Peculiarities of the technology and physicomechanical properties of a laminated Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al cermet

A technological approach permitting one to obtain laminated Al₂O₃-Al cermet is considered. The industrial PAP-2 powder with laminated particles served as the starting crude. The powder billets were obtained by compaction under pressure (P) from 100 to 1000 MPa and thermally treated in air by heating in the furnace to 600°C. It is established that either the solid-phase sintering or reaction sintering of the billets in the mode of filtration combustion can be achieved depending on the value of P. In the produced composite, the content of the oxide phase varies from 5 to 40%, while the density and strength upon bending vary in the limits 2.53–2.00 g/cm³ and 330-98 MPa, respectively. The laminated structure of the material is retained after thermal aging in air at t= 600°C for no less than 1000 h.     

Kinetics study on non-isothermal crystallization of Cu<Subscript>50</Subscript>Zr<Subscript>50</Subscript> metallic glass

In this paper, the crystallization kinetics of melt-spun Cu₅₀Zr₅₀ amorphous alloy ribbons has been investigated using differential scanning calorimetry. Moreover, the Kissinger, Ozawa and isoconversional approaches have been used to obtain the crystallization kinetic parameters. As shown in the results, the onset crystallization activation energy E _x is less than crystallization peak activation energy E _p. The local activation energy E _α increases at the crystallized volume fraction α < 0.2 and decreases at the rest, which suggests that crystallization process is increasingly hard (α < 0.2) at first, after which it become increasingly easy (α > 0.2). The nucleation activation energy E _nucleation is greater than grain growth activation energy E _growth, indicating that the nucleation is harder than growth. In terms of the local Avrami exponent n(α), it lies between 1.27 and 8, which means that crystallization mechanism in the non-isothermal crystallization is interface-controlled one- two- or three-dimensional growth with different nucleation rates.     

Infrared Brazing of Ti<Subscript>50</Subscript>Ni<Subscript>50</Subscript> Shape Memory Alloy and Inconel 600 Alloy with Two Ag-Cu-Ti Active Braze Alloys

Infrared brazing of Ti₅₀Ni₅₀ SMA and Inconel 600 alloy using Cusil-ABA and Ticusil filler metals has been investigated. The joints were dominated by Ag-Cu eutectic with proeutectic Cu in the Cusil-ABA brazed joint and with proeutectic Ag in the Ticusil one. A continuous curved belt composed of a Ni₃Ti layer and a (Cu _x Ni_1?x )₂Ti layer formed in the brazed Ti₅₀Ni₅₀/Ticusil/Inconel 600 joint. On the Ti₅₀Ni₅₀ SMA side, an intermetallic layer of (Cu _x Ni_1?x )₂Ti formed in all joints, with x values around 0.81 and 0.47. Layers of (Cu _x Ni_1?x )₂Ti, Ni₃Ti, and mixed Ni₃Ti and Ni₂Cr intermetallics were observed next to the Inconel 600 substrate in the brazed Ti₅₀Ni₅₀/Cusil-ABA/Inconel 600 joint. The maximum shear strengths of the joints using the Cusil-ABA filler metal and the Ticusil filler metal were 324 and 300 MPa, respectively. In the Cusil-ABA brazed joint, cracks with cleavage-dominated fracture propagated along the (Cu _x Ni_1?x )₂Ti interfacial layer next to the Ti₅₀Ni₅₀ SMA substrate. In the Ticusil brazed joint, ductile dimple fracture occurred in the Ag-rich matrix near the Inconel 600 alloy substrate. The absence of a detrimental Ti-Fe-(Cu) layer on the Inconel 600 substrate side can effectively improve the shear strength of the joint.     

Synthesis and Non-isothermal Carbothermic Reduction of FeTiO<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Solid Solution Systems

To investigate the carbothermic reduction behaviors of xFeTiO₃·(1 ? x)Fe₂O₃ solid solutions, the solid solutions with different x values were synthesized and used in the corresponding reactions. With an increase in x, the temperature pertaining to the onset of carbothermic reduction increased, while the rate of reduction of the solid solutions, α, decreased. The lattice parameters calculated from XRD patterns indicated that the solid solution with a higher x led to a larger lattice distortion. The non-isothermal kinetics were calculated, and an average activation energy E value of 3.0 × 10² kJ/mol was obtained.     

Separation of Fine Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Inclusion from Liquid Steel with Super Gravity

An innovative approach of super gravity was proposed to separate fine Al₂O₃ inclusions from liquid steel in this study. To investigate the removal behaviors of inclusions, the effects of different gravity coefficients and time on separating the inclusions were studied. The results show that a large amount of Al₂O₃ inclusions gathered at the top of the sample obtained by super gravity, whereas there were almost no inclusions appearing at the bottom. The volume fraction and number density of inclusions presented a gradient distribution along the direction of the super gravity, which became steeper with increasing gravity coefficient and separating time. As a result of the collision between inclusions, a large amount of inclusions aggregated and grew during the moving process, which further decreased the removal time. The experimental required removal time of inclusions is close to the theoretical values calculated by Stokes law under gravity coefficient G ≤ 80, t ≤ 15 minutes, and the small deviation may be because the inclusion particles are not truly spherical. Under the condition of gravity coefficient G = 80, t = 15 minutes, the total oxygen content at the bottom of the sample (position of 5 cm) is only 8.4 ppm, and the removal rate is up to 95.6 pct compared with that under normal gravity.     

Understanding the Relationship Between Structure and Thermophysical Properties of CaO-SiO<Subscript>2</Subscript>-MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Molten Slags

In the present work, the relationship between the microscopic structure and macroscopic thermophysical properties in a basic CaO-SiO₂-MgO-Al₂O₃ quaternary system was identified using Fourier transformation infrared, Raman and ²⁷Al magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The Raman spectra quantitatively proved that with increasing Al₂O₃ content, the concentrations of the symmetric units of Q⁰(Si) and Q²(Si) decreased, while those of the asymmetric units of Q¹(Si) and Q³(Si) increased; consequently, the degree of polymerization of the networks increased, which resulted in an increase in slag viscosity. The ²⁷Al MAS-NMR spectra demonstrated that three structural units of Al atoms, namely, AlO₄, AlO₅, and AlO₆, mainly existed in the networks. With increasing Al₂O₃ content, the concentration of AlO₄ slightly decreased, while those of AlO₅ and AlO₆ increased; overall, Al₂O₃ acted as a network former in the present system. The increasing Al₂O₃ content led to additional AlO₆ and Si-NBO-Ca-NBO-Al frameworks, which replaced Si-NBO-Ca-NBO-Si in the networks (NBO: non-bridging oxygen) and induced a change in the primarily precipitated crystalline phase from Ca₂MgSi₂O₇ and Ca₂Al₂SiO₇ to MgAlO₄.     

Abnormal growth of TiB<Subscript>2</Subscript> crystals during sintering of TiB<Subscript>2</Subscript>-Ni<Subscript>3</Subscript>(Al,Ti) cemented borides

TiB₂-Ni₃(Al,Ti) cermets present both normal and abnormal growth of faceted titanium diboride (TiB₂) grains during liquid-phase sintering. Abnormal grain growth (AGG) is preferentially found at high sintering temperatures in specimens processed from powder mixtures with a wide particle size distribution. The WC additions to the initial powder mixtures have proved efficient in reducing the number and size of these large TiB₂ grains. However, the sinterability of these materials is dramatically reduced, which suggests that TiB₂ AGG control is obtained by decreasing TiB₂ dissolution kinetics in the liquid phase. On the other hand, an alternative method based on intensive powder milling not only reduces TiB₂ AGG but also the porosity levels obtained by previous powder processing routes. TiB₂ cermets produced by aggressive milling present a higher amount of alumina particles in the matrix after sintering, which, in addition, appear more homogeneously dispersed in the microstructure. The distortion produced by these particles on the facets of TiB₂ growing grains suggests a possible dragging effect responsible for the AGG reduction found in these cermets. Moreover, aggressive milling removes large TiB₂ particles from the powder mixtures, which could act as seeds for TiB₂ uncontrolled growth. TiB₂-Ni₃(Al,Ti) cermets obtained by intensive milling combine hardness over 20 GPa with K _IC of about 10 MPa √m, data clearly out of the range covered so far by other TiB₂-based materials.     

Structure and magnetic properties of the Nd<Subscript>9.5</Subscript>Fe<Subscript>84.5</Subscript>B<Subscript>6</Subscript> alloy subjected to severe plastic deformation and annealing

The effect of severe plastic deformation (SPD) by torsion and subsequent annealing on the structure and magnetic properties of the cast Nd_9.5Fe_84.5B₆ alloy is studied. SPD by torsion is shown to lead to partial amorphization of the Nd₂Fe¹⁴B phase and the precipitation of α-Fe; subsequent annealing results in the crystallization of the amorphous phase and the formation of a nanocomposite Nd₂Fe₁₄B/α-Fe structure. After SPD by torsion at 20 revolutions and annealing at 873 K, the (101) texture is formed; in this case, the coercive force is H _c = 360 kA/m and the maximum energy product is (BH) _max = 166 kJ/m3. The residual magnetization and the squareness ratio of the hysteretic loop of the textured alloy decrease as the ambient temperature decreases.     

Effect of Slag Composition on the Crystallization Kinetics of Synthetic CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO Slags

The crystallization kinetics of CaO-SiO₂-Al₂O₃-MgO (CSAM) slags was studied with the aid of single hot thermocouple technique (SHTT). Kinetic parameters such as the Avrami exponent (n), rate coefficient (K), and effective activation energy of crystallization (E _A ) were obtained by kinetic analysis of data obtained from in situ observation of glassy to crystalline transformation and image analysis. Also, the dependence of nucleation and growth rates of crystalline phases were quantified as a function of time, temperature, and slag basicity. Together with the observations of crystallization front, they facilitated establishing the dominant mechanisms of crystallization. In an attempt to predict crystallization rate under non-isothermal conditions, a mathematical model was developed that employs the rate data of isothermal transformation. The model was validated by reproducing an experimental continuous cooling transformation diagram purely from isothermal data.     

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.     

Morphology-Dependent Hardness of Cr<Subscript>7</Subscript>C<Subscript>3</Subscript>-Ni-Rich Alloy Composite <Emphasis Type="Italic">vs</Emphasis> Orientation Independent Hardness of Cr<Subscript>7</Subscript>C<Subscript>3</Subscript> Primary Phase in a Laser Clad Microstructure

Microstructural evolution with superheating was studied in chromium carbide-nickel coatings deposited by laser cladding. At lower superheating, selective growth of 〈0001〉 direction from the high density of Cr₇C₃ grains nucleated resulted in a columnar structure with (0001) texture. Increased superheating lead to the loss of columnar structure as well as the (0001) texture. The hexagonal Cr₇C₃ showed an unusual isotropic nanoindentation hardness evidently correlated with its low c/a ratio. However, the rod-like morphology of the carbide dendrites resulted in significant anisotropy in the hardness of the composite.     

Microstructure and High Temperature Impression Creep Properties of Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) Alloys

The current study has investigated the influence of zirconium (Zr) addition to Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) alloys prepared using argon arc melting on the microstructure and impression properties at 448–498 K under constant stress of 380 MPa. Microstructural analysis of as-cast Mg–3Ca–xZr alloys showed grain refinement with Zr addition. The observed grain refinement was attributed to the growth restriction effect of Zr in hypoperitectic Mg–3Ca–0.3 wt% Zr alloys. Heterogeneous nucleation of α-Mg in properitectic Zr during solidification resulted in grain refinement of hyperperitectic Mg–3Ca–0.6 wt% Zr and Mg–3Ca–0.9 wt% Zr alloys. The hardness of Mg–3Ca–xZr alloys increased as the amount of Zr increased due to grain refinement and solid solution strengthening of α-Mg by Zr. Creep resistance of Mg–3Ca–xZr alloys increased with the addition of Zr due to solid solution strengthening of α-Mg by Zr. The calculated activation energy (Q_a) for Mg–3Ca samples (131.49 kJ/mol) was the highest among all alloy compositions. The Q_a values for 0.3, 0.6 and 0.9 wt% Zr containing Mg–3Ca alloys were 107.22, 118.18 and 115.24 kJ/mol, respectively.     

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.     

Rare-earth metals (REMs) in nickel aluminide-based alloys: I. Physicochemical laws of interaction in the Ni-Al-REM and Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>-REM-AE (alloying element) systems

The data on the Ni-Al-R (R = REM Sc, Y, La, lanthanides) binary and ternary systems and the interactions of three rare-earth metals (yttrium, lanthanum, cerium) with the main alloying elements (Ti (Zr, Hf), Cr (Mo, W) that are introduced into Ni₃Al-based VKNA alloys are analyzed. The binary aluminides of REMs in the Ni-Al-R ternary systems are shown to be in equilibrium with neither NiAl nor Ni₃Al. The solid solution of aluminum in RNi₅, which penetrates deep into these ternary systems, is the most stable phase in equilibrium with Ni₃Al. In the NiAl (Ni₃Al)-AE-R systems, REM precipitation (segregation) on various defects and interfaces in nickel aluminides is likely to be the most probable, and REMs are thought to interact with the most active impurities in real alloys (C, O, N), since REMs have a large atomic radius and, thus, are virtually undissolved in nickel, aluminum, and nickel aluminides.     

Structure and phase composition of alloys of the Al-Ce-Cu system in the region of the Al-Al<Subscript>8</Subscript>CeCu<Subscript>4</Subscript> quasi-binary join

Phase diagram of the Al-Cu-Ce system is investigated in the region of the quasi-binary join Al-Al₈CeCu₄. The parameter of the eutectic reaction L → (Al) + CeCu₄Al₈ are found: T = 610°C; composition 14% Cu and 7% Ce. This eutectic has a dispersed structure, and the ternary compounds, which is involved in the eutectic, is capable to fragmentation and spheroidism in the course of heating starting from 540°C. It is shown that the region of optimal compositions of alloys based on the eutectic (Al) + CeCu₄Al₈ lies in narrow limits. This is caused by the fact that an abrupt decrease of the solidus and, as a consequence, significant broadening of the crystallization range occurs at a relatively small deviation from the ratio Cu: Ce = 2.     

Crystal and Electronic Study of Neodymium-Substituted CuFeO<Subscript>2</Subscript> Oxide

Neodymium-substituted CuFeO₂ samples were investigated according to their crystal and electronic properties via the general formula Nd _x Cu_1?x FeO₂. The crystal structure analysis results revealed polycrystalline formations in the sample and a change in crystalline sizes with the substituted heavy fermion “Nd.” Increasing the Nd amount in the sample was determined to cause a disturbance on the Cu-Fe planes that supports the formation of crystal structures with low crystal symmetries such as monoclinic or triclinic geometries. To obtain the background mechanisms of the crystal properties, the X-ray absorption fine structure spectroscopy technique was used to study the electronic properties of the samples. Prominent changes in the crystal structures due to 4f electrons’ contributions from the substituted Nd atoms as the main “role player” in the phase transitions were determined. The Nd atoms were observed as the key element guiding the entire phenomenon as a result of their large size and narrow 4f levels. Also, magnetic properties of the samples were tested at room temperature and without an applied magnetic field by X-ray magnetic circular dichroism study due to previous studies that reported the parent oxide CuFeO₂ to have magnetic ordering at T _N = 11 K (?262 °C). Except the sample for x = 1.0 (NdFeO₃), no magnetic ordering was observed at room temperature; i.e., all of the samples showed paramagnetic behaviors.     

Heterogeneous Creep Deformations and Correlation to Microstructures in Fe-30Cr-3Al Alloys Strengthened by an Fe<Subscript>2</Subscript>Nb Laves Phase

A new Fe-Cr-Al (FCA) alloy system has been developed with good oxidation resistance and creep strength at high temperature. The alloy system is a candidate for use in future fossil-fueled power plants. The creep strength of these alloys at 973 K (700 °C) was found to be comparable with traditional 9 pct Cr ferritic–martensitic steels. A few FCA alloys with general composition of Fe-30Cr-3Al-.2Si-xNb (x = 0, 1, or 2) with a ferrite matrix and Fe₂Nb-type Laves precipitates were prepared. The detailed microstructural characterization of samples, before and after creep rupture testing, indicated precipitation of the Laves phase within the matrix, Laves phase at the grain boundaries, and a 0.5 to 1.5 μm wide precipitate-free zone (PFZ) parallel to all the grain boundaries. In these alloys, the areal fraction of grain boundary Laves phase and the width of the PFZ controlled the cavitation nucleation and eventual grain boundary ductile failure. A phenomenological model was used to compare the creep strain rates controlled by the effects of the particles on the dislocations within the grain and at grain boundaries. (The research sponsored by US-DOE, Office of Fossil Energy, the Crosscutting Research Program).     

Fabrication of Porous Ti-rich Ti<Subscript>51</Subscript>Ni<Subscript>49</Subscript> by Evaporating NaCl Space Holder

Net-shaped porous Ti-rich Ti₅₁Ni₄₉ alloy with well-controlled porosity, pore size, and pore shape are fabricated by pressing-and-sintering compacts containing fine Ti and Ni powders and coarse NaCl powders. After sintering at 1323 K (1050 °C) for 30 minutes in a high vacuum, the NaCl space holder is removed by evaporation, and the remaining Ti and Ni powders are sintered with about 2.3 vol pct liquid phase. The sintered Ti₅₁Ni₄₉ compacts have porosities of 26, 64, 70, 78, and 85 pct, and no distortion is observed. DSC tests show that the M _S temperature and ΔH are about 347 K (74 °C) and 28 J/g, respectively, and that they are almost independent of the porosity and close to those of wrought Ti-rich TiNi alloys. These porous Ti₅₁Ni₄₉ compacts exhibit a homogeneous microstructure, and the compressive properties and porosity are close to those of human bones.     

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.