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Ni 0.26 Cu 0.22 Zn 0.52 Fe 2 O 4 ferrites doped with different Bi 2 O 3 contents (0–2.0 wt% in intervals of 0.5 wt%) were successfully prepared by conventional solid-state reaction method at 920 °C. The phase composition, microstructure, and magnetic properties, especially gyromagnetic properties of these samples were systematically investigated. First, X-ray diffraction patterns demonstrated that all samples exhibit a single spinel phase. Moreover, scanning electron microscopy image analysis revealed that Bi 2 O 3 can significantly promote grain growth and densification of NiCuZn ferrites. In terms of magnetism, the compact and uniform sample doped with 1.0 wt% Bi 2 O 3 possessed low coercivity (H C = ∼193.60 A/m) and high saturation magnetization (4π M S = ∼3959 Gs). More importantly, due to the grain growth and reduction of porosity, the ferromagnetic resonance linewidth (Δ H) of the samples decreased from 288.9 Oe to 218.8 Oe. These results suggested that Bi 2 O 3 is an effective sintering aid to enhance the gyromagnetic properties of ferrite materials used in microwave devices. • Microstructure of NiCuZn ferrite was improved by Bi 2 O 3 doping. Grain growth and uniformity were obviously promoted. • Magnetic properties, including 4π M s and H c , were optimized by Bi 2 O 3 doping. • Ferromagnetic resonance linewidth (Δ H) was decreased significantly by Bi 2 O 3 doping. [ABSTRACT FROM AUTHOR]

Spark plasma sintering (SPS) shows great potential in the fabrication of bulk YH 2- x. For the first time, the high-pressure SPS (HPSPS) of YH 2- x is explored and compared with the routine SPS. It is found that HPSPS remarkably reduces the densification temperature, and thus the thermal dehydrogenation phase transition (δ-YH 2- x → α-Y) and the hydrogen loss of YH 2- x can be avoided. Nearly fully dense δ-YH 1.80 monolith is successfully prepared by HPSPS under 500 MPa at a relatively low temperature of 800 °C. HPSPS is effective in overcoming the thermal dehydrogenation problem during the sintering of YH 2- x. Compared with significant grain growth in the routine SPS, the grain growth in the HPSPS is very limited. In terms of thermal properties, the thermal conductivity of HPSPS prepared YH 2- x is relatively low below 600 °C, then tends to be closed above 600 °C, compared with routine SPS prepared and directly hydrided YH 2- x. The thermal expansion of HPSPS prepared dense YH 2- x is basically consistent with that of directly hydrided bulk. This study provides a valuable reference for the sintering of high-quality δ-YH 2- x and other metal hydrides monoliths. • High-pressure SPS (HPSPS) is used to fabricate dense δ-YH 2- x for the first time. • The differences between routine SPS and HPSPS of dense YH 2- x are clarified. • HPSPS provides a "low-temperature sintering" and very limited grain growth. • The thermal dehydrogenation problem in the sintering of YH 2- x is overcome by HPSPS. [ABSTRACT FROM AUTHOR]

In this work, NiCuZn ferrites with different CuO contents were prepared by solid-state method. The influences of the divalent Cu2+ on the crystal structure, microstructure and magnetic properties of NiCuZn ferrite were studied in detail. X-ray diffraction characterization showed that Cu2+ may either replace Ni2+ and enter into crystal lattice, or distributed at grain boundaries in the form of compound. SEM results showed that adding appropriate amount of CuO can promote grain growth and prepare dense NiCuZn ferrites. Especially, the density of the ferrite sample reaches its maximum value of 5.23 g/cm3 when the amount of CuO is 0.20. However, superfluous Cu2+ exists in the form of liquid phase at local grain boundaries once the content of Cu2+ reached 0.25. Moreover, the magnetic hysteresis loops revealed that the specific saturation magnetization first increased and then decreased and the highest value of 76.6 emu/g was obtained at x = 0.10. Consequently, a NiCuZn ferrite with an appropriate microstructure and with high density (5.16 g/cm3), high saturation magnetization (76.0 emu/g), low ferromagnetic resonance (FMR) linewidth (160 Oe) and 4π Ms (4930 G) could be obtained at a Cu content of x = 0.15. • High density NiCuZn ferrites are prepared by solid state method. • The NiCuZn ferrite possesses excellent gyromagnetic properties (Δ H =160 Oe, H c =3.9 Oe, 4π M s =4930 G). • Appropriate amount of CuO is conducive to grain growth and the reduction of porosity for the NiCuZn ferrites. [ABSTRACT FROM AUTHOR]

In this paper, we report the fabrication of 90W–7Ni–3Fe refractory alloy using a novel oscillating pressure sintering (OPS) technique. The technique is similar to conventional hot pressing (HP), excepting that an oscillating pressure replaces the static pressure in HP. The results show that compared to HP, OPS can significantly improve the sintering ability of the alloy by decreasing the sintering temperature required for the densification of the alloy and inhibiting grain growth. The sample obtained at 1250 °C exhibits an HV hardness of 450 HV0.5, which is not only much higher than that for the HP prepared sample, but also much higher than materials with similar compositions ever reported. The results clearly demonstrate that OPS is a very promising technique for the fabrication of high performance refractory alloys. • For the first time, refractory alloy has been sintered by a novel oscillating pressure sintering (OPS) technique. • OPS can significantly improve the sintering ability of refractory alloy by lowering sintering temperature. • The activation energy for grain growth in OPS is about six time lower than that in hot pressing (HP). • The material prepared by OPS exhibits much higher hardness than that prepared by HP and other techniques. [ABSTRACT FROM AUTHOR]

The present work investigates the effects of Mn substitution with additions of Fe (0.5, 1, 2, and 3 at%) on the crystal structure, phase transformation temperatures, and magnetic properties of casted and heat-treated Ni 49.8 Mn 28.5−x Ga 21.7 Fe x magnetic shape memory (MSM) alloys. The alloys doped with 0.5 and 1 at% Fe exhibited single-phase seven-layered modulated (14 M) and five-layered modulated (10 M) martensite structures at ambient temperature, whereas the alloys doped with 2 and 3 at% Fe exhibited L2 1 Heusler austenite structures at ambient temperature. The Ni 49.8 Mn 27.5 Ga 21.7 Fe 1 alloy exhibiting the 10 M crystal structure at ambient temperature was selected for making ribbons using the melt-spinning process. The effects of heat treatment on grain growth, crystal structure, and other functional properties of the melt-spun ribbons were studied. The ribbons heat-treated at 1273 K exhibited a 10 M martensite structure and an average grain size of 220 µm along the ribbon plane. The results show that Ni 49.8 Mn 27.5 Ga 21.7 Fe 1 is a particularly promising composition for designing and manufacturing functional MSM micro-actuators. • Compositions of Ni49.8Mn28-xGa21.7Fex (x = 0.5, 1, 2, 3 at%) was casted. • Ni49.8Mn27.5Ga21.7Fe1 alloy show (10 M) martensite structures at room temperature. • Heat-treated Ni49.8Mn27.5Ga21.7Fe1 melt-spun ribbons at 1273 K show 10 M structure. • An average grain size of 220 µm along the ribbon plane was observed. • For designing functional MSM micro-devices, Ni49.8Mn27.5Ga21.7Fe1 is promising. [ABSTRACT FROM AUTHOR]

The magnetic properties and thermal stability are associated with the grain size and defects around grain boundaries in Sm 2 Co 17 permanent magnets. It is of scientific and practical interest to study the grain growth and the evolution of defects around grain boundaries during heat treatment process. In this study, the grain sizes after sintering, solution, isothermal aging and final aging are quantitatively characterized, and its influence on magnetic properties and flux losses are systematically analyzed. In addition, the Cu-rich and Zr-rich precipitates and Cu-lean regions around grain boundaries are carefully examined from sintering to final aging. The results show that solution treatment is the most effective approach to promote the grain growth, while the grain growth during isothermal aging and final aging is also non-negligible. The grain growth helps to reduce the grain boundaries and reduce the flux loss. This study provides a convenient and cost-effective approach (increasing the heat treatment time) to improve the thermal stability without significant sacrifice of magnetic properties. On the other hand, the Cu-lean regions and incomplete cellular nanostructures form during isothermal aging, while the Cu-rich and Zr-rich precipitates form during sintering. The formation of Cu-rich and Zr-rich precipitates mainly stems from the excess addition of Cu and Zr, which is indispensable to improve the working temperature. • The grain growth is quantitatively analyzed to find an effective approach to tune the grain size and flux loss. • Increasing the heat treatment time can enhance the thermal stability without significant sacrifice of magnetic properties. • The defects evolution around grain boundaries is systematically characterized during heat treatment process. [ABSTRACT FROM AUTHOR]

Poor performance of advanced engineering materials, during long term servicing at high temperature, is closely related to thermal stability of the microstructures. Instability of the microstructures specially in respect of the grain size, deteriorates mechanical properties and also has a detrimental effect on physical and functional properties of the components. In this respect, any of the High Entropy Alloys (HEAs) as a promising candidate has attracted academic and industrial attention according to their excellent high-temperature resistance and thermal stability compared with conventional engineering alloys. In this study we investigated effect of alloying element, annealing conditions (temperature, time), and pre-treatment (cold working) on grain growth behavior of HEAs. The retarding/accelerating effect of sluggish diffusion, solute drag, local concentration fluctuation, Zener factor, stacking fault energy, second phases, and fine particles were discussed in details. Grain growth kinetics was investigated with emphasis on grain growth exponent (n) and correlated activation energy (Q). Effectiveness of Hall-Petch relationship was finally studied to consider the frictional stress and slip transition behavior across grain boundaries. This review, overall, indicates high thermal stability of HEAs and also which one's high capability to be considered in high temperature engineering applications. [ABSTRACT FROM AUTHOR]

Two types of mechanism of spherulite formation in semi-solid metal processing have been proposed in academic circles, the dendrite breakage mechanism and the copious nucleation mechanism, but there is still no completely unified viewpoint. In this work, in order to further reveal the mechanism of semi-solid processing, the effects of; pouring temperature T 0 , rotating speed of turntable v 0 , group number of stirrer rods n 0 and quenching medium (air/water) on grain size and morphology of semi-solid microstructure of Al–Si7Mg alloy were investigated, and the results mainly show that the percentages of quantity of both; grains with mean diameter below 25 μm and grains with roundness within 1–2, increase with the increase of rotating speed of turntable v 0 , or group number of stirrer rods n 0. Finally, several conclusions have been reached. The formation of spherulite is usually a result of interference of growth directions of adjacent dendrite arms during solidification, which does not depend on, but can be promoted indirectly by flow or stirring. As the velocity of flow or stirring increases, it weakens the effect of dendrite breakage and strengthens the effect of copious nucleation. Image 1 • Spherulite formation is a result of growth directions interference of dendrite arms. • Spherulite formation does not depend on flow or stirring condition. • Spherulite formation can be promoted indirectly by flow or stirring condition. • The higher the velocity of flow or stirring, the weaker the effect of dendrite breakage. • The higher the velocity of flow or stirring, the stronger the effect of copious nucleation. [ABSTRACT FROM AUTHOR]

The present work evaluates the effect of both, Fe impurities and Cr addition, in nanostructured WC-10Co cemented carbides, which are sintered by hot isostatic pressing. Fe impurities and Cr addition in nanostructured WC-10Co alloy generate a series of microstructural and structural changes in the morphology, present phases, crystallite size and density, which in turn influences the microhardness of the samples. Such changes are mainly related to the nature of binder, generation of a bimodal grain size distribution and an abnormal grain growth of the WC phase and the formation of the η phase. • Fe impurities change the nature of binder producing an abnormal grain growth. • Pure Cr additions generate a bimodal grain size distribution and formation of η-phase. • Pure Cr additions affect the crisyallite size and density influencing the hardness. [ABSTRACT FROM AUTHOR]

An abnormal growth of Cu 3 Sn through the grain boundaries of Cu 6 Sn 5 formed in Ni/Sn/Cu ternary diffusion couples is reported in this study. The Ni/Sn/Cu diffusion couples are prepared by thermal compression bonding, with the Sn thickness controlled at 10 μm. The diffusion couples are aged at 200 °C for different periods of time. Due to the thinness of the initial Sn layer, the entire Sn layer ware converted into Cu 6 Sn 5 and Cu 3 Sn only after 52 h or aging. At this stage, both compounds exhibit the layered structure. Afterward, as the reaction continues, Cu 3 Sn grows thicker at the expense of Cu 6 Sn 5. Interestingly Cu 3 Sn now preferably grows along the grain boundaries of Cu 6 Sn 5. The rationalization for this abnormal growth pattern is discussed. • An abnormal growth of Cu 3 Sn along the grain boundaries of Cu 6 Sn 5 is discovered. • Such abnormal growth occurs only after the exhaustion of Sn. • Rapid grain boundary penetration causes a faster conversion of Cu 6 Sn 5 into Cu 3 Sn. • A mechanism for this abnormal growth is proposed from the Cu and Sn diffusivities. [ABSTRACT FROM AUTHOR]

In the present work, Li 0.35 Zn 0.30 Mn 0.05 Ti 0.15 Fe 2.15 O 4 ferrites were successfully synthesized via solid-state reaction method with the assistance of Bi 2 O 3 -MgO mixture. It was observed that a pure spinel phase could be formed at low temperatures (880 °C–920 °C), suggesting the compatibility of co-firing with silver internal electrodes. The employment of Bi 2 O 3 -MgO mixture could not only achieve the low-temperature sintering, but also facilitate the grain growth and subsequently promote the magnetic properties. SEM results revealed that the ferrites grain size was significantly increased (from 1 to 20 μm) with an appropriate dopant addition (1.2 wt %). Meanwhile, the saturation induction was enhanced from 141.2 to 345.9 mT, the coercivity was decreased from 515.2 to 176.6 A/m, and the FMR linewidth was dramatically decreased from 749.0 to 245.0 Oe at 9.3 GHz. Thus it is expected that the improved properties will allow the Li 0.35 Zn 0.30 Mn 0.05 Ti 0.15 Fe 2.15 O 4 ferrites to be a promising candidate for low temperature co-fired ceramics (LTCC) applications. Image 1 • Low-temperature preparation of LiZn ferrites (below 950 °C). • All the samples with Bi 2 O 3 -MgO mixture show a typical spinel structure. • Bs increased from 141 to 345 mT with the ΔH decreased from 749 to 245 Oe. [ABSTRACT FROM AUTHOR]

Understanding the effect of temperature variation on the microstructural evolution is particularly important to refractory high-entropy alloys (RHEAs), given their potential high-temperature applications. Here, we experimentally investigated the grain-growth behavior of the HfNbTaZrTi RHEAs during recrystallization at temperatures from 1,000 to 1,200 °C for varied durations, following cold rolling with a 70% thickness reduction. Following the classical grain-growth kinetics analysis, two activation energies are obtained: 205 kJ/mol between 1,000 and 1,100 °C, and 401 kJ/mol between 1,100 and 1,200 °C, which suggests two mechanisms of grain growth. Moreover, the yield strength – grain size relation was found to be well described by the Hall-Petch relation in the form of σ y = 942 + 270 D − 0.5 . It was revealed that the friction stress, 942 MPa, in the HfNbTaZrTi HEA is higher than that of tungsten alloys, which indicates the high intrinsic stress in the BCC-RHEA. The coefficient, 270 MPa/μm −1/2, is much lower than that in the 316 stainless steel and Al 0.3 CoCrFeNi HEAs, which indicates low grain-boundary strengthening. • HfNbTaTiZr HEA with a 70% cold-rolled reduction was annealed from 1000 from 1200 °C. • Grain-growth exponent and activation energy were obtained by grain-growth kinetic. • Yield strength – grain size relation was described by the Hall-Petch relation. • A high friction stress is found in the HfNbTaZrTi HEA. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of TiO 2 nanoparticle with the variation from 0 to 3 wt% on microstructural modifications and strength enhancement of pure Al fabricated via ARB technique. Results of microstructural characterization such as FESEM and TEM revealed that the attainment of homogeneous distribution of reinforcement particulates, ultrafine matrix grains and dislocations and elongated grains are due to rolling after eight passes, respectively. Reinforcement addition decreased the size of the matrix grains owing to nucleation sites generation and grain growth deceleration. Mechanical properties exhibited that hardness and tensile test were significantly improved more than three times compared with the Al matrix due to superior bonding among the matrix and interlocking of reinforcement particles between the matrix sheets. • Fabrication of Al 1100 – TiO 2 nanocomposites through ARB process. • TiO 2 nanoparticles enhanced the load carrying capacity. • Reinforcement distribution, grain refinement and dislocations led to improvement in strength. [ABSTRACT FROM AUTHOR]

(1- x)ZnGa 2 O 4 - x TiO 2 (x = 0.05–0.20) composite ceramics were fabricated via traditional solid state method. The experimental and theoretical value of ɛ r , τ f and Q × f shows similar trend. Tunable microwave dielectric performance was achieved due to the effect of TiO 2 , especially for temperature coefficient and quality factor. The large negative temperature coefficient at resonant frequency (τ f) of ZnGa 2 O 4 was continuously tailored from negative (−70 ppm/oC) to positive (+13 ppm/oC) 2 For practical application, 15 mol% (about 6.9 V%) TiO 2 can adjust τ f value to near zero. The tailoring effect on quality factor (Q × f) was significant. Due to the smaller Q × f values of TiO 2 , the Q × f value decreases with the increasing content of TiO 2. The inhomogeneous microstructure results in the increasing difference between calculated and experimented Q × f value. In addition, compositing TiO 2 with ZnGa 2 O 4 ceramic not only promote the grain growth but also reduce its sintering temperature from 1400 °C to 1300 °C. The dielectric constant (ɛ r) was not significant affected by TiO 2 , only varied from 10.8 to 12.7. The ɛ r value of 12.3, Q × f value of 73,000 GHz (at 11.8 GHz) and τ f value of +3 ppm/°C were achieved for 0.85ZnGa 2 O 4 -0.15TiO 2 , sintered at 1300 °C for 2 h. Image 1 • The compositing effect of TiO 2 results in tunable microwave dielectric performance. • The large negative τ f continuously shifts from negative to positive. • Endows ZnGa 2 O 4 -TiO 2 with additional application potential as high quality MDCs. • ZnGa 2 O 4 -TiO 2 provides a good example of rational design to tailor τ f. [ABSTRACT FROM AUTHOR]

Understanding how grains grow and how growth direction can deviate considerably from build direction (BD) during selected laser melting (SLM) is necessary for SLM of the difficult-to-weld IN738LC Ni-based alloy. In the present study, samples were made with two laser power (P) values while other parameters were kept unchanged, corresponding to SLM keyhole mode with two melt penetration depths. Aspect ratios (width/depth) of tracks, dendrite arm spacing, and grain growth directions have been measured and determined. The optimal SLM condition for defect free SLM of the alloy previously identified in the literature has been found to be a stable keyhole SLM condition. High P increases the depth of keyhole, causing it to be unstable and pores to form likely due to the periodic collapse of the keyhole. In keyhole mode SLM, heat is conducted away more horizontally and thus grains grow in directions considerably different from BD. Under the stable keyhole condition, primary dendrite arm spacing (λ 1) ranges from 0.32 μm at the track bottom to just over 1 μm in the top track region corresponding to cooling rates (T ˙) equal to from 1 × 107 K/s to 3 × 105 K/s, respectively, during solidification. Significantly lower λ 1 observed at the track bottom indicating T ˙ being up to 108 K/s under the condition of flow instability will also be presented and discussed. • In keyhole mode, grains mostly grow at high angles to build direction. • Primary dendrite arm spacing ranges from <0.2 to 1 μm within a track. • Cooling rate ranges from >107 K/s at track bottom to 105 K/s in track surface. • A deep keyhole is detrimental as it periodically collapses, causing pore formation. [ABSTRACT FROM AUTHOR]

Nanocrystalline CoCrFeNi and CoCrFeMnNi high entropy alloys have been processed by mechanical alloying followed by spark plasma sintering. Grain growth kinetics has been estimated for both the alloys by subjecting them to heat treatment in the temperature range 1073–1373 K. These alloys possess a thermally stable single phase FCC structure along with Cr 7 C 3 contamination. Electron back scattered diffraction (EBSD) has been used to determine grain size of all the heat treated samples. Both CoCrFeNi and CoCrFeMnNi alloys exhibit a grain growth exponent, n = 3, suggesting long-range diffusion-controlled grain growth in these alloys. Activation energies for grain growth are 134 and 197 kJ/mol for CoCrFeNi and CoCrFeMnNi, respectively, which are significantly lower than the activation energy of lattice diffusion in these alloys. Hardness is measured for CoCrFeMnNi alloy as function of grain size and is found to follow the Hall-Petch type relation. The strength coefficient (slope of Hall-Petch relation) is calculated as 1.92 GPa, which is nearly three times that of the value reported in literature for coarse grained CoCrFeMnNi. Presence of carbides enhances the hardness of these HEAs. The maximum contribution to strengthening comes from the FCC-carbide phase boundaries. • SPSed CoCrFeNi and CoCrFeMnNi HEAs show thermally stable FCC and Cr 7 C 3 phases. • Grain growth activation energy is lower than the energy barrier for bulk diffusion. • Coarsening of carbide particles is the rate controlling step for grain growth. • Hardness of SPSed CoCrFeMnNi follows Hall-Petch behaviour. • Maximum contribution to strengthening comes from FCC-carbide phase boundaries. [ABSTRACT FROM AUTHOR]

Ultrafine WC cemented carbides with 10 wt% mechanically alloyed Al x CoCrCuFeNi (x is the aluminium content in molar ratio and ranges from 0 to 1.5) high-entropy alloy (HEA) binders were fabricated by spark plasma sintering. The influences of the HEA binders on the microstructures and mechanical properties of WC-HEA cemented carbides were discussed. Due to the sluggish diffusion effect of the HEA binders, the WC grain growth activation energy of WC-HEA cemented carbides is significantly higher than that of WC-Co alloy. Consequently, the grain growth of WC is inhibited during sintering, and an ultrafine microstructure can be obtained. With increasing Al content of HEA binders, both the relative density of WC-HEA cemented carbides and the hardness of HEA binders increase, which contributes to the high hardness of WC-HEA cemented carbides. The fracture toughness of WC-HEA cemented carbides is codetermined by the wettability of HEAs on WC and the intrinsic sintering property and deformability of HEA binders. Therefore, the WC-HEA cemented carbide with 10 wt% Al 0.5 CoCrCuFeNi high-entropy alloy binder exhibits the best combination of Vickers hardness and fracture toughness, which are 2071 ± 6 HV 30 and 10.3 ± 0.1 MPa m1/2, respectively. • Ultrafine WC-HEA composites without grain growth inhibitor were fabricated by SPS. • The component of HEA binder strongly affected WC grain growth activation energy. • Effects of HEA binders on mechanical properties of WC-HEA composites were studied. [ABSTRACT FROM AUTHOR]

2D grain coarsening CA models based on the grain boundary curvature models of Kremeyer and Mason were established. The parameters needed in the two models were obtained via different methods. Then, the grain growth kinetics, grain size distribution, topological aspects and individual grain growth kinetics were deeply studied with these two curvature based CA models. The grain growth exponents of both models were close to 2 which was a constant derived from theory and verified experimentally. The Weibull function has a better fitting for the simulation results than the other analytical distributions proposed by Hillert and Rios. The topological aspect of both models was analyzed with the Aboav-Weaire relation. Excellent agreements between the simulation results and the Aboav-Weaire relation were obtained. At last, a new relationship was proposed to calculate the growth rate of individual grains. • Two curvature based grain coarsening CA models were established. • The parameters of curvature models were obtained with simulation methods. • Grain growth kinetics and topological aspects were discussed in depth. • New individual grain growth kinetics equation was established. [ABSTRACT FROM AUTHOR]

Abstract The microstructural evolutions in terms of dislocation density, annealing twin density as well as with respect to microstructural changes due to recrystallization and grain growth were investigated in pure Ni, equiatomic FeNiCo alloy, and FeNiCoCrMn high entropy alloy (HEA) during the thermomechanical process. All samples were single phase and showed a face-centered cubic (FCC) lattice structure. This was maintained during thermomechanical processing comprising of cold swaging by 85% reduction of cross-sectional area and subsequent annealing at 800 °C. The level of dislocation accumulation during cold swaging increased with the number of constituent elements. The FeNiCoCrMn HEA obtained the highest dislocation density, followed by the FeNiCo and Ni, respectively. After the annealing at 800 °C for 0.5 h, all samples achieved the large fraction of recrystallized grains with minor fraction of substructured grains and no deformed grain. The FeNiCoCrMn HEA obtained the smallest recrystallized grain size (∼5 μm) after the annealing at 800 °C for 0.5 h. This could be a result of the highest dislocation density generated during cold swaging prior to the annealing. The prolonged annealing at 800 °C for up to 24 h led to a grain growth for all the samples, however, at different growth rates. The FeNiCoCrMn HEA revealed the lowest rate of grain growth, but the microstructural changes during the annealing were not significantly different between the FeNiCo and Ni samples. Besides the effect of the number of constituent elements, the type and the combination of constituent elements have an effect on the microstructural evolution during the annealing. Highlights • The level of dislocation accumulation increases with the element number. • The FeNiCoCrMn reveals the lowest rate of grain growth during isothermal annealing. • The number of elements is not only a factor in microstructural change. • The type and combination of elements are also considered in microstructural change. [ABSTRACT FROM AUTHOR]

To investigate the microstructure evolution of powder metallurgy (P/M) superalloys during high-strain-rate deformation, a P/M nickel-base superalloy is subjected to thermal compression at temperatures ranging from 1000 °C to 1100 °C and strain rates ranging from 1 s−1 to 10 s−1. The analysis regarding the flow behaviors and microstructure observation indicates that discontinuous softening is significant at high strain rates. Moreover, based on experimental measurement and theoretic estimation, the adiabatic heating under high-strain-rate deformation is hardly neglectable, which enhances the dynamic softening via dynamic recovery (DRV), dynamic recrystallization (DRX), and grain growth. In order to obtain refined and homogeneous grains, deformation at temperature range of 1025–1050 °C with strain rate rang of 1–10 s−1 or at 1000 °C/1 s−1 is suggested for high-strain-rate compression on the P/M superalloy, where DRX plays more dominating roles. • Discontinuous hardening and softening are observed at high-strain-rate compression. • The adiabatic heating under higher strain rate is more significant. • A processing window is preferred to obtain refined grains after high-speed deformation. [ABSTRACT FROM AUTHOR]

Abstract We investigated he thermoelectric (TE) properties and microstructures of Na-doped PbTe compounds, synthesized by various milling and sintering processes. It has been generally accepted that spark plasma sintering (SPS) inhibits grain growth due to the short sintering time, which is beneficial to the nano bulk composite. In contrast, we observed abnormal grain growth for SPS, unlike hot press (HP) sintering. Considering the Gibbs free energy change during sintering, the HP sintering increases internal energy while the SPS increases entropy energy, which causes the abnormal grain growth. Lattice strain and Fourier transform analyses of the transmission electron microscope images showed that the SPS sintered samples had more significant lattice strains and defects than the HP sintered samples. The low thermal conductivity of the SPS sintered samples was not from grain boundary phonon scattering but from phonon scattering by lattice strains and defects. The lattice strains and defects decreased electrical conductivity as well, resulting in deterioration of the power factor and thermoelectric performance. This suggests that the lattice strains and defects are more critical factors for enhancing thermoelectric performance than particle and grain size control. Highlights • Abnormal grain growth driven by entropy energy change is significant in spark plasma sintering. • SPS sintered samples have more significant lattice strains and defects than those of hot press. • Phonon scattering by lattice strains and defects decreases lattice thermal conductivity in SPS. • The lattice strains and defects decreases electrical conductivity as well. [ABSTRACT FROM AUTHOR]

Abstract Non-equiatomic Co 17.5 Cr 12.5 Fe 55 Ni 10 Mo 5 (Mo5) and Co 18 Cr 12.5 Fe 55 Ni 7 Mo 7.5 (Mo7.5) medium-entropy alloys were synthesized by vacuum induction melting, cold rolling, and subsequent annealing treatment at various temperatures (900–1200 °C) and they were investigated to exploit the precipitation strengthening in addition to solid solution strengthening of alloys. The effect of annealing temperature and Mo content on the microstructure and mechanical properties are systematically analyzed. From the microstructural analysis, a Mo-rich μ phase is observed in the face-centered cubic (fcc) matrix. Increasing the Mo content and low annealing temperature enhance the formation of μ phase, which is consistent with the thermodynamic calculation results. The formation of μ phase effectively enhances the strength of the Mo7.5 alloy by precipitation strengthening, and suppression of grain growth and recrystallization by Zener pinning effect. These lead to superior combination of tensile strength as high as 1100 MPa and large ductility. Our results provide insights not only into μ-phase strengthening of fcc-structured alloys, but also into the future development of high-performance MEAs. Graphical abstract Image 1 Highlights • The effect of μ-precipitates in the non-equiatomic CoCrFeNiMo alloys is discussed. • Further addition of Mo and decrease in annealing temperature enhances the formation of μ phase. • Formation of μ phase retards the recrystallization and grain growth by Zener pinning effect. • The present non-equiatomic CoCrFeNiMo alloys exhibits superior tensile properties by multiple strengthening mechanisms. [ABSTRACT FROM AUTHOR]

Abstract A novel Ti-2Si-2Nb-2Fe-1Hf-1Ta-1W alloy consisting of α phase, retained β phase, and submicron scale (TiHf) 5 Si 3 precipitates has been fabricated successfully. The incorporation of Hf in the silicon-containing alloys affects the solidification in a special way. The Hf 5 Si 3 particles as inoculants can provide sites for the nucleation of the Ti 5 Si 3 phase due to their similar crystal structure, which leads to the formation of (TiHf) 5 Si 3 compound phase. A large number of spherical (TiHf) 5 Si 3 particles around 800 nm in diameter form and uniformly distribute at α p /β interfaces. The (TiHf) 5 Si 3 precipitates hinder the grain growth of α phase and the movement of the activated dislocations, therefore strengthen the alloy by multi-mechanisms. The alloy exhibits high tension strength (942 MPa) with a high level of plasticity (14%). The good plasticity can be achieved through the homogeneous distribution of (TiHf) 5 Si 3 phase together with the refinement for equiaxed α phase. Graphical abstract Image 1 Highlights • A novel Ti alloy with in situ (TiHf) 5 Si 3 particles has been designed. • The alloy showed a good combination of strength and plasticity. • The (TiHf) 5 Si 3 particles in submicron-scale were distributed at α p /β interfaces. • The (TiHf) 5 Si 3 particles and equiaxed α phases contributed to the good performances. [ABSTRACT FROM AUTHOR]

Abstract High-entropy alloy fibers with excellent performance potential are desired for functional applications. A previous study on the Al 0.3 CoCrFeNi high-entropy fiber reported a tensile fracture strength of 1200 MPa and elongation of 8% at room temperature (Acta Mater. 123 (2017) 285). The goal of this study is to improve the ductility of Al 0.3 CoCrFeNi high-entropy fiber by manipulating the microstructure through annealing. Al 0.3 CoCrFeNi fibers at Φ1.0 mm and Φ1.6 mm diameters were annealed at 900 °C for 10 min, 30 min, 300 min and 720 min, respectively. The resulting microstructure is a fine face-centered cubic (FCC) structure with grain sizes less than ∼3 μm, which were strengthened by dense NiAl-type ordered body-centered cubic (B2) precipitation. The fibers achieved a fracture strength greater than 900 MPa with an elongation of over 25% at room temperature. Graphical abstract Image 1 Highlights • The annealed fiber showed a microstructure of disordered FCC matrix with nano-sized ordered B2 precipitates. • The grain growth rate slowed down substantially after 30 min at 900 °C. • The average grain size was less than 3 μm after 720 min at 900 °C. • The heat-treated fibers achieved a fracture strength ≥900 MPa with an elongation ≥25% at room temperature. • The annealed fibers demonstrate superior mechanical properties to conventional fibers. [ABSTRACT FROM AUTHOR]

Abstract NiCuZn ferrite ceramics with high permeability and low magnetic loss have great values in high frequency applications. Here, we synthesized uniform and compact NiCuZn ferrites with small grains (about 1.5 μm) at 875 °C via adjusting additive amount of Nb 2 O 5 and Bi 2 O 3. The influence of Bi 2 O 3 additives on the microstructure and magnetic properties of NiCuZn ferrite, especially for grain growth and grain size, have been investigated. SEM results indicated that Nb 2 O 5 can obviously suppress grain growth when a small amount of Bi 2 O 3 was added. Also, the liquid phase of Bi 2 O 3 only can promote movement of grain boundary and reduce porosities between grains. Thus, a NiCuZn ferrite with high permeability (μ i ′ = 472.79), high saturation flux density (B s = 0.313 T), high Q value (66.3) and low coercivity (H c = 94.75 A/m) was obtained when 0.25 wt % Nb 2 O 5 -0.50 wt % Bi 2 O 3 was added. It is proved that improvement of compactness can enhance magnetic properties even though grain growth was suppressed. However, over much Bi 2 O 3 (more than 1.00 wt %) reduced the magnetic properties due to deterioration of grains uniformity and existence of non-magnetic Bi 2 O 3 liquid phase. Such a low temperature solid phase synthesis method (i.e., adding composite additive with different melting point oxide) should also facilitate preparation of other advanced ceramics for practical applications. Highlights • Nb 2 O 5 was a feasible additive to suppress abnormal grain growth of NiCuZn ferrite. • A NiCuZn with high permeability and low magnetic loss was prepared at 875 °C. • Low temperature solid phase synthesis method was presented for practical applications. [ABSTRACT FROM AUTHOR]

Abstract Oligocrystalline Cu-Al-Mn shape memory foams with a pore size of 0.8–1.1 mm and a porosity of ∼70% were prepared by the silica-gel beads infiltration method, subjected to long-time and cyclic heat treatments. The effect of grain size and oligocrystallinity (ratio of grain size to strut node diameter) on the damping and pseudoelastic properties of the foams were investigated. The peak damping increases with oligocrystallinity because a higher oligocrystallinity favors the martensite accommodation and mobility of phase interfaces during martensitic transformation. The low-amplitude martensite damping first increases and then decreases with increasing oligocrystallinity, because the martensite plates grow wider in larger grains with lower grain constraints, leading to fewer interfaces and lower damping. The high-amplitude martensite damping increases linearly with increasing oligocrystallinity, despite the wider martensite plates and reduced interfaces, indicating that the mobility of martensite plates for higher displacements is more favored by reduced grain constraints. The maximum recovery strain increases linearly with oligocrystallinity and a high value of 5.53% was achieved after cyclic heat treatment for 16 times, corresponding to an oligocrystallinity of 7.88. The high recovery strain results from the reduced triple junctions and grain boundary area due to grain enlargement that lowers the grain constraints. Graphical abstract Image 1 Highlights • Various oligocrystallinities of Cu-Al-Mn oSMFs were obtained by heat treatments. • Grain growth in the oSMFs was limited by the complex pore structure and overheating. • The peak damping increases and martensite plates widen as oligocrystallinity grows. • The high-amplitude martensite damping increases linearly with oligocrystallinity. • The max recovery strain increases linearly with oligocrystallinity, reaching 5.53%. [ABSTRACT FROM AUTHOR]

Abstract Up to now, attempts for developing coarse-grained SnO 2 -based varistors which exhibit high nonlinearity property at lower voltage have become a challenge without any prominent result because of its unknown grain growth mechanism. In this study, the effect of CuO addition to SnO 2 -based varistors as a grain growth enhancer additive on microstructural development, grain growth kinetics, and electrical properties was investigated. The characterization of grain growth kinetics showed that CuO addition encouraged grain growth and enhanced the grains size as it could be seen in the activation energy which decreased from 594 kJ/mol to 364 kJ/mol. In the samples with a low amount of CuO, the solute drag force is the controlling mechanism of grain growth. By further addition, the mechanism changed to the Sn4+ solution-precipitation in CuO-rich liquid phase. Also, the electrical properties of CuO doped samples showed that they are so promising for low voltage applications. Graphical abstract Image 1 Highlights • Grain growth kinetics of CuO-doped SnO 2 varistors were characterized. • The controlling mechanism is solute drag in 0.1% CuO doped sample. • By further addition, the mechanism changed to solution-precipitation in liquid phase. • CuO doped samples are so promising for low-voltage applications. [ABSTRACT FROM AUTHOR]

Abstract Ca2+ doped SrLa-ferrite powder was synthesized through molten salt assisted method. The influence of Ca2+ doping on the microstructure and magnetic properties of SrLa-ferrite poweder was discussed. The results showed that non-agglomerated Sr 0.7- x Ca x La 0.3 Fe 12 O 19 ferrite powder with narrow particle size distribution could be synthesized by molten salt assisted calcination process. This powder exhibited excellent magnetic properties after eliminating the impurity phase through Ca2+ doping. Highlights • Ca2+ doped SrLa ferrite powder is synthesized by molten salt assisted calcinations. • The effects of Ca2+ doping on La3+ solubility in SrLa ferrites are studied. • The powder exhibits good magnetic properties after eliminating the impurities. [ABSTRACT FROM AUTHOR]

Nanocrystalline Fe-18Cr-8Ni (at%) stainless steels were produced by mechanical alloying from elemental powders with Zr and Y 2 O 3 additions and subjected to annealing treatments at various temperatures. X-ray diffraction experiments, transmission electron microscopy and focused ion beam microscopy were used to investigate the microstructural evolution as a function of alloy composition and annealing temperature. The dependence of hardness on the microstructure was utilized to study the mechanical changes with temperature. It was found that the resulting microstructures by mechanical alloying were bcc solid solution, the so-called α′-martensite structure whereas, depending on the composition and temperature, partial reverse transformation from martensite to austenite was induced by annealing. As-milled nanocrystalline Fe-18Cr-8Ni stainless steel yielded grain growth upon annealing reaching to micron sizes at 1100 °C while addition of Zr and Y 2 O 3 stabilized the microstructure below approximately 250 nm grain size and close to 5 GPa hardness after annealing at the same temperature. Such microstructural features may facilitate the consolidation process of nanocrystalline stainless steel powders as well as enabling the use of these materials at elevated temperatures. [ABSTRACT FROM AUTHOR]

6H-SiC porous SiC ceramics accompanied by the formation of large clubbed and tabular grains were successfully fabricated at 1800 °C under an applied pressure of 50 MPa for 5 min by spark plasma sintering technique without introducing any pore-creating agent. The phase composition, microstructure and properties of porous SiC ceramics were investigated. The measured porosity of the specimens was 35.7% and the mean pore size varied in the range of 0.3–3 μm. The sintered specimen had a strength of 103 MPa, a fracture toughness of 2.89 MPam 1/2 , and a density of 1.85 g/cm 3 . The mechanisms of porous structure and grain growth were elucidated. [ABSTRACT FROM AUTHOR]

In this study, a solution chemical route for the synthesis of ultrafine WC-15 wt %Co cemented carbides was proposed with WC-6Co aggregates as raw materials. The chemical Co was uniformly distributed around the WC-6Co aggregates and the Co layers in the raw materials had been well preserved. During sintering, the chemical Co could diffuse along the Co layers and thus avoid the aggregation and growth of WC grains. Additionally, the homogeneous distribution of Co phase and the existent of Co layers promoted the WC reprecipitations on the same crystal during the solution/re-precipitation process. The fine WC grains and the homogeneous of WC and Co phases resulted in the high hardness and transverse rupture strength. [ABSTRACT FROM AUTHOR]

We report on an investigation of the influence of sintering temperature on microstructure and mechanical behaviors of the Al matrix composites. In this paper, the ultrafine grained AA7075/B 4 C composites was synthesized via cryomilling and one-step consolidation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were utilized for characterization of the grain size of the AA7075/B 4 C composites consolidated at various sintering temperatures. Our results indicated that the grain size increased gradually from ∼73.1 nm to ∼184.7 nm with the sintering temperature increasing from 350 °C to 450 °C. The formation of abnormal grain growth was observed in the AA7075/B 4 C composite consolidated at 500 °C B 4 C particles distributed homogenously, discretely and randomly in the Al matrix based on the observation in Field-emission scanning electron microscopy (FESEM). The porosities were found to decrease in the AA7075/B 4 C composites with the rising of sintering temperature. The Vickers hardness, compressive yield strength and fracture strength of the AA7075/B 4 C consolidated at 450 °C were 233 HV, 724.9 MPa and 834.5 MPa, respectively. The analysis of strengthening mechanisms revealed that increasing of sintering temperature resulted in the sacrifice of grain-boundary strengthening and dislocation strengthening. [ABSTRACT FROM AUTHOR]

A bulk ultrafine grained Al-0.6 wt%Mg-0.4 wt%Si-5vol.%SiC nanocomposite was fabricated by spark plasma sintering (SPS) of a corresponding nanocrystalline metal matrix nanocomposite powder produced by high energy mechanical milling. The as-SPSed samples were either heat treated or hot extruded at 500 °C. Microstructural characterization of the samples revealed that the ultrafine Al(Mg,Si) grains in the as-SPSed sample grew slightly and underwent recovery during heat treatment, and dynamic recrystallization, rapid grain growth and grain boundary dragging of SiC nanoparticles occurred during extrusion. The Al(Mg,Si) grain growth and grain boundary dragging of the SiC nanoparticles during extrusion resulted in aggregation of a large fraction of the SiC nanoparticles which in turn caused formation of regions with finer and coarser Al(Mg, Si) grains respectively. [ABSTRACT FROM AUTHOR]

MgAlON transparent ceramics are fabricated by pressureless sintering using the carbothermal raw powder. The obtained MgAlON powder is well crystallined and exhibits a spinel structure. It shows a bimodal particle size distribution (PSD) at 0.3 μm and 0.9 μm. An investigation on the microstructural sintering evolution indicates the stages of significant densification at the intermediate temperature regions (1600–1700 °C) and rapid grain growth at higher temperature (1750–1850 °C). Additional holds at the intermediate temperature are effective to controlling the microstructure with reduced porosity, which in turns, improving the transmittance. The sample with hold at 1700 °C for 2 h followed by 1850 °C for 20 h exhibits excellent transmittance from the visible to middle infrared (IR) regions, achieving 86.59% at 3.70 μm and 82.37% at 0.60 μm. [ABSTRACT FROM AUTHOR]

The phase transformation and grain growth behaviors of commercial Ni-Fe-base superalloy 718 at 1323, 1373, 1423 and 1473 K were investigated through DSC and SEM methods. The transformation temperatures of γ + NbC → L and γ → L were determined as 1495 and 1555 K, respectively, and TiN was shown to gradually dissolve into the formed L. The pinning effect caused by Nb-rich carbide (NbC) and Ti-rich nitride (TiN) was observed, and the mean size of the grains increased with holding time at each temperature. The grain growth exponent, m, was confirmed to be 4, indicating that grain growth was controlled by the coarsening of the precipitate through grain boundary diffusion. The grain boundary diffusion of Nb and N was confirmed to control the coarsening of NbC and TiN, respectively. The major factor for γ grain growth was confirmed to be the coarsening of NbC, and the activation energy for grain growth was calculated as 417 kJ·mol −1 . The equations for grain growth were determined as G 4 -G 0 4 = 0.10 × 10 6 × t (1323 K), G 4 -G 0 4 = 0.49 × 10 6 × t (1373 K), G 4 -G 0 4 = 2.01 × 10 6 × t (1423 K) and G 4 -G 0 4 = 3.89 × 10 6 × t (1473 K), for all four temperatures respectively. The predicted grain growth curves were in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The present study focuses on a novel approach to broaden the phase transition in Ba(Zr 0.2 Ti 0.8 )O 3 by the combined effect of oxygen annealing and La-doping. The (Ba 1-x La x )(Ti 0.8 Zr 0.2 )O 3 , Pb-free ceramics, with nominal compositions (x = 0.00, 0.01, 0.02 and 0.03) are synthesized in oxygen annealing atmosphere at 1673 K for 11 h using solid-state reaction method. While the X-ray diffraction confirmed the single phase formation, the secondary electron images revealed inhibited grain growth at a low concentration of La-doping but intermediate 2-dimensional grain growth at higher La-doping. The Raman peak appearing at 836 cm −1 indicates La-substitution at Ba-site and vacancies at Ti-sites. The temperature dependent dielectric permittivity exhibits a broad diffuse phase transition at T m = 230 K with a full width at half maxima (FWHM) of 289 K for 3 atomic % La-doped sample. The combined effect of oxygen annealing and La-doping results in an extremely broad diffuse phase transition. Such an extremely broad phase transition close to room temperature due to La-doping and oxygen annealing is useful for capacitor applications. [ABSTRACT FROM AUTHOR]

The recrystallization behavior of alloy 617B is investigated by isothermal hot compression tests in a temperature range of 1120–1210 °C with a strain rate scope of 0.01–20 s −1 . The effect of deformation parameters on DRX behavior is studied by optical microscopy and electron backscatter diffraction (EBSD) technique. The major dynamic recrystallization (DRX) mechanism of alloy 617B is confirmed to be discontinuous dynamic recrystallization (DDRX), accompanied by some characteristics of continuous dynamic recrystallization (CDRX). The DRX process is apparently influenced by strain rate and is accelerated in high strain rate condition, which is different from traditional awareness that high strain rate can inhibit DRX. As a result, a segmented model of strain rate is proposed to describe the DRX kinetics of alloy 617B. Furthermore, a grain growth model is also developed for the simulation of actual manufacture process. DEFORM-2D software is adopted for hot extrusion simulation and FORTRAN language is used for secondary development to invoke the developed model effectively. The simulated microstructure agrees well with the actual manufactured pipe of alloy 617B, demonstrating that the models and simulation method proposed in present study can be used for microstructure prediction and optimization for alloy 617B during hot deformation. [ABSTRACT FROM AUTHOR]

Ca 2+ doped Sr 0.45- x Ca x La 0.55 Fe 11.6 Co 0.4 O 19 ( x = 0, 0.15, 0.3, and 0.45) ferrites were fabricated through a conventional ceramic process. The influences of Ca 2+ doping on the microstructure and magnetic properties of ferrites were investigated. Ca 2+ doping could mitigate the presence of impurity phase (CoFe 2 O 4 ) in ferrites. Single phase M-type ferrites could be fabricated when x ≥ 0.3. Additional Co 2+ ions entered the crystal lattice and preferentially occupied the 4f 2 site with Ca 2+ doping. This effect greatly improved the remanence (B r ) and intrinsic coercivity (H cj ) when x increased from 0 to 0.3. The average grain size of sintered ferrites slightly increased with the amount of doped Ca 2+ ions. This behavior led to the deterioration of H cj when x increased from 0.3 to 0.45. Consequently, ferrite prepared with x = 0.3 presented the highest maximum energy product ((BH) max ) of 5.24MGOe. This performance is much higher than that of conventional La-Co substituted Sr-ferrites. [ABSTRACT FROM AUTHOR]

(Zr,Hf)B 2 -SiC ceramics were densified at 2200 °C without the existence of external pressure, using commercially available ZrB 2 , SiC, HfC and B 4 C powders as raw materials. HfC reacted with B 4 C to form HfB 2 and C in-situ: the continuous solid solution formation of ZrB 2 -HfB 2 inhibited the grain growth of matrix during high temperature effectively, and meanwhile played a critical role in enhancing densification. The mechanical properties, including flexural strength, elastic modulus, Vickers hardness and indentation toughness were tailored by compositional designing of original ZrB 2 -SiC-HfB 2 -B 4 C (ZSHB) recipe, which excelled its ZrB 2 -SiC counterpart. Novel reactive densification mechanism was discussed as well. [ABSTRACT FROM AUTHOR]

Melt-derived glass ceramics were prepared having the following chemical composition 33SiO 2 -21CaO-32.5Na 2 O-12P 2 O 5 -1.5MgO (mol %). Samples were sintered at three different temperatures (750, 800, and 850 °C). Thermal, structural, and bioactivity analyses were carried out using TGA-DSC, XRD, and in vitro immersion tests, respectively. XRD results indicated that CaSiO 3 was the major phase while Na 2 Ca 2 Si 3 O 9 was the minor phase in a glass matrix. The crystallite size and degree of crystallization increased with sintering temperature. Additionally, SEM images showed grain growth and reduction of pores with increasing sintering temperature. The bioactivity of the specimens were assessed by XRD; all specimens exhibited hydroxyapatite phase on their surfaces after immersion in a simulated body fluid, indicating the bioactive nature of the material. Further, the sample sintered at 750 °C was observed to be more bioactive as indicated by crystallization of Ca 10 (PO 4 ) 6 (OH) 2 on its surface. These results indicate that sintering at high temperature increases the crystallinity, microhardness and chemical stability of this bioactive glass ceramic. [ABSTRACT FROM AUTHOR]

The grain growth behaviors of a nickel-based superalloy after full recrystallization are investigated by hot compression test plus annealing treatment. Electron backscattered diffraction technology (EBSD) is utilized to analyze the grain boundary features. It is found that the annealing parameters greatly affect the average grain size, and annealing twin boundaries, including ∑3, ∑9, and ∑27 boundaries. The fully-recrystallized grains can rapidly grow up at relatively high annealing temperatures with the increase of annealing time. Meanwhile, large fractions of annealing twin boundaries form at the initial stage of annealing treatment. However, with the further increase of annealing time, the content of annealing twins slightly drops due to the migration of grain boundaries or twin boundaries. When the annealing temperature is increased, the shape of annealing twin is apparently lengthened while the number of annealing twin sharply decreases. In addition, the kinetics model for grain growth after full recrystallization is established and validated by the experimental observations. [ABSTRACT FROM AUTHOR]

CeO 2 films with mixed doping of gadolinium and zirconium were deposited on NiW substrates by chemical solution deposition. The influences of mixed doping on the epitaxial growth and microstructure of films were systematically investigated. The morphological evolution of films with different dwell times was also discussed. The phase formation, texture and surface morphology of (Ce 0.8 Gd 0.2 ) 1- x Zr x O 2-δ (CGZO) films were characterized by X-ray diffraction and atomic force microscopy. It was noticed that Zr 4+ doping had stronger effect on the crystal structure of CeO 2 than Gd 3+ doping. The increasing doping content of Zr 4+ could be favorable for the self-limited grain growth of the CGZO films and promote the lattice match with substrate. Moreover, the sharp texture and smooth surface of CGZO film could be easily acquired by the mixed doping. The results indicated that the (Ce 0.8 Gd 0.2 ) 1- x Zr x O 2-δ film was beneficial for the subsequent film growth, which could be a candidate buffer layer for the coated conductors. [ABSTRACT FROM AUTHOR]

It is well-known that the Co-doping of ferromagnetic shape memory alloys (FSMAs) is a crucial tool to control their multifunctional properties. The present work investigates the use of small quantities of Co to fine-tune the transformation, structure, microstructure, mechanical and magnetic properties of the polycrystalline Ni 49.8 Mn 28.5 Ga 21.7 (at%) alloy, as the representative of the most elaborated magnetostrain-active Ni-Mn-Ga FSMAs. A series of seven alloys, undoped and doped with 0.5, 1, 1.5, 2, 3, and 4 at% Co, was fabricated using a standard induction melting technique with subsequent heat treatment. Alongside establishing the evolution of the basic characteristics as a function of the Co content in this series, an unusual effect of Co-doping on the grain microstructure was found. A Co-doping up to 1.5 at% instead of Mn significantly increased the average grain size while importantly maintaining the 10 M martensitic crystal structure. At Co concentrations of 1–1.5 at%, a microstructure with an average grain size of about 2.00 mm was formed with a twin structure, enabling the experimental observation of magnetic-field-induced twin variant rearrangement. At higher levels of Co-doping, the grain size was essentially reduced, and the crystal structure of the martensitic phase became 2 M martensite. The decreasing grain size and changing crystal structure are attributed to the progress of γ-phase precipitates. Alongside the academic aspect, the results of the present work point to the commercial advantage of fabricating 10 M Co-doped Ni-Mn-Ga actuating elements made from large grains of polycrystalline ingots obtained by a standard melting facility instead of grown single crystals. [Display omitted] [ABSTRACT FROM AUTHOR]

Sintering titanium (Ti) materials to high densities while maintaining fine grain sizes is a great challenge, which severely restrains their engineering application. Herein, we fabricated a high-density and fine-grain Ti material by a small addition of CaB 6 via powder metallurgy (PM) pressureless sintering route. The effect of CaB 6 addition on the grain growth kinetics and sintering densification mechanism were systematically investigated. The CaB 6 oxygen-scavenger breaks the surface oxide layer and promotes the mutual diffusion of Ti atoms during sintering, resulting in the in-situ formation of nano-sized CaTiO 3 particles and increase the sintered density. Moreover, the micro-sized TiB whiskers with the length from 10 µm to 30 µm and width from 1 µm to 4 µm are also formed in the Ti matrix. The grain microstructure of Ti/CaB 6 composite displays a random orientation feature with the fine and uniform equiaxed crystallites. The presence of in situ TiB and CaTiO 3 second-phase particles makes a greater grain growth activation energy Q for Ti/CaB 6 composites, from the 373 kJ/mol of pure Ti to the 522 kJ/mol of Ti-1.0CaB 6 composite, creating a smaller grain size. The grain refining effect by CaB 6 addition is more effective at high temperature. As a result, the grain size of Ti-1.0CaB 6 composite sintered at 1300 ℃/2 h is only 74 µm, much smaller than the 163 µm of pure Ti. This study offers a feasible way to produce the high-density and fine-grain Ti materials. • The TiB whiskers and CaTiO 3 particles are formed in the Ti/CaB 6 composites. • CaB 6 addition promotes the sintering densification process. • CaB 6 addition makes a greater grain growth activation energy and refines the grain size. [ABSTRACT FROM AUTHOR]

Thermal stability and microstructure evolution in nanocrystalline Ti-5Al-2Sn-2Zr-4Mo-4Cr were investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were applied to characterize grain size change and microstructure evolution after annealing at the temperatures ranging from 300 °C to 650 °C. The results showed that nanograins slowly grew from ∼11.0 nm to ∼32.8 nm as the annealing temperature increased to 500 °C at which the grains were generally homogeneous in size. Re-ordering of grain boundaries (GBs) was shown to be the responsible for the change in grain size annealed at 500 °C and lower temperatures, in which sharp GBs occurred due to strain relaxation and dislocations annihilation. However, an abnormal grain growth was observed at annealing temperatures of 550 °C and 600 °C in which grains grew to ∼85.5 nm and ∼168 nm, respectively. It was further confirmed that the abnormal grain growth was due to synergistic effect of GBs migration, grain rotation, phase boundaries (PBs) migration, and intrinsic difference in α / β PBs. [ABSTRACT FROM AUTHOR]

(Yb 1/2 Nb 1/2 ) 0.05 Ti 0.95 O 2 ceramics are fabricated by the solid state reaction method. The effects of oxygen partial pressure in the sintering atmosphere (10% ≤ x ≤ 100%) on crystal structures, microstructure and dielectric properties of (Yb 1/2 Nb 1/2 ) 0.05 Ti 0.95 O 2 are investigated. All samples have rutile structure, and average grain size rises from 5 μm to 28 μm with x increasing from 10% to 100%. All samples show colossal permittivity (above 10 4 ). The dielectric properties of x ≥ 50% samples show well temperature (120 K–370 K) and frequency stability (100 Hz–100 kHz). The grain resistivity of x = 100% sample is three orders of magnitude higher than that of x = 10%. The breakdown voltage improves from 246 to 716 V/cm with increasing oxygen partial pressure. Both the Ti valence and oxygen concentration have been influenced by sintering atmosphere. [ABSTRACT FROM AUTHOR]

A fascinating structure transition of cerium around 5 GPa has been studied using high-resolution synchrotron angle-dispersive powder diffraction techniques. This study indicates that the structural transition of cerium strongly depends on the process of compression. Two runs experiments with different compression conditions demonstrate two different structural transition sequences at room temperature around 5 GPa, fcc′→ C 2/ m →bct for regular compression, fcc′→ C 2/ m →α-U→bct for the pre-compression. These results show that pressure is not the only factor to determining structural transformation at high pressure, and the structural transformation sequences can be varied by changing the external conditions e.g. pre-compression. [ABSTRACT FROM AUTHOR]

In the present work, the microstructure evolution of WC grains in WC–Co–Ni–Al alloys with different Co–Ni–Al binder phase composition, have been investigated. By combination of thermodynamic calculations and decisive experiments, a series of WC–24 wt.% (Co–Ni–Al) alloys were designed and prepared by liquid phase sintering at 1450 °C for 1 h, 8 h and 20 h, respectively. The influence of Ni 3 Al content in Co–Ni–Al binder on the WC morphology was investigated by scanning electron microscopy (SEM). The results show that, with the increase of Ni 3 Al content, the increasing interface energy raises both the energy barrier for two-dimensional (2-D) nucleation and the energy barrier for W migration. Under the influence of these two factors, the micro-faceted and stepped planes on the WC grains become more and more obvious and the WC grains become finer and blunter simultaneously. Combining the thermodynamic calculation with the experiment, the mechanism for WC morphology evolution has been revealed. The mechanical properties of the alloys were also discussed. [ABSTRACT FROM AUTHOR]

The paper dwells on the research conducted into high-rate consolidation of pure tungsten carbide (WC) nanopowders using the Spark Plasma Sintering technology. Studies included the effect that the original size of WC nanoparticles and their preparation modes have on density, structure parameters, and mechanical properties of tungsten carbide. Samples of high-density nanostructured tungsten carbide characterized by high hardness (up to 31–34 GPa) and improved fracture toughness (4.3–5.2 MPa m 1/2 ) were obtained. It has been found that materials that show abnormal grain growth during sintering have lower values of sintering activation energy as compared to materials the structure of which is more stable during high-rate heating. A qualitative model is proposed that explains this effect through the dependence of the grain boundary diffusion coefficient on the grain boundary migration rate. [ABSTRACT FROM AUTHOR]

Almost single phase quasicrystalline powders consisting of icosahedral Al 65 Cu 23 Fe 12 and decagonal Al 73 Cu 11 Cr 16 phases were produced by mechanical alloying (MA) and subsequent heat-treatment. Microstructure, particle size distribution, chemical and phase composition of crystalline powder precursors forming under MA from elemental powders of Al, Cu, Fe and Cr were investigated. Phase transformations leading to formation of quasicrystals during heating of precursors were determined by differential thermal analysis and X-ray diffraction. The growth of quasicrystalline grains studied by SEM is discussed. [ABSTRACT FROM AUTHOR]