Grain Boundaries Of Matrix Research Articles

Effect of the Thermodynamic Behavior of Selective Laser Melting on the Formation of In situ Oxide Dispersion-Strengthened Aluminum-Based Composites

This paper presents a comprehensive investigation of the phase and microstructure, the thermodynamic behavior within the molten pool, and the growth mechanism of in situ oxide dispersion-strengthened (ODS) aluminum-based composites processed by a selective laser melting (SLM) additive manufacturing/3D printing process. The phase and microstructure were characterized by X-ray diffraction (XRD) and a scanning electronic microscope (SEM) equipped with EDX, respectively. The thermodynamic behavior within the molten pool was investigated for a comprehensive understanding on the growth mechanism of the SLM-processed composite using a finite volume method (FVM). The results revealed that the in situ Al2Si4O10 ODS Al-based composites were successfully fabricated by SLM. Combined with the XRD spectrum and EDX analysis, the new silica-rich Al2Si4O10 reinforcing phase was identified, which was dispersed around the grain boundaries of the aluminum matrix under a reasonable laser power of 200 W. Combined with the activity of Marangoni convection and repulsion forces, the characteristic microstructure of SLM-processed Al2Si4O10 ODS Al-based composites tended to transfer from the irregular network structure to the nearly sphere-like network structure in regular form by increasing the laser power. The formation mechanism of the microstructure of SLM-processed Al2Si4O10 ODS Al-based composites is thoroughly discussed herein.

Enhanced Thermoelectric Performance of Cu₂SnSe₃-Based Composites Incorporated with Nano-Fullerene.

In this study, nano-sized fullerene C60 powder was sufficiently mixed with Cu2SnSe3 powder by ball milling method, and the C60/Cu2SnSe3 composites were prepared by spark plasma sintering technology. The fullerene C60 distributed uniformly in the form of clusters, and the average cluster size was less than 1 μm. With increasing C60 content, the electrical conductivity of C60/Cu2SnSe3 composites decreased, while the Seebeck coefficient was enhanced. The thermal conductivity of composites decreased significantly, which resulted from the phonon scattering by the C60 clusters located on the grain boundaries of the Cu2SnSe3 matrix. The highest figure of merit ZT of 0.38 was achieved at 700 K for 0.8% C60/Cu2SnSe3 composite.

Microwave Synthesis of the Composites (α-Al<sub>2</sub>O<sub>3</sub>+TiB<sub>2</sub>)/NiAl from Al-TiO-B-Ni System

NiAl matrix composites reinforced with a-Al2O3 and TiB2 were fabricated by microwave synthesis from Al-TiO2-B-Ni system. The reaction process and microstructures were analyzed by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM).The results showed that the ignition temperatures of the reaction heating by microwave and conventional method were approximately 556°C and 592°C respectively. Furthermore, the fabrication time by microwave synthesis was about several minutes, which was much shorter than two hours spent usually in conventional heating method. The a-Al2O3 phase aggregated at the trigonal grain boundary of the NiAl matrix, and the TiB2 phase distributed uniformly in the NiAl matrix.

Effects of alloyed Si on the oxidation behaviour of Co–29Cr–6Mo alloy for solid-oxide fuel cell interconnects

To evaluate the suitability of the Co–29Cr–6Mo alloy as an interconnect in solid-oxide fuel cells (SOFCs), the oxidation behaviour of Co–29Cr–6Mo alloys with various Si concentrations was investigated in air at 700–1000°C. The presence of alloyed Si improved the oxide-scale adhesion by promoting the formation of a continuous Cr2O3 film. The SiO2 particles in the inner layer and the grain boundaries of alloy matrix beneath the inner layer inhibited the inward oxygen diffusion and outward chromium diffusion. The results indicate that the Co–29Cr–6Mo alloy with added Si is appropriate for SOFC applications.

Annealing Effect on the Structural and Magnetic Properties of Granular Cu80Fe10Ni10 Ribbons

We report on the effect of annealing process on the structural and magnetic properties of granular Cu80Fe10Ni10 ribbons prepared by melt spinning technique. Energy-filtered transmission electron microscopy measurements show that the precipitates (Fe10Ni10) are localized at the grain boundaries of the Cu matrix for the non-annealed samples. After an annealing treatment at 600 °C, a strong diffusion of the precipitates within the Cu matrix is observed. The temperature dependence of magnetization has been analyzed using the Bloch law. Spin wave stiffness constant D and the exchange constant A were calculated from the experimental results. Furthermore, we show that the random magnetic anisotropy (RMA) model is applicable to describe the experimental results. Other fundamental parameters have also been calculated using the approach to saturation magnetization. Ab initio calculations based on Korringa-Kohn-Rostocker (KKR) method are carried out in order to characterize both electronic and magnetic properties.

Influence of Al2O3 particles on the microstructure and mechanical properties of copper surface composites fabricated by friction stir processing

The influence of three factors, such as volume percentage of reinforcement particles (i.e. Al2O3), tool tilt angle and concave angle of shoulder, on the mechanical properties of Cu–Al2O3 surface composites fabricated via friction stir processing was studied. Taguchi method was used to optimize these factors for maximizing the mechanical properties of surface composites. The fabricated surface composites were examined by optical microscope for dispersion of reinforcement particles. It was found that Al2O3 particles are uniformly dispersed in the stir zone. The tensile properties of the surface composites increased with the increase in the volume percentage of the Al2O3 reinforcement particles. This is due to the addition of the reinforcement particles which increases the temperature of recrystallization by pinning the grain boundaries of the copper matrix and blocking the movement of the dislocations. The observed mechanical properties are correlated with microstructure and fracture features.

BaZr0.85-xPdxY0.15O3-δ/ Carbonates 복합전도체 전기적 특성 연구

PdO-doped BaZr 0.85-x Pd x Y 0.15 O 3-δ (BZPY) proton conductors have been proposed as applicable for intermediate temperature electrolytes for protonic ceramic fuel cells (PCFCs) because the PdO doping is effective for improving the proton conductivity of BaZr 0.85-x Pd x Y 0.15 O 3-δ (BZY) with high affinity for hydrogen. In order to further improve the conductivity of BZPY, two-phase composite electrolytes consisting of a BZPY and molten carbonate were designed. Dense BZPY-based composite electrolytes were fabricated after sintering at 670oC for 4 h, since molten carbonates fill the grain boundary of the porous BZPY matrix. Furthermore, BZPY/(Li-0.5Na) 2 CO 3 composites show a significantly enhanced protonic conductivity at intermediate temperatures. This may be because easy proton transport is possible through the interface of the carbonate and oxide phase.

Zirconia–alumina–nanodiamond composites with gemological properties

Nanodiamonds have excellent mechanical and optical properties with a wide range of potential applications as a filler material for nanocomposites. Here, we present a new family of zirconia–alumina–nanodiamond composites using two main processing routes: (1) a colloidal method, and (2) power mixing homogenization. Composites with detonation nanodiamonds quantities ranging within 0.3–5 vol.% followed by a pulsed electrical current sintering at a temperature range from 1,200 to 1,500 °C have been analyzed, and a significant enhancement in mechanical properties, i.e., indentation hardness (16.17 GPa), fracture toughness (15.5 MPa m1/2), and bending strength (1,600 MPa), could be observed. To support these excellent properties, TEM, color, reflectivity, and Raman spectroscopy measurements were also carried out. The microstructure of the composites is very homogeneous with average grain sizes between 200 and 500 nm depending on the processing temperature. Two morphologies are present: (a) intergranular dispersion of alumina grains and nanodiamonds distributed along the grain boundaries of the ZrO2 matrix, and (b) intragranular nano-dispersion of ZrO2 particles with sizes 20–80 nm located inside the alumina grains. In the present article, we show, for the first time in the scientific literature, a continuous palette of gray color gradation of new ceramic materials of metalized colors (white index L* 98–40) for gemological applications.

A Novel Approach for Fabrication of Cu-Al2O3 Surface Composites by Friction Stir Processing

In this study Copper- Al2O3 surface composites are produced with different volume percentages using micron sized particles via friction stir processing in order to enhance surface mechanical properties. Tool rotational speed and traverse speeds were fixed at 900rpm and 40mm/min respectively. The fabricated surface composites have been examined by optical microscope for dispersion of reinforcement particles and found that Al2O3 particles are uniformly dispersed in the stir zone. It is also observed that the microhardness at the higher volume percentage increases due to presence of hard Al2O3 particles. The tensile properties of the surface composites increased with the increase in the volume percentage of the Al2O3 particles. This is due to the addition of the reinforcement particles which increases the temperature of recrystallization by pinning of grain boundaries of the copper matrix and blocking the movement of the dislocations. The observed mechanical properties have been correlated with microstructure and fracture features.

The effect of manganese on phase formation and properties of Bi2212 ceramics

In this work we present a systematic study of the Mn influence superconducting properties. Attempts have been made to identify the optimum inclusion of MnO2 in Bi2Sr2Ca1Cu2O8+δ superconductors. The phase formation, texture and grain alignments were analysed by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry (SEM, EDS) and electrical resistivity. It was found that Mn addition has affected the formation of the desired Bi-2212 phase and the microstructure of these samples thereby influencing on the resistivity. The resistivity of all the Bi2Sr2Mn x Ca1Cu2O8+δ samples shows metallic behaviour. It reveals that, 4 wt% composite exhibits a better superconducting property in comparison with pure BSCCO. It has been observed that Mn residing at the grain boundary of BSCCO matrix influences the tailing region with having significant change in the critical temperature. The microstructures observed by SEM indicate segregation of an additional phase. The EDS revealed that this phase is stoichiometric. The results show that the doping leads to a reduction of cell volume as well as the c axis.

The Microstructures and Mechanical Properties of V2O5-Doped Al2O3/TiAl In-Situ Composites by Reactive Hot Pressing Process

Al2O3/TiAl composites are successfully fabricated by the in-situ hot pressing method from the elemental powders of Ti, Al, TiO2, and V2O5. The effect of V2O5 addition on the microstructure and mechanical properties of the Al2O3/TiAl in-situ composites is investigated in detail. It is found that the as-synthesized composites mainly consist of V-dissolved γ-TiAl, α2-Ti3Al, and Al2O3 particles along with a small amount of V3Al phase, and the in-situ-formed fine Al2O3 particles tend to disperse on the grain boundaries of TiAl matrix. With increasing V2O5 content, the density and Vickers hardness of the resulting composites gradually increase, whereas the fracture toughness and flexural strength first increase and then decrease with the increase of V2O5 content. The composite with 3.5 wt.% V2O5 has the maximum value of 9.35 MPa m1/2 and 713.36 MPa for the fracture toughness and flexural strength, respectively. The toughening mechanism is also discussed in detail.

Synthesis of Al2O3 nanoparticles highly distributed in YBa2Cu3O7 superconductor by citrate–nitrate auto-combustion reaction

The effects of Al2O3 nanoparticles on the structure and superconducting properties of YBa2Cu3O7-δ matrix prepared by auto-combustion reaction were investigated. The auto-combustion reaction has successfully transformed the Al nitrate added YBCO precursor gels to very fine ashes which yielded to Al2O3 and YBCO phases after the calcination process at 900°C. The resultant reactions produced nanocrystalline YBa2Cu3O7-δ powders having well distributed Al2O3 nanoparticles (∼10nm). The TG/DTA analysis reveals that the Al nitrate added precursor gels decomposed by two-steps reaction at temperature of 180 and 220°C due to the decomposition of Al nitrate followed by Y, Ba and Cu nitrates. The XRD pattern showed the orthorhombic structure of Al2O3 added YBa2Cu3O7-δ powders having the particle size ranged in between 20 and 25nm. SEM analysis showed that Al2O3 nanoparticles were distributed along the grain boundaries of YBa2Cu3O7-δ matrix for the higher mol of Al nitrate. The higher concentration of Al2O3 reacts with the YBa2Cu3O7 matrix to form Al3+ rich spots and diffuse within the YBa2Cu3O7-δ superconducting matrix which was confirmed by EDX analysis. The samples produced in this work were electrically superconducting at temperature above 85K as measured by using standard four-probe technique. Formation of alumina precipitates and incorporation of Al3+ into YBa2Cu3O7-δ structure was found to significantly reduce the Tc of pure YBa2Cu3O7-δ.

Spatial Distribution of Cementite Particles in Fe-0.67% C Steel

The particles arrangement in material space is represented by point field determined by the particle reference points, i.e., particle centers which can be described by the pair-correlation function (PCF) g3(r); r - correlation distance. Information about g3(r) can be obtained by stereological method based on the PCF g2(r), which describes the point field on the planar section determined by the centers of particle planar sections. In this paper the arrangement of cementite (Fe3C) particles during coarsening in Fe - 0,67%C steel at 715ºC in a form of two materials (A, B) of different microstructure of the coarse spheroidite (with different matrix grain size and particles position) was investigated. In material A, the particles are mainly at grain (subgrain) boundaries of fine-grained matrix. In material B, particles are mainly inside grains of coarse-grained ferrite. For material A, the empirical PCF g2(r) for a long time of coarsening (600 hours) is shifted towards larger r and is more flat near the g2(r) =1 than the one of coarsening for 50 hours. For material B, the g2(r) for both annealing times are not significantly different. This is consistent with the results of the probability density function f2(d) analysis for diameter (d) of the particle sections. Obtained PCF g2(r) are similar to the PCF g2(r) for planar section of the Stienen model. This means that for both type of microstructures the PCF - g3(r) =1, i.e., particles are distributed randomly in space and the sizes of the neighboring particles are correlated with each other.

Synthesis and thermoelectric properties of CoSb3/WO3 thermoelectric composites

In this study, nano-sized WO3 powder was dispersed into CoSb3 powder by ball milling and CoSb3/WO3 thermoelectric composites were fabricated using hot-pressing sintering. The results showed that the WO3 phase distributed uniformly in the form of clusters and the average size of cluster was lower than 4 μm. As the content of WO3 increased, the electrical conductivity and Seebeck coefficient of CoSb3/WO3 composites decreased. The thermal conductivity of composites decreased obviously which resulted from the phonon scattering by the WO3 inclusions locating on the grain boundaries of CoSb3 matrix. The highest thermoelectric figure of merit ZT = 0.40 was achieved at 650 K for CoSb3/2%WO3 composite.

Analysis of phase in Cu–15%Cr–0.24%Zr alloy

The vacuum medium-frequency induction melting technology was employed to prepare the Cu–15%Cr–0.24%Zr alloy. The scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to analyze the phase composition, morphology and structure of the alloy. The results reveal that the as-cast structure of the alloy consists of Cu matrix, Cr dendrite, eutectic Cr and Zr-rich phase. A large number of Cr-precipitated phases occur in the Cu matrix, and Cu5Zr particles can be found in the grain boundary of Cu matrix. The HRTEM images prove that there is a semi-coherent relationship between Cu5Zr and Cu matrix.

Effect of Sn addition on microstructure, mechanical and casting properties of AZ91 alloy

In this study, effect of Sn addition on microstructure, mechanical and the casting properties of AZ91 magnesium alloy have been studied. Results from the microstructural analysis showed that refinement of Mg17Al12 phase took place and new Mg2Sn phase was formed as Sn was added into the AZ91 alloy. Fluidity increased with 0.5wt.% Sn content then decreases rapidly as the Sn content exceeded above 0.5wt.%. Hot tear susceptibility (HTS) decreased with 0.5wt.% Sn addition to AZ91 magnesium alloy above which it increased considerably. Tensile strength and elongation increased by addition of up to 0.5wt.% Sn above which it decreased with increasing Sn content. The increase of mechanical properties was attributed to transformation of lamellar to fully divorced eutectic β phases by 0.5wt.% Sn addition existed in grain boundaries of the magnesium matrix. The reduction in the mechanical properties above 0.5wt.% Sn was attributed to formation of clustered Mg2Sn phase.

Recovery of mechanical strength by surface crack disappearance via thermal oxidation for nano-Ni/Al2O3 hybrid materials

Recovery of mechanical strength as a function of heat-treatment temperature and time was investigated in α-Al2O3-based hybrid materials containing with 5vol% dispersed Ni nanoparticles (nano-Ni/Al2O3) via fraction of surface crack disappearance. Surface cracks introduced by Vickers indentation disappeared completely because of the oxidation product NiAl2O4. Bending strengths of as-sintered and as-cracked samples were 490±58 and 180±15MPa, respectively. Heat-treatment at 1000°C for 1h resulted in recovery of bending strength up to 550±190MPa with 10% fraction of crack disappearance. The bending strength of samples heat-treated at higher temperatures or for longer durations was comparable with that of the as-sintered samples. Bending strength reached and remained at approximately 604MPa when the fraction of surface crack disappearance was over 55%. As-recovered samples did not fracture at the surface cracks during the three-point bending test. Thus, recovery of mechanical strength was achieved by partial disappearance of the surface cracks.This observed recovery of mechanical strength was caused by a reduction in stress concentration at crack-tips covered with NiAl2O4 formed from Ni2- along grain boundaries of the Al2O3 matrix.

Study on excess magnetoconductivity in (1−x)YBa2Cu3O7 + xBaTiO3 composites

(1−x)YBa2Cu3O7+xBaTiO3 composites were synthesized following the standard solid state reaction route. Analysis of the resulting morphological structure confirmed that BaTiO3 resides at the grain boundary of the granular matrix of YBCO. Fluctuation conductivity obtained for zero magnetic field confirms that superconducting region is affected by the BaTiO3 incorporation. The values of the crossover temperature from 2D to 3D behavior are found to shift towards higher temperatures with increasing BaTiO3 concentration. The excess magnetoconductivity measured at 8T revealed a dimensionality crossover in accordance with the Aslamazov–Larkin theory. The overall analysis of the obtained experimental results suggests manifestation of Gaussian, critical and short wavelength type fluctuations in the behavior of the observed paraconductivity.

Quantifying boundary effect of nanoparticles in metal matrix nanocomposite fabrication processes

Lightweight, high-strength Metal Matrix NanoComposites (MMNCs) are promising materials for use in automotive, aerospace, and numerous other applications. A uniform distribution of nanoparticles within the metal matrix is critical to the quality of such composites. In current MMNC fabrication processes, however, a boundary effect often occurs where the nanoparticles tend to gather around the grain boundaries of the metal matrix. To realize quality control and guide process improvement efforts, this article proposes a method for quantitatively assessing the boundary effect observed in microstructure images of MMNC samples based on the theory of spatial statistics. Two indices for quantifying the degree of boundary effect in an image, called Boundary Indices (BIs), are developed and their statistical properties are provided. The performances of the BIs are shown and compared in a numerical study. They are also applied to images from a real MMNC fabrication process to validate the effectiveness of the proposed method.

Study on Effect of Different Preparation Process Parameters on Properties and Microstructure of SiO<sub>2</sub>/Cu Composites

The SiO2 nanoparticles reinforced Cu-matrix composites were prepared by powder metallurgy technology．The influences of SiO2 volume fraction on the properties of hardness、conductivitity rate and wear behavior of Cu-matrix composites were studied. The results showed that conductivity rate was decreased with the increase of the SiO2 volume fraction；whereas the hardness was increased, then decreased and wear behavior was increased. Sintering an hour of performance was superior to the sintering half an hour.When SiO2 nanoparticle volume fraction was achieved 2.5%, comprehensive properties of SiO2/Cu composite were obviously increased.The microstructures revealed that the second phase particles precipitated dispersedly in copper matrix after hot extrusion. with the increase of the strengthen phase particle volume fraction, nanoparticles appeared together and gathered in grain boundary of copper matrix.