Grain Growth Inhibition Research Articles

Effect of the Mg<sup>2</sup><sup>+</sup> Substitution on the Sintering Behavior and Compressive Strength of Doped Β-TCP/CPP Ceramics

β-Tricalcium phosphate (β-TCP) ceramics are of interest for bone requirements implants due to resoption behavior. The mechanical properties of β-TCP, however, are not yet sufficient to allow load bearing application of implants. The aim of this work was to investigate the effect of Mg2+substitution on the strength sintered TCP. Due to promotion of a liquid phase at 1200°C, Calcium pyrophosphate (CPP-C2P2O7) was used to improve the sintering of the samples. The introduction of CPP was promoted by use of a Ca/P molar ratio of 1.45. The powders were synthesized using a mixture of Ca (OH)2suspension and diluted H3PO4with addition of MgO and calcined at 750 °C, 900 °C and 1050 °C. The cold isostatic pressing compacts were sintered at 1200 °C and 1300 °C, respectively.It was shown that a small Mg content (1.5 mol%) increased both compressive strength and fractional density of the TCP material sintered at 1200 °C from 132 ± 39 MPa at 92.1 % of fractional density to 193 ± 29 MPa at 94.5 % of theoretical density. Higher amounts of Mg inhibited the grain growth provoking a increase of the boundary mobility activation energy. Abnormal grain growth (AGG) was observed after sintering at 1300°C, as result CPP - liquid phase formation. Increase of Mg content promoted AGG, due to inhibition of grain growth during normal grain growth resulting in a increase of the residual elastic energy of the system.

Nearly amorphous Mo-N gratings for ultimate resolution in extreme ultraviolet interference lithography

We present fabrication and characterization of high-resolution and nearly amorphous Mo1 − xNx transmission gratings and their use as masks for extreme ultraviolet (EUV) interference lithography. During sputter deposition of Mo, nitrogen is incorporated into the film by addition of N2 to the Ar sputter gas, leading to suppression of Mo grain growth and resulting in smooth and homogeneous thin films with a negligible grain size. The obtained Mo0.8N0.2 thin films, as determined by x-ray photoelectron spectroscopy, are characterized to be nearly amorphous using x-ray diffraction. We demonstrate a greatly reduced Mo0.8N0.2 grating line edge roughness compared with pure Mo grating structures after e-beam lithography and plasma dry etching. The amorphous Mo0.8N0.2 thin films retain, to a large extent, the benefits of Mo as a phase grating material for EUV wavelengths, providing great advantages for fabrication of highly efficient diffraction gratings with extremely low roughness. Using these grating masks, well-resolved dense lines down to 8 nm half-pitch are fabricated with EUV interference lithography.

Grain growth, densification and electrical properties of lead-free piezoelectric ceramics from nanocrystalline (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 powder by sol–gel technique

The sintering behavior revealed in the sintering processes of the conventional and a two-step process and electrical properties of the (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 ceramics from the nanocrystalline powders synthesized by a sol–gel technique were systematically studied. It was found that the sintering process of the (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 ceramics made from nanocrystalline powders was significantly improved, the sintering temperature was reduced markedly from 1,540 to 1,280 °C, as well as a high relative density (>97 %) was obtained in the conventional sintering. Under the two-step sintering conditions, the full densification and the most suppression of grain growth was achieved simultaneously. The (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 ceramics from nanocrystalline powders sintered by the two-step sintering technique (sintered at T1 of 1,300 °C for 1 min and T2 of 1,150 °C for 20 h) exhibited the optimum average grain size of 700 nm and a high relative density of 98 %. The electrical properties of the (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 ceramics were greatly influenced by the grain size and phase structure formed under the both sintering conditions, with sintering temperature and grain size increased, the electrical properties of the (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 ceramics, which made from nanocrystalline powders, shows an enhancing trend: d33 ~100 pC/N, kp ~53.3 % for the specimen sintered at 1,300 °C for 1 min and 1,150 °C for 20 h, d33 ~310 pC/N, kp ~53.3 % for the specimen sintered at 1,350 °C for 2 h respectively.

Structural and optoelectronic properties of indium doped SnO2 thin films deposited by sol gel technique

Indium doped tin oxide (SnO2:In) thin films were deposited on glass substrates by sol–gel dip coating technique. X-ray diffraction pattern of SnO2:In thin films annealed at 500 °C showed tetragonal phase with preferred orientation in T (110) plane. The grain size of tin oxide (SnO2) in SnO2:In thin films are found to be 6 nm which makes them suitable for gas sensing applications. AFM studies showed an inhibition of grain growth with increase in indium concentration. The rms roughness value of SnO2:In thin films are found to 1 % of film thickness which makes them suitable for optoelectronic applications. The film surface revealed a kurtosis values below 3 indicating relatively flat surface which make them favorable for the production of high-quality transparent conducting electrodes for organic light-emitting diodes and flexible displays. X-ray photoelectron spectroscopy gives Sn 3d, In 3d and O 1s spectra on SnO2:In thin film which revealed the presence of oxygen vacancies in the SnO2:In thin film. These SnO2:In films acquire n-type conductivity for 0–3 mol% indium doping concentration and p type for 5 and 7 mol% indium doping concentration in SnO2 films. An average transmittance of >80 % (in ultra-violet–Vis region) was observed for all the SnO2:In films he In doped SnO2 thin films demonstrated the tailoring of band gap values. Photoluminescence spectra of the films exhibited an increase in the emission intensity with increase in indium doping concentration which may be due structural defects or luminescent centers, such as nanocrystals and defects in the SnO2.

Effect of Suppression of Grain Growth of Hot Extruded (Bi0.2Sb0.8)2Te3 Thermoelectric Alloys by MoS2 Nanoparticles

Nanostructured bulk materials are regarded as a means of enhancing the performance of thermoelectric (TE) materials and devices. Powder metallurgy has the distinct advantage over conventional synthesis that it can start directly from nanosized particles. However, further processing, for example extrusion, usually requires elevated temperatures, which lead to grain growth. We have found that introduction of semiconductor nanoparticles of molybdenum disulfide (MoS2), a well-known solid lubricant, suppresses grain growth in bismuth telluride-based alloys, thus improving the extrusion process. Scanning electron microscope images show that adding MoS2 particles at concentrations of 0.2, 0.4, and 0.8 wt% to p-type (Bi0.2Sb0.8)2Te3, under otherwise identical extrusion conditions, reduces average grain size by a factor of four. Scherer’s formula applied to x-ray diffraction data indicates that average crystallite sizes (∼17 nm) of powders are not significantly different from those of alloys extruded with MoS2 (∼18 nm), which is in stark contrast with those for conventional alloy (Bi0.2Sb0.8)2Te3 extruded under the same conditions (∼80 nm). Harman measurements of TE properties reveal a decrease of the thermal conductivity accompanied by reduction of the room-temperature figure of merit (ZT) from 0.9 to 0.7, because of a lower power factor. Above 370 K, however, the performance of alloys containing MoS2 surpasses that of (Bi0.2Sb0.8)2Te3, with reduction of the thermal conductivity which is more significant at temperatures above the cross point of the ZT values.

3%Si鋼中のMnS，MnSeおよびAlNとの複合析出と粒成長抑制効果

The precipitation behavior of MnS, MnSe and AlN in 3% Si steel was investigated for understanding inhibition of grain growth under isothermal annealing. It became clear that the precipitation of AlN was greatly influenced by that of MnSe. The precipitates became fine when hot-rolled at low temperature, and therefore the grain size after the recrystallization annealing became small. Similarly, the grain size after the isothermal annealing became small when the precipitates became fine. When MnS or MnSe precipitates formed complex with AlN, Ostwald ripening was suppressed, as a result, grain growth was inhibited.

Simultaneous Synthesis and Consolidation of Nanostructured MgSiO<sub>3</sub>–Mg<sub>3</sub>Al<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> Composite and Its Mechanical Properties

Nanopowders of MgO, Al2O3 and SiO2 were made by high energy ball milling. The simultaneous synthesis and consolidation of nanostuctured MgSiO3­Mg3Al2Si3O12 composites from milled 4MgO, Al2O3 and 4SiO2 powders was investigated by the high-frequency induction heated sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured MgSiO3­Mg3Al2Si3O12 composites were produced with a simultaneous application of 80MPa pressure and an induced current within 1min. The microstructure, sintering behavior and mechanical properties of MgSiO3­ Mg3Al2Si3O12 composite were evaluated. [doi:10.2320/matertrans.M2014018]

Synthesis and ceramization of polycarbosilane containing beryllium

Polycarbosilane containing beryllium (BPCS) precursors was prepared by the reaction of polycarbosilane (PCS) with beryllium acetylacetone (Be (acac)2). The analysis of structures and components of BPCS demonstrates that their main structures are basically the same as PCS. Ceramization of BPCS precursors shows that BPCS precursors are organic below 600 °C and inorganic at 800 °C. At 1400 °C, BPCS precursors convert into silicon carbide ceramics. The ceramization of different beryllium content precursors were studied, which show that beryllium plays an important role in the inhibition of crystalline grain growth of β-SiC at high temperature and it can adjust the dielectric constant of silicon carbide ceramics.

CeO2가 졸겔법으로 합성한 CeO2-TiO2계 SCR용 촉매의 활성에 미치는 물리화학적 영향

The effects of CeO2 on catalytic activity of CeO2-TiO2 for the selective catalytic reduction (SCR) of NOx were investigated in terms of structural, morphological, and physico-chemical analyseis. CeO2-TiO2 catalysts were synthesized with three different additions, 10, 20, and 30 wt% of CeO2, by the sol-gel method. The XRD peaks of all specimens were assigned to a TiO2 phase (anatase) and the peaks became broader with the addition of CeO2 because it was dispersed as an amorphous phase on the surface of TiO2 particles. The specific surface area of TiO2 increased with the addition of CeO2 from 60.6306 m 2 /g to 116.2791 m 2 /g due to suppression of TiO2 grain growth by CeO2. The 30 wt% CeO2-TiO2 catalyst, having the strongest catalytic acid sites (BrΦnsted and Lewis), showed the highest NOx conversion efficiency of 98 % at 300 o C among the specimens. It was considered that CeO2 contributes to the improvement of the NOx conversion of CeO2-

Experimental and Simulation Studies on the Solid-Particle Erosion of WC-MgO Composites

This article reports our recent studies on WC-4.3 wt% MgO composites with a particular interest in the effect of grain-growth inhibitors (VC and Cr3C2) addition on its resistance to erosive wear. It is shown that the maximum erosion rate of the WC-MgO composite occurred at an impingement angle of 90°. With the addition of the grain-growth inhibitors (0.25 wt% VC and 0.25 wt% Cr3C2), the erosion resistance increased, particularly profound at the impingement angle of 90°, due to refined microstructures with improved mechanical properties. In addition, computational simulation based on a microscale dynamic model was conducted to investigate the effects of the grain boundary strength and grain size on the erosion resistance of the WC-MgO composites in order to better understand the microstructural effect on the erosive performance of the composites. It is demonstrated that the grain refinement with weak grain boundary strength has a negative effect on the erosion resistance.

Change in microstructures and physical properties of ZrB2–SiC ceramics hot-pressed with a variety of SiC sources

ZrB2–SiC ceramics were fabricated by hot pressing with a variety of SiC sources in order to examine the effect of the SiC size on the microstructures and physical properties, such as hardness and thermal conductivities, of ZrB2–SiC composite ceramics. Three different ZrB2–SiC ceramics, ZPS (ZrB2–20vol% polycarbosilane), ZFS (ZrB2–20vol% fine-grained SiC), and ZNS (ZrB2–20vol% nano-sized SiC), were prepared for this study. PCS is effectively transformed into β-SiC after hot pressing. By using PCS as a precursor for SiC, ZrB2 particles are surrounded by fine particles of SiC, which results in the grain-growth inhibition of ZrB2. The effects of the SiC size on the microstructures and the physical properties of ZrB2–SiC ceramics were also investigated. ZrB2–SiC ceramics were produced by using various SiC sources in order to investigate the grain-growth inhibition and the mechanical/thermal properties of ZrB2–SiC. The sizes of ZrB2 or SiC particles in the sintered bodies highly depend on the initial size of SiC. ZrB2–SiC ceramics with smaller SiC show enhanced mechanical properties, consistently with the Hall–Petch relation. The thermal conductivities of ZrB2–SiC ceramics with nano-SiC or PCS-derived SiC are higher than that of ceramics with conventional SiC, which can be explained by the percolation theory.

Properties and pulsed current activated consolidation of nanostuctured MgSiO3-MgAl2O4 composites

Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. Nanopowders of MgO, Al2O3 and SiO2 were made by high energy ball milling. The simultaneous synthesis and consolidation of nanostuctured MgAl2O4-MgSiO3 composites from milled 2MgO, Al2O3 and SiO2 powders was investigated by the pulsed current activated sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured MgAl2O4-MgSiO3 composites were produced with a simultaneous application of 80 MPa pressure and a pulsed current of 2000A within 1min. The fracture toughness of MgAl2O4-Mg2SiO4 composites sintered from 60 mol%MgO-20 mol%Al2O3-20mol%SiO2 powders milled for 4 h was 3.2MPa·m1/2. The fracture toughness of MgAl2O4-MgSiO3 composite is higher than that of monolithic MgAl2O4.

Effects of extrusion speed on the microstructure and mechanical properties of ZK60 alloys with and without 1 wt% cerium addition

The effects of extrusion speed on the microstructure and tensile properties of the ZK60 and ZK60-1Ce alloys were investigated by performing indirect extrusion at three ram speeds (0.3, 1.0 and 3.0mm/s). All of the extruded alloys showed a bimodal microstructure consisting of equiaxed fine recrystallized (DRXed) grains and elongated coarse unDRXed grains. With increasing extrusion speed, the exit temperature increased due to deformation heating, resulting in a larger grain and a higher DRXed fraction. The yield and ultimate tensile strengths and elongation at RT decreased with an increase of extrusion speed. The ZK60-1Ce alloys exhibited a finer grain size, a higher DRXed fraction, and weaker texture intensity than the ZK60 alloys at the same extrusion speed due to the inhibition of grain growth by the pinning effect and the promotion of DRX by particle-stimulated nucleation. The yield and ultimate tensile strengths at room and elevated temperatures were increased by the addition of Ce, while elongation was decreased due to cracking at the Mg–Zn–Ce particles.

CaO 첨가에 의한 AZ31 합금 미세조직의 열적 안정성 변화

Grain growth behaviors of hot-rolled AZ31 (Mg-3%Al-1%Zn) and AZ31-0.3%CaO alloys at elevated temperatures have been investigated in order to clarify the effect of CaO addition on grain stability of Mg-Al-based wrought alloy. The grain size of CaO-free alloy increased steeply from 673 K with an increase in annealing temperature from 573 to 773 K, whereas the grains of CaO-containing alloy were relatively stable up to 723 K. The activation energies for grain growth (<TEX>$E_g$</TEX>) were 12.2 and 18.3 kJ/mole between 573 and 673 K and 119.2 and 126.9 kJ/mole between 673 and 773 K in the AZ31 and AZ31-0.3%CaO alloys, respectively. This result indicates that grains in the CaO-added alloy possess higher thermal stability than CaO-free alloy. SEM observations on the annealed alloy samples revealed that higher grain stability resulting from CaO addition would be associated with the suppression of grain growth by Ca-related precipitate particles distributed in the microstructure.

Effects of Ni doping on ferroelectric and ferromagnetic properties of Bi0.75Ba0.25FeO3

Abstract Variants of Ni-added Bi 0.75 Ba 0.25 FeO 3 (BBFO) multiferroic ceramic were prepared by the sol–gel method. The first variation line was the synthesis of Bi 0.75 Ba 0.25 Fe 1− x Ni x O 3 ( x =0, 0.025) solid solutions. The second variation was the preparation of BBFO impregnated with nickel oxide. Synthesized materials were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Ferroelectric and ferromagnetic measurements were conducted as well. XRD data suggest the coexistence of a rhombohedral and a tetragonal phase when Ba 2+ and Ni 2+ cation substitutions are present. Ni acts as an inhibitor of grain growth and coalescence. After sintering, it reduces the average size from 88 nm to 67 nm. Furthermore, the presence of the Ni 2+ cation in the Bi 0.75 Ba 0.25 Fe 0.975 Ni 0.025 O 3 octahedral position increases the saturation magnetization and suppresses the leakage current, which dampens the ferroelectric character of the non-doped perovskite family of BBFO. The Ni-doped BBFO ceramic achieves an interesting compromise between ferromagnetic and ferroelectric properties.

Microstructure and physical properties of sol gel derived SnO2:Sb thin films for optoelectronic applications

Antimony doped tin oxide thin films were deposited on glass substrates by sol-gel dip coating technique. X-ray diffraction pattern showed the deterioration of the crystallinity of the films with increase in antimony doping concentration. Atomic force microscopy studies showed an inhibition of grain growth with increase in Sb concentration.The rms roughness value of SnO2:Sb thin films are found to 1% of film thickness which makes them suitable for optoelectronic applications. The film surface revealed positive skewness and high kurtosis values which make them favorable for tribological applications. The lowest resistivity (about10−5Ωm) was obtained for the 5mol% Sb doped SnO2: Sb films. These films acquire n-type conductivity due to non- stoichiometry (oxygen vacancies and interstitial tin atoms) and by the addition of Sb. The optical properties of the films have been studied from transmission spectra. An average transmittance of >80% (in UV–vis region) was observed for all the films. Optical band gap energy of SnO2:Sb films were found to vary in the range of 3.69–3.97eV with the increase in Sb doping concentration. Photoluminescence spectra of the films exhibited an increase in the emission intensity with increase in antimony doping concentration which is due the combined effect of charge balance and decrease in grain size. The enhancement of PL intensity in the antimony doped SnO2 thin films make it suitable for generation of solid state lighting in light emitting diode.

Suppression of abnormal grain growth in fine grained polycrystalline diamond materials (PCD)

During the sintering of fine grained (0.5μm) polycrystalline diamond (PCD) composite materials under high pressure-high temperature (HPHT) conditions, abnormal grain growth (AGG) of the diamond was observed. These abnormally grown diamond grains were up to several hundreds of microns in diameter. Diamond enhanced carbide substrates were used to suppress the abnormal grain growth. Electron backscattered diffraction was used to obtain grain orientation of the single crystals. The AGG was explained in a framework of the changed driving forces of the grain growth due to different initial carbon concentrations in the melt, particle size distribution and growth mechanisms.

Mechanical Properties and Fracture Behavior of Hot Extruded Mg-5Al-3Ca-xNd Alloys at Elevated Temperature

In this study, effects of Nd addition on mechanical properties and fracture behaviors of as-extruded Mg-5Al-3Ca based alloy were investigated by a tensile test at elevated temperatures. For all temperatures, addition of Nd elements resulted in further increase of strength both yield and ultimate strength compared to the Mg-5Al-3Ca alloy. At 150°C, the ductility in Nd-added alloys is lower than that of no-Nd addition alloy. However, at 250°C, the ductility in Nd-added alloys is improved for no-Nd addition alloy because of fine grain and suppression of grain growth by formation of thermally stable Al2Nd intermetallic compounds.

Properties of Nanostructured TiCN and TiCN&amp;ndash;TiAl Hard Materials Sintered by the High-Frequency Induction-Heating

In the case of cemented TiCN, Ni or Co is added as a binder for the formation of composite structures. However, the high cost of Ni or Co and the low corrosion resistance of the TiCN­Ni cermet have generated interest in recent years for alternative binder phases. In this study, TiAl was used as a binder and consolidated by the high-frequency induction heated sintering (HFIHS) method. Highly dense TiCN­TiAl with a relative density of up to 100% was obtained within 2min by HFIHS under a pressure of 80MPa. The method was found to enable not only the rapid densification but also the inhibition of grain growth preserving the nano-scale microstructure. The average grain sizes of the sintered TiCN and TiCN­TiAl were lower than 100nm. The addition of TiAl to TiCN enhanced the hardness and toughness due to increase of relative density. [doi:10.2320/matertrans.M2013200]

Microstructural control of macroporous silicon carbide

Wide range of porosity in 30–90 vol % could be created into silicon carbide by employing carefully selected manufacturing methods. Two fabrication methods have been proposed and reviewed in the present paper: (1) partial sintering of submicrometer-sized silicon carbide particle with a suitable amount of sintering additive, acting as an inhibition of grain growth during sintering; (2) the use of ice crystals, as sacrificial pore formers, formed by freezing a silicon carbide particle dispersed gel body, leading to highly porous silicon carbide after sublimating ice crystals by vacuum drying and subsequently sintering. Depending on the processing route adopted, average pore size could be modulated in the range from 0.03 to 0.70 µm and 30 to 150 µm by partial sintering and gelation freezing, respectively. All fabrication methods proposed are simple, economical and versatile to produce macroporous body with tailored pore architecture and engineering porosity.