by discovering new structure-property relationships in advanced nanomaterials. His current research includes nanocrystalline metals and alloys, thin film materials, and the study of interfaces and defect phases at the atomic level. Using a combination of computational and experimental techniques, he works to optimize materials for extreme environments, with applications in nuclear energy and defense.

Research topics

• Materials science
• Metallurgy
• Condensed matter physics
• Crystallography
• Composite material

Selected publications

• Composition-driven nanotwin engineering in sputtered Ni-Fe and Ni-Cr films: linking fault energetics to twin thickness

  Acta Materialia · 2026-01-06 · 3 citations

  article
  PublisherDOI

• Kinetics of Amorphous Defect Phases Measured Through Ultrafast Nanocalorimetry

  ArXiv.org · 2025-06-13

  preprintOpen access

  Recognition of the role of extended defects on local phase transitions has led to the conceptualization of the defect phase, localized thermodynamically stable interfacial states that have since been applied in a myriad of material systems to realize significant enhancements in material properties. Here, we explore the kinetics of grain boundary confined amorphous defect phases, utilizing the high temperature and scanning rates afforded by ultrafast differential scanning calorimetry to apply targeted annealing/quenching treatments at high rates capable of capturing the kinetic behavior. Four Al-based nanocrystalline alloys, including two binary systems, Al-Ni and Al-Y, and two ternary systems, Al-Mg-Y and Al-Ni-Y, are selected to probe the materials design space (enthalpy of mixing, enthalpy of segregation, chemical complexity) for amorphous defect phase formation and stability, with correlative transmission electron microscopy applied to link phase evolution and grain stability to nanocalorimetry signatures. A series of targeted isothermal annealing heat treatments is utilized to construct a Time-Temperature-Transformation curve for the Al-Ni system, from which a critical cooling rate of 2,400 °C/s was determined for the grain boundary confined disordered-to-ordered transition. Finally, a thermal profile consisting of 1,000 repeated annealing sequences was created to explore the recovery of the amorphous defect phase following sequential annealing treatments, with results indicating remarkable microstructural stability after annealing at temperatures above 90% of the melting temperature. This work contributes to a deeper understanding of grain boundary localized thermodynamics and kinetics, with potential implications for the design and optimization of advanced materials with enhanced stability and performance.

  PublisherOA PDFDOI

• Amorphous complexion-aided sintering enables scalable processing of bulk nanocrystalline Cu-Zr with high strength and compressive plasticity

  2025-06-04

  preprintOpen accessSenior author

  Nanocrystalline alloys can have exceptional strengths, yet due to limited microstructural stability it is difficult to fabricate bulk pieces through traditional processing routes that retain nanosized grains. In this study, centimeter-sized Cu-Zr alloy pellets were fabricated via a simple and improved powder metallurgy processing route. Different consolidation temperatures and times were employed to investigate the effect of amorphous grain boundary complexions on densification and the resulting mechanical properties. Bulk compression tests were carried out, with the samples that were hot pressed at 900 o C for 10 h exhibiting an excellent combination of 2 average yield strength of 722 ± 45 MPa and average failure strain of 25.3 ± 2.4%. Therefore, we find that a powder processing route which enables amorphous complexion-assisted sintering leads to bulk nanocrystalline alloys that (1) reach full density without requiring quenching treatments or other complex processing, (2) demonstrate appreciable plasticity, and (3) have strengths that compete with commercially available high-strength Cu alloys.

  PublisherOA PDFDOI

• Human perception-inspired grain segmentation refinement using conditional random fields

  Materials Characterization · 2025-10-23

  articleOpen access

  Automated detection of grain boundaries in electron microscope images of polycrystalline materials could help accelerate the nanoscale characterization of myriad engineering materials and novel materials under scientific research. Accurate segmentation of interconnected line networks, such as grain boundaries in polycrystalline material microstructures, poses a significant challenge due to the fragmented masks produced by conventional computer vision algorithms, including convolutional neural networks. These algorithms struggle with thin masks, often necessitating post-processing for effective contour closure and continuity. Previous approaches in this domain have typically relied on custom post-processing techniques that are problem-specific and heavily dependent on the quality of the mask obtained from a computer vision algorithm. Addressing this issue, this paper introduces a fast, high-fidelity post-processing technique that is universally applicable to segmentation masks of interconnected line networks. Leveraging domain knowledge about grain boundary connectivity, this method employs conditional random fields and perceptual grouping rules to refine segmentation masks of any image with a discernible grain structure. This approach significantly enhances segmentation mask accuracy by correctly reconstructing fragmented grain boundaries in electron microscopy images of a polycrystalline oxide. The refinement improves the statistical representation of the microstructure, reflected by a 51 % improvement in a grain alignment metric that provides a more physically meaningful assessment of complex microstructures than conventional metrics. This method enables rapid and accurate characterization, facilitating an unprecedented level of data analysis and improving the understanding of grain boundary networks, making it suitable for a range of disciplines where precise segmentation of interconnected line networks is essential. • Enhanced Segmentation Accuracy: The post-processing method significantly improves segmentation accuracy, as evidenced by metrics commonly used for segmentation tasks, like pixel accuracy, intersection-over-union (IoU), and Dice similarity coefficient (DSC). • Time Efficiency: The method drastically reduces the time required for grain segmentation compared to manual labeling, which is crucial for applications requiring real-time analysis, such as in-situ materials science experiments. • New Grain Alignment Metric: The development of a novel grain alignment metric offers a more robust measure for segmented region accuracy, especially useful in thin segmentation masks. • Applicability Across Materials and Domains: Unlike prior custom post-processing approaches, this methodology is robust and generalizable and can be applied to a wide range of crystalline materials, enhancing its utility in materials science research.

  PublisherDOI

• Amorphous complexion-aided sintering enables scalable processing of bulk nanocrystalline Cu-Zr with high strength and compressive plasticity

  2025-08-04

  preprintOpen accessSenior author

  Nanocrystalline alloys can have exceptional strengths, yet due to limited microstructural stability it is difficult to fabricate bulk pieces through traditional processing routes that retain nanosized grains. In this study, centimeter-sized Cu-Zr alloy pellets were fabricated via a simple and improved powder metallurgy processing route. Different consolidation temperatures and times were employed to investigate the effect of amorphous grain boundary complexions on densification and the resulting mechanical properties. Bulk compression tests were carried out, with the samples that were hot pressed at 900 o C for 10 h exhibiting an excellent combination of 2 average yield strength of 722 ± 45 MPa and average failure strain of 25.3 ± 2.4%. Therefore, we find that a powder processing route which enables amorphous complexion-assisted sintering leads to bulk nanocrystalline alloys that (1) reach full density without requiring quenching treatments or other complex processing, (2) demonstrate appreciable plasticity, and (3) have strengths that compete with commercially available high-strength Cu alloys.

  PublisherOA PDFDOI

• Kinetics of amorphous defect phases measured through ultrafast nanocalorimetry

  Acta Materialia · 2025-11-25

  articleOpen access
  PublisherDOI

• Grain boundaries amplify local chemical ordering in complex concentrated alloys

  ArXiv.org · 2025-01-07

  preprintOpen accessSenior author

  Local chemical ordering strongly influences the behavior of complex concentrated alloys, yet its characterization remains challenging due to the nanoscale dimensions and scattered spatial distribution of the ordered domains. Here, we study chemical ordering near grain boundaries, demonstrating they can act as microstructural anchor points that amplify chemical order and drive the formation of compositional nanopatterns. Atomistic simulations reveal the development of composition waves with ordering vectors normal to the boundary plane in two distinct material systems, CrCoNi and NbMoTaW. These waves manifest as periodic enrichment-depletion patterns that reflect the underlying chemical ordering tendencies of each system, but with amplified contrast that extends several nanometers into the grain interior before gradually decaying. By examining multiple grain boundary orientations and alloys, we show that both the interfacial segregation profile and the crystallographic terminating plane govern the extent and character of this amplification. This interplay between boundary-dictated directional ordering and the diffuse, untemplated chemical domain evolution within the grain advances our understanding of interface-mediated ordering phenomena and suggests new opportunities for experimentally detecting local chemical order in complex concentrated alloys.

  PublisherOA PDFDOI

• Bulk nanocrystalline Al–Mg–Y alloys with amorphous grain boundary complexions display high strength and compressive plasticity

  Journal of Materials Science · 2025-08-21 · 1 citations

  articleSenior authorCorresponding
  PublisherDOI

• Tuning grain boundary cation segregation with oxygen deficiency and atomic structure in a perovskite compositionally complex oxide thin film

  ChemRxiv · 2024-02-02 · 1 citations

  preprintOpen access

  Compositionally complex oxides (CCOs) are an emerging class of materials encompassing high entropy and entropy stabilized oxides (HEOs, ESOs). These promising advanced materials leverage tunable chemical bond structure, lattice distortion, and chemical disorder for unprecedented properties. Grain boundary (GB) and point defect segregation to GBs is relatively understudied in CCOs even though they can govern macroscopic material properties. For example, GB segregation can govern local chemical (dis)order and point defect distribution, playing a critical role in electrochemical reaction kinetics, and charge and mass transport in solid electrolytes. However, compared with conventional oxides, GBs in multi-cation CCO systems are expected to exhibit more complex segregation phenomena and thus prove more difficult to tune through GB design strategies. Here, GB segregation was studied in a model perovskite CCO LaFe0.7Ni0.1Co0.1Cu0.05Pd0.05O3-x textured thin film by (sub-)atomic-resolution scanning transmission electron microscopy imaging and spectroscopy. It is found that GB segregation is correlated with cation reducibility—predicted by an Ellingham diagram—as Pd and Cu segregate to GBs rich in oxygen vacancies (𝑉 𝑂 ∙∙). Furthermore, Pd and Cu segregation is highly sensitive to the concentration and spatial distribution of 𝑉 𝑂 ∙∙ along the GB plane, as well as fluctuations in atomic structure and elastic strain induced by GB local disorder, such as dislocations. This work offers a perspective of controlling segregation concentration of CCO cations to GBs by tuning reducibility of CCO cations and oxygen deficiency, which is expected to guide GB design in CCOs.

  PublisherOA PDFDOI

• Grain size dependent indentation response of single-phase (CoCuMgNiZn)O high entropy oxides

  Journal of the European Ceramic Society · 2024-06-13 · 13 citations

  article
  PublisherDOI

Recent grants

• CAREER: Nanocrystalline Grain Boundary Network Engineering Enabled by New Deformation Mechanisms

  NSF · $537k · 2013–2019

• Predicting Changes in Structure and Properties During Wear in Metallic Systems

  NSF · $345k · 2015–2018

• BRIGE: Interfacial Defects and the Failure of Nanostructured Metals

  NSF · $175k · 2012–2014

Frequent coauthors

• Vladyslav Turlo

  Swiss Federal Laboratories for Materials Science and Technology

  53 shared

• Enrique J. Lavernia

  Texas A&M University

  46 shared

• Jennifer D. Schuler

  Sandia National Laboratories

  45 shared

• Julie M. Schoenung

  University of California, Irvine

  42 shared

• Zhiliang Pan

  40 shared

• Tianjiao Lei

  Massachusetts Institute of Technology

  39 shared

• Xin Wang

  University of California, Irvine

  38 shared

• Zhifeng Huang

  32 shared

Education

• Ph.D., Materials Science and Engineering

  Massachusetts Institute of Technology

  2011

• B.S./M.S., Mechanical Engineering

  Johns Hopkins University

  2007

Awards & honors

• 2025 Brimacombe Medalist by The Metals, Minerals, and Materi…