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Strength and toughness limits of a newly developed low alloy martensitic steel are explored using impact toughness experiments and room temperature tensile testing. These steel samples are subjected to either a selected heat treatment, to obtain tempered martensite, or equal channel angular pressing (ECAP) performed between 950 °C and 1050 °C, to refine prior austenite grains. Martensite refinement through ECAP led to a significantly enhanced mechanical response, resulting in impact toughness above 55 J at -40 °C and ultimate tensile strengths above 2 GPa at room temperature. Consequently, this new low alloy steel can be an excellent candidate for high specific strength transportation applications.

The shock and spall behavior of tempered AF9628, an ultra-high strength (UHSS) martensitic low-alloy carbon steel, is investigated using gun-driven, symmetric, planar impacts. The study utilized laser velocimetry to obtain transmitted wave velocity histories that were analyzed to obtain the Hugoniot Elastic Limit (HEL), the shock Hugoniot, and the spall strength. The work was limited to the stress range below 13 GPa (below the e phase transition), and an HEL of 2.35 GPa and a spall strength of 6.8 GPa are reported. The HEL and spall strength of AF9628 are both above the typical values for inexpensive low-alloy steels, and only slightly below those for a much more expensive Aermet steel. The dynamic compressive yield strength (as calculated from the HEL) is only slightly higher than the quasi-static compressive yield strength when compared using a similar yield assignment convention, indicating a small, but positive, value of strain-rate sensitivity. The Hugoniot for AF9628, US = 0.67uP + 5.01 km/s, is in good agreement with other low-alloy martensitic steels for which data is available, and distinctly different than the Hugoniot for ferritic steels. The Hugoniot extrapolates to a bulk sound speed significantly higher than what is measured at ambient conditions, an incongruity that is unusual among metals and that the authors attribute to the unsteady nature of the shock waves generated in this work. Finally, it is suggested that there may be a relationship between dynamic compressive yield strength (calculated from the HEL) and dynamic tensile failure strength (the spall strength).

In this work, a CALPHAD thermodynamic model is used to assess the thermodynamic stability of austenite in an Ultra-High Strength Martensitic Steel (i.e., Eglin Steel) in order to refine parent austenite-grain sizes, via high temperature equal-channel angular pressing (ECAP). The parent austenite-grain sizes are reduced from 188 µm to 14.8 µm, which in turn, led to the refinement of martensite lath sizes. This approach produced a yield strength of 1.68 GPa, ultimate strength of 1.98 GPa, and an elongation of 16.1%. Overall, this method reduced development cycle times and achieved alloy performance on par with Ni-Co secondary hardening steels.

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A newly developed ultra-high strength martensitic steel, AF9628, has generated academic and industrial attention due to its combination of high yield strength and ductility at a low cost. Several studies have demonstrated that this steel can be successfully additively manufactured (AM) using laser powder bed fusion (LPBF). However, as-printed parts have displayed microstructural inhomogeneity, anisotropy, and a discrepancy in mechanical properties as compared to the traditionally processed material. There is currently no work detailing the effects of post processing heat treatments on the microstructure or mechanical properties of as-printed AF9628. In the interest of producing robust near-net-shape parts with complex geometries, this work explores the effects of LPBF and post processing heat treatments on the microstructure and mechanical properties of AF9628. Parts fabricated by LPBF were subjected to three different quench and temper heat treatment schedules. Quench and temper treatments displayed refined equiaxed prior-austenitic grain structures, reducing grain size by up to 45%. Significant variability was observed in Vickers hardness measurements of as-printed samples due to tempered and untempered bands of martensite alternating throughout the microstructure caused by thermal cycling during printing. Heat treatments were observed to increase the overall hardness of the material and reduce variability. As-printed samples displayed a tensile strength of 1.41 GPa, 10% elongation, and a Charpy impact toughness of 28 J. Quench and temper heat treatments were observed to increase tensile strengths to 1.66 GPa, but reduce the elongation to 7.6% and impact toughness to 24 J. Understanding the effects of these post-processing treatments is expected to allow for property optimization of AF9628 additively manufactured parts.

In general, the forward phase stability problem consists of mapping thermodynamic conditions (e.g., composition, temperature, pressure) to corresponding equilibrium states. In this paper, we instead focus on the generalized inverse phase stability problem (GIPSP) that deals with mapping a set of phase constitutions to a set of corresponding thermodynamic conditions. Specifically, we define the GIPSP as mapping of sets of phase constitution definitions in a multidimensional phase constitution search space to corresponding ranges of thermodynamic conditions. Mathematically, the solution to the GIPSP corresponds to all solutions to a continuous constraint satisfaction problem (CCSP). We present novel algorithms combining computational thermodynamics, evolutionary computation, and machine learning to approximate solution sets to the GIPSP as a CCSP. Some preliminary examples demonstrating the algorithms are presented. Moreover, the implications of the proposed framework for the larger problem of materials design are discussed, and future work is suggested.

In this work, the effects of small ternary additions to B2 NiTi structures was investigated through DFT calculations. The analysis considered deviations from stoichiometry arising from either simple substitution of host atoms in a given sublattice or from the formation of anti-sites. The calculations enabled the determination of the site preference of X ternary additions. Moreover, the results suggest that ternary additions located in the central region of the transition metal group across all periods tend to occupy Ni sites due to favorable X–Ti nearest neighbor (NN) interactions. This occupancy is achieved through substitution or through the generation of anti-site defects. On the other hand, ternary additions at both ends of a given transition metal row tend to occupy Ti sites due to favorable X–Ni NN interactions. Once site preferences are determined, the effect of alloying on the thermodynamic and mechanical properties of B2 NiTi–X structures are presented and trends are discussed.

During the photolithographic process, a photoresist is exposed to EUV photons; it is believed that the secondary low energy electrons generated during this exposure decompose the PAG molecule, producing acid. Regardless of how these secondary electrons are produced, whether by incident electrons or photons, the number of acids produced will lead to a solubility change within the photoresist. The goal of this study is to observe the solubility changing reactions due to low energy electron exposures (approximately 5-80 eV). The reactions occurring in the photoresist are monitored through outgassing measurements during EUV photon exposures, and low energy electron exposures. Outgassing results indicate that PAG decomposition occurs with electrons as low as 4.5 eV, and subsequent deprotection reactions are observed due to the acid generated from the PAG. Without being in the presence of PAG decomposition, deprotection reactions are caused by electron exposures with energies down to at least 15 eV. These deprotections that occur in the absence of PAG decomposition are referred to as direct deprotection reactions. Sentaurus Lithography simulations show that these direct deprotection reactions can affect the resist modeling.

The photo-mechanism of EUV exposures in chemically amplified photoresists are much different than that of previous lithographic wavelengths. Electrons generated during EUV exposure are demonstrated to be a source of acid production through a process referred to as electron trapping. Density functional theory modeling indicates that it is energetically favorable for the PAG molecule to decompose if an electron is trapped. Low-energy electrons unlikely to produce holes and secondary electrons generate acid indicating electron-PAG interactions are capable to induce decomposition. Additionally, a more easily reduced PAG (i.e. higher likelihood of trapping an electron) produces a higher acid yield supporting electron trapping as a process of acid production. An acid indicator, Coumarin 6, was used to determine the number of acids generated per absorbed EUV photon. The results of these measurements indicate that electron-PAG interactions are a source of acid production through electron trapping; thus, increasing the number of electron-hole pairs available to induce chemical reactions would improve sensitivity. It is expected that lower band gap materials produce more electron-hole pairs after an absorption event. Subsequently, these measurements show that lower band gap polymers generate higher acid yields.

This work addresses the microstructure evolution during transient liquid phase bonding (TLP) of high-density (small volume) interconnects, which are relevant for 3D packaging in the microelectronics industry. Specifically, the intermetallic compound (IMC) growth in the Cu/Sn/Cu sandwiched soldering joint configuration is characterized through predicted processing maps. These maps are derived from phase-field modeling simulations that incrementally vary geometrical and thermal conditions (i.e., initial solder thicknesses ranging from 4 μm to 28 μm and system temperatures ranging from T = 240 °C to 310 °C). The calculations consider the concurrent evolution of the Cu3Sn and Cu6Sn5 IMC layers at the expense of the liquid solder (i.e., Sn) and the substrates (i.e., α -Cu) given their respective chemical potentials and associated driving forces for diffusion and phase transformation. Additionally, materials properties (e.g., diffusivity, interfacial energy, and mobility) are adjusted in order to account for varying processing temperatures that are relevant to the transient liquid phase (TLP) joining process. Through this study, it is shown how temperature, initial liquid solder thickness, and hold time influence (1) how the IMC phases evolve, (2) whether or not IMC phases are eliminated, and (3) how IMC grains coarsen. These results make it possible to develop practical strategies for the use of TLP joining process in high-density interconnects.

In this work, we compare the microstructural evolution of Sn/Cu/Sn and Cu/Sn/Cu ‘sandwich’ configurations under metallurgical bonding conditions. These simulations are relevant in explaining experimental observations that suggest that the resulting dominant intermetallic compound in Cu-Sn systems depends on the relative supply of Cu and Sn. Through the analysis of morphological evolution and growth rate, it is shown that the Cu6Sn5 layer becomes dominant in the Sn/Cu/Sn structure, while the Cu/Sn/Cu structure is dominated by Cu3Sn after extended reaction periods.

Researchers have used the (calculation of phase diagram) CALPHAD method to solve the forward phase stability problem of mapping from specific thermodynamic conditions (material composition, temperature, pressure, etc.) to the associated phase constitution. Recently, optimization has been used to solve the inverse problem: mapping specific phase constitutions to the thermodynamic conditions that give rise to them. These pointwise results, however, are of limited value since they do not provide information about the forces driving the point to equilibrium. In this paper, we investigate the problem of mapping a desirable region in the phase constitution space to corresponding regions in the space of thermodynamic conditions. We term this problem the generalized inverse phase stability problem (GIPSP) and model the problem as a continuous constraint satisfaction problem (CCSP). In this paper, we propose a new CCSP algorithm tailored for the GIPSP. We investigate the performance of the algorithm on Fe–Ti binary alloy system using ThermoCalc with the TCFE7 database against a related algorithm. The algorithm is able to generate solutions for this problem with high performance.

Chills are used in the production of metal castings as a thermal aid to promote directional solidification in casted sections. This study will review microstructure and thermal circumstances of the internal chill interface where the chill is intended to be incorporated into the structure of the cast section. The conditions for interface coherency of cast steel sections from 25 to 50mm will be shown. Solidification proceeds away from the interface chill growing to a maximum thickness and then melting back to the original chill geometry. Furthermore, it is shown that promoting section solidification prior to the complete melting of the internal chill can lead to the formation of interfaces will be coherent across the chill and cast sections for compatible steel alloys. A computer model of the heat transfer and interface evolution show the possibility of using the coherent interface of internal chills in the design of other cast components.

In this work, we present a preliminary model based on the multiphase-field formalism that is used to investigate the evolution of intermetallic compound (IMC) layers in the Cu/Sn solder system under electromigration conditions. The simulation considers the concurrent evolution of the Cu3Sn and Cu6Sn5 IMC layers under electrochemical driving forces. We use CALPHAD descriptions for the thermodynamics of the bulk phases (Cu, Sn and both IMCs) and incorporate electrochemical contributions to the total free energy of the microstructure in order to simulate the evolution of the interfacial microstructure due to mass–current couplings. The simulation considers grain-boundary diffusion as the dominant mechanism for chemical-potential-driven mass flux. The simulation considers the effect of current density and polarity on the growth of IMCs. The simulations are in turn compared to experimental measurements of growth rates, morphology of IMC grains and evolution of interface roughness. The analysis of experiments and simulations suggest that back-stress resulting from the non-equilibrium vacancy generation due to diffusive flux imbalance among the individual diffusants (Cu and Sn) plays a fundamental role in the evolution of the IMC layers. Overall, the simulations and experiments show good qualitative agreement.

Background: The Patient-Specifi c Functional Scale (PSFS) questionnaire was developed by Stratford and colleagues to provide a method for eliciting, measuring and recording descriptions of patients ’ disabilities. It can be used to guide treatment and assess patient outcome. The aim of the study was to translate and validate a Finnish version of the internationally used PSFS questionnaire, by testing its content validity and responsiveness, and to conduct a cross-cultural adaptation of the measure. Methods: The fi nal version of the Finnish questionnaire underwent a cross-cultural adaptation before the validation study. The subjects of the study were patients receiving physiotherapy for low back pain ( n 78). They completed the PSFS questionnaire prior to physiotherapy treatment and after treatment series. Roland – Morris Disability Questionnaire (RMDQ) and the visual analogue scale (VAS) were recorded before and after the treatment series. Results: For content validity, a good correlation of the scores between baseline measures of PSFS and RMDQ were 0.65 (Pearson ’ s rho) ( p 0.01). For responsiveness, moderate to good correlation among the measures between changes of the PSFS, RMDQ and VAS (0 – 100 mm) scores were analysed. Conclusions: The Finnish translation of the PSFS questionnaire performs as the original, is proven to have adequate content validity and responsiveness, and could be recommended as an assessment tool for clinical and research use.

In this work, the impact of microvoids on the microstructural evolution of η-Cu6Sn5 and ɛ-Cu3Sn in the Cu-Sn system is evaluated numerically. Through the use of the multiphase-field method, the systems of interest are allowed to evolve using a solid-state aging temperature of 453 K in conjunction with material parameters and reaction conditions adopted from previous research. The simulation results are then analyzed and compared with previous experiments in terms of the morphological evolution of the intermetallic compounds (IMCs), the IMC layer thicknesses, and the corresponding interfacial roughness. It is shown that the presence of microvoids at the ɛ/Cu interface interferes with the flow of mass throughout the phases, impeding phase transformations and grain coarsening. This ultimately affects the IMC coarsening rate and overall IMC layer thicknesses. Additionally, it was observed that the presence of microvoids at the ɛ/Cu interface affects the formation of both IMC layers and their corresponding interfaces, and the changes in roughness for the interfaces are quantitatively provided. Overall, the simulations are found to be within the range of accepted experimental values for the morphology of the IMC grains, the evolution of IMC layer thicknesses, and the evolution of interface roughness.

The microstructural evolution of η(Cu6Sn5) and e(Cu3Sn) in a Cu/Sn/Cu structure under transient liquid phase bonding conditions is numerically investigated through the use of the multiphase-field method. The material parameters and reaction conditions were adopted from relevant experimental research. Simulation results were then analyzed and compared with the experiments in terms of morphology of intermetallic compound (IMC) grains, growth ratio of the η layer with respect to the e layer, evolution of each layer and roughness of each interface. Additionally, it is shown through the use of simulation data that, while liquid Sn is present, the growth of the η IMC layers is dominant and that, upon the exhaustion of liquid Sn, the η grains of the upper and lower layers impinge on one another, at which time the larger grains continue to coarsen at the expense of the smaller grains. Concurrently, the growth of the e layers becomes significant and continues to increase until the η layer is fully consumed or the reaction is thermally arrested. Overall, the simulations were found to be in good qualitative agreement with experiments for morphology of the IMC grains, while showing good quantitative agreement, in spatial extent and elapsed time frames, for the evolution of each of the IMC layers and the derived growth ratio of the η layer with respect to the e layer. Furthermore, it is shown that the results corresponding to different thickness values for the initial Sn layer suggest that the IMC evolution can be reasonably predicted in advance of experimental studies.

Cu/Sn soldering alloys have emerged as a viable alternative to Pb-based solders, and thus have been extensively explored in the past decade, although the fine-scale behavior of the resulting intermetallic compounds (IMCs), particularly during the early stages of interface formation, is still a source of debate. In this work, the microstructural evolution of Cu6Sn5, in a Cu/Sn soldering reaction at 523 K, was experimentally investigated by dipping a single Cu sample into molten Sn at a near-constant speed, yielding a continuous set of time evolution samples. The thickness, coarsening and morphology evolution of the Cu6Sn5 layer is investigated through the use of scanning electron microscopy. The experimental results are also compared to phase-field simulations of the microstructural evolution of the Cu6Sn5 layer. The influence of model parameters on the kinetics and morphological evolution of the IMC layer was examined. In general, good qualitative agreement is found between experiments and simulations and for a limited parameter set there appears to be good quantitative agreement between the growth kinetics of the Cu6Sn5 layer, the grain boundary (GB) effect on grain coarsening, and the substrate/IMC interface roughness evolution. Furthermore, the parametric investigations of the model suggests that good agreement between experiments and simulations is achieved when the dominant transport mechanism for the reacting elements (Cu and Sn) is GB diffusion.

The photomechanism of extreme ultraviolet (EUV) exposures in chemically amplified photoresists is much different than that of previous lithographic wavelengths. Electrons generated during EUV exposure are demonstrated to be a source of acid production through a process referred to as electron trapping. Density functional theory modeling indicates that it is energetically favorable for the photoacid generator (PAG) molecule to decompose if an electron is trapped. Low-energy electrons (

The development of new materials must start with an understanding of their phase stability. Researchers have used the CALPHAD method to develop self-consistent databases encoding the thermodynamics of phases. In this forward approach, thermo dynamic conditions (processing conditions such as composition, temperature, pressure, etc.) are mapped to equilibrium states. In this research, we are instead interested in the inverse problem of mapping a set of desired phase constitutions to the set of thermodynamic conditions that give rise to them. Recently, search and optimization techniques have been used to determine thermodynamic conditions that yield a particular phase stability state (point-to-point mapping). In this research, we focus on a more general problem: mapping of specific regions in multi-dimensional phase constitution spaces to ranges in values of thermodynamic conditions(set-to-set mapping). In the context of search theory, we are interested in finding all solutions to a Continuous Constraint Satisfaction Problem (CCSP). The problem is typically multi-dimensional, highly nonlinear, and, importantly, contains non-isolated solutions (the solution is ranges of values rather than finite points). Numerical methods for finding all solutions to CCSPs typically rely on branch-and-prune methods, which interleave branching with pruning steps. These methods are mainly designed to address CCSPs with isolated solutions and would be inefficient if applied to the problem at hand. In this work, we describe a novel algorithm to search the thermodynamic phase field for the full set of thermodynamic conditions that result in user-specified phase constitutions. The approach combines techniques from computational materials science, evolutionary computation, and machine learning to approximate the non-isolated solution set to the CCSP. We investigate the performance of the algorithm on an Fe-Ti binary alloy system using ThermoCalc with TCFE7 database. For this system, the algorithm is able to generate solutions with low error rates.Copyright © 2014 by ASME

Background Individuals with chronic low back pain (CLBP) have altered activations patterns of the anterior trunk musculature when performing the abdominal hollowing manœuvre (attempt to pull umbilicus inward and upward towards the spine). There is a subgroup of individuals with CLBP who have high neurocognitive and sensory motor deficits with associated primitive reflexes (PR). The objective of the study was to determine if orienting the head and extremities to positions, which mimic PR patterns would alter anterior trunk musculature activation during the hollowing manoeuvre. Methods This study compared surface electromyography (EMG) of bilateral rectus abdominis (RA), external oblique (EO), and internal obliques (IO) of 11 individuals with CLBP and evident PR to 9 healthy controls during the hollowing manoeuvre in seven positions of the upper quarter. Results Using magnitude based inferences it was likely (>75%) that controls had a higher ratio of left IO:RA activation with supine (cervical neutral), asymmetrical tonic neck reflex (ATNR) left and right, right cervical rotation and cervical extension positions. A higher ratio of right IO:RA was detected in the cervical neutral and ATNR left position for the control group. The CLBP group were more likely to show higher activation of the left RA in the cervical neutral, ATNR left and right, right cervical rotation and cervical flexion positions as well as in the cervical neutral and cervical flexion position for the right RA. Conclusions Individuals with CLBP and PR manifested altered activation patterns during the hollowing maneuver compared to healthy controls and that altering cervical and upper extremity position can diminish the group differences. Altered cervical and limb positions can change the activation levels of the IO and EO in both groups.

Background Practice guidelines recommend various types of exercise for chronic back pain but there have been few head-to-head comparisons of these interventions. General exercise seems to be an effective option for management of chronic low back pain (LBP) but very little is known about the management of a sub-acute LBP within sub-groups. Recent research has developed clinical tests to identify a subgroup of patients with chronic non-specific LBP who have movement control dysfunction (MD). Method/Design We are conducting a randomized controlled trial (RCT) to compare the effects of general exercise and specific movement control exercise (SMCE) on disability and function in patients with MD within recurrent sub-acute LBP. The main outcome measure is the Roland Morris Disability Questionnaire. Discussion European clinical guideline for management of chronic LBP recommends that more research is required to develop tools to improve the classification and identification of specific clinical sub-groups of chronic LBP patients. Good quality RCTs are then needed to determine the effectiveness of specific interventions aimed at these specific target groups. This RCT aims to test the hypothesis whether patients within a sub-group of MD benefit more through a specific individually tailored movement control exercise program than through general exercises.

In this work, the electronic, structural, elastic, and thermodynamic properties of Ti2AX MAX phases (A = Al or Ga, X = C or N) were investigated using density functional theory (DFT). It is shown that the calculations of the electronic, structural, and elastic properties of these structures, using local density approximation (LDA) and generalized gradient approximation (GGA) coupled with projected augmented-wave (PAW) pseudopotentials, agree well with experiments. A thermodynamic model, which considers the vibrational and electronic contributions to the total free energy of the system, was used to investigate the finite-temperature thermodynamic properties of Ti2AX. The vibrational contribution was calculated using the supercell method, whereas the electronic contribution resulted from one-dimensional integration of electronic density of states (DOSs). To verify the model, the specific heats of pure elements were calculated and compared to experimental data. The DFT-D2 technique was used to calculate the ...