Progression Of Heat Treatment Research Articles

Study on precipitation in (CoCrFeMnNi)90Al6Ti4 high entropy alloy

(CoCrFeMnNi)90Al6Ti4 high entropy alloy (HEA) was prepared by adding Al and Ti elements into CoCrFeMnNi HEA. The alloy underwent processes including copper mold suction casting, 1473 K homogenization, 30 % cold rolling + 1273 K annealing + 1073 K aging, and water quenching and heating treatment. Microstructure and phase composition of both as-cast and heat-treated (CoCrFeMnNi)90Al6Ti4 HEA were studied using metallographic microscope, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and transmission electron microscope (TEM). The effect of heat treatment processes on the precipitation of second phases in (CoCrFeMnNi)90Al6Ti4 HEA was investigated, and mechanical properties of as-cast and heat-treated (CoCrFeMnNi)90Al6Ti4 HEA were studied via hardness tests. The results show that in as-cast (CoCrFeMnNi)90Al6Ti4 HEA, the second phase precipitated is primarily L21 structured AlTiNi2 phase. After homogenization, cold rolling, annealing, and aging processes, both the quantity and size of the second phase increase, with a small amount of nanoscale L12 phase appearing after aging treatment. With the progression of heat treatment, the hardness of (CoCrFeMnNi)90Al6Ti4 HEA increases, and mechanical properties are improved.

Graphitization behavior of medium-carbon high-silicon steel and its dependence on temperature and grain size

The graphitization behavior of medium-carbon, high-silicon steel (Fe-0.55C-2.3Si) is investigated with particular focus on the effects of heat-treatment temperature and initial grain size on the graphitization rate and mechanical properties. With the progress of heat treatment, pearlite gradually disappears because of the decomposition of the cementite layers and graphites are formed because of the diffusion and aggregation of carbon atoms; these occurrences lead to a gradual decrease in the hardness of the material. A higher heat-treatment temperature promotes the graphitization behavior, which consequently leads to a decrease in the time taken for completion of graphitization and an increase in the average graphite size. Graphites are dominantly formed at grain boundaries owing to the high energy and disordered atomic arrangements at these boundaries. Further, because grain boundaries act as graphite nucleation sites, a smaller grain size corresponds to faster graphitization as well as the formation of finer and more abundant graphites. The complete graphitization treatment causes a significant reduction in the tensile and compressive strengths of the material and a considerable improvement in its ductility and cold forgeability.

Comprehensive study on structural and optical properties of Tm2O3 doped zinc silicate based glass–ceramics

In this research, Tm2O3 doped zinc silicate based glass–ceramics were prepared by using conventional melt-quenching method and has been successfully derived from ZnO-WRHA glasses with control heat treatment process. The formation of zinc silicate phase affected by heat treatment process was investigated using X-ray diffraction. Fourier transform infrared reflection spectroscopy (FTIR) analysis was used to determine the crystallization of Zn2SiO4 in the glass matrix. FTIR analysis showed the appearance of Zn2SiO4 and SiO2 bands that supported the formation of Zn2SiO4 crystal phase in the glass matrix. The optical absorption and energy band gap of the glass and glass–ceramics was investigated using UV–Vis spectroscopy. The absorption edge shows the movement towards longer wavelength with increasing heat treatment temperature. Besides, the energy band gap decreased with the progression of heat treatment. This ability to enhance optical properties in glass–ceramics was expected to have bright future in the opto-electronics devices.

Microstructural evolution and compositional homogenization of a low Re-bearing Ni-based single crystal superalloy during through progression of heat treatment

Microstructural and chemical heterogeneities may exacerbate the high-temperature mechanical properties of single crystal turbine blades. The evolution of microstructure and compositional homogeneity of an as-cast low Re-containing multicomponent DD6 alloy during through progression of heat treatment was detailedly studied. Using optical microscope, field emission gun scanning electron microscope, electron probe microanalysis, differential scanning calorimetry, and complementary thermodynamic calculations, we investigated the time-dependent size and volume fraction variations of γ/γ′ eutectic during specific solution heat treatment steps, the evolution of γ′ precipitates, carbides, and compositional homogeneity, and the thermo-physical changes of as-cast DD6 alloy during through progression of heat treatment. Based on our experimental and theoretical results, the mechanism underlying the microstructure formation and chemical segregation of as-cast DD6 alloy was clarified. The mechanism of microstructural evolution and compositional homogenization, and the diffusion mechanism of elements that occurs between dendritic and interdendritic regions of as-cast DD6 alloy during through progression of heat treatment were elucidated. The correlations between microstructural evolution, compositional homogenization, and thermo-physical changes of as-cast DD6 alloy during through progression of heat treatment were established.

Localized Surface Plasmon Absorption and Photoluminescence of In Situ-Generated Nano Silver in a Novel Chloroborosilicate Glass and Glass Ceramics

Silver (Ag) nanoparticles (NPs) have been generated in situ in a novel chloroborosilicate glass system SiO2–B2O3–BaO–K2O–Al2O3–BaCl2 in the presence of a small amount of SnO as a reducing agent. The glass–metal nanocomposite has been synthesized by a single-step melt-quenching technique followed by a carefully designed heat treatment schedule. Absorption and photoluminescence properties have been studied before and after matrix crystallization along with the progress of heat treatment. The x-ray diffraction and transmission electron microscopy confirms the crystallization of the glass matrix at higher temperature. Both UV–Vis absorption and photoluminescence (PL) spectra of the samples reveal the formation of Ag NPs. Multiple peaks in the UV–Vis absorption spectra of Ag-doped samples have been explained by combined surface plasmon resonance and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) of inter (d–sp) and intra (sp–sp) band transitions. The observed PL bands have been considered to be originated from the radiative decay of the surface plasmon resonance and inter-band (sp–d) LUMO-HOMO transitions. The PL intensity is found to increase with heat treatment up to 40 min, and then, decreases. This indicates that when larger than a certain size limit of nano silver (∼6.5 nm), they are not photoluminescent. Crystallization of glass matrix has also a significant effect on the PL intensity and intensity distribution of different emission bands along with band shapes. These nanocomposites are promising materials for various nanophotonic applications as revealed in their different properties.

Thermal, Structural, and Enhanced Photoluminescence Properties of Eu3+‐doped Transparent Willemite Glass–Ceramic Nanocomposites

The precursor glass in the ZnO–Al2O3–B2O3–SiO2 (ZABS) system doped with Eu2O3 was prepared by the melt‐quench technique. The transparent willemite, Zn2SiO4 (ZS) glass–ceramic nanocomposites were derived from this precursor glass by a controlled crystallization process. The formation of willemite crystal phase, size, and morphology with increase in heat‐treatment time was examined by X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 18–70 nm whereas the grain size observed in FESEM is 50–250 nm. The refractive index value is decreased with increase in heat‐treatment time which is caused by the partial replacement of ZnO4 units of ZS nanocrystals by AlO4 units due to generation of vacancies. Fourier transform infrared (FTIR) reflection spectroscopy was used to evaluate its structural evolution. Vickers hardness study indicates marked improvement of hardness in the resultant glass‐ceramics compared with its precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7Fj (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 395 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 17‐fold with the process of heat treatment. This enhancement is caused by partitioning of Eu3+ ions into glassy phase instead of into the willemite crystals with progress of heat treatment. Such luminescent glass–ceramic nanocomposites are expected to find potential applications in solid‐state red lasers, phosphors, and optical display systems.

Enhanced photoluminescence and structure of Dy3+-doped SrBi2Ta2O9-containing transparent glass-ceramics

Trivalent dysprosium (Dy3+)-doped precursor glass in the K2O–SiO2–SrO–Bi2O3–Ta2O5 (KSSBT) system have been prepared by melt-quench technique and strontium bismuth tantalate, SrBi2Ta2O9 (SBT) glass-ceramics has been synthesized by a controlled crystallization process of the precursor glass. With progression of heat-treatment it is observed that Dy3+:glass exhibit a blue emission at 486nm (4F9/2→6H15/2) and also a bright fluorescent yellow emission at 576nm (4F9/2→6H13/2) have been observed with λex=455nm (6H15/2→4I15/2). These spectra reveal that the Dy3+ ions are gradually entering into the SBT nanocrystals of the glass-ceramics. The photoluminescence characteristics originating from Dy3+-doping in nanocrystalline SBT reveals the dependence of the luminescent intensity on heat-treatment time. Their structural properties have also been evaluated by FTIR spectroscopic and microstructural studies. Such luminescent glass-ceramics are expected to find potential applications such as solid-state yellow lasers and optical display systems.

Effects of nano-YAG (Y 3Al 5O 12) crystallization on the structure and photoluminescence properties of Nd 3+-doped K 2O–SiO 2–Y 2O 3–Al 2O 3 glasses

Nd 3+-doped precursor glass in the K 2O–SiO 2–Y 2O 3–Al 2O 3 (KSYA) system was prepared by the melt-quench technique. The transparent Y 3Al 5O 12 (YAG) glass–ceramics were derived from this glass by a controlled crystallization process at 750 °C for 5–100 h. The formation of YAG crystal phase, size and morphology with progress of heat-treatment was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transformed infrared reflectance spectroscopy (FT-IRRS). The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range 25–40 nm. The measured photoluminescence spectra have exhibited emission transitions of 4F 3/2 → 4I J ( J = 9/2, 11/2 and 13/2) from Nd 3+ ions upon excitation at 829 nm. It is observed that the photoluminescence intensity and excited state lifetime of Nd 3+ ions decrease with increase in heat-treatment time. The present study indicates that the incorporation of Nd 3+ ions into YAG crystal lattice enhance the fluorescence performance of the glass–ceramic nanocomposites.

Processing and Properties of Eu3+‐Doped Transparent YAG (Y3Al5O12) Nanoglass–Ceramics

An Eu3+‐doped novel mother glass in the K2O–SiO2–Y2O3–Al2O3 (KSYA) system was prepared by the melt‐quench technique. The transparent Y3Al5O12 (YAG) glass–ceramics were derived from this glass by a controlled crystallization process. The formation of YAG crystal phase, size and morphology with the progression of heat treatment was examined by X‐ray diffraction (XRD), transmission electron microscopy, field‐emission scanning electron microscopy, and Fourier transformed infrared reflectance spectroscopy. The crystallite sizes obtained from XRD are found to increase with heat‐treatment time and vary in the range of 35–45 nm. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7Fj (j=0, 1, 2, 3, and 4) and its excitation spectra show a charge transfer band around 280 nm. From these emissions, the site symmetry in the vicinity of Eu3+ ions has been found to be Cs or lower than Cs in the nanoglass–ceramics. Absorption and fluorescence spectra reveal that the Eu3+ ions are entering into the YAG nanocrystals of the glass–ceramics. The present study indicates that the incorporation of Eu3+ ions into the YAG crystal lattice enhance the fluorescence performance of the nanoglass–ceramics. We believe that this work would generate new avenues in the exploration of YAG nanoglass–ceramics in particular and other glass–ceramics of very high‐temperature melting crystals in general.

Processing and Properties of Eu3+:LiTaO3TransparentGlass-Ceramic Nanocomposites

We report here the processing and properties of transparent glass and glass-ceramic nanocomposites in the Li 2 O―Ta 2 O 5 ―SiO 2 ― Al 2 O 3 system in the presence of Eu 2 O 3 as luminescent probe. The formation of the LiTa0 3 crystal phase, the crystallite size, and the morphology with the progression of heat treatment have been examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transformed infrared reflectance spectroscopy measurements. The crystallite sizes obtained from XRD and TEM are found to increase with heat-treatment time and vary in the range of 2-20 nm. The measured phototuminescence spectra exhibit emission transitions of 5 D 0,1 → F j (j = 0, 1, 2, 3, and 4) of Eu 3+ ions. From the nature of the emission transitions, the site symmetry in the vicinity of Eu 3+ ions has been found to be near C 3v in the glass-ceramic nanocomposites. An inverse correlation has been observed between the asymmetric ratio (I ED /I MD ) of Eu 3+ ions and the dielectric constant (e r ), with an increase in the heat-treatment time of glass, which is caused by the dipole―dipole interaction.