Cavitation-resistant intergranular precipitates enhance creep performance of '-strengthened Al-Cu based alloys.

Tensile and compressive creep properties of a quaternary Al-Cu-Mn-Zr (ACMZ) alloy and its commercial counterpart (Al-Cu-Mn-Zr with Ni, Co and Sb additions, RR350) are investigated at 300° C. At low stresses up to 30 MPa where diffusional creep dominates, creep resistance is the same in tension and compression and RR350 deforms more slowly than ACMZ, consistent with RR350 alloy's larger linear fraction of intergranular precipitates (Al Cu (NiFe) and Al FeNi for RR350 vs. -Al Cu for ACMZ) and a reduced fraction of precipitate-free zones near grain boundaries.

Solute-induced strengthening during creep of an aged-hardened Al-Mn-Zr alloy.

We examine the precipitation and creep behavior of (at.%) alloys, with and without the L1-forming elements Zr and Er (0.09 and 0.

Enhanced age-hardening response and creep resistance of an Al-0.5Mn-0.3Si (at.%) alloy by Sn inoculation.

Precipitation-strengthening at ambient and high temperatures is examined in (at.%) alloys with and without 0.02 at.

Threshold damage mechanisms in brittle solids and their impact on advanced technologies.

Threshold damage mechanisms in brittle covalent-ionic solids are outlined. Fracture and deformation modes are analyzed in terms of classical contact mechanics. Distinctions are made between brittle, ductile and quasiplastic mechanisms in both axial and translational contact.

Effect of vacancy creation and annihilation on grain boundary motion.

Interaction of vacancies with grain boundaries (GBs) is involved in many processes occurring in materials, including radiation damage healing, diffusional creep, and solid-state sintering. We analyze a model describing a set of processes occurring at a GB in the presence of a non-equilibrium, non-homogeneous vacancy concentration. Such processes include vacancy diffusion toward, away from, and across the GB, vacancy generation and absorption at the GB, and GB migration.

Precipitation kinetics, microstructure evolution and mechanical behavior of a developed Al-Mn-Sc alloy fabricated by selective laser melting.

The dynamic metallurgical characteristics of the selective laser melting (SLM) process offer fabricated materials with non-equilibrium microstructures compared to their cast and wrought counterparts. To date, few studies on the precipitation kinetics of SLM processed heat-treatable alloys have been reported, despite the importance of obtaining such detailed knowledge for optimizing the mechanical properties. In this study, for the first time, the precipitation behavior of an SLM fabricated Al-Mn-Sc alloy was systematically investigated over the temperature range of 300-450 °C.

Experimental and numerical study of mechanical properties of multi-phase medium-Mn TWIP-TRIP steel: influences of strain rate and phase constituents.

In the current work we investigate the room temperature tensile properties of a medium-Mn twinning- and transformation-induced plasticity (TWIP-TRIP) steel from quasi-static to low-dynamic strain rates ( to ). The multi-phase microstructure consists of coarse-grained recovered -martensite (inherited from the cold-rolled microstructure), multiple morphologies of ultrafine-grained (UFG) austenite (equiaxed, rod-like and plate-like), and equiaxed UFG ferrite. The multi-phase material exhibits a positive strain-rate sensitivity for yield and ultimate tensile strengths.

Residual stress in polycrystalline alumina: Comparison of two-dimensional maps and integrated scans in fluorescence-based measurements.

The spatially heterogeneous residual stress fields in a series of three polycrystalline alumina materials are compared using two fluorescence-based measurement techniques. In the first technique, 18 hyperspectral arrays of the Cr-based and ruby fluorescence line shifts are formed into two-dimensional maps of stress components, and experimental stress distributions are calculated using both spectral lines jointly. In the second technique, the data are formed into integrated scans reflecting the average spectra within the maps and assumed Gaussian stress distributions are calculated, using the spectral lines singly.

Effect of heat treatment on the microstructural evolution of a nickel-based superalloy additive-manufactured by laser powder bed fusion.

Elemental segregation is a ubiquitous phenomenon in additive-manufactured (AM) parts due to solute rejection and redistribution during the solidification process. Using electron microscopy, synchrotron X-ray scattering and diffraction, and thermodynamic modeling, we reveal that in an AM nickel-based superalloy, Inconel 625, stress-relief heat treatment leads to the growth of unwanted δ-phase precipitates on a time scale much faster than that in wrought alloys (minutes versus tens to hundreds of hours). The root cause for this behavior is the elemental segregation that results in local compositions of AM alloys outside the bounds of the allowable range set for wrought alloys.

Application of Finite Element, Phase-field, and CALPHAD-based Methods to Additive Manufacturing of Ni-based Superalloys.

Numerical simulations are used in this work to investigate aspects of microstructure and microseg-regation during rapid solidification of a Ni-based superalloy in a laser powder bed fusion additive manufacturing process. Thermal modeling by finite element analysis simulates the laser melt pool, with surface temperatures in agreement with thermographic measurements on Inconel 625. Geometric and thermal features of the simulated melt pools are extracted and used in subsequent mesoscale simulations.

Effect of powder oxidation on the impact toughness of electron beam melt Ti-6Al-4V.

Powder quality in additive manufacturing (AM) electron beam melt (EBM) of Ti-6Al-4V components is crucial in determining the critical material properties of the end item. In this study, we report on the effect of powder oxidation on the Charpy impact energy of Ti-6Al-4V parts manufactured using EBM. In addition to oxidation, the effects on impact energy due to hot isostatic pressing (HIP), specimen orientation, and EBM process defects were also investigated.

Multiaxial constitutive behavior of an interstitial-free steel: Measurements through X-ray and digital image correlation.

Constitutive behaviors of an interstitial-free steel sample were measured using an augmented Marciniak experiment. In these tests, multiaxial strain field data of the flat specimens were measured by the digital image correlation technique. In addition, the flow stress was measured using an X-ray diffractometer.

Microstructure-based knowledge systems for capturing process-structure evolution linkages.

This paper reviews and advances a data science framework for capturing and communicating critical information regarding the evolution of material structure in spatiotemporal multiscale simulations. This approach is called the MKS (Materials Knowledge Systems) framework, and was previously applied successfully for capturing mainly the microstructure-property linkages in spatial multiscale simulations. This paper generalizes this framework by allowing the introduction of different basis functions, and explores their potential benefits in establishing the desired process-structure-property (PSP) linkages.

Quantitative Mapping of Stress Heterogeneity in Polycrystalline Alumina using Hyperspectral Fluorescence Microscopy.

The microstructurally-induced heterogeneous stress fields arising in a series of Cr-doped polycrystalline alumina materials are mapped with sub-micrometer sub-grain size resolution using fluorescence microscopy. Analysis of the hyperspectral data sets generated during imaging enabled both the amplitude and position of the characteristic Cr R1 fluorescence peak to be determined at every pixel in an image. The peak amplitude information was used to segment the images into individual grains and grain boundary regions.

A NON-SCHMID CRYSTAL PLASTICITY FINITE ELEMENT APPROACH TO MULTI-SCALE MODELING OF NICKEL-BASED SUPERALLOYS.

This paper develops non-Schmid crystal plasticity constitutive models at two length scales, and bridges them in a multi-scale framework. The constitutive models address thermomechanical behavior of Nickel-based superalloys for a large temperature range, viz. 300K to 1223K, and include orientation dependencies and tension-compression asymmetry.

Synchrotron X-Ray Microbeam Diffraction Measurements of Full Elastic Long Range Internal Strain and Stress Tensors in Commercial-Purity Aluminum Processed by Multiple Passes of Equal-Channel Angular Pressing.

Synchrotron X-ray microbeam diffraction was used to measure the full elastic long range internal strain and stress tensors of low dislocation density regions within the submicrometer grain/subgrain structure of equal-channel angular pressed (ECAP) AA1050 after 1, 2, and 8 passes. This is the first time that full tensors were measured in plastically deformed metals at this length scale. This work supplements previous studies that measured long range internal stresses (LRIS) in ECAP AA1050 of multiple passes, but only for a single direction.

Structural Characterization of Ageing Kinetics in Aluminum Alloy 2024 across Angstrom-to-Micrometer Length Scales.

The precipitate structure and precipitation kinetics in an Al-Cu-Mg alloy (AA2024) aged at 190 °C, 208 °C, and 226 °C have been studied using Transmission Electron Microscopy (TEM) and synchrotron-based, combined ultra-small angle X-ray scattering, small angle X-ray scattering (SAXS), and wide angle X-ray scattering (WAXS) across a length scale from sub-Angstrom to several micrometers. TEM brings information concerning the nature, morphology, and size of the precipitates while SAXS and WAXS provide qualitative and quantitative information concerning the time-dependent size and volume fraction evolution of the precipitates at different stages of the precipitation sequence. Within the experimental time resolution, precipitation at these ageing temperatures involves dissolution of nanometer-sized small clusters and formation of the planar S phase precipitates.

MAGNETOCALORIC RESPONSE OF NON-STOICHIOMETRIC NiMnGa ALLOYS AND THE INFLUENCE OF CRYSTALLOGRAPHIC TEXTURE.

Currently, there is significant interest in magnetocaloric materials for solid state refrigeration. In this work, polycrystalline Heusler alloys belonging to the NiMnGa family, with x between 0.08 and 0.

Kinetic analysis of MgB layer formation in advanced internal magnesium infiltration (AIMI) processed MgB wires.

Significantly enhanced critical current density () for MgB superconducting wires can be obtained following the advanced internal Mg infiltration (AIMI) route. But unless suitable precautions are taken, the AIMI-processed MgB wires will exhibit incomplete MgB layer formation, i.e.

Growth kinetics of particles in -Ti matrix studied by in-situ small-angle x-ray scattering.

Nucleation and growth kinetics of nanoparticles of hexagonal phase in a body-centered cubic titanium matrix in single crystals of -Ti alloys were investigated by small-angle x-ray scattering measured during ageing at various temperatures up to 450 °C. The experimental data were compared with numerical simulations based on a three-dimensional short-range order model of nanoparticle self-ordering. The x-ray contrast of the particles is caused by an inhomogeneous distribution of impurity atoms (Mo, Fe and Al), whose density profile around growing nanoparticles was simulated by solving the corresponding diffusion equation with moving boundary conditions.

Complementary ab initio and X-ray nanodiffraction studies of TaO.

The complex structure of TaO led to the development of various structural models. Among them, superstructures represent the most stable configurations. However, their formation requires kinetic activity and long-range ordering processes, which are hardly present during physical vapor deposition.

Direct evidence for grain boundary motion as the dominant restoration mechanism in the steady-state regime of extremely cold-rolled copper.

Ultra-fine-grained high-purity copper (99.99%) deformed by means of high-pressure torsion into the steady-state regime was subjected to additional rolling deformation. The microstructural changes as a function of the applied strain were analysed by means of orientation imaging microscopy.

Grain boundary excess volume and defect annealing of copper after high-pressure torsion.

The release of excess volume upon recrystallization of ultrafine-grained Cu deformed by high-pressure torsion (HPT) was studied by means of the direct technique of high-precision difference dilatometry in combination with differential scanning calorimetry (DSC) and scanning electron microscopy. From the length change associated with the removal of grain boundaries in the wake of crystallite growth, a structural key quantity of grain boundaries, the grain boundary excess volume or expansion [Formula: see text] m was directly determined. The value is quite similar to that measured by dilatometry for grain boundaries in HPT-deformed Ni.