Thomas Rector Bieler

• Ph.D.
• Professor (Full) at Michigan State University

The performance of individual high-RRR niobium cavities for superconducting radiofrequency applications must be consistent to facilitate advancements in accelerator performance and technology. Despite standardized production guidelines, the performance of cavities can be highly variable. The current standard is to draw high-RRR niobium sheets into...

A fully recrystallized microstructure with a fine grain size can improve the performance of superconducting radio-frequency (SRF) cavities produced from high-purity Nb (ASTM B393–18 Type 5 Nb) while providing mechanical strength. Recrystallization depends on impurity content, initial microstructure, deformation state, and annealing conditions. To b...

We introduce a cluster-based technique to automate pixel-wise reconstruction of $\beta$ orientations from parent $\alpha$ orientations over large, indexed regions. This approach provides a valuable tool for analyzing problems that require historical information about current $\alpha$ microstructures, such as investigating variant selection mechanis...

Plastic deformation behavior is most conveniently assessed by characterization on a surface, but whether such observations are representative of bulk properties is uncertain. Motivated by reported inconsistencies in slip resistance probed at different depths, we investigated (i) whether the average slip family activity is affected by the presence o...

With the standard material and cavity production guidelines, the properties and performance of industrially produced high-purity niobium superconducting radiofrequency (SRF) cavities are unpredictably variable. Currently, assembled niobium SRF cavities undergo post-purification vacuum heat treatment at 800°C for three hours to remove hydrogen; howe...

Plastic deformation behavior is most conveniently assessed by characterization on a surface, but whether such observations are representative of bulk properties is uncertain. Motivated by reported inconsistencies in slip resistance probed at different depths, we investigated (i) whether the average slip family activity is affected by the presence o...

The hardness and orientations of the primary α grains (αp) and the transformed β (βt) grains in segmented chips obtained by turning an as-received solution treated-and-aged bar of Ti–6Al–4V (wt.%) at cutting speeds of 1, 1.5 and 2 m/s (61, 91, and 122 m/min) were analyzed using nanoindentation mapping and electron backscattered diffraction (EBSD) m...

Titanium (Ti) alloys are classified as difficult-to-machine materials due to low thermal conductivity, low modulus, and high chemical reactivity. In this paper, a Ti-6Al-4V alloy bar in a solution treated and aged (STA) microstructure is turned using uncoated carbide, two commercial multilayered coated carbides (Sandvik® MM1115 and MM11125), and se...

Nb is an elemental superconductor with a critical temperature of 9.3 K and is widely used to fabricate superconducting radiofrequency (SRF) cavities for particle accelerators. However, microstructural defects in Nb, such as grain boundaries (GBs) and dislocations, can act as pinning centers for magnetic flux that can degrade SRF cavity performance....

Background: Inverse indentation analysis (IIA) optimizes the adjustable parameters in a chosen constitutive description of crystal plasticity until the load--depth response and the residual surface topography match between real and simulated nanoindentation into one (or multiple) grains. Based on synthetic data, past work demonstrated that initial...

Turning experiments on Ti-6Al-4V using uncoated carbide inserts at cutting speeds of 1 m/s, 1.5 m/s, and 2 m/s exhibited shorter tool life on solution-treated and aged than mill-annealed microstructures. Finite element analysis was performed to identify Johnson-Cook material model parameters that enabled matching of the measured segmented adiabatic...

The correlation between plastic strain and crystallographic misorientation, grain size, grain orientation, distance from grain boundary, and loading history were investigated experimentally and numerically for body-centered-cubic (BCC) polycrystalline microstructures based on a misorientation deviation (MD) approach. Nine monotonic tensile experime...

High energy X-ray diffraction microscopy (HEDM) was employed to index nearly 1000 grains in a polycrystalline Ti specimen and characterize their deformation during an incremental tensile test. For each grain, the positions of its associated diffraction peaks were used for analyzing its evolving crystal orientation and stress tensor. The azimuthal b...

The metal current collectors used in electronic, energy conversion, and energy storage devices often have difficulty wetting and adhering to ceramic substrates. Here, a novel Particle Interlayer Directed Wetting and Spreading (PIDWAS) technique is demonstrated that utilizes 1) the low wetting angle of silver on nickel and 2) the high work of adhesi...

Sn based solders used in the electronic packaging industry exhibit unpredictable failures due to their highly anisotropic properties, where thermal stresses, position within a package and microstructure evolution affect the property evolution and hence, lifetime of solder joints. In the present work, non-destructive high energy-X-ray diffraction me...

An investigation of the mechanical properties of high-purity niobium single crystals is presented. Specimens were cut with different crystallographic orientations from a large grain niobium disk and uniaxial tensile tests were conducted at strain rates between 10-4 and 103 s-1. The logarithmic strain rate sensitivity for crystals oriented close to...

The relationship between grain boundary sliding (GBS) and slip transmission is investigated experimentally at grain boundaries in 99.99% aluminum with a through-thickness, coarse-grained microstructure deformed in tension at 190 °C. Using scanning electron microscope-enabled digital image correlation (SEM-DIC) and electron backscatter diffraction (...

An artificial neural network is used to evaluate the effectiveness of six metrics and their combinations to assess whether slip transfers across grain boundaries in coarse-grained oligocrystalline Al foils [1, 2]. This approach extends the one-or two-dimensional projections formerly applied to analyze slip transfer. The accuracy of this binary clas...

First-principles methods were used to understand magnetic flux trapping at vacancies, dislocations, and grain boundaries in high-purity superconducting niobium. Full-potential linear augmented plane-wave methods were applied in progressively greater complexity, starting at simple vacancies and extending to screw dislocations and tilt grain boundari...

An artificial neural network is used to evaluate the effectiveness of six metrics and their combinations to assess whether slip transfers across grain boundaries in coarse-grained oligocrystalline Al foils \citep{Bieler_etal2019_2,Alizadeh_etal2020}. This approach extends the one- or two-dimensional projections formerly applied to analyze slip tran...

The slip transfer phenomenon was studied at the grain boundaries of pure Aluminum by means of slip trace analysis. Either slip transfer or blocked slip was analyzed in more than 250 grain boundaries and the likelihood of slip transfer between two slip systems across the boundary was assessed. The experimental results indicate that slip transfer was...

The slip transfer phenomenon was studied at the grain boundaries of pure Aluminum by means of slip trace analysis. Either slip transfer or blocked slip was analyzed in more than 250 grain boundaries and the likelihood of slip transfer between two slip systems across the boundary was assessed. The experimental results indicate that slip transfer was...

Crystallographic slip in hexagonal metals involves several geometrically distinct slip families characterized by their slip direction and slip plane (basal, prismatic, and pyramidal). Owing to the low symmetry of hexagonal lattices, each of these slip families only has a few symmetrically equivalent slip systems (family members). Furthermore, diffe...

Heterogeneous internal elastic strain in polycrystalline hexagonal close-packed materials is found to originate from the intrinsic anisotropy in thermal expansivity. As most noncubic metals have anisotropic thermal expansivity, cooling from elevated temperature leads to internal stresses. To simulate the internal stresses present in a polycrystal p...

The effect of slip transfer on the deformation mechanisms of Al bicrystals was explored using a rate-dependent dislocation-based crystal plasticity model. Three different types of grain boundaries (GBs) were included in the model by modifying the rate of dislocation accumulation near the GB in the Kocks-Mecking law, leading to fully-opaque (disloca...

The effect of slip transfer on the deformation mechanisms of Al bicrystals was explored using a rate-dependent dislocation-based crystal plasticity model. Three different types of grain boundaries (GBs) were included in the model by modifying the rate of dislocation accumulation near the GB in the Kocks-Mecking law, leading to fully-opaque (disloca...

Nb superconducting radio-frequency (SRF) cavities are observed to break down and lose their high-Q superconducting properties at accelerating gradients below the limits imposed by theory. The microscopic origins of SRF cavity breakdown are still a matter of some debate. To investigate these microscopic issues, temperature- and power-dependent local...

Silver—copper oxide brazes are commonly used to bond zirconia to stainless steel (SS) for Solid Oxide Fuel Cell (SOFC) and other high temperature joining applications. In fact, conventional Ag-CuO compositions (where Cu segregates to the surface, oxidizes, and reduces the silver wetting angle on zirconia from ∼85 to ∼40°) allow brazing to be perfor...

Nb Superconducting Radio-Frequency (SRF) cavities are observed to break down and lose their high-Q superconducting properties at accelerating gradients below the limits imposed by theory. The microscopic origins of SRF cavity breakdown are still a matter of some debate. To investigate these microscopic issues temperature and power dependent local t...

Slip transfer across grain boundaries was studied in annealed polycrystalline Al foils deformed in uniaxial tension by means of the analysis of the slip traces on the specimen surface. Grain orientations and selected grain boundary misorientations were measured on both surfaces of the sample using electron back-scattered diffraction mapping. It was...

Slip transfer across grain boundaries was studied in annealed polycrystalline Al foils deformed in uniaxial tension by means of the analysis of the slip traces on the specimen surface. Grain orientations and selected grain boundary misorientations were measured on both surfaces of the sample using electron back-scattered diffraction mapping. It was...

Slip transfer across grain boundaries was studied in annealed polycrystalline Al foils deformed in uniaxial tension by means of the analysis of the slip traces on the specimen surface. Grain orientations and selected grain boundary misorientations were measured on both surfaces of the sample using electron back-scattered diffraction mapping. It was...

Two major goals of superconducting radio frequency cavity research and development are achieving higher accelerating gradient and gaining the highest quality factor, a measure of efficiency. However, the consistent improvement of these performance metrics is restricted by many factors, one of which is microstructural defects, such as dislocation su...

Niobium provides the basis for all superconducting radio frequency (SRF) cavities in use, however, hydrogen is readily absorbed by niobium during cavity fabrication and subsequent niobium hydride precipitation when cooled to cryogenic temperatures degrades its superconducting properties. In the last few years the addition of dopant elements such as...

Niobium provides the basis for all superconducting radio frequency (SRF) cavities in use, however, hydrogen is readily absorbed by niobium during cavity fabrication and subsequent niobium hydride precipitation when cooled to cryogenic temperatures degrades its superconducting properties. In the last few years the addition of dopant elements such as...

From a collection of scattering vectors obtained by synchrotron X-ray diffraction, the lattice strain can be spatially quantified. This paper explores the inherent accuracy limits by comparing a least-squares regression and an optimization method applied to synthetic diffraction data excluding any measurement uncertainties potentially present in re...

The disclosure relates to method for controlled wetting and spreading of metals on substrates, in particular where the substrates are difficult to wet with molten metal, such as in the case of ceramic substrates. The method includes formation of a porous first metal layer on a substrate to assist wetting of the substrate with a molten second metal,...

Silver-copper oxide reactive air brazes are the most widely used Solid Oxide Fuel Cell (SOFC) brazes. However, the conventional Ag-4 wt.% Cu composition has a high wetting angle of ∼40° in air on yttria-stabilized-zirconia (YSZ) that leads to manufacturing defects (denoted as Type I pores). Also, many elements that oxidize during brazing to promote...

Ag–CuO is a broadly used reactive air brazing (RAB) system for effectively bonding ceramics and metal interfaces, especially for sealing yttria-stabilized zirconia (YSZ) to metals in solid-oxide fuel cells (SOFCs). To understand the superior performance of this braze, density functional theory (DFT) calculations were employed to investigate two mec...

Constitutive models based on thermally-activated stress-assisted dislocation kinetics have been successful in predicting deformation behavior of crystalline materials, particularly in face-centered cubic (fcc) metals. In body-centered cubic (bcc) metals, success has been more or less limited, owing to the ill-defined nature of slip planes and non-p...

It is well known that the formation and growth of niobium hydride degrades the superconducting radio frequency (SRF) properties of niobium cavities and the treatments that reduce hydrogen concentration improve the cavity quality factor. Recently it has also been shown that the addition of nitrogen through doping or infusion improves the quality fac...

The anisotropy of Sn crystal structures greatly affects the electromigration (EM) and thermomechanical fatigue (TMF) of solder joints. The size of solder joint shrinkage in electronic systems further makes EM and TMF an inseparably coupled issue. To obtain a better understanding of failure under combined moderately high (2000 A/cm²) current density...

The subsurface dislocation content in a Ti-5Al-2.5Sn (wt%) uniaxial tension sample deformed at ambient temperature was characterized by peak streak analysis of micro-Laue diffraction patterns collected non- destructively by differential aperture X-ray microscopy, and with focused ion beam transmission electron microscopy of material in the same vol...

The current go-to braze for SOFC applications is the Ag-CuO reactive air braze (RAB). As with other RAB brazes, the ability to use this braze with ceramic materials (such as yttria stabilized zirconia (YSZ) and oxide-protected stainless steel (SS)) is enabled by a braze component (in this case Cu) reacting with the brazing atmosphere to form a surf...

This study shows that low angle grain boundaries(LAGBs) can be created by small 5% strains in high purity (residual resistivity ratio ≥ 200) superconducting radio frequency (SRF)-grade single crystalline niobium(Nb) and that these boundaries act as hydrogen traps as indicated by the distribution of niobium hydrides (Nb1-xHx). Nb1-xHx is detrimental...

This patent application describes a brazing method for joining substrates utilizing an interlayer of porous metal. One of the applications is to use a porous nickel interlayer to join YSZ substrates to stainless steel in SOFC applications. More detail can be found in the paper "Transient Porous Nickel Interlayers for Improved Silver-Based Solid Oxi...

Knowledge of the critical resolved shear stress (CRSS) values of different slip modes is important for accurately modeling plastic deformation of hexagonal materials. Here, we demonstrate that CRSS can be directly measured with an in-situ high energy X-ray diffraction microscopy (HEDM) experiment. A commercially pure Ti tensile specimen was deforme...

Titanium alloys typically do not contain hard inclusion phases typically observed in other metallic alloys. However, the characteristic scoring marks and more distinctive micro- and/or macro-chippings are ubiquitously observed on the flank faces of cutting tools in machining titanium alloys, which is the direct evidence of abrasive wear (hard phase...

A multistep, non-destructive grain morphology reconstruction methodology that is applicable to near-surface volumes is developed and tested on synthetic grain structures. This approach probes the subsurface crystal orientation using differential aperture x-ray microscopy on a sparse grid across the microstructure volume of interest. Resulting orien...

The mechanical stability of Sn-Ag-Cu interconnects with low and high silver content against mechanical shock at room and elevated temperatures was investigated. With a heating element-embedded printed circuit board design, a test temperature from room temperature to 80°C was established. High impact shock tests were applied to isothermally pre-cond...

Introduction Solid oxide fuel cells (SOFC) are high efficiency devices for converting the chemical energy from a wide range of fuels and energy-carriers directly into electricity [1]. One of the major challenges for the viability of commercial SOFC devices is the development of suitable sealing technologies to prevent air and fuel crossover at SOFC...

The influence of grain boundaries on plastic deformation was studied by carrying out nanoindentation near grain boundaries (GBs). Surface topographies of indentations near grain boundaries were characterized using atomic force microscopy (AFM) and compared to corresponding single crystal indent topographies collected from indentations in grain inte...

Unlike ferrous materials, where the cementite (Fe3C) phase acts as an abrasive that contributes to flank wear on the cutting tool, most titanium (Ti) alloys possesses no significant hard phase. Thus, the origin of flank wear is unclear in machining Ti alloys. To address this question, a Ti-6Al-4V bar was turned under various conditions with uncoate...

The deformation behavior of ?+? titanium alloys was investigated during in-situ SEM deformation. Tensile experiments were performed at temperatures between 296K and 728K (?0.4Tm). The active deformation systems were identified using an electron backscattered diffraction-based slip-trace analysis. The distribution of the active deformation systems v...

Published in PHYSICAL REVIEW B 92, 134513 (2015). DOI: 10.1103/PhysRevB.92.134513

Large grain niobium (Nb) is being investigated for fabricating superconducting radiofrequency cavities as an alternative to the traditional approach using fine grain polycrystalline Nb sheets. Past studies have identified a surface damage layer on fine grain cavities due to deep drawing and demonstrated the necessity for chemical etching on the sur...

The physical and mechanical metallurgy underlying fabrication of large grain cavities for superconducting radio frequency accelerators is summarized, based on research of 1) grain orientations in ingots, 2) a metallurgical assessment of processing a large grain single cell cavity and a tube, 3) assessment of slip behavior of single crystal tensile...

The mechanical stability and thermo-mechanical fatigue performance of solder joints with low silver content Sn-1.0Ag-0.5Cu (wt.%) (SAC105) alloy based on different cooling rates are investigated in high G level shock environment and thermal cycling conditions. The cooling rate-controlled samples ranging from 1°C/min to 75°C/min cooling rate, not on...

Study of Bi-Crystal Grain Boundary Deformation in Commercially Pure Tantalum.

Understanding multifaceted microstructural evolution mechanisms is a key enabling foundation that will enable computational modeling and prediction of electronic system lifetimes before anything is built.

In addition to thermal strains, other mechanical strains arising from handling (such as bending, drop, or shock), and transport (vibration) add energy to joints that affects the rate and nature of microstructural evolution and damage generation.

On-off operation of electronic systems leads to thermal cycling, which introduces thermal and strain energy into solder joints, resulting in microstructural evolution mechanisms of recovery, recrystallization and damage nucleation. The thermal strain history is very sensitive to the package design. The effects of microalloying on microstructure evo...

Expanding use of electronic systems in close proximity to biological systems, marine environments, and polluted air introduce elements that attack solder joints. Mechanisms that cause damage and their effects on the lifetime of electronic system are discussed.

The thermodynamic driving forces that govern non-equilibrium solidification and subsequent microstructural evolution of solder joint microstructures are discussed in detail, including formation of intermetallic phases within, and at the interface that creates the bond between the solder, package, and board.

With the thermodynamic driving forces in mind, the observed microstructures and microstructural evolution that follows nonequilibrium solidification are discussed, with consideration of defect formation, intermetallic phases, and the influence of surface finish and microalloying on microstructure evolution.

The geometry of interconnections used in current electronic systems is described, and issues related to the reflow process that melts and re-solidifies the solder to make the interconnection are introduced.

The Matlab toolbox STABiX provides a unique and simple way to analyse slip transmission in a bicrystal. Graphical User Interfaces (GUIs) are implemented in order to import EBSD results, and to represent and quantify grain boundary slip resistance. Key parameters, such as the number of phases, crystal structure (fcc, bcc, or hcp), and slip families...

The performance of Niobium-based Superconducting Radio Frequency (SRF) particle accelerator cavities can be sensitive to localized defects that give rise to quenches at high accelerating gradients. In order to identify these material defects on bulk Nb surfaces at their operating frequency and temperature, a wide bandwidth microwave microscope with...

A multiscale modeling framework is proposed in this study to capture the influence of the inherent elastic anisotropy of single crystal Sn and the inherent heterogeneous microstructure of a single crystal SnAgCu (SAC) solder grain on the secondary creep response of the grain. The modeling framework treats the SAC microstructure as having several di...

The deformation behavior of titanium (Ti) can be complex due to the lower crystal symmetry of the hexagonal α phase compared with metals based on cubic phases. The tensile and tensile-creep deformation behavior of a Ti–8Al–1Mo–1V(wt%) alloy with a weak crystallographic texture was investigated in-situ straining scanning electron microscopy. Tensile...

This paper provides fundamental mechanistic insights into the significant piece-to-piece variability that many researchers have reported in the creep response of micron-scale high-Sn SAC solder joints in the as-fabricated state, due to coarse-grained microstructure and the anisotropy of Sn. A multiscale mechanistic creep modeling approach is propos...