Search

Sr ferrites with x wt% Li2O–B2O3–Bi2O3–SiO2 glass (x for 0–2 wt%) calcined at 850 °C and 1150 °C were synthesized by the traditional solid phase method of ceramics. The main phase of the sintered samples was standard Sr ferrite structure. The XRD results showed that the addition of LBBS glass enhances the peak of Sr ferrites and weakens the peak of Fe2O3, combined with SEM images, LBBS glass has a significant effect on reducing the sintering temperature. At low temperature (850 °C), the coercivity, saturation magnetization and residual magnetization of the samples all show an increasing trend. This is mainly attributed to the increase of M phase, the increase of densification, the more complete grain growth and the decrease of Fe2O3 in liquid phase sintering (LBBS glass after melting). At the same time, part of the electromagnetic properties of the samples also improved at high temperature (at 1150 °C). Among them, the Sr ferrites sintering at 850 °C with 1.2 wt% LBBS glass achieving excellent magnetic properties, including Ms = 41.25 emu/g, reach the standard of 96.08%; Hcj = 3423.8Oe, reach the standard of 134.48%; Mr = 25.12 emu/g, reach the standard of 101.57%, the sample of x = 0.0 sintering 1150 °C as the standard sample.

The influences of initial grain size (IGS) with 20 µm and 50 µm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623–1073 K and strain rate range of 0.001–0.1 s−1. The effects of critical stress and corresponding critical strain were studied based on the internal and external processing parameters. The critical stress and strain decreased with increasing temperature and decreasing strain rate. The investigation results of the microstructure and true strain–stress diagrams showed that dynamic recovery, dynamic recrystallization (DRX), and twinning mechanisms were caused during the hot deformation of pure copper. Microstructure evolution indicated some DRXed fine-grain took place around grain boundary of hot deformed samples with IGS of 20 µm whereas DRXed fine-grain took place in interior grains for samples with larger IGS. The results also showed that grain growth is also dependent on IGS as the grain growth rate for samples with the larger IGS is greater than the smaller IGS. The critical strain rate and the temperature were obtained at 0.01 s−1 and 973 K, respectively, for the sudden change in the grain growth rate. Also, twinning highly depended on IGS which almost did not happen in fine grain size while the volume fraction of twinning increased with increasing grain size.

The magnetocrystalline anisotropy and the exchange bias in nanocrystalline FeCo with and without a post-synthesis high-temperature thermal treatment have been investigated. The synthesized products were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and dc magnetization. The XRD spectra revealed the presence of secondary phases which reduced after thermal treatment resulting in the formation of single-phase polycrystalline FeCo. The FE-SEM micrographs confirmed the formation of impurities, which disappeared after thermal treatment, along with the substantial grain growth. The uniform distribution of the elements was confirmed through EDS spectra. The temperature and the magnetic field-dependent magnetization measurements under various conditions showed that, as a consequence of thermal treatment, the saturation magnetization and the magnetocrystalline anisotropy has been enhanced along with the generation of exchange bias. The phenomena of grain growth, formation of grain boundary and the exchange interactions have been described with the help of the proposed mechanism. In brief, the post-synthesis high-temperature thermal treatment induced structural as well as microstructural variations leading to the formation of grain boundaries. These grain boundaries provided interface regions for the occurrence of exchange interactions, which enhanced the magnetocrystalline anisotropy and induced exchange bias in nanocrystalline FeCo.

YBa2Cu3O7-x (YBCO) is a kind of high-temperature superconducting material that has important application in information, energy, medical treatment, etc., and the superconducting properties of YBCO are closely related to its internal microstructure. In this study, the microwave heating method was adopted to prepare the YBCO materials. The internal 3D online evolution observation based on the synchrotron radiation computed tomography technology shows that there was directional grain growth phenomenon of YBCO during microwave sintering process. In local regions with special microstructure, these particles grew to the same point. Here, the theoretical models of single and multiple particles in the microwave electromagnetic fields were established. Based on these theoretical models and finite element analysis, it shows that the YBCO particles can modulate the distribution of electromagnetic fields, resulting in the significantly higher electric field intensity at the particle junctions than other regions. Moreover, there were very high electric field intensity and temperature gradients in the directions of particle growth. These factors were crucial in directional sintering. These results will provide theoretical basis and technical guidance for the controllable preparation and performance optimization of the internal microstructure of superconducting materials in the preparation process.

The grain structure and macrosegregation directly affect the mechanical properties of electroslag remelting (ESR) ingots which are important raw materials in industry. In this paper, an axisymmetric multiscale multicomponent transient model based on cellular automaton-finite element (CAFE) method is developed by coupling macroscopic phenomena (including fluid flow, heat and solute transfer) and the mesoscopic structure evolution (e.g. nucleation and grain growth) to predict grain structure and macrosegregation. The solutions of the mass, momentum, energy, solute conservation equations and grain growth kinetics are calculated simultaneously. The single grain information (e.g., the size, shape and aspect ratio) is obtained by minimal oriented bounding box (MOBB) method and statistically analyzed. Firstly, the accuracy of this multiscale mathematical model is validated by comparing grain structures and solute concentration profile from simulation with those from experiments. Secondly, the effects of two processing factors, the melting rate and heat transfer coefficient, on the grain structure and macrosegregation are investigated. When the melting rate increases from 12.7 to 25.5 g/s, the maximum positive segregation index of carbon increases from 4.5 pct to 9 pct and the average grain size decreases from 120.0 to 21.0 mm2. When the heat transfer coefficient increases from 250 to 500 W/(m2 K), the maximum positive segregation index of carbon decreases from 5.6 pct to 3.7 pct and the average grain size increases from 44.6 to 76.8 mm2. Finally, the coupling effect of grain growth and macroscopic fields including fluid flow and macrosegregation is analyzed. When the fluid flow is decoupled from grain growth, the predicted angle between the columnar grain and the ingot axis is 4.85 deg larger than that of fully coupled case and the predicted average length of columnar grain becomes smaller. When the macrosegregation is ignored in the ESR process, the predicted depth of liquid pool decreases by 2.0 mm, and the equiaxed grain zone at the center of the ESR ingot becomes small. This multiscale transient model using CAFE method could be able to set processing parameters for the desired products with adequate accuracy.

To investigate lattice distortion evolutions of CrCoNi medium-entropy alloy (MEA), CrFeCoNi, and CrMnFeCoNi high-entropy alloys (HEAs) with temperature increasing from 300 to 1323 K, we conduct in situ synchrotron-radiation-based X-ray diffraction experiments. Electron backscattering diffraction, energy-dispersive X-ray spectroscopy and X-ray absorption near edge fine structure spectra (XANES) are further carried out to uncover variations of microstructure, morphology and oxidation resistance. Generally, the lattice will expand continuously with temperature increasing, however, the expansion rate is affected by grain growth and oxidation. The oxidation resistance of CrCoNi MEA is slightly higher than CrFeCoNi HEA, and much higher than CrMnFeCoNi HEA. The XANES spectra demonstrate higher oxidation resistance of Ni, Co, and Fe than Cr and Mn. Formation of local short-range order structures around Ni and Co is observed, but no such features are observed around Fe and Mn. The present findings are significant on deepening the understandings of correlations between atomic structure and mechanical properties in advanced HEAs.

AM technologies allow for the fabrication of complicated geometric components at reduced costs and with better functionality. Aside from design complexity, regulating desired textures during AM processes can provide a substantial advantage. Microstructures are typically columnar along the build direction and equiaxed across the build plane. Columnar grain structures are characterized by a high crystallographic texture and mechanical anisotropy. The crystallographic texture is a key material parameter that has a significant impact on a product's functionality. Mechanical anisotropies result from preferred crystallographic orientations. Additive manufacturing processes acquire crystallographic texture primarily through solidification, which is influenced by local heat flow directions and competing grain growth in the chosen crystallographic direction. This paper provides a comprehensive explanation of the foundations of solidification structure and texture as they pertain to additive manufacturing in some of the most widely researched structural metals, particularly steels, nickel-base superalloys, and titanium alloys.

In this work, the thermal stability of nanocrystalline (NC) AZ31/TiB2 magnesium matrix composites was investigated, while the microstructure evolution and mechanical properties were analyzed. The results indicated the AZ31/TiB2 still maintained NC structure after annealing at 350 °C for 180 min. Even at the high annealing temperature of 400 °C and 450 °C for 180 min, their average grain size just reached about 124 nm and 155 nm, indicating excellent thermal stability. The TiB2 particles with sub-micron size uniformly distributed in Mg matrix had no change in size and no reaction with matrix during the annealing treatment. Due to the strong Zener pinning effect of TiB2 particles, the grain growth of Mg matrix at high temperature was effectively inhibited. Meanwhile, the solution and precipitation behavior of Al atoms were completed in a short time, due to the existence of many grain boundaries and structural defects. By calculation, the grain growth kinetics was described by the kinetics equation $$D^{8} - D_{0}^{8} = kt$$ and the activation energy Eg for grain growth was 131.6 kJ/mol, which was much higher than that of pure Mg (92 kJ/mol). Due to their excellent thermal stability, the decrease in both compressive yield strength and ultimate compressive strength was no more than 12.2% after annealing treatment. Even annealing at 450 °C for 180 min, the CYS and UCS of the samples were still above 283 MPa and 295 MPa, respectively.

The electron beam additive manufacturing (EBAM) method was applied in order to fabricate rectangular-shaped NiTi component. The process was performed using an electron beam welding system using wire feeder inside the vacuum chamber. NiTi wire containing 50.97 at.% Ni and showing martensitic transformation near room temperature was used. It allowed to obtain a good quality material consisting of columnar grains elongated into the built direction growing directly from the NiTi substrate, which is related to the epitaxial grain growth mechanism. As manufactured material showed martensitic and reverse transformations diffused over the temperature range from −10 to 44 °C, the applied aging at 500° C moved the transformation to higher temperatures and transformation peaks became sharper. The highest recoverable strain of about 3.5% was obtained in the as-deposited sample deformed along the deposition direction. In the case of deformation of the alloy aged at 500 °C for 2h, the formation of martensite occurs at significantly lower stress; however, at about 2.5% the stress begins to increase gradually and only a small shape recovery was observed due to a higher martensitic transformation temperature. In situ SEM tensile deformation in the direction perpendicular to deposition direction showed that the martensite began to appear at the surface of the sample and at the grain boundaries due to heterogeneous nucleation. In situ studies allowed to determine the following crystallographic relationships between B2 and B19’ martensite: (100)B2||(100)B19’and (100) B2 || (011)B19’; (011)B2|| (001)B19’and$${(011)}_{\mathrm{B}2}||{\left(11\bar{1 }\right)}_{\mathrm{B}1{9}^{\mathrm{^{\prime}}}}$$(011)B2||111¯B19′. Samples aged at 500 °C exhibited fully austenitic microstructure; however, with increasing degree of deformation, the formation of martensite was observed. The majority of needles were tilted about 45° with respect to the tensile direction, and the presence of type I (11$$\bar{1 }$$1¯) invariant twin boundaries was observed at higher degrees of deformation.

0.675BiFeO3-0.3BaTiO3-0.025LaFeO3-x mol% Nb2O5 (x = 0–1.25) multiferroic lead- free ceramics, fabricated by conventional solid-state reaction, were studied to reveal the effects of Nb2O5 on the structural, morphology, dielectric, ferroelectric, magnetic and magnetoelectric properties of the BiFeO3-based ceramics. After the addition of Nb2O5, the crystal structure of as-prepared samples remained orthorhombic phase. The doping Nb5+ ion could be able to inhibit grain growth remarkably and suppress the creation of oxygen vacancies of this ceramics, which resulted in the improvement of electrical insulation by two orders of magnitude. The ferromagnetism was apparently enhanced with increasing content of Nb2O5, and the observed remanent magnetization Mr peaked at 0.022 emu/g for x = 1. Suitable amount of Nb2O5 could be beneficial to the dielectric properties, with the optimal x at 0.75, with dielectric constant er of 918 at 100 Hz. The observed magnetoelectric coefficient αME suggested the existence of magnetoelectric coupling effect in these ceramics. The αME value almost decreased after adding Nb2O5, possibly due to the obvious degradation of ferroelectric behaviors.

In this research paper, microstructural, electromagnetic properties, and thermal stability, of (Mg0.3Cu0.2Zn0.5O) (Fe2O3) ceramics were adjusted by using low-melting point molybdenum trioxide (MoO3) as additive. The required ferrite powders were synthesized through a cost-effective sol–gel method. The ferrite ceramics with high density and high permeability were prepared, using various content of MoO3 (from 0.00 to 1.00 wt%) at low sintering temperature. Results indicate that MoO3 not only improves density and grain growth of ferrite samples, but also effectively tailors the saturation magnetization (Ms), coercive field strength (Hc), initial permeability (µi), and Curie temperature (TC). For a qualitative comparison, the SEM images of both surface and fracture surface of the specimens were obtained. The results indicate that 0.25 wt% MoO3 can promote grain growth, densification and uniformity, and reduce pores between grains of the sintered sample. In particular, MgCuZn ferrite with high bulk density (ρ = 4.7 g/cm3), high initial permeability (μ′ = 460), high saturation magnetization (Ms = 50.6 emu/g), and low coercivity (Hc = 1.4 Oe) are obtained when the content of additive is 0.25 wt%. However, the excessive amount of MoO3 deteriorates the grain size uniformity and weakens the magnetic properties due to the production of non-magnetic MoO3 liquid phase.

Copper and its alloys have been in the service of humankind earlier than any other metal throughout history. In the present review, all aspects of the SPS of copper and its alloys are comprehensively investigated, and their potential effects on the microstructure and properties of alloys are thoroughly reviewed. In this regard, the densification phenomenon during SPS treatment is fully investigated. The effects of raw powder characteristics involving particle size, contamination content, and powder morphology on the sinterability of these materials are examined. Then, the influence of SPS operation parameters consisting of pressure, heating rate, dwelling time, pulsed electrical current, electrical pulses pattern, sintering temperature, and sintering tooling on densification of these materials is extensively discussed. Furthermore, the microstructure evolution and grain growth behaviors during SPS are explored. In addition, current challenges and future perspectives of this field are addressed.

The effect of aging on a mechanical alloyed (MA) ferritic oxide dispersion strengthened (ODS) alloy was investigated focusing on the B2-NiAl nano-precipitates. The matrix of the alloy is decorated with a high volume fraction of B2-NiAl precipitates and dispersed nano-oxide particles. Due to the coarsening effect of Al on oxides and the changed Zener drag effect on grain growth, the bimodal grain structure was formed. With the extension of the aging time, the size of nano-precipitate increases and its morphology changed from near spherical to rodlike. The temporal evolution of nano-precipitates upon aging treatment is consistent with the modified Lifshitz–Slyozov–Wangner (LSW) theory. In addition, the quantitative calculation reveals the weakening effect caused by nano-precipitates coarsening during aging is the main reason for the decrease in alloy strength.

Alumina-based composites have been prepared through reaction sintering of alumina and zircon. To develop these advanced composites, the effects of the addition of MnO2 and ZnO (1 wt.% and 2 wt.%) on the sintering behavior, phase content, microstructure, and mechanical properties of the prepared composites were investigated. It was found that MnO2 retarded the formation of mullite but increased the stability of tetragonal zirconia, whereas ZnO had the opposite effect. At 1 wt.%, both additives formed a solid solution with alumina, but using 2 wt.% resulted in the formation of a secondary phase. Both additives restricted the grain growth of alumina and hence enhanced the mechanical properties and thermal shock resistance of the composites. The results also revealed that, when using the additives, the porosity content increased slightly, but on the other hand, the formation of solid solution, refinement of grain size, stabilization of tetragonal zirconia, and increase in the mullite content were beneficial effects of these additives.

The influences of Lu3+ doping on the structure and electrical properties of CaCu3Ti4O12 (CCTO) ceramics are systematically studied. We find that Lu3+ doping inhibits the grain growth of CCTO while the dielectric constant decreases firstly and then increases with the increase of Lu3+ content. The positron annihilation results indicate defect concentrations increase with the increment of Lu3+ content. At low Lu3+ doped level, the huge dielectric response of the samples mainly derives from the internal barrier layer capacitor (IBLC) effect while intrinsic polarization as defect dipoles makes more contribution at higher doped level. The dielectric loss is depressed due to the increase of cation vacancies and grain boundary resistivity. Good performances (high e′ of ∼ 1.1 × 104 and low tanδ of ∼ 0.025) at 1 kHz are obtained in Ca0.85Lu0.15Cu3Ti4O12 sample. Moreover, the enhanced nonlinear electrical properties are associated with cation vacancy defects generated by Lu3+ doping in the GB region. These findings are helpful in exploring the physical nature of the dielectric properties of CCTO.

In the present study, WC-10Co with TiC, VC and (Ta, Nb)C as the inhibitors to the grain growth was prepared using high energy ball milling and the subsequent HIP process at various temperatures. Phase evolution and microstructural studies were performed for the milled and sintered samples by x-ray diffraction, vibrating sample magnetometry, field emission scanning electron microscopy and transmission electron microscopy. Also, the density and microhardness of the sintered samples were measured. It was found that densification and grain-growth rate were sensitive to the sintering temperature, type and overall content of the additives. The samples sintered at the higher temperature showed better densification and hardness, with lower porosities. The additives were found to have significant influence on the microstructure and properties of the sintered products. Sintered samples containing additives had considerably improved microhardness, but densification was lowered up to 4.8%. However, the highest microhardness was 1920 HV for the sample with the three types of additives sintered at 1480 °C.

The solid-state joining of oxide-dispersion-strengthened (ODS) austenitic steels was achieved using a pulsed electric current joining (PECJ) process. Microstructures of the austenitic grain structures and oxide dispersions in the joint areas were characterized using electron microscopy. Negligible grain growth was observed in austenitic grain structures, while slight coarsening of oxide dispersions occurred at a short holding time. The mechanisms of the PECJ process may involve three steps that occur simultaneously, including the sintering of mechanical alloying powders in the bonding layer, formation of oxide dispersions, and bonding of the mechanical alloying powders with the base alloy. The high hardness and irradiation resistance of ODS alloys were retained in the joint areas. This research revealed the fundamental mechanisms during the PECJ process, which is beneficial for its potential applications during the advanced manufacturing of ODS alloys.

Lead-free ceramics ((Bi0.5Na0.5)0.7(Sr0.7Bi0.2)0.3)1-xSmx)TiO3 (x = 0.0, 0.005, 0.01, 0.02, 0.03) with a novel phase boundary structure were successfully synthesized. All samples sintered well and shown pure perovskite structure. The doping of Sm3+ inhibits the grain growth and enhanced the relaxor properties. Besides, the activity of polar nanoregion (PNRs) is improved. Ferroelectric analysis showed that proper Sm3+ doping played a pegging role on the saturated polarized Pm, leading to a higher and slimmer P-E loop. As a result, a large energy storage density (~ 1.25 J/cm3) with high energy efficiency (~ 73%) were achieved at x = 0.005 under an electric field of 90 kV/cm. Further, the sample was found to have good temperature stability between room temperature and 110 °C. This study shows that ceramic material has great potential for the application of high-temperature stability energy storage capacitors.

High energy mechanically milled Alloy 617 ODS powder was consolidated by Spark Plasma Sintering (SPS) technique and subsequently annealed at 650 °C and 1050 °C (923 K and 1323 K). Microstructure and microtexture evolution during SPS and annealing have been investigated. SPS consolidated sample exhibited heterogeneous microstructure with ultra-fine grains surrounded by coarse grains. Inhomogeneous distribution of plastic deformation induced during ball milling resulted in heterogeneous nucleation and further grain growth during consolidation. The bimodal microstructure is advantageous with coarse grains providing ductility and fine grains providing strength by the Hall–Petch relationship. The bimodal grains structure was also retained during annealing. As-sintered specimen showed 〈100〉 texture parallel to the compression axis due to dynamic recrystallization during the SPS process. At 650 °C, annealed sample exhibited 〈111〉 annealing texture parallel to compression axis. The texture was randomized in sample annealed at 1050 °C. Precipitation analysis by SEM, XRD and TEM showed the presence of M23C6, M6C and Al2O3 in both As-sintered and annealed samples. Dispersoids analysis showed the presence of fine and uniform Y3Al5O12, Y4Al2O9 and a complex oxide rich in Ni, Y, Al and O. Stress–strain analysis from instrumented indentation test shows higher yield strength for Alloy 617 ODS in comparison with conventional Alloy 617.

The solvus temperature of face-centered cubic (FCC) phase in Fe–34Mn–xAl–4Cr–7.5Ni (x = 13, 14, and 15) shape memory alloys with different Al contents, and their abnormal grain growth and superelasticity at various temperatures were evaluated. With increasing Al content, the solvus temperature of the FCC phase decreased and the FCC precipitates became finer. Whereas cyclic heat treatment induced abnormal grain growth (AGG) in all samples, large grains were obtained more easily in the alloys with higher Al content. The critical stress for martensitic transformation increased with increasing Al content. The x = 14 alloy is the optimal composition considering grain growth and superelasticity. The newly developed Fe–34Mn–14Al–4Cr–7.5Ni alloy, in which single-crystal can easily be fabricated by AGG, exhibited superelasticity at temperatures ranging from − 263 °C (10 K) to 27 °C (300 K), with a very small temperature-dependence of the critical stress, comparable to that of conventional Fe–34Mn–13.5Al–3Cr–7.5Ni alloy.

In situ synchrotron X-radiography was carried out on Al–13Cu and Al–13Cu–7Si alloys with and without addition of Al–5Ti–1B master alloy. The effects of Si content on grain growth and the solute-suppressed nucleation zone (SSNZ) were quantitatively studied. The average grain size can be refined to 164 μm of Al–13Cu alloy inoculated by Al–5Ti–1B. After addition of 7% Si content, a large number of TiB2 sites in the melt lost the inoculating ability due to “Si poisoning.” The radius of the dendrite tip curvature of Al–13Cu is more than two times as large as that of Al–13Cu–7Si. The sharper tip is able to disperse the solute more effectively and thus grains can grow more rapidly. This causes that the dendrite arm growth rate with addition of 7% Si solute is about 2.6 times that of no Si addition. In addition, the solute enrichment in the SSNZ of Al–13Cu is faster, and the area change of SSNZ is slower than that of Al–13Cu–7Si. Thus more nucleation sites in the SSNZ cannot be activated with addition of Si. This study will shed light on the understanding of Si poisoning in casting Al–Cu–Si alloys.

Lead-free perovskite materials Barium Magnesium Titanate (BMT) and composite of BMT/Ga2O3were prepared using environment friendly low temperature method. XRD peak profile analysis of pure BMT and nanocomposite of BMT/Ga2O3 to determine the crystallite size have been carried out using various calculations methods like Scherrer, Williamson–Hall, and Size–Strain plot. The crystallite size was found to increase with the addition of Ga2O3 in BMT. Moreover, XRD patterns reveal the pure and crystalline phase of the prepared samples. Raman study of BMT and BMT/Ga2O3 are showing the tetragonal symmetry. SEM studies revealed that the addition of Ga2O3 accelerates the grain growth of BMT whereas EDX indicated that there is no significant trace of any impurity and confirmed the stoichiometric presence of the expected elements within the sample. SAED patterns demonstrate broad concentric rings, which confirm the presence of crystalline powder. P–E hysteresis loop confirms the ferroelectric behaviour of the samples with increase in remnant polarization and the increase in coercive field.

Manufacturing defects, heterogeneous microstructure, and micro-segregation of secondary laves phases are the major issues to be resolved during the fabrication of alloy Inconel 718 (IN718) fabrication through metal additive manufacturing (AM). The present study delivers the importance of post AM double aging heat treatment (HT) of alloy IN718 fabricated through laser-based powder bed fusion process (L-PBF). Initially, the as-built IN718 sample was subjected to solution annealing at 980 °C for the duration of 1 hour followed by air cooling. Then, the L-PBF sample was subjected to double aging at 720 °C for 8 hours followed by furnace cooling to 620 °C in 2 hours. The specimen was kept at 620 °C for 8 hours and then cooled to room temperature. The beneficial influence of HT on the closure of AM-induced manufacturing defects such as pores and voids, microstructural changes, and microhardness have been reported. As-built microstructure showed the presence of heterogeneous columnar dendrites along the build direction with the presence of a large number of laves phases in the interdendritic regions. HT microstructure resulted in the formation of homogeneous austenite gamma (γ) matrix in which the strengthening phases such as gamma prime (γ′) (Ni3 (Al, Ti)) and gamma double prime (γ″) (Ni3Nb) were observed. As a result of HT, laves phases ((Ni, Fe, Cr)2·(Nb, Mo, Ti)) were dissolved in the grain interiors and precipitated in the grain boundaries as delta (δ) phase (NbNi3). The δ phase in the grain boundaries arrested the grain boundary dislocation, as well as grain growth, and revealed the relatively finer and homogenous grain structures. Further, a Micro-computed tomography (micro CT) examination revealed the absence of AM-induced pores after HT. The hardness of the heat-treated samples was increased to 35% and it showed an increase in hardness from 417 to 564 HV. Dimensional analysis was performed on the alloy IN718 to study the effect of thermal loading. The volumetric shrinkage of 3.084% was noted as a result of heat treatment at the micron-scale.

This work focuses on the effects of Bi compensation on the phase structure, microstructure, ferroelectric, and piezoelectric performances of new 0.69Bi1 + xFeO3-0.31BaTiO3 (x, 0–0.08) piezoceramics fabricated by traditional sintering techniques. X-ray diffraction (XRD) results indicated that Bi compensation has slight influences on the phase structure and all the ceramics locate near the morphotropic phase boundary of rhombehedral–pseudocubic phase coexistence. The rhombehedral phase fraction of all the ceramics fluctuates slightly in the range of 41.7–49.1 %. X-ray photoelectron spectroscopy (XPS) results confirmed that Bi compensation favors the decrease in the percentage of oxygen vacancy in the ceramics. An appropriate content of Bi compensation facilitates the densification, grain growth as well as enhancement of piezoelectric property of the materials. In addition, Bi compensation makes the materials “soft” along with the lower EC compared with the no compensation ceramics. Significantly, the excellent piezoelectric performance (d33 = 207 pC/N) was achieved in the 0.69Bi1.04FeO3-0.31BaTiO3 ceramics, which is higher than the results obtained in the previously reported BiFeO3-BaTiO3-based ceramics. This work would trigger further study on the BiFeO3-BaTiO3-based piezoceramics for practical application.

The aim of the present study was to determine the evolution of resistance to pitting corrosion and changes in the mechanical properties of ultrafine-grained aluminium during annealing. In contrast to the numerous papers devoted to the topic of the corrosion resistance of severely deformed aluminium alloys, a unique approach has been taken in this study. The size and distribution of the primary intermetallic particles, which are crucial in terms of corrosion resistance, remain constant during annealing. Therefore, the influence of other microstructural features could be investigated and compare with the results of mechanical properties. It was shown that the ultrafine-grained structure of commercially pure aluminium was stable up to 200 °C. Higher annealing temperatures caused significant grain growth and a reduction in dislocation density, which resulted in a drop in mechanical strength. Also, the corrosion resistance slightly decreased, since with an increase in annealing temperature a decrease in the corrosion potential, pit size, and the area damaged by corrosion attack were noted. The best combination of mechanical strength and resistance to pitting corrosion has been achieved for as-deformed state.

The volumetric growth rate of individual grains has been found empirically to be directly proportional to their individual volume, dV/dt = β(V0 − V). This simple result extends from the relationship $${\mathrm{d}}V/{\mathrm{d}}t=-k{M}_{\mathrm{S}},$$ where MS is integral mean curvature of the boundaries of individual grains and k the grain growth rate constant, and the experimentally observed linear relationship between $${M}_{\mathrm{S}}$$ and individual grain volume, $${M}_{\mathrm{S}}$$ = α(V0 − V). Here, α is a scaling parameter that collapses the relationships for separate times of growth into a single trend. It has been shown that α = $$\gamma {\bar{V}}^{-2/3}$$ where γ is an experimentally determined constant ≃ − 2.7 and $${\bar{V}}$$ is the mean grain volume. Thus, β = −kα = 2.7k $${\bar{V}}^{-2/3}$$ , simply proportional to the scale of the overall grain structure. These relationships have been tested successfully in numerous 3D grain growth simulations and experiments. This paper describes the relationships among these kinetic and geometric grain characteristics that provide this surprisingly simple description of 3D grain growth, i.e., a linear relationship between the growth rate of an individual grain and its volume.

Equal channel angular extrusion (ECAE) of 49Fe-49Co-2V, also known as Hiperco® 50A or Permendur-2V, greatly improves the strength and ductility of this alloy, while sacrificing soft magnetic performance. ECAE Hiperco specimens were subjected to post-ECAE annealing in order to improve soft magnetic properties. The microstructure, mechanical properties, and magnetic performance are summarized in this study. Annealing begins above 650°C and a steep decline in yield strength is observed for heat treatments between 700 and 840°C due to grain growth and the Hall-Petch effect, although some strength benefit is still observed in fully annealed ECAE material compared to conventionally processed bar. Soft magnetic properties were assessed through B-H hysteresis curves from which coercivity (Hc) values were extracted. Hc decreases rapidly with annealing above 650°C as well, i.e. improved soft magnetic behavior. The observed trend is attributed to annealing and grain growth in this temperature regime, which facilitates magnetic domain wall movement. The coercivity vs. grain size results generally follow the trend predicted in the literature. The magnetic behavior of annealed ECAE material compares favorably to conventional bar, possibly due to mild crystallographic texturing which enhances properties in the post-ECAE annealed material. Overall, this study highlights a definitive tradeoff between mechanical and magnetic properties brought about by post-ECAE annealing and grain growth. ®Hiperco is a tradename of Carpenter Technology Corp., Reading, PA.

Additive manufacturing (AM) is a powerful tool for fabricating ceramics with novel and/or improved properties by enabling access to unique part architecture and geometry, and control of pore structure and distribution. In this review we show that layer-wise and direct writing AM processes can be used to fabricate microscopically-textured ceramics with unique crystallographic orientations by combining templated grain growth (TGG) with manipulation of the rheological properties of the feedstock, printhead geometry and printing speed during layer-wise and direct writing AM processes. For TGG the shear gradient, and resultant local torque, during printing aligns anisotropically-shaped template particles which serve as substrates for subsequent oriented grain growth and increase in crystallographic texture in the final part during sintering. We show how the deposition flow field and rheology of AM feedstocks coupled with anisotropic printing nozzles enables enhanced template alignment by impacting the torque gradient during deposition. Prospects for AM of textured ceramics are presented.

As a typical varistor with a relative low breakdown voltage and high nonlinear coefficient, TiO2 varistor can be applied in electronic field with low voltage. Even so, further efforts need to be dedicated so as to improve the comprehensive properties. In this work, the effects of Sb2O3 varying from 0 to 0.4 mol% on the microstructure and electrical properties of TiO2-Nb2O5-SiO2-Ho2O3 varistor ceramics sintered via a conventional solid-state reaction method have been investigated by means of different characterization methods involving in phase composition, morphology, varistor and dielectric properties. The SEM analysis indicates that although the appropriate doping of Sb2O3 is beneficial to coarsen the grains, the grain growth is inhibited once the doping content of Sb2O3 is beyond 0.1 mol%. The XPS analysis demonstrates that during the sintering process at a high temperature in air, a part of Sb3+ ions would be oxidized as Sb5+ ions, releasing free electrons, as a result, the resistivity of the grain decreases, accompanying with continuous decline of the breakdown voltage from 6 V/mm to 1.9 V/mm with the doping content of Sb2O3 rising from 0.1 mol% to 0.4 mol%. Meanwhile, the relative dielectric constant and nonlinear coefficient are both improved initially, reaching the maximum 4.05 × 105 and 7.4 respectively at the 0.2 mol% of doping Sb2O3, and then decrease. Since it is noted that doping Sb2O3 has a negative effect on the dielectric loss, this kind of varistor needs to be further focused on controlling the ratio of Sb3+/Sb5+.

Selective laser melting (SLM) is a manufacturing technology that involves melting metal powder beds. Due to the temperature gradient during the course of forming, anisotropy is further caused by oriented grain growth. However, the influence of process parameters on anisotropy has not been studied. Two types of parameter scanning strategies and rotation angle increments were selected to alter the growth tendency of grains, thus affecting anisotropy. Comparing the STRIPES scanning strategy and the CHESS strategy, the latter can restrain anisotropy, while in the former, the anisotropy of tensile stress is influenced by the layer angle increment. The maximum tensile strength of SLM-formed parts in the formed direction deviates from an angle of 60° (1235 MPa and elongation of 5.3%), and the maximum microhardness property appears at the formed direction surface, namely, the top side surface (487 HV).

Several studies had been performed on accumulative roll bonding (ARB) for AA1050; however, most of them were conducted at room temperature. Here, the ARB process was performed on AA1050 plates through nine cycles at elevated temperature. An innovation introduced a new parameter ( $$\frac{UTS\times El.}{\varepsilon }$$ ) to compare the strength-elongation balance between the present study and previous works. Also, as another parameter, the toughness was compared. Comparing these parameters with previous works showed that the considered samples in the present study performed 14 to 63% better than the other samples, so they were more industrially favorable in terms of mechanical behavior and performance. ARB process at elevated temperature may slightly lead to grain growth compared to room/cryogenic temperature, but creates a better elongation, which ultimately leads to a better balance of the strength-elongation parameter. The results showed that the effect of inter-cycle heating was found significant on microstructural evolution and mechanical behavior. Upon five cycles of the process, the grain size was decreased from 35 to 1.8 μm. The yield strength and ultimate strength increased up to 305% and 94%, respectively. Microhardness test showed that warm ARB reduces inhomogeneity factor in the thickness after 3 cycles. Fractography by SEM showed that the sample failed through shear ductile rupture and that the dimples became smaller, more elongated, and shallower onto the failure surface as the number of ARB cycles increased. In short, the warm process is preferred to the cold process to achieve better mechanical performance and toughness.

In this research, transient liquid phase (TLP) bonding method was used to join Al-2%Nanoclay composite, using a Cu interlayer. The samples were bonded for 60 to 240 min at 580 °C. Microstructural evaluations showed that the bond line was widened by increment in holding time due to dissolution of joint zone and base material. However, bond width decreased in 240-min sample due to the completion of isothermal solidification and subsequent homogenization. Phase assessment revealed CuAl2 precipitates in joint zone. Since the Al base material contained Nanoclay particles, it prevented extensive grain growth after TLP bonding. Mechanical properties tests exhibited that shear strength increased from 60 MPa in 60-min sample to 88 MPa in 180-min sample, owing to advance in homogenization and dissolution following the completion of isothermal solidification.

Nanocrystalline metals are generally unstable due to a large volume fraction of high-energy grain boundaries associated with a small grain size. Preferential dopant segregation to the high-energy grain boundaries is observed to enhance the stability of the material’s microstructure by minimizing its energy. Nanocrystalline aluminum-dopant systems were evaluated for thermodynamic stability against grain growth and phase precipitation via the mechanism of grain boundary segregation according to a modified regular nanocrystalline solution model. Fifty-one potential dopant elements have been evaluated for their efficacy in stabilizing nanostructures with three potential candidates, magnesium, lanthanum, and silicon, identified possessing the characteristics to promote grain boundary segregation and a state of thermodynamic stability in aluminum’s nanocrystalline regime. The minimum dopant content required to achieve nanocrystalline microstructure stability is identified for each of the three candidate elements. Beyond this minimum content, further addition of the dopant elements decreased the final microstructure’s stability with no effects on the existence of a stable nanocrystalline state.

Perovskite-structured Dy-doped BZT–BCNT system has been investigated with variation of Dy doping through the solid-state reaction method. X-ray diffraction (XRD) and microscopic studies confirm the results in the rhombohedral stoichiometry without any secondary phases and uniform grain growth, respectively. Tolerance factor and electronegativity also confirm the presence of Dy doping in BZT–BCNT ceramic system with a stable rhombohedral crystallinity forming vacancy sites for oxygen ions. Optimum piezoelectric (PE) properties in non-Pb PE ceramic systems obtained due to trivalent donor Dy doping at A-site and pentavalent donor Nb at B-site are possible members for actuator and energy harvesters. Dielectric and PE studies signifying the rhombohedral perovskite behavior of this lead-free ceramic system confess that the proposed investigation could yield further potential PE sensors and actuator applicative futuristic studies.

Increasing static recrystallization (SRX) nucleation rate and decreasing grain growth rate are the main ways to obtain uniform and fine grain microstructure by annealing treatment. However, it is contradictory to raise the SRX nucleation rate and reduce grain growth rate during isothermal annealing treatment. This is because the increase of the SRX nucleation rate needs to raise annealing temperature, while the decline of grain growth rate needs to reduce the annealing temperature. To solve the contradiction, a novel method named cooling recrystallization annealing treatment (CRT) is designed and verified. For the CRT, the relatively high annealing temperature in the primary stage can promote SRX nucleation, and the gradually decreased annealing temperature can reduce the growth rate of SRX grains. Besides, an aged treatment is first carried out to precipitate high content of the δ phase before the CRT. Enough δ phases not only provide large numbers of sites for SRX nucleation but also limit the grain growth due to the pinning effect, especially in the primary high-temperature stage. The results show that the novel method can refine deformed mixed grain microstructure well when the suitable cooling rate, start and final recrystallization annealing temperatures are employed. The deformed mixed grain can be uniformly refined to an average size of 8.26 μm with the route of 900°C×12 h+1020°C→970°C×20 min.

Fe–Mn–Al–Ni superelastic alloy is a potential candidate for diverse engineering applications due to its outstanding properties and low material costs. Recent studies suggest that slight changes in the chemical composition severely affect superelastic response, phase stability and grain growth kinetics. In this paper, we found that the Al stabilizes the parent α phase at high temperature and promotes the formation of β precipitation at lower temperature. An alloy with a 3:1 ratio between Al and Ni produces homogeneously distributed β precipitates with high phase fraction in the alpha matrix after quenching from 1200 °C. The presence of these precipitates stabilizes the α phase, lowers the martensitic transformation temperature and gives the alloy a fully-reversible stress-induced martensitic transformation behaviour without the need to apply an aging step. In alloys with lower Al content the β precipitation produced during quenching is severely restricted and pseudoelasticity is impaired.

A-site donor-doped NBT systems (Na0.5Bi0.5)1-xMxTi(1-x/4)O3 (M = La and Sm) were synthesized by microwave-assisted solid-state reaction route. Effects of doping concentration on phase, microstructure, dielectric, and ferroelectric properties were characterized and discussed. X-ray diffraction study revealed the existence of single perovskite phase in all the studied ceramics and indicated the solubility limit of La and Sm in NBT system is up to 3 mol%. Doping of La and Sm in NBT system acted as grain growth inhibitors, because donor doping results in formation of cation vacancies which concentrate near grain boundaries and weaken the mass transportation. Doped NBT systems, with higher densities, showed higher dielectric constant and lower leakage current density. Compared to parent NBT system, transition temperature (Tm) shifts toward higher temperature side with the increase of doping concentration. 1 mol% Sm-doped NBT system showed lesser diffusivity and better ferroelectric properties compared to rest of the systems.

Composite powders of pre-alloyed 316 L austenitic stainless steel with yttria (Y2O3) powder in various compositions (0.3, 1.0, 1.5 and 2 wt%) were synthesized by mechanical alloying using a high energy ball mill. The 25-h milled powder has shown no changes other than exhibiting an austenite phase of FCC (a = 3.54 A) structure. Milled powders were found to contain nano-yttria dispersed in the austenitic stainless steel matrix of nano-crystallite size and with high lattice strain. Milled powders were cold pressed and sintered at 1100 °C (1373 K) in a controlled atmosphere. It can be inferred that nano-yttria dispersion restricts grain growth of matrix even during conventional sintering. The present yittria dispersed austenitic alloy showed the low physical density and increase in compressive strength (194–374 MPa) and hardness (477–528 HV). The compressive strength and hardness enhancement can be attributed primarily to the dispersoids of nano-yttria in the austenitic matrix by dispersion strengthening/hardening mechanisms.

The Sr2Ce0.665Ti0.335O4–0.75 wt% LiF-x mol% CaCO3 (SCT-xCa, x = 0, 0.25, 0.5, 1.0, 1.5, 2.5) ceramics were prepared by a conventional solid-state reaction technique. The effect of Ca2+ substitution for Sr2+ on the phase composition, microstructure and microwave dielectric properties was investigated systematically. The coexistence of Sr2CeO4 and Sr2TiO4 without any other phases indicates that Ca2+ can dissolve into the SCT lattice. An appropriate amount of Ca2+ can accelerate the grain growth and produce a compact and homogeneous microstructure, so an ultra-high Q × f value can be achieved. The deterioration in Q × f values with further increasing x is caused by the abnormal grain growth, as well as the increased internal strain, which tends to decrease the structural stability. Meanwhile, the τf values were found to slightly shift toward the positive direction with decreasing unit cell volume. Excellent microwave dielectric properties of er = 20.9, Q × f = 168,580 GHz (8.14 GHz) and τf = + 0.8 ppm/oC can be obtained in the x = 0.25 sample sintered at 1150 °C for 4 h, showing great potentials in millimeter wave devices.

The effect of crystallography and elastic coefficient heterogeneity between a thin film and its substrate has been theoretically investigated on the shear-coupled grain boundary migration in the film. A drag force associated with the elastic energy has been determined by a disclination-based description of the grain boundary migration. Considering also the capillarity driving force derived from the Burke-Turnbull model of normal grain growth, it has been found in case of an Al thin film that the grain growth stagnation occurs beyond a critical film thickness that decreases as the shear modulus and/or Poisson’s ratio of the substrate increase from the corresponding values of the film. In case of $$[001 ]$$ grain boundaries in a Cu thin film, the effect of crystallography on the GB displacement has also been characterized.

In this research, the effect of annealing heat treatment on microstructure, mechanical properties and wear behavior of an Al–Zn–Mg/3 wt.% Al2O3 composite that was previously thermomechanically processed (TMPed) in its semisolid temperature range was investigated. The annealing treatment was conducted at 400 ˚C for 15, 30, 45 and 60 min, respectively. The results revealed that this treatment led to the better distribution of alumina reinforcement particles. Also, it was proved that no substantial grain growth occurred which shows the grain size stability of the TMPed composite. In addition, owing to the better distribution of reinforcements, the microhardness values of the composites improved while the compressive strength did not increase noticeably. The wear test results revealed that the wear mode in the non-annealed sample was adhesive whereas in the annealed sample, the abrasive wear was dominant.

Nanocrystalline oxide-dispersion strengthened ferritic alloy formation and its annealing behavior were examined through modern X-ray diffraction pattern analysis and supplemented by microhardness and microscopic measurements. The basic microstructure features, with particular emphasis on evolution of domain size distribution and defect content during mechanical and thermal treatment, were quantified via the whole powder pattern modeling approach. The microstructure of the powdered alloy, formed during mechanical alloying, evolved toward nanocrystalline state consisting of narrow dispersion of very fine crystallites with substantial dislocation density, which exhibited relatively high stability against elevated temperature. It was shown that crystallite size is seriously sustained by the grain-boundary strain, therefore coarsening of grains begins only after the density of dislocations drops below certain level. Obtaining correct results for the annealing-related data at specific temperature range required the incorporation of the “double-phase” model, indicating possible bimodal domain size distribution. The dislocation density and grain size were found not to be remarkably affected after consolidation by hot isostatic pressing.

The grain growth mode of titanium alloys remains controversial. In this study, ANSYS and cellular automaton-finite difference code μMatIC were coupled to simulate the multi-scale solidification process of commercial purity titanium and two types of titanium alloys with different solute concentrations. Investment casting of Ti–6Al–4V was carried out in counter-gravity casting method in vacuum environment. Results showed that the grain growth mode of titanium alloys depended on the solute compositions. Grain growth mode of titanium alloys transfers from planar to dendritic with the increased solute. The grain growth morphology of Ti–6Al–4V alloy presents cellular dendritic due to slight solute segregation in the solidification. The predicted grain structure was validated by comparison with the microstructural observation results. Both the prediction and experimental results revealed that equiaxed grains were obtained in investment casting of Ti–6Al–4V regardless of the thickness. The grain size increased with the wall thickness of the cast part.

The billets of 2A12 aluminum alloy were prepared by a novel method called semisolid isothermal treatment of hot-rolled aluminum alloy (SSITHRAA). The spheroidizing process of elongated grains during temperature rising stage and semisolid isothermal treatment stage was investigated. The results showed that recrystallization degree increased with the increase in temperature or time. Appreciable recrystallization happened above 520 °C and even occurred in the semisolid region. Deformation textures (Brass and Copper) and recrystallization texture (Cube) were found in the microstructure at 580 °C. The semisolid isothermal treatment temperature and holding time had greatly influenced the grain morphologies. Average grain size increased with holding time or heating temperature in the proper range of 590-620 °C for 5-30 min generally. The spheroidization degree increased firstly and then decreased with time. Under the optimized condition of 620 °C and 25 min, near globular grains with average diameter (D) of 105 μm and roundness (R) of 1.24 were obtained. The fitting degree of coarsening kinetics curves showed slight differences among various exponents, and the grain growth constants ranged from 370 to 657 μm3/s with n = 3. Based on the principle of minimum Gibbs free energy, the whole processing could be explained from the point of thermodynamics and kinetics. EDS showed that eutectic phases rich in Cu and precipitates containing Fe appeared at the grain boundaries.

Severe plastic deformation (SPD) based on local canning compression is imposed on Ni-rich Ni50.7Ti49.3 (at.%) shape memory alloy (SMA) with B2 austenite phase and equiatomic Ni50Ti50 (at.%) SMA with B19′ martensite phase in order to induce the amorphization of the two alloys. SPD-processed Ni50.7Ti49.3 and Ni50Ti50 samples are annealed at 450°C for various times in order to comparatively investigate grain growth dynamics of severely deformed austenite and martensite NiTi SMAs after complete crystallization of amorphous phase. The grain growth exponent of B2 austenite Ni50.7Ti49.3 SMA is 2.78, whereas the grain growth exponent of B19′ martensite Ni50Ti50 SMA is 3.18. The results show that grain growth dynamics of amorphous NiTi samples is sensitive to the chemical composition. The grain growth of equiatomic B19′ martensite Ni50Ti50 sample is inhibited to a greater extent than that of Ni-rich B2 austenite Ni50.7Ti49.3 one. The mechanisms for grain growth of NiTi SMAs deal with formation of nano-clusters due to crystallization of amorphous phase, recovery of retained nanocrystalline grains containing dislocations under thermal driving force, growth of retained nanocrystalline grains as well as new nanocrystalline grains and incorporation of nano-clusters or smaller nanocrystalline grains into larger nanocrystalline grains. The grains of Ni50.7Ti49.3 sample absorb nano-clusters more readily than that Ni50Ti50 one during grain growth. Investigation on grain growth dynamics of severely deformed NiTi SMAs lays the foundation for fabricating nanocrystalline NiTi SMAs with tailored grain size.

Advanced additive manufacturing technology of direct energy deposition type called x Beam 3D Metal Printing was employed for manufacturing of articles of various size and shape using titanium Ti-6Al-4V alloy wire as a feedstock material. The key distinctive feature of this process is applying of the hollow conical electron beam generated by low-voltage (< 20 kV) gas-discharge electron beam gun for heating and melting of the substrate and wire, which ensures precisely controllable liquid metal transfer from the wire end to the substrate, specific temperature gradients at the fusion area and heat flow from liquid metal pool. Such conditions of heating, melting and cooling during deposition of molten additive material provide controllable microstructure formation, including grain size and material texture. Influence of processing parameters and cooling conditions on fusion, crystallization, grain growth and intragrain structure of manufactured “chunky” Ti-6Al-4V blocks was discussed. The post-processing heat treatment was used to relieve residual stresses formed during article manufacturing. Tensile and fatigue testing has been performed for samples cut in various directions of produced articles to investigate the material uniformity. Optimization of processing parameters allowed production of 3D printed articles from Ti-6Al-4V with isotropic microstructure and mechanical characteristics which met standard requirements for Ti-6Al-4V material.

Immiscible alloys, whether in well-mixed or layered forms, are of increasing interest based on their novel structural and functional properties, such as enhanced thermal stability against grain growth or radiation-induced defect trapping at the interfaces. To address the need for new approaches to tailor microstructures, the microstructural development of an immiscible Cu-4 wt.% Nb alloy processed via friction consolidation of elemental powders is investigated. Friction consolidation is a solid phase processing technique that imparts severe plastic strain into a deforming volume resulting in elevated temperatures below the melting temperature of the alloy. Two distinct processing pathways were chosen to understand the effect of thermomechanical conditions on the final microstructure. The microstructure was characterized using scanning electron microscopy, scanning transmission electron microscopy, and X-ray diffraction techniques. Path 1 exhibited larger strain, strain rate, and temperature as compared with path 2. In path 1, agglomerated Nb particles were present in the recrystallized ultrafine-grained Cu matrix, while in path 2 extremely fine and dispersed Nb particles were present in a highly deformed Cu matrix. In both pathways, supersaturation of Cu in Nb lattices was noted, but not vice versa. The asymmetry in mixing is explained based on deformation-based, thermodynamic and kinetic factors. These findings provide a pathway for creation of novel tailored microstructures and improved properties in any number of binary immiscible alloy systems.

18Ni-2000 MPa maraging steel (M300 grade) is extensively used for performance critical aerospace applications where strength-toughness balance is the basis for material selection. The key to achieve the desired mechanical properties in the final product is to process the material under conditions that will impart an equiaxed, fine grained microstructure. This in turn is controlled by the selected deformation processing conditions such as strain, strain rate and temperature. Therefore, hot deformation behavior of the material is usually studied under wide temperature, and strain rate ranges to map the microstructural evolution with specimens deformed to a given strain. However, the effect of strain on the microstructural evolution, its effect on the initiation and termination of dynamic recrystallization are essential to obtain balanced mechanical properties. In this study, analysis of stress-strain curves was conducted with an intention to obtain fine prior austenite grain (PAG) size through dynamic recrystallization (DRX), and the same was verified experimentally from the microstructures evolved through hot isothermal compression tests on cylindrical specimens subjected to different strains. A single peak type DRX curve was identified for analysis from the high temperature stress-strain curves. The theoretically determined critical strain was used to experimentally verify the initiation of DRX (DRXI) and transition from DRX dominant region to grain growth dominant region (DRXT). Hot isothermal compression tests have been conducted at T=1100°C and e = 0.1s−1 and obtained PAG size of 7.68 µm in the specimen deformed to theoretically determined optimum strain of 0.6, thereby validating the used models.

Most biomedical implants are predominantly Mg-based because of their degradable properties. The effect of recrystallization and local misorientation induced by various rolling parameters on the biodegradation of pure Mg has been systematically studied. The results reveal that an increase in recrystallization fraction and a reduction in local misorientation of grains as the rolling temperature increased was beneficial to the degradation rate of pure Mg. There is basal texture variation arising from the occurrence of high twinning activity at a lower rolling temperature which suppresses the maximum texture intensity and also increases the degradation rate. This result also reveals that grain growth was beneficial to the degradation rate of Mg, as larger grain size give a lower degradation rate. The degradation rate generally increased with decreasing rolling temperature (i.e., 350°C

A series of Sr1−x−yErxYbyMoO4 phosphor compositions codoped with Er3+ (x = 1 mol%) and varying Yb3+ (y = 0–9 mol%) dopants have been evaluated for luminescence-based thermometry. Sintered ceramics exhibit enhanced grain growth at an optimum Yb3+ content (y = 0.03) and exhibit improved upconversion luminescence and a relatively better thermometric performance over the phosphors in the powder form. Strong upconversion (UC) luminescence at ~ 529, ~ 552, and ~ 662 nm assisted by a 2-photon process, cooperative luminescence from Yb3+ ion pair at 495 nm, and weak UC emissions at ~ 380 and ~ 410 nm due to 3-photon process are identified. Luminescence quenching is observed in all the UC emission bands for Yb3+ content y > 3 mol%. Sensitization from Yb3+ to Er3+ and Yb3+–(MoO4)2− dimer to Er3+ ions results in selective enhancement of the green emission. Variation of UC emission intensity with increasing dopant concentration is analyzed using Dexter’s energy transfer formula, which supports the dipole–dipole interaction between Yb3+ and Er3+ ions. Changes in fluorescence intensity ratio (I529/I552) with temperature reveal the potential usefulness of the optimized Sr0.96Er0.01Yb0.03MoO4 phosphor composition in the ceramic form for non-contact optical thermometry and exhibits good repeatability for temperature sensing applications.