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Introduction
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June 2013 - present
July 2012 - July 2013
August 2009 - May 2012
Publications
Publications (120)
Elastocaloric cooling, which exploits superelastic transitions of shape memory alloys to pump heat, has recently emerged as a frontrunner in alternative cooling technologies. Despite its intrinsic high efficiency, elastocaloric materials exhibit hysteresis associated with input work, a common attribute of caloric cooling materials. In this study, t...
The deformation mechanisms that dictate the tribological performances of heat treated Ni55Ti45, Ni54Ti45Hf1 and Ni56Ti36Hf8 alloys are revealed through rolling contact fatigue (RCF) testing and transmission electron microscopy (TEM) analyses. Analysis of worn samples that passed a 5×10⁸ cycle RCF runout condition shows that damage is primarily conf...
The effects of various heat treatments on the microstructure and hardness of new Ni56Ti41Hf3 and Ni56Ti36Hf8 (atomic %) alloys were studied to evaluate the suitability of these materials for tribological applications. A solid-solution strengthening effect due to Hf atoms was observed for the solution annealed (SA) Ni56Ti36Hf8 alloy (716 HV), result...
Adopting new metals 3D printers introduces time and cost obstacles to printing parts with the same quality as was attained on existing printers. A large number of trial-and-error experiments or computationally intense simulations for property prediction and process optimization are often required. However, machine learning (ML) promises the ability...
Machine learning (ML) is shown to predict new alloys and their performances in a high dimensional, multiple-target-property design space that considers chemistry, multi-step processing routes, and characterization methodology variations. A physics-informed featured engineering approach is shown to enable otherwise poorly performing ML models to per...
This paper presents a novel multiscale approach for analyzing multi-axial stress-strain evolution in Ti-7Al cruciform specimens under dwell loading, through the use of an uncertainty-quantified, parametrically homogenized constitutive model (UQ-PHCM). The thermodynamically-consistent UQ-PHCM is built from rigorous upscaling of crystal plasticity FE...
In metals additive manufacturing (AM), materials and components are concurrently made in a single process as layers of metal are fabricated on top of each other in the near-final topology required for the end-use product. Consequently, tens to hundreds of materials and part design degrees of freedom must be simultaneously controlled and understood;...
The effects of various heat treatments on the microstructure and hardness of new Ni56Ti41Hf3 and Ni56Ti36Hf8 (atomic %) alloys were studied to evaluate the suitability of these materials for tribological applications. A solid-solution strengthening effect due to Hf atoms was observed for the solution annealed (SA) Ni56Ti36Hf8 alloy (716 HV), result...
The tribological performance and underlying deformation behavior of Ni55Ti45, Ni54Ti45Hf1 and Ni56Ti36Hf8 alloys were studied using rolling contact fatigue (RCF) testing and transmission electron microscopy (TEM). TEM results of the as-machined RCF rods, prepared using focus ion beam, revealed some damage very close to the surface. TEM results afte...
An expanded strain energy-based criterion for predicting preferred martensite variants and multivariant clusters is developed and verified. Building upon previous inclusion-based formulations that considered only the strain energy of lattice stretches, here the authors also incorporate the strain energy of lattice rotations that result from martens...
Nickel-rich (54–56 at.% Ni) NiTi-based alloys have gained increased attention for their high hardness, corrosion resistance, strength, and wear resistance, leading to their development for high-performance bearings and other wear applications. An investigation of a broader compositional range of NiTiHf alloys, in terms of Ni and Hf content, is pres...
In metals additive manufacturing (AM), materials and components are concurrently made in a single process as layers of metal are fabricated on top of each other in the near-final topology required for the end-use product. Consequently, tens to hundreds of materials and part design degrees of freedom must be simultaneously controlled and understood;...
This manuscript expands the existing framework for single-material laser powder bed fusion printed dissolvable supports to Inconel 718 (IN718). Prior work with stainless steel leveraged a sensitization heat treatment using sodium hexacyanoferrate to precipitate chromium carbides over the top 100 μm to 200 μm of material, decreasing the corrosion re...
Habit plane variants (HPVs) are traditionally used as the fundamental microstructure unit in micromechanical models of shape memory alloys. Recently, an approach using Correspondence Variants (CVs) has emerged. Previous research has shown that HPVs cannot completely explain superelastic deformation of Nitinol, especially beyond initiation of the ma...
Machine learning using limited data from physical experiments is shown to work to predict new shape memory alloys in a high dimensional alloy design space that considers chemistry and thermal post-processing. The key to enabling the machine learning algorithms to make predictions of new alloys and their post-processing is shown to be a physics-info...
A million times cooler
Elastocaloric materials can be used for solid-state cooling applications because they can pump heat out of a system using a reversible phase transformation. However, many such materials fail after a small number of cycles. Hou et al. found that laser melting of elastocaloric metals can create fatigue-resistant microstructures...
One of the primary goals of the Consortium for the Advancement of Shape Memory Alloy Research and Technology is to enable the design of revolutionary applications based on shape memory alloy technology. To advance this goal and reduce the development time and required experience for the fabrication of shape memory alloy actuation systems, several m...
Simultaneous nanometer-scale spatial resolution and fractions of a second temporal resolution at controlled temperatures are desired to directly investigate the earliest stages of materials transformations. In this work, laser annealing of an amorphous Fe-Si-Nb-Cu-B alloy within an atom probe instrument is used to induce and subsequently probe in 3...
Dislocation structures, chemical segregation, γ′, γ″, δ precipitates, and Laves phase were quantified within the microstructures of Inconel 718 (IN718) produced by laser powder bed fusion additive manufacturing (AM) and subjected to standard, direct aging, and modified multi-step heat treatments. Additionally, heat-treated samples still attached to...
Dislocation structures, chemical segregation, {\gamma ^{\prime}, {\gamma ^{\prime \prime}}, {\delta} precipitates and Laves phase were quantified within the microstructures of Inconel 718 (IN718) produced by laser powder bed fusion additive manufacturing (AM) and subjected to standard, direct aging, and modified multi-step heat treatments. Addition...
Elastocaloric cooling, which exploits the latent heat released and absorbed as stress-induced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in non-vapor-compression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hyst...
In situ Crystallization of Metallic Glass in an Atom Probe Instrument - Volume 25 Supplement - David R. Diercks, Rajesh Jha, Cristian V. Ciobanu, Aaron P. Stebner
Three-Dimensional in situ Reconstructions of Microstructures with Bimodal Grain Size Distributions - Volume 25 Supplement - Ashley Bucsek, Lee Casalena, Darren C. Pagan, Partha P. Paul, Yuriy Chumlyakov, Michael J. Mills, Aaron P. Stebner
In this work, we measure the microstructure response of the austenite phase during martensitic phase transformation tens of micrometers beneath the surface of a bulk single crystal nickel-titanium shape memory alloy. Using an emerging dark-field X-ray microscopy (DFXM) technique, the austenite phase fraction, relative misorientation, and elastic la...
Reactive thermoplastics are advantageous for wind turbine blades because they are recyclable at end of life, have reduced manufacturing costs, and enable thermal joining and shaping. However, there are challenges with manufacturing wind components from these new materials. This work outlines the development of manufacturing processes for a thick gl...
An experimental platform for multiscale studies of materials subjected to plane stress loads is presented. Coupling with far-field high-energy diffraction microscopy for grain-by-grain measurements of elastic strains and rotations provides an additional benefit; it enables the direct assessment of elastic vs. inelastic deformation of the gauge sect...
Infusible liquid resins that polymerize into a thermoplastic are desirable for many applications. Similar to unsaturated and vinylester thermosetting systems, they consist of polymers dissolved in reactive monomer. This work presents a method to decrease cycle time by tuning the molecular weight and concentration of the predissolved polymer in the...
Using a combination of numerical simulations and atom-probe tomography experiments, we determine the interfacial energy of Cu nanocrystals precipitated within the amorphous matrix of FINEMET (molar composition Fe72.89Si16.21B6.90Nb3Cu1). Specifically, we use the Langer-Schwartz model implemented in the software Thermocalc to carry out parametric si...
Near-field and far-field high-energy diffraction microscopy and microcomputed tomography X-ray techniques were used to study a bulk single crystal nickel‑titanium shape memory alloy sample subjected to thermal cycling under a constant applied load. Three-dimensional in situ reconstructions of the austenite microstructure are presented, including th...
Void detection in fiber-reinforced composites traditionally relies on precise density measurements before and after the physical removal of the polymer matrix; consequently, this method only provides data on the total volume of voids within the material without information about void sizes, shapes, and distributions. Despite advances in X-ray compu...
The near equiatomic NiTi alloy is the most successful shape memory alloy by a large margin. It is widely used in biomedical devices and is the focus of nearly half of all research on metallic materials. Yet, despite having a repeatable pseudoelastic effect and excellent shape-memory, NiTi is very far from satisfying any of the conditions of compati...
We report on the phase separation of methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) during bulk free-radical polymerization. The phase separation is induced when the reaction is initiated at room temperature by the redox reaction of benzoyl peroxide in the presence of an amine. During the reaction, the ratio of MMA and PMMA changes...
Two low-carbon 9-Cr ferritic-martensitic steels were designed with the aim of decreasing M23C6 and maintaining or increasing MX phase fraction. A low-carbon (LC) alloy and a low-carbon, zero-niobium (0 Nb) alloy were fabricated, their designs based upon the P92 alloy system. Solutionizing temperatures to maximize V and Nb in solution while avoiding...
Near-field and far-field high-energy diffraction microscopy and microcomputed tomography X-ray techniques were used to study a bulk single crystal nickel-titanium shape memory alloy sample subjected to thermal cycling under a constant applied load. Three-dimensional in situ reconstructions of the austenite microstructure are presented, including th...
Three-dimensional (3D) X-ray diffraction methods were used to resolve sequential snapshots of the load-induced rearrangement of monoclinic twin microstructures through bulk nickel-titanium specimens in 3D and across three orders of magnitude in length scales. The volumes of each crystallographic variant and the elastic strains and rotations of sele...
Thermoplastic resin systems have long been discussed for use in large-scale composite parts but have yet to be exploited by the energy industry. The use of these resins versus their thermosetting counterparts can potentially introduce cost savings due to non-heated tooling, shorter manufacturing cycle times, and recovery of raw materials from the r...
Mechanisms of crack propagation in a NiTiHf sample were studied from post-mortem microstructure characterizations about cracks. Transmission electron microscopy (TEM) analysis showed that a crack propagated within a martensite band along 〈011〉 type II twin planes. The crack was observed to switch between different twin planes to avoid precipitates....
This study investigates the thermal and
mechanical properties that arise from aging Ni-rich Ni–Ti
(Nitinol) at temperatures below 250 �C, well below those
commonly used to fabricate medical devices. We demonstrate
that the Ni50.8–Ti49.2 composition decomposes at
temperatures as low as room temperature and discuss the
unusual changes in thermal and...
The interfacial energy of Cu nanocrystals precipitated within the amorphous matrix of FINEMET (molar composition Fe72.89Si16.21B6.90Nb3Cu1) was determined through a combined experimental-numerical approach. Specifically, we used the Langer-Schwartz model implemented in the software Thermocalc to carry out parametric simulations of growth and coarse...
Experiments, upper bound models, and finite element simulations are used to determine forming loads needed to microcoin surface ripples in thin metal foils. Coining is traditionally performed in a closed die, however enclosing all non-patterned surfaces is difficult to directly scale down to sub-millimeter foils. We find different forming regimes c...
FINEMET alloys have desirable soft magnetic properties due to the presence of Fe3Si nanocrystals with specific size and volume fraction. To guide future design of these alloys, we investigate relationships between select processing parameters (composition, temperature, annealing time) and structural parameters (mean radius and volume fraction) of t...
High purity polycrystalline tantalum (Ta) was shocked through 1 to 3.5 Mbar pressures creating Richtmyer-Meshkov unstable interfaces that were used to determine the dynamic material strength. The experiments were performed on the Omega laser at the University of Rochester Laboratory for Laser Energetics. Prior to shock, the driven surfaces of the t...
Modern X-ray diffraction techniques are now allowing researchers to collect long-desired experimental verification data sets that are in situ, three-dimensional, on the same length scales as critical microstructures, and using bulk samples. These techniques need to be adapted for advanced material systems that undergo combinations of phase transfor...
The propensity for activation of uniaxially loaded slip systems within uniquely oriented crystals can be calculated via Schmid's law. A similar procedure for multiaxial loads is desired. We present a method for bounding tensor-based resolved shear stress calculations by [0, 0.5] using normalized multiaxial stress tensors, allowing interpretation an...
The authors report on a relatively new alloy, Ni54Ti45Hf1, that exhibits strengths more than 40% greater than those of conventional NiTi‐based shape memory alloys − 2.5 GPa in compression and 1.9 GPa in torsion − and retains those strengths during cycling. Furthermore, the superelastic hysteresis is very small and stable with cycling. Aging treatme...
Porous NiTi shape memory alloys have applications in the biomedical and aerospace fields. Recent developments in metal additive manufacturing have made fabrication of near-net-shape porous products with complicated geometries feasible. There have also been developments in tailoring site-specific microstructures in metals using additive manufacturin...
Transmission electron microscopy and mechanical testing were used to determine the effect of
pre-aging (300 °C for 12 h) on microstructure and mechanical behavior of a series of Ni50.3Ti49.7-
xHfx shape memory alloys (x = 6, 8, 8.5, 9 at. %) prior to normal aging at 550 °C for 3.5 h. Preaging
was found to promote homogenous nucleation of nanosized...