Dartmouth Engineering

Research Interests

Materials for energy systems; mechanical behavior; phase tranformations; electron microscopy; x-ray topography; x-ray diffraction; microstructure and mechanical behavior of snow, firn, and ice; magnetic materials; intermetallic compounds; high entropy alloys; high temperature materials; nanoparticles for magnetic hyperthermia; biomaterials

Education

BA, Metallurgy and Science of Materials, University of Oxford 1979
D.Phil, Metallurgy and Science of Materials, University of Oxford 1982

Awards

2015 Fellow, American Association for the Advancement of Science (AAAS)
2012 Fellow, Minerals, Metals & Materials Society (TMS)
2011 Fellow, Materials Research Society
2003 Listed in ISI citation index of highly-cited Materials Scientists
2002 Fellow, The Institute of Materials, Minerals and Mining (U.K.)
2001 Fellow, ASM international
1993 Chartered Engineer (C.Eng.) of The Engineering Council (U.K.)

Professional Activities

Field-Chief-Editor, Frontiers in Metals and Alloys (2022–)
Co-Editor-in-Chief, High Entropy Alloys & Materials (2022–)
Organizer, Physics and Chemistry of Ice, Dartmouth (2014)
Organizer, MRS Fall Meeting Symposium on Intermetallic-based Alloys — Science, Technology, and Applications (2014)
Editorial Board, Nano Life (2009–)
Editorial Advisory Board, Intermetallics (1998–)
Editorial Board, Metals (2010–)
Editor in Chief, Materials Characterization (2009–2020)
Editorial Board, International Materials Reviews (2002–2020)
Reviewer for various US, Canadian, Hong Kong, Swiss, French, and Australian government agencies and numerous journals
Consultant to various companies on microstructural characterization and materials processing
Editor of the proceedings of five conferences

Research Projects

High entropy alloy soft magnets

High entropy alloy soft magnets

Soft magnets play a vital role in efficient energy conversion in a variety of important applications and industries including wide-bandgap semiconductors, electric vehicles, aeronautics, and aerospace, particularly at high temperatures. Improving the efficiency of modern power electronics and electrical machines via advanced soft magnets has the potential to significantly contribute to global energy savings, thereby leading to a reduction of the associated carbon footprint. In this project, we are working on two novel FeCoMnAl high-entropy alloy (HEA) soft magnets, one of which is single-phase B2 (Fe₃₀Co₄₀Mn₁₅Al₁₅) and the other consists of an ordered B2-phase matrix enriched with Co/Al and uniformly distributed BCC nanoprecipitates enriched with Fe/Mn (Fe₄₀Co₃₀Mn₁₅Al₁₅). The two HEAs show similar properties, viz., a high saturation magnetization of 158-162 Am² kg^-1, a high Curie temperature of 1020-1081 K, a low coercivity of 108-114 A m^-1, a high electrical resistivity of ~230 µΩ cm, and good thermal stability. We are processing these HEAs using both a powder metallurgy route and via additive manufacturing. The magnetic properties and microstructures of the resulting materials are being examined using combination of a VSM, TEM, SEM and XRD examinations.
Biodegradable zinc alloys for orthopedic implants

Biodegradable zinc alloys for orthopedic implants

Orthopedic implants are widely used to treat bone and joint disorders, such as fractures, osteoarthritis, and spinal deformities. However, conventional implant materials, such as stainless steel, titanium, and cobalt-chromium alloys, have several limitations: (i) they may cause adverse reactions and metal sensitivity due to their foreign ions and corrosion products; (ii) they may fail prematurely due to stress concentration and fatigue; (iii) they may interfere with bone remodeling and healing due to their mismatched mechanical properties with the host tissue; (iv) they can become a nidus for bacterial infection and biofilm colonization. Therefore, there is a need for novel implant materials that can overcome these challenges and improve the clinical outcomes of orthopedic surgery. Zinc is an attractive candidate for orthopedic implants because it is an essential trace element in the human body that plays a key role in bone metabolism and wound healing. Moreover, Zn is biodegradable and can be gradually resorbed by the body without leaving any permanent foreign material. The typical in vivo corrosion rates of unalloyed zinc in rats is 0.03 mm/yr, which is a useful rate for biodegradation. However, unalloyed Zn has very poor mechanical strength, which limits its application as an implant material. To address these issues, we are developing new Zn-based alloy that contains small amounts of silver, calcium, iron, magnesium, and manganese, and using a novel processing route. These alloying elements are chosen based on their beneficial effects on the biological and mechanical properties of Zn. Specifically, Ag has antibacterial activity and can reduce the risk of infection; Ca can promote bone formation and integration; Fe can enhance fracture fixation and blood compatibility; Mg can improve biocompatibility and corrosion resistance; Mn can increase ductility and strength. An adequate rate of implant degradation will allow the bone to heal properly before degrading and allowing the bone to support any loads.
Observations and micromechanical modeling of the behavior of snow/ice lenses under load in order to understand avalanche nucleation

Observations and micromechanical modeling of the behavior of snow/ice lenses under load in order to understand avalanche nucleation

The microstructual evolution of snow under a temperature gradient has been of interest for many years since this can lead to persistent weak layers, which are possible microstructural causes of avalanches. Ice crusts can form on top or within a snowpack from a variety of meteorological conditions including significant melt/freeze or freezing rain events, and once buried, they can persist throughout the entire winter season and act as an ideal sliding surface for dangerous slab avalanches in seasonal mountain snowpacks. Both of these phenomena are important because the number of fatalities from avalanches in the US has increased annually since the 1970s. Avalanches can also have substantial economic impacts due to road closures, the costs of rescue and building damage, and, with continued global warning, more avalanches are expected in Arctic regions. To understand avalanche nucleation, we are deforming two types of specimens (heterogeneously-layered snow and snow containing an ice lens) in a micro CT located in a cold room, in which the specimens are repeatedly imaged during loading. We are also performing more macroscopic deformation experiments on larger samples at both different rates and different temperatures, which are imaged using a high-speed video camera during loading. The final deformed microstructures in both cases are imaged at high resolution using a scanning electron microscope, which provides information on both the effects of crystal orientation on deformation while clearly delineating one ice crystal orientation from another. Based on the experimental observations, a multiscale computational model is being built to understand crack initiation/crack propagation as well as the deformation mechanisms in heterogenously-layered snow samples containing persistent weak layers and ice/snow interfaces.
Using first principles calculations and electro-pulse annealing to design and manufacture low-cost permanent magnets

Using first principles calculations and electro-pulse annealing to design and manufacture low-cost permanent magnets

Demand for high-performance permanent magnets for motors is increasing rapidly for applications such as wind turbine generators and motors in both electric and hybrid cars. Samarium-Cobalt and Neodymium-Iron-Boron Rare Earth magnets are generally used for such challenging applications. While Rare Earth magnets are the best currently available permanent magnets, they are not without problems such as being brittle, suffering from thermal shock, and experiencing corrosion. Further, over 95% of Rare Earths are produced in China and there has been substantial price volatility. Finally, Rare Earth mining has been associated with severe environmental degradation and large energy usage. NiFe, which has been identified in meteorites as the compound Tetrataenite where it transformed from the high temperature (disordered) f.c.c. phase over thousands of years, has magnetic properties comparable to that of Rare Earth magnets. This research award develops new, low-cost, environmentally-friendly NiFe-based permanent magnets, using both quantum-mechanical calculations to predict the effects of alloying with other elements coupled with experiments to verify the effects of these additional elements on the transformation kinetics and magnetic properties. It uses the novel approach of pulsed electrical heating, which has been shown to accelerate transformations. Both women and under-represented minorities will be engaged in the research. The development of novel NiFe magnets will enable production of permanent magnets to be relocated to the USA. As part of the work, the project develops a web site that offers simple virtual experiments to explain to a wide audience magnetism and the materials science of permanent magnets.

The L1₀-structured compound Nickel-Iron (NiFe) has the potential to replace Rare Earth (RE) magnets at low cost: NiFe has a magnetic anisotropy energy, k_u, of 1.3 x 10⁶ J.m^-3 and a saturation magnetization m₀M_S of 1.59 Tesla, which is comparable to that of Nd₂Fe₁₄B. In addition, it has good corrosion resistance. The challenge is that the binary L1₀ compound has a very low transformation temperature from the high-temperature f.c.c. phase of about 320^oC that forms on casting and, thus, orders very slowly at temperatures where it is stable. This project combines ab initio quantum mechanical calculations and experimental work to design new L1₀-structured NiFe magnets with ternary elemental additions. These ternary compounds potentially have a significantly higher f.c.c.-to-L1₀ transformation temperatures and higher diffusivities than binary NiFe, but have similar saturation magnetizations. Thus, the L1₀phase can be produced at higher temperature in short, commercially-viable times utilizing electro-pulse annealing of cold-worked material, which has also been shown to dramatically accelerate recrystallization in NiFe. The TEM-based technique ALCHEMI is used to determine the atom site locations of these ternary additions in the L1₀unit cell. This work demonstrates a practical paradigm for designing magnets and leads to new commercially-viable permanent magnet. Commercially, NiFe can be manufactured by continuous electro-pulse annealing of rolls of sheet material or of rods. NiFe is very ductile and can easily be machined into various shapes.
High-strength, high-ductility, high entropy alloys with high-efficiency native oxide solar absorbers for concentrated solar power systems

High-strength, high-ductility, high entropy alloys with high-efficiency native oxide solar absorbers for concentrated solar power systems

This project is investigating the synergy between the excellent mechanical behavior of FeMnNiAlCr high entropy alloys (HEAs) and the high solar absorptance of their native thermal oxides for high efficiency concentrated solar thermal power (CSP) systems working at >700^oC. The alloy itself would be used in high-temperature tubing to carry molten salts or supercritical carbon dioxide (sCO2), while the native oxide would act as a high-efficiency solar thermal absorber. The oxide layer is also dense and protective against oxidation (parabolic growth kinetics) at 750 °C. This new Fe-Mn based HEA system has already demonstrated a higher tensile strength and ductility than more expensive Ni-based Inconel 740 superalloys at both room temperature (with carbon doping) and 750^oC (with Ti doping), and their native thermal oxides have achieved a high optical-to-thermal conversion efficiency of ηtherm=90.8% at 750°C under 1000x solar concentration ratio. In preliminary corrosion studies, two-phase Cr-modified HEAs have sustained bromide molten salts for 14 days at 750°C with <2% weight loss. The project has close collaborations with the Oak Ridge National Laboratory (ORNL) and the Ames Laboratory in computational materials science and atom probe tomography (APT) to understand the fundamental structure-property relationship in FeMnNiAlCr HEAs.

Funded by DOE.
New Hampshire Center for Multiscale Modeling and Manufacturing of Biomaterials (NH Bio-MADE)

New Hampshire Center for Multiscale Modeling and Manufacturing of Biomaterials (NH Bio-MADE)

Orthopedic implants are often required to replace or support damaged skeletal structures. For this application and many others, an individualized component, determined, through, for example, an MRI scan, is required for repairs. Thus, the ability to rapid prototype biomedical implants for mass customization is desirable. Furthermore, the final product properties and characteristics are critical to, for example, reduce the gauge thickness and, thus, the weight of the component. Computational modeling is necessary to optimize the final product. Cost is important so creating the component from stock sheet metal, as opposed to from metal powder, machining from a large workpiece, or casting the component, is advantageous. Furthermore, by work hardening of the material through forming, increased strength is achieved.

With respect to sheet metal, characterizing the material behavior thoroughly is essential to produce an optimal final product. Tests to characterize the material, e.g. uniaxial tension/compression (Marciniak tests), are typically performed under proportional loading and follow a linear deformation path. Such testing can produce a failure criterion for the material, e.g., a forming limit curve (FLC), which represents the planar strain values in sheet metal above which the deformation localizes into a diffuse neck. The strain path dependence of FLCs has been documented by a number of workers. During forming, the deformation path can be intentionally manipulated to improve the forming process. For example, if a sharp corner feature is desired in a component, a generous radius is formed first, then a restrike operation is performed in the corner with the desired sharp punch tool. The variation in the deformation path allows the final strain values to be below the FLC and, thus, avoids failure. While such industrial applications are well known, the phenomenon which allows this increased formability during non-linear deformation path loading is poorly understood. This project will test the hypothesis that the increased formability exhibited by metallic alloys during non-linear deformation paths results from dislocation mechanisms, i.e., recombination and change of glide systems upon strain-path change, which prevents strain localizations due to pile-ups at grain or phase boundaries or other interfaces in the microstructure. Increment forming of stainless steel and titanium parts is being performed at the University of New Hampshire alongside numerical modeling of the process, while analysis of the dislocation structures using transmission electron microscopy and scanning electron microscopy is being performed at Dartmouth.

Funded by the U.S. National Science Foundation EPSCOR program.
The impact of impurities and stress state on polycrystalline ice deformation
The impact of impurities and stress state on polycrystalline ice deformation
Despite the ubiquitous use of the constitutive relation for ice commonly referred to as “Glen’s Flow Law,” significant uncertainty exists particularly with regard to the role of impurities and the development of oriented fabrics. The aim of this project is to improve the constitutive relationship for ice by performing deformation tests and microstructural characterization of pure and sulfuric acid-doped ice. The research proposed here will focus on sulfuric acid’s impact on ice viscosity, fabric evolution, and diffusivity. Sulfuric acid can have both direct—by changing the dislocation velocity and/or density—and indirect—by changing the grain size and fabric—effects on the mechanical properties of polycrystalline ice. The complexity and interaction of these effects means that one cannot understand the effects of sulfuric acid by simply examining ice core specimens.

In this project, we will deform four types of ice:
1. lab-grown ice samples doped with similar-to-natural concentrations of sulfuric acid,
2. lab-grown high-purity ice,
3. layered doped and pure ice, and
4. natural ice from Antarctic ice cores.
Deformation will be performed in both uniaxial compression and simple shear. The addition of simple shear tests is critical for relating the laboratory-observed deformation behavior to the behavior of polar ice sheets where the shear strain dominates ice motion in basal ice. After deformation to strains from 5% up to 25%, the microstructural development will be assessed with state-of-the-art methods including a variety of scanning electron microscope techniques, Raman microscopy, synchrotron-based Nano-X-ray fluorescence and ion chromatography.

These analysis techniques will allow the determination of:
1. the segregation and movement of impurities;
2. the rate of grain boundary migration;
3. the number of recrystallized grains; and
4. the full orientation of the ice crystals.
The results will enable both microstructural modeling of the effects of H2SO4 and numerical modeling of diffusion in ice cores. The net result will be a better understanding of ice deformation that improves ice-core interpretation and ice-sheet modeling. The work will lead to the education of a PhD student at Dartmouth, introduce undergraduate students to research at both the University of Washington and Dartmouth, and bring together the microstructural expertise of Dartmouth with the ice-core measurement and modeling emphasis at the University of Washington.

Funded by the US National Science Foundation
Porous thermoelectric cells (TECs) for waste heat recovery

Porous thermoelectric cells (TECs) for waste heat recovery

Porous thermoelectric cells (TECs) are being developed for waste heat recovery. This project seeks to convert waste thermal energy directly into electricity potentially increasing overall energy efficiency by 15-20% and providing new portable electric power sources, particularly for cold regions. The project is focusing on low cost, nanostructure-engineered TEC (NETECs) materials based on earth-abundant, highly machinable metallic alloys and intermetallic compounds by engineering the grain sizes, second phase precipitation, and nanopores in transition metal intermetallic compounds. The project is currently focusing on the compound Fe2AlV. The location of quaternary atoms in the lattice is being determined by the TEM-based technique ALCHEMI.

Funded by USA-CRREL

Selected Publications

Ye Y, Lish SD, Xu L, Chen S, Ren Y, Saksena A, Gault B, Wittmann MW, Xu H, Baker I. (2022) "Fe₃₀Co₄₀Mn₁₅Al₁₅: a novel single-phase B2 multi-principal component alloy soft magnet." High Entropy Alloys and Materials.
Li Y, Baker I. (2022) "Metamorphism observation and model of snow from Summit, Greenland under both positive and negative temperature gradients in a micro computed tomography." Hydrological Processes. 36, e14696.

Ye Y, Lish SD, Xu L, Woods E, Chen S, Ren Y, Wittmann MW, Xu H, Gault B, Ian Baker I. (2022) "Exceptional soft-magnetic properties of an ordered multi-principal element alloy with disordered nanoprecipitates." High Entropy Alloys and Materials.

Antonov S, Prithiv TS, Zhou X, Peterson A, Gault B, Baker I. (2023) "Phase transformations in the alumina-forming austenitic stainless steel Fe-20Cr-30Ni-2Nb-5Al during creep at 750ºC 45 MPa." Materialia. 30: 101849.

Peng H, Hu L, Huang S, Baker I. (2023) "A comparison of thermo-mechanically-treated and electron-beam-welded strong, ductile medium-entropy alloy: microstructural evolution and deformation mechanisms." Materials Science and Engineering: A. 882: 145449.

Ren Y, Liu X, Wang H, Yang Y, Baker I, Wang I, Wu H. (2023) "Unraveling the inherent anisotropic properties of in situ alloyed copper-modified titanium alloys produced by laser powder bed fusion." Journal of Alloys and Compounds. 966: 171323.
Keller T, Barbagallo D, Sheremetyeva N, Gosh T, Shanks KS, Hautier G Baker I. (2023) "The phase transformation behavior of Mn-Al rare-earth-free permanent magnets." Journal of Magnetism and Magnetic Materials. 587: 171331.

Patents

High-entropy alloys with high strength | 11,530,468
Oxidation resistant high-entropy alloys | 10,190,197
Nanostructured Mn-Al permanent magnets and methods of producing same | 8,999,233
Joining of parts via magnetic heating of metal aluminum powders | 8,444,045
Joining of parts via magnetic heating of metal-aluminum powders | 8,172,126
System and method for use of nanoparticles in imaging and temperature measurement | 7,994,786
High-strength nanostructured alloys | 7,815,850