A Developed Method for Fabricating <Emphasis Type="Italic">In-Situ</Emphasis> TiC<Subscript><Emphasis Type="Italic">p</Emphasis></Subscript>/Mg Composites by Using Quick Preheating Treatment and Ultrasonic Vibration

Quick preheating treatment of the Al-Ti-C pellets and high-intensity ultrasonic vibration are introduced in the fabrication of in-situ TiC _p /Mg composites. Al-Ti-C pellets are preheated for about 130 seconds in the furnace at 1023 K (750 °C), in which magnesium is melted as well. In this process, plenty of heat can be accumulated due to the reactive diffusion between liquid aluminum and solid titanium in Al-Ti-C, and a small amount of Al₃Ti phase is formed as well. After adding the preheated Al-Ti-C into the molten magnesium, thermal explosion takes place in a few seconds. In the meantime, high-intensity ultrasonic vibration is applied into the melt to disperse in-situ formed TiC particles into the matrix and degas the melt as well. Microstructural characterization indicates that in-situ formed TiC particles are spherical in morphology and smaller than 2 μm in size. Furthermore, a homogeneous microstructure with low porosity of the magnesium composite is obtained due to the effect of ultrasonic vibration. A novel approach using the quick preheating treatment technique and high-intensity ultrasonic vibration to synthesize in-situ TiC _p /Mg composites is proposed in our research.     

Thermodynamics and Kinetics to Alloying Addition on <Emphasis Type="Italic">In-Situ</Emphasis> AlN/Mg Composites Synthesis <Emphasis Type="Italic">via</Emphasis> Displacement Reactions in Liquid Mg Melt

Based on the Wilson equation, extended Miedema model, and hard sphere theory, new models are developed theoretically only using the quantities of the pure component and are applied to investigate the thermodynamical and kinetic effect of alloying additions on in-situ AlN formation via displacement reaction in Mg-Al alloy melt. The results show that the alloying additions such as Si, Zn, and Cu can promote the formation of AlN in Mg-Al melt both in thermodynamics and kinetics. Meanwhile, other elements, including Mn, Nd, Ce, Ni, and La, must be matched properly in order to produce the desired reinforcement AlN in liquid Mg-Al melt.     

Mechanochemical preparation of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites

The mechanochemical preparation of nickel aluminide/corundum (Ni _x Al _y /Al₂O₃) powder nanocomposites is shown to be possible during the mechanochemical aluminum reduction of nickel oxide at various weight proportions of the components.     

Slip-System-Related Dislocation Study from <Emphasis Type="Italic">In-Situ</Emphasis> Neutron Measurements

A combined experimental/computational approach is employed to study slip-system-related dislocation-substructure formation during uniaxial tension of a single-phase, face-centered-cubic (fcc), nickel-based alloy. In-situ neutron-diffraction measurements were conducted to monitor the peak-intensity, peak-position, and peak-broadening evolution during a displacement-controlled, monotonic-tension experiment at room temperature. The measured lattice-strain evolution and the macrostress/macrostrain curves were used to obtain the material parameters required for simulating the texture development by a visco-plastic self-consistent (VPSC) model. The simulated texture compared favorably with experimentally-determined texture results over a range of 0 to 30 pct engineering strain. The grain-orientation-dependent input into the Debye-intensity ring was considered. Grains favorably oriented relative to the two detector banks in the geometry of the neutron experiment were indicated. For the favorably oriented grains, the simulated slip-system activity was used to calculate the slip-system-dependent, dislocation-contrast factor. The combination of the calculated contrast factor with the experimentally-measured peak broadening allows the assessment of the parameters of the dislocation arrangement within the specifically oriented grains, which has a quantitative agreement with the transmission-electron-microscopy results. This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,” which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee.

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Functionally Graded Al Alloy Matrix <Emphasis Type="Italic">In-Situ</Emphasis> Composites

In the present work, functionally graded (FG) aluminum alloy matrix in-situ composites (FG-AMCs) with TiB₂ and TiC reinforcements were synthesized using the horizontal centrifugal casting process. A commercial Al-Si alloy (A356) and an Al-Cu alloy were used as matrices in the present study. The material parameters (such as matrix and reinforcement type) and process parameters (such as mold temperature, mold speed, and melt stirring) were found to influence the gradient in the FG-AMCs. Detailed microstructural analysis of the composites in different processing conditions revealed that the gradients in the reinforcement modify the microstructure and hardness of the Al alloy. The segregated in-situ formed TiB₂ and TiC particles change the morphology of Si particles during the solidification of Al-Si alloy. A maximum of 20 vol pct of reinforcement at the surface was achieved by this process in the Al-4Cu-TiB₂ system. The stirring of the melt before pouring causes the reinforcement particles to segregate at the periphery of the casting, while in the absence of such stirring, the particles are segregated at the interior of the casting.     

Fabrication of High-Strength Al/SiC<Subscript><Emphasis Type="Italic">p</Emphasis></Subscript> Nanocomposite Sheets by Accumulative Roll Bonding

Accumulative roll bonding (ARB) was successfully used as a severe plastic deformation method to produce Al-SiC nanocomposite sheets. The effects of process pass and amount of SiC content on microstructure and mechanical properties of the composites are investigated. As expected, production of ultrafine grain structures by the ARB process as well as nanosize particulate reinforcements in the metal matrix composite (MMC) resulted in excellent mechanical properties. According to the results of the tensile tests, it is shown that the yield and tensile strengths of the composite sheet increased with the number of ARB cycles without saturation at the last cycles. Scanning electron microscopy (SEM) revealed that the particles had a random and uniform distribution in the matrix by the last ARB cycles, and strong mechanical bonding takes place at the interface of the particle matrix. Transmission electron microscopy (TEM) and the corresponding selected area diffraction (SAD) demonstrate ultrafine grains with large misorientation in the structure. It is also shown that by increasing the volume fraction of particles up to 3.5 vol pct, the yield and tensile strengths of the composite sheets increased more than 1.3 and 1.4 times the accumulative roll-bonded aluminum sheets, respectively.     

<Emphasis Type="Italic">In-Situ</Emphasis> Investigation of Local Boundary Migration During Recrystallization

A combination of electron channeling contrast (ECC) and electron backscatter diffraction pattern (EBSP) techniques has been used to follow in situ the migration during annealing at 323 K (50 °C) of a recrystallizing boundary through the deformed matrix of high-purity aluminum rolled to 86 pct reduction in thickness. The combination of ECC and EBSP techniques allows both detailed measurements of crystallographic orientations to be made, as well as tracking of the boundary migration with good temporal resolution. The measured boundary velocity and the local boundary morphology are analyzed based on calculations of local values for the stored energy of deformation. It is found that the migration of the investigated boundary is very complex with significant spatial and temporal variations in its movement, which cannot directly be explained by the variations in stored energies, but that these variations relate closely to local variations within the deformed microstructure ahead of the boundary, and are found related to the local spatial arrangements and misorientations of the dislocation boundaries. The results of the investigation suggest that local analysis, on the micrometer length scale, is necessary for the further understanding of recrystallization boundary migration mechanisms.     

Synthesis of Al-Zr Alloys <Emphasis Type="Italic">Via</Emphasis> ZrO<Subscript>2</Subscript> Aluminum-Thermal Reduction in KF-AlF<Subscript>3</Subscript>-Based Melts

Physical–chemical investigations of KF-AlF₃ melts were carried out in order to develop the scientific basis of the technology for Al-Zr alloy synthesis. The possibility of Al-Zr alloy synthesis via the aluminum-thermal method was shown. The liquidus temperatures of KF-AlF₃ and KF-NaF-AlF₃ melts with additions of Al₂O₃ and ZrO₂ were determined using the thermal analysis method in the temperature range from 873 K to 1173 K (600 °C to 900 °C). The dependency of the solubility of ZrO₂ in KF-AlF₃ and KF-NaF-AlF₃ melts on Al₂O₃ concentration was measured.     

<Emphasis Type="Italic">In-Situ</Emphasis> High-Energy X-Ray Diffuse-Scattering Study of the Phase Transition in a Ni<Subscript>2</Subscript>MnGa Ferromagnetic Shape-Memory Crystal

The full information on the changes in many crystallographic aspects, including the structural and microstructural characterizations, during the phase transformation is essential for understanding the phase transition and “memory” behavior in the ferromagnetic shape-memory alloys. In the present article, the defects-related microstructural features connected to the premartensitic and martensitic transition of a Ni₂MnGa single crystal under a uniaxial pressure of 50 MPa applied along the [110] crystallographic direction were studied by the in-situ high-energy X-ray diffuse-scattering experiments. The analysis of the characteristics of diffuse-scattering patterns around different sharp Bragg spots suggests that the influences of some defect clusters on the pressure-induced phase-transition sequences of Ni₂MnGa are significant. Our experiments show that an intermediate phase is produced during the premartensitic transition in the Ni₂MnGa single crystal, which is favorable for the nucleation of a martensitic phase. The compression stress along the [110] direction of the Heusler phase can promote the premartensitic and martensitic transition of the Ni₂MnGa single crystal. This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,” which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee.     

<Emphasis Type="Italic">In-Situ</Emphasis> Electrochemical Investigations of a Nickel-Based Alloy Subjected to Fatigue

The HASTELLOY C2000 superalloy is a commercially designed superalloy manufactured to function in reducing and oxidizing corrosive solutions. The industrial applications have tremendous potential in automotive, structural, aviation, and storage components. Although C2000 demonstrates good reducing and oxidizing traits in extremely aggressive media (which are attractive features of its chemistry), changes in the mechanical properties are believed to be insignificant due to its strong propensity to passivate under corrosive conditions. The ductility behavior and corrosion properties of C2000 are superior to those of stainless steels. The objective of the present study is to examine the corrosion-fatigue behavior of C2000 in a 3.5 wt pct sodium-chloride (NaCl) solution. C2000 submerged in 3.5 wt pct NaCl at room temperature is not susceptible to localized corrosion, such as pitting, during fatigue. At an accelerated potential of 350 mV, the current responses show an increase in the current due to slip steps emerging to the surface as a result of fatigue. The crack-initiation site and the examination of the fracture morphology are discussed. This article is based on a presentation given in the symposium entitled “Deformation and Fracture from Nano to Macro: A Symposium Honoring W.W. Gerberich’s 70th Birthday,” which occurred during the TMS Annual Meeting, March 12–16, 2006 in San Antonio, Texas and was sponsored by the Mechanical Behavior of Materials and Nanomechanical Behavior Committees of TMS.

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Self-propagating high-temperature synthesis of ceramic materials based on the M<Subscript><Emphasis Type="Italic">n</Emphasis> + 1</Subscript>AX<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> phases in the Ti-Cr-Al-C system

Compact ceramic materials based on the M_{n + 1}AX _n phases in the Ti-Cr-Al-C system are produced by forced self-propagating high-temperature synthesis (SHS) compaction. The mechanisms of the structure and phase formation in synthetic products, as well as the combustion macrokinetics of the SHS mixture, are studied. Complex investigations of the structure, phase composition, and physical and mechanical properties of new Ti_{2 ? x} Cr _x AlC ceramic materials synthesized at different charging parameters (x = 0, 0.5, 1, 1.5, and 2) are performed. The highest content (96–98%) of the M_{n + 1}AX _n phase in the composition of synthetic products is found to be in samples where just one of the host elements (titanium (x = 0) or chromium (x = 2)) is present. The produced materials have a high heat resistance, and the increase in the chromium concentration is favorable to an appreciable growth in resistance to high-temperature oxidation.     

<Emphasis Type="Italic">In-Situ</Emphasis> Observation on the Diversified Morphology and Growth Behavior of Al<Subscript>3</Subscript>Ni Phase at the Liquid Al/Solid Ni Interface

The morphology and growth behavior of Al₃Ni in the liquid Al/solid Ni interface were observed through synchrotron radiation. The formation time and mechanism of Al₃Ni are connected with saturation of the molten layer. In unsaturated conditions, the growth of columnar Al₃Ni formed during solidification governed by the melting of small grains accompanied by the growth of adjacent large grains and coalescence of grains near the tips. Conversely, the scallop-type Al₃Ni formed in holding showed annexation of adjacent small grains with its morphology changing from scallop to hemisphere.     

Kinetics of Reduction of CaO-FeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-MgO-PbO-SiO<Subscript>2</Subscript> Slags by CO-CO<Subscript>2</Subscript> Gas Mixtures

Kinetics of the reaction of lead slags (PbO-CaO-SiO₂-FeO _x -MgO) with CO-CO₂ gas mixtures was studied by monitoring the changes in the slag composition when a stream of CO-CO₂ gas mixture was blown on the surface of thin layers of slags (3 to 10 mm) at temperatures in the range of 1453 K to 1593 K (1180 °C to 1320 °C). These measurements were carried out under conditions where mass transfer in the gas phase was not the rate-limiting step and the reduction rates were insensitive to factors affecting mass transfer in the slag phase. The results show simultaneous reduction of PbO and Fe₂O₃ in the slag. The measured specific rate of oxygen removal from the melts varied from about 1 × 10^?6 to 4 × 10^?5 mol O cm^?2 s^?1 and was strongly dependent on the slag chemistry and its oxidation state, partial pressure of CO in the reaction gas mixture, and temperature. The deduced apparent first-order rate constant increased with increasing iron oxide content, oxidation state of the slag, and temperature. The results indicate that under the employed experimental conditions, the rate of formation of CO₂ at the gas-slag interface is likely to be the rate-limiting step.     

Effect of heat treatments on <Emphasis Type="Italic">In-Situ</Emphasis> Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiAl<Subscript>3</Subscript> composites produced from squeeze casting of TiO<Subscript>2</Subscript>/A356 composites

In-situ Al₂O₃/TiAl₃ intermetallic matrix composites were fabricated via squeeze casting of TiO₂/A356 composites heated in the temperature range from 700 °C to 780 °C for 2 hours. The phase transformation in TiO₂/A356 composites employing various heat-treatment temperatures (700 °C to 780 °C) was studied by means of differential thermal analysis (DTA), microhardness, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). From DTA, two exothermic peaks from 600 °C to 750 °C were found in the TiO₂/A356 composites. The XRD showed that Al₂O₃ and TiAl₃ were the primary products after heat treatment of the TiO₂/A356 composite. The fabrication of in-situ Al₂O₃/TiAl₃ composites required 33 vol pct TiO₂ in Al and heat treatment in the range from 750 °C to 780 °C. The hardness (HV) of the in-situ Al₂O₃/TiAl₃ composites (1000 HV) was superior to that of nonreacted TiO₂/A356 composites (200 HV). However, the bending strength decreased from 685 MPa for TiO₂/A356 composites to 250 MPa for Al₂O₃/TiAl₃ composites. It decreased rapidly because pores occurred during the formation of Al₂O₃ and TiAl₃. The activation energy of the formation of Al₂O₃ and TiAl₃ from TiO₂ and A356 was determined to be about 286 kJ/mole.     

<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.     

Water Network in Room-Temperature Ionic Liquid: <Emphasis Type="Italic">N,N</Emphasis>-Diethyl-<Emphasis Type="Italic">N</Emphasis>-Methyl-<Emphasis Type="Italic">N</Emphasis>-2-Methoxyethyl Ammonium Tetrafluoroborate

Crystal structures of room-temperature ionic liquid (RTIL)-H₂O mixtures are determined by the X-ray diffraction method. The RTIL is N,N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate, [DEME][BF₄]. At 0.9 mol pct H₂O, two kinds of superstructures occur simultaneously without a strain. Also, the volume of the unit cell is very small only at 0.9 mol pct additives. This relates to the composite domain structure, including a twin-related one, as an elastic anomaly. At other water concentrations, such an extraordinary behavior is not observable. By assuming a sublattice having an equivalent lattice constant, a water network at 1 mol pct H₂O is simulated using a Monte Carlo (MC) method. The network develops over the medium range in the simulation box.     

Microstructure and Properties of Fe<Subscript>3</Subscript>Al-Fe<Subscript>3</Subscript>AlC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Composite Prepared by Reactive Liquid Processing

A Fe₃Al-Fe₃AlC _x composite was prepared using reactive liquid processing (RLP) through controlled mixture of carbon steel and aluminum in the liquid state. The microstructure and phases of the composite were assessed using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, optical microscopy, and differential scanning calorimetry. In addition, the density, hardness, microhardness, and elastic modulus were evaluated. The Fe₃Al-Fe₃AlC _x composite consisted of 65 vol pct Fe₃Al and 35 vol pct Fe₃AlC _x (κ). The κ phase contained 10.62 at. pct C, resulting in the stoichiometry Fe₃AlC_0.475. The elastic modulus of the Fe₃Al-Fe₃AlC_0.475 composite followed the rule of mixtures. The RLP technique was shown to be capable of producing Fe₃Al-Fe₃AlC_0.475 with a microstructure and properties similar to those achieved using other processing techniques reported in the literature.