<Emphasis Type=Italic>In-Situ</Emphasis> Synchrotron Characterization of Transformation Sequences in TiNi-Based Shape Memory Alloys during Thermal Cycling

In-situ synchrotron radiation has been used to provide direct analysis of the transformation sequences in TiNi-based shape memory alloys during thermal cycling. The high resolution, narrow peak width Debye–Scherrer diffraction spectra enabled positive identification and quantification of the phase transformation sequences, which is not possible through normal laboratory studies. The results facilitate a clearer understanding of the development and influence of intermediate phases such as R or B19 on sequential martensitic transformations. Ti_50.2Ni_49.8 transformed predominately via a single-step B2 ↔ B19′ transformation, although evidence of the R phase was found during cooling in every cycle. The martensitic start temperature was depressed by ~0.6 °C per cycle, while the R-phase start temperature was found to be unaffected. Ti₅₀Ni₄₁Cu₉ transformed through a two-step B2 ↔ B19 ↔ B19′ sequence, with the B2 → B19 transformation reaching completion prior to the formation of any B19′. The transformation temperatures of Ti₅₀Ni₄₁Cu₉ were found to be insensitive to thermal cycling, remaining constant over the studied cycle range.     

<Emphasis Type=Italic>In-Situ</Emphasis> Observations of Martensitic Transformation in Blast-Resistant Steel

A hybrid in-situ characterization system, which couples the laser scanning confocal microscopy (LSCM) with the time-resolved X-ray diffraction (TRXRD) measurement with synchrotron radiation, was used to characterize the microstructure evolution during heat-affected zone (HAZ) thermal cycling of high-strength and blast-resistant steel. The combined technique has a time resolution of 0.3 seconds that allows for high-fidelity measurements of transformation kinetics, lattice parameters, and morphological features. The measurements showed a significant reduction in the martensite start transformation temperature with a decrease in the prior austenite grain size. In addition, the LSCM images confirmed the concurrent refinement of martensite packet size with smaller austenite grain sizes. This is consistent with dilatometric observations. The austenite grain size also influenced the rate of transformation (df _m /dT); however, the measurements from the hybrid (surface) and dilatometric (volume) measurements were inconsistent. Challenges and future directions of adopting this technique for comprehensive tracking of microstructure evolution in steels are discussed.     

Texture Evolution and Phase Transformation in Titanium Investigated by <Emphasis Type=Italic>In-Situ</Emphasis> Neutron Diffraction

Time-of-flight neutron diffraction was used to study in-situ texture evolution and the α → β phase transformation in cold-drawn titanium upon continuous heating. The texture changes in the α phase at elevated temperatures upon recrystallization are presented. For the first time, a transient β texture was observed during the α → β transformation, as indicated by the initial rise and the final drop of the {110} _β reflection intensity. This unusual observation is explained in terms of competitive growth between inter- and intragranular β allotriomorphs.     

<Emphasis Type=Italic>In-Situ</Emphasis> Microtomographic Characterization of Single-Cavity Growth During High-Temperature Creep of Leaded Brass

Synchrotron microtomography was used for in-situ characterization of high-temperature creep damage in leaded brass. Applying image registration to subsequent tomographic reconstructions, the volumetric growth rate of single cavities with equivalent radii between 2 and 4.3 μm was assessed. We conclude from the volume dependence of the growth rates that both the viscous flow and grain boundary (GB) diffusion mechanisms influence void growth. We show that void growth in leaded brass is retarded by negative stress triaxiality, which develops in the matrix during heating the specimen to the deformation temperature.     

<Emphasis Type=Italic>In-Situ</Emphasis> Neutron Diffraction Study of the Bauschinger Effect in B2 Structured CoZr

A combination of in-situ neutron diffraction and elastoplastic self-consistent (EPSC) modeling have been used to elucidate the role played by intergranular stresses in the Bauschinger effect in B2 structured CoZr at room temperature and 423 K (150 °C). It is shown that, when insufficient slip modes are present to accommodate arbitrary strains, the large intergranular stresses built up due to inhomogeneous plastic deformation are responsible for the observed Bauschinger effect. Upon the onset of secondary deformation mechanism(s), the stresses are more uniformly distributed among the grains and the influence of intergranular stresses on the Bauschinger effect diminishes. On the other hand, it is speculated that the contribution of intragranular (dislocation-based) stresses is responsible for the persistent Bauschinger effect past the transition point. Similar results are obtained at both room temperature and 423 K (150 °C), and while the yield strength decreases with temperature, the high-temperature stress-strain curve progressively becomes harder than the room temperature one. In light of this, the previously characterized yield strength anomaly in CoZr has been re-examined.     

<Emphasis Type=Italic>In-Situ</Emphasis> X-Ray Diffraction Observations of Low-Temperature Ag-Nanoink Sintering and High-Temperature Eutectic Reaction with Copper

Nanoinks, which contain nanometer-sized metallic particles suspended in an organic dispersant fluid, are finding numerous microelectronic applications. One characteristic of nanoinks is that they sinter at much lower temperatures than bulk metals due to their high surface area to volume ratio and small radius of curvature, which reduces their melting points significantly below their bulk values. The unusually low sintering temperatures have unique potential for materials joining, since their melting points increase dramatically afterward. In this article, the sintering kinetics of Ag nanoink is studied using in-situ synchrotron methods to determine diffraction peak characteristics during the sintering cycle, and to subsequently calculate particle size and growth during sintering. Ag nanoink is further explored as a eutectic bonding medium by tracking phase transformations between sintered Ag nanoink and a Cu substrate to high temperatures, where melting occurs at the Ag-Cu eutectic, demonstrating nanoinks as a viable eutectic bonding medium.     

<Emphasis Type=Italic>L</Emphasis><Subscript>3</Subscript>-XANES spectroscopy of the valence-unstable cerium in intermetallic compounds with 3<Emphasis Type=Italic>d</Emphasis> metals

The effective valence of cerium is studied by L ₃-XANES spectroscopy using synchrotron radiation in the following valence-unstable systems with different types of magnetic ordering: a CeNi matrix doped with neodymium, praseodymium, and gadolinium ions in the temperature range 5–300 K and the Ce₂Fe1_{7 − x} Mn _x intermetallic compound. The obtained dependences are discussed in terms of generally accepted models of states with an intermediate valence of rare-earth ions. Possible correlations between the effective valence of cerium and the magnetic properties of the substances are taken into account.     

A Derivation of a Quadratic Activity Coefficient <Emphasis Type=Italic>vs</Emphasis> Composition Relationship in a Quaternary System, <Emphasis Type=Italic>A-B-C-D</Emphasis>

In the literature, no direct derivation exists of the quadratic activity coefficient vs composition relationships for a quaternary system with high solute concentrations. Such relations for a ternary system (1-2-3) were derived by Darken by extending the results of a binary system (1-2), introducing a new concept of “hypothetical system” (2-3). To present a better scheme to find the activity coefficient-composition relations for multicomponent systems, derivations are made for a quaternary system A-B-C-D in the current work. Using a MacLaurin series expansion, the (Raoultian) activity coefficient, ln γ _i , of each component is equated with a quadratic expression of mole fractions (x), involving the activity coefficient at zero concentration ( g_i⁰ ) left( {gamma_{i}^{0} } right) and nine interaction coefficients (ε). Subsequently, with the help of a Gibbs–Duhem equation, followed by a comparison of coefficients, most preceding 9 × 4, i.e., 36 interaction coefficients are eliminated, leaving behind only three self- and three ternary interaction coefficients, which are enough to express the activity coefficient vs composition relationships for the solutes B, C, and D, as well as for the solvent A. Setting the mole fraction x _D  = 0, the preceding expressions establish the same relations as proposed by Darken for the ternary system A-B-C. The derivation also clarifies how the quadratic concentration terms accompany the first-order interaction coefficients, not the second-order ones. Applications of the derived relations to determine simultaneously the activity coefficients g_i⁰ gamma_{i}^{0} and the interaction coefficients ε in a new way in some iron- and steelmaking systems are presented. A new data on interaction coefficients in liquid iron at 1873 K (1600 °C), e_textV^textV = - 6. 1, varepsilon_{text{V}}^{text{V}} = - 6. 1, has been generated through such an application.     

Anomalous Mixing State in Room-Temperature Ionic Liquid-Water Mixtures: <Emphasis Type=Italic>N,N</Emphasis>-diethyl-<Emphasis Type=Italic>N</Emphasis>-methyl-<Emphasis Type=Italic>N</Emphasis>-(2-methoxyethyl) Ammonium Tetrafluoroborate

The mixing states of room-temperature ionic liquid (RTIL) H₂O mixtures (x = 0.0 mol pct to 99.5 mol pct H₂O) were investigated using wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and optical absorption in an ultraviolet and visible (UV-vis) region. The RTIL is N, N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate, [DEME][BF₄]. In a “prepeak” region of the WAXS, the scattered intensities increased at 85 mol pct to 95 mol pct. A medium-range order (MRO) in the liquid structure as observed in network-forming materials developed markedly. In the SAXS experiments, we can detect nanoscale fluctuations relating to polar and nonpolar regions. At 65 mol pct to 85 mol pct, the SAXS intensity increased unexpectedly. Furthermore, entirely different optical absorption spectra in the UV-vis region were observed as a macroscopic property from 90 mol pct to 95 mol pct. We suppose that these anomalies relate to the MRO of the liquid structure. All anomalies probably are induced by an intrinsic property in [DEME][BF₄]-H₂O mixtures.     

Ultrasound velocity and adiabatic compressibility of GdCl<Subscript>3</Subscript>-<Emphasis Type=Italic>M</Emphasis>Cl (<Emphasis Type=Italic>M</Emphasis> = Na,Cs) melts

The ultrasound velocity in GdCl₃ + MCl (M = Na, Cs) chloride melts is measured over wide temperature and composition ranges, and their adiabatic compressibility is calculated. A correlation is established between the relative deviations of these properties from their values in hypothetic ideal salt mixtures and the reciprocal alkali-metal cation radii. The role of lanthanide compression in the propagation of sound vibrations in the chlorides of cerium group REMs is revealed.     

Co-deformation processing and modeling of <Emphasis Type="Italic">In-Situ</Emphasis> multiphase composites

A series of in-situ, deformation-processed metal matrix composites were produced by direct powder extrusion of blended constituents. The resulting composites are comprised of a metallic Ti-6Al-4V matrix containing dispersed and co-deformed discontinuously reinforced-intermetallic matrix composite (DR-IMC) reinforcements. The DR-IMCs are comprised of discontinuous TiB₂ particulate within a titanium trialuminide or near-γ Ti-47Al matrix. Thus, an example of a resulting composite would be Ti-6Al-4V+40 vol pct (Al₃Ti+30 vol pct TiB₂) or Ti-6Al-4V+40 vol pct (Ti-47Al+40 vol pct TiB₂), with the DR-IMCs having an aligned, high aspect ratio morphology as a consequence of deformation processing. The degree to which both constituents deform during extrusion has been examined using systematic variations in the percentage of TiB₂ within the DR-IMC, and by varying the percentage of DR-IMC within the metal matrix. In the former instance, variation of the TiB₂ percentage effects variations in relative flow behavior; while in the latter, varying the percentage of DR-IMC within the metallic matrix effects changes in strain distribution among components. The results indicate that successful co-deformation processing can occur within certain ranges of relative flow stress; however, the extent of commensurate flow will be limited by the constituents’ inherent capacity to plastically deform.     

Phase evolution during laser <Emphasis Type="Italic">In-Situ</Emphasis> carbide coating

With the help of laser surface engineering, in-situ carbide composite coating on the surface of plain carbon steel was achieved. Energy dispersive spectroscopy (EDS) in supplement with X-ray diffractometry indicated the evolution of TiC, Fe−Cr, and M₇C₃ as major phases in the coating. A variation in the evolution of M₇C₃ phase was observed with respect to the laser power over the range of 900 to 2100 W (3 mm×600 μm rectangular beam spot) during processing. Computational techniques were employed with the aim of studying possible reasons for phase evolution, stability of phases, solidification path, and optimization of parameters to stabilize the M₇C₃ phase and hence tailor properties.     

<Emphasis Type="Italic">In-Situ</Emphasis> Analysis of Coarsening during Directional Solidification Experiments in High-Solute Aluminum Alloys

Coarsening within the mushy zone during continuous directional solidification experiments was studied on an Al-30 wt pct Cu alloy. High brilliance synchrotron X-radiation microscopy allowed images to be taken in-situ during solidification. Transient conditions were present during directional solidification. Under these conditions, solute-rich settling liquid flow affects the dendritic array and thus coarsening. Coarsening was studied by following the secondary dendrite arm spacing (SDAS) of a developing dendrite at different local solidification times according to the mush depth and instant interface velocity. Solute enrichment and liquid flow cause deceleration and acceleration of the solidification front, which in turn influences both the mush depth and local growth and coarsening due to variations in solutal gradients and thus local undercooling. In addition, spacing between neighboring dendrites (i.e., primary dendrite arm spacing), which determines permeability within the mushy zone, affects the development of high-order branches. This article is based on a presentation given at the International Symposium on Liquid Metal Processing and Casting (LMPC 2007), which occurred in September 2007 in Nancy, France.     

Thermal conductivity of NdCl<Subscript>3</Subscript>-<Emphasis Type=Italic>M</Emphasis>Cl (<Emphasis Type=Italic>M</Emphasis> = Na,K, Cs) melts

The thermal conductivities of individual NdCl₃, the K₃NdCl₆ chemical compound, an equimolar 0.5NdCl₃-0.5NaCl mixture, and eutectic 0.5NdCl₃-0.5KCl and 0.45NdCl₃-0.55CsCl mixtures are measured. For all melts, the concentration and temperature dependences of the thermal conductivity are found.     

Characterization of Damage Evolution in SiC Particle Reinforced Al Alloy Matrix Composites by <Emphasis Type=Italic>In-Situ</Emphasis> X-Ray Synchrotron Tomography

We carried out a detailed investigation of the damage behavior of SiC particle reinforced 2080 Al alloy matrix composites by in-situ X-ray synchrotron tomography. We studied the tensile damage behavior of a peak-aged aluminum matrix composite. The main damage mode was SiC particle fracture with a very small contribution from void growth. The onset of damage takes place very close to the ultimate tensile strength of the composite. Particle fracture damage is stochastic in nature and is confined to a small distance from the fracture plane. Minimal void growth is observed, primarily at pre-existing microscopic voids from processing. Microstructure-based simulations, based on two-dimensional (2-D) images from the tomography data sets, show the importance of particle distribution and morphology on the evolution of plastic strain and damage in the composite.     

<Emphasis Type=Italic>In Situ</Emphasis> Observation of Strain Evolution in Cp-Ti Over Multiple Length Scales

The strain evolution in polycrystalline CP-Ti strip under tension was studied in situ and at two length scales using Synchrotron X-ray diffraction. To establish the bulk material behavior, experiments were performed at the Australian Synchrotron facility. Because of the relatively large grain size, discontinuous “spotty” Debye ring patterns were observed, and a peak fitting algorithm was developed to determine the individual spot positions with the necessary precision for strain determination. The crystallographic directional dependence of strain anisotropy during the loading cycle was determined. Strain anisotropy and yielding of individual crystallographic planes prior to the macroscopic yield point were further clarified by in situ loading experiments performed at the Advanced Light Source (ALS). The deviatoric strain accumulation and plastic response were mapped on a grain-by-grain basis. The onset of microscopic yielding in the grains was identified and correlated with the relative orientation of the grains with respect to the loading direction.     

Ultrasound velocity and adiabatic compressibility of LaCl<Subscript>3</Subscript> + <Emphasis Type=Italic>M</Emphasis>Cl (<Emphasis Type=Italic>M</Emphasis> = Li,Na, K,Rb, and Cs) melts

The ultrasound velocity in binary LaCl₃ + MCl (M = Li, Na, K, Rb, and Cs) melts is measured, and their adiabatic compressibility is calculated as a function of temperature and composition. A relation is established between the relative deviations of these properties from their values for hypothetic ideal salt mixtures, on the one hand, and the ionic potentials of the alkali-metal cations, on the other.