Water Quench Research Articles

Investigations on Crystallization Processes of Three Oxidic Gasifier Slag Systems

Abstract In entrained flow gasifiers, the production of oxidic slag accompanies the gasification process. This slag forms a layer on the refractory walls, flows downwards gravitationally, and is collected in a water quench. Hence, the slag flow must be constant, since a slag blockage represents a worst-case-scenario. Crystallization of the slag increases slag viscosity, subsequently leading to a possible slag blockage. Therefore, crystallization processes in oxidic slags need to be understood and hence investigated. In this study, three artificial, coal ash related oxidic slag systems were analyzed on their crystallization behavior. Therefore, their melt behavior was investigated via hot-stage microscopy and differential thermal analysis (DTA). Additional thermochemical calculations were performed to predict crystallized phases. Subsequently, quenching experiments were conducted to generate supercooled crystallization in the slag samples. These samples were analyzed afterward via X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the morphologies of crystals were characterized/described. In-situ observations on crystallization growth were performed by using a confocal laser scanning microscope (CLSM). Finally, crystallized phases were compared with results obtained from thermochemical calculations, and the impact of kinetics on the distributed phases was discussed. The knowledge on the crystallization behavior of various phases can be transferred to other slag systems and can improve general crystallization predictions made by thermochemical calculations.

The effect of two-step solution heat treatment on the impact properties of Hadfield austenitic manganese steel

Hadfield austenitic manganese steel is made of iron with 1.0–1.4 percentage Carbon and 10–14 percentage Manganese. Hadfield steel was processed to solution heat treatment to eliminate the carbide (Fe, Mn)3C. This study aims to make a smaller grain size of Hadfield steel at once with solution heat treatment. It was expected to improve toughness of Hadfield steel. Solution heat treatment was carried out in stages by implementing pre-isothermal heating at a lower temperature with two variations at 600 degree C and 700 degree C before undergoing high austenitization heating. Pre-isothermal heat at above 450 degree C was promoting pearlite growth. Pearlite growth starting from austenite grain boundary then reformed new grain, which has a smaller size than prior austenite. Second, stage of austenitization heating then was performed at 980 degree C to transform new small grain pearlite to austenite. An agitated water quench was used to ensure a faster cooling rate to achieve 100 percentage austenite structure. Results demonstrate that sample that underwent a stepped heat treatment process at 600 degree C followed by austenitization at 980 degree C produced finer (smaller) austenite grains. That sample had the highest impact value of 329.1 J/Cm2 in comparison to other specimens.

Processing by Additive Manufacturing Based on Plasma Transferred Arc of Hastelloy in Air and Argon Atmosphere

This research was carried out to determinate the effect of the atmosphere processing conditions (air and argon) and two specific thermal treatments, on the properties of specimens made from the nickel-based alloy Hastelloy C-22 by plasma transferred arc (PTA). Firstly, the additive manufacturing parameters were optimized. Following, two walls were manufactured in air and argon respectively. Afterwards, a determinate number of specimens were cut out and evaluated. Regarding the comparison performed with the extracted specimens from both walls, three specimens of each wall were studied as-built samples. Furthermore, a commonly used heat treatment in Hastelloy, with two different cooling methods, was selected to carry out additional comparisons. In this respect, six additional specimens of each wall were selected to be heat treated to a temperature of 1120 °C for 20 min. After the heat treatment, three of them were cooled down by rapid air cooling (RAC), while the other three were cooled down by water quenching (WQ). In order to study the influence degree of the processing conditions, and how the thermal treatments could modify the final properties of the produced specimens, a detailed characterization was performed. X-ray diffraction and microstructural analyses revealed the phases-presence and the apparition of precipitates, varying the thermal treatment. Moreover, the results obtained after measuring mechanical and tribological properties showed slight changes caused by the variation of the processing atmosphere. The yield strength of the extracted specimens from the two walls achieved values closer to the standards ones in air 332.32 MPa (±21.36 MPa) and in argon 338.14 MPa (±9 MPa), both without thermal treatment. However, the effect of the cooling rate resulted as less beneficial, as expected, reducing the deformation properties of the specimens below 11%, independently of the air or argon manufacturing atmosphere and the cooling rate procedure.

Influence of Microstructures on Tensile Properties at 400℃ of TC4 Titanium Alloy

The effects of primary α phase volume fraction on the tensile properties at 400℃ of TC4 titanium alloy was studied by different solution temperature(Tβ-(10~80)℃). The effects of the thick of secondary α phase on the tensile properties at 400℃ of TC4 titanium alloy was studied by different cooling speed after solution treatment (water quench, air cooling, furnace cooling). The results show that with the decrease of primary α phase, the tensile and yield strength increase up, but the ductility has a little change. The thick of secondary α phase increases with the deceases of cooling speed after solution treatment, highest tensile and yield strength by water quench, the tensile strength of air cooling and furnace cooling were basically the same, but the yield strength of furnace cooling was 40MPa lower than air cooling. Therefore, the influence of the primary α phase volume fraction on the tensile strength at 400℃ was particularly obvious, we can control solution treatment and cooling way in combination with different requirements.

Effects of hot forming cold die quenching and inter-pass solution treatment on the evolution of microstructure and mechanical properties of AA2024 aluminum alloy after equal channel angular pressing

The aim of this research is to investigate the effect of hot forming cold die quenching (HFQ) equal channel angular pressing (ECAP) on the microstructural evolution and mechanical properties of AA2024 aluminum alloy. For this purpose, solution treated AA2024 aluminum alloy was initially ECAPed in HFQ and water quenched (WQ). Microstructural evolutions, dislocation density, and mechanical properties were investigated after up to 3 (WQ-ECAP) and 5 (HFQ-ECAP) passes of deformation. Intermediate solution treatment was conducted after each ECAP pass. The samples underwent aging treatment after deformation. Large amount of shear banding was observed in samples after the first ECAP pass which was reduced in the successive passes of ECAP through intermediate solution treatment. Tensile properties and microhardness enhanced by increasing number of ECAP passes. However; after the fifth pass of HFQ-ECAP, sudden decrease in mechanical properties was observed. Partial decomposition of supersaturated solid solution was found to occur at higher strains. Mechanical properties and deformability were improved in the HFQ-ECAP samples with respect to WQ-ECAP.

Investigation of Isothermal Oxidation on Heat- treated Fe-40Ni-24Cr Alloy at 950°C

In this research, Ni-based superalloy which is Fe-40Ni-24Cr alloy was experienced a heat treatment process to alter the grain size of the sample to observe its influence on the oxidation properties. The alloys were heat-treated at temperatures of 950°C, 1050°C, and 1150°C for 2 hours followed by water quench. The heat-treated alloys were undergoing an isothermal oxidation test at 950°C for 150 hours in laboratory air. The weight gain of oxidized heat-treated alloy was recorded in order to determine the oxidation kinetic of the test samples. Scanning electron microscopy (SEM) technique was employed in this study to analyze the oxidation behaviour of heat-treated samples. Grain size measurement shows that the grain size increases as the heat treatment temperature increases. The oxidation rate of heat-treated Fe-40Ni-24Cr alloy obeys the parabolic rate law indicating the diffusion-controlled oxide growth mechanism. The fine grain size of alloy heat-treated at 950°C possess a better oxidation resistance and has a lower oxidation rate compared to coarse grain samples. The surface morphology indicate that the fine grain heat-treated alloy at 950°C shows uniform oxide layer formed on the surface, while alloy heat-treated at 1050°C and 1150°C shows the uneven oxide growth, oxide flaking and oxide spallation.

Oxide scale growth on Fe-40Ni-24Cr alloy at high temperature oxidation

Fe-40Ni-24Cr alloy is a Ni-based alloy used at high temperature application. In this study, Fe-40Ni-24Cr alloy had undergo a solution treatment at two different temperatures, namely 1050° and 1150°, for 3 hours soaking times followed by water quench. A solution-treated Fe-40Ni- 24Cr alloy was experienced a high temperature isothermal oxidation test at 500° for 500 hours exposures duration. The growth of oxide scale was characterized in terms of oxidation kinetics and surface morphology using field emission scanning electron microscope equipped with energy dispersive x-ray spectroscopy. The oxidation kinetics of all samples shows an increasing weight gain pattern as the exposure durations increases. The oxidation kinetics was obeyed a parabolic rate law, indicating the oxide growth rate was followed diffusion-controlled mechanism. The surface morphology of oxidized solution-treated Fe-40Ni-24Cr alloy displayed a formation of continuous oxide scale with evidence of overgrown Nb-rich oxide particles distributed along the oxidized samples surface. Oxidized Fe- 40Ni-24Cr alloy which undergo solution treatment at 1150° exhibited the formation of oxide spallation. The spallation has a tendency to occur around the area of overgrown Nb-rich oxide particles.

Treatment of High-strength CFB-QP Forged Parts by Stepwise Water Quenching

The forging industry, and the production of high-strength forged parts in particular, saw no substantial progress in recent decades. High-strength parts continued to be made of well-tried steel grades which meet the economic and environmental production requirements, using mainly the conventional quenching and tempering. However, the latest findings in physical metallurgy of higher-silicon steels suggest that high-strength forgings can also be obtained by producing bainitic and martensitic microstructures. The first are of the CFB (carbide-free bainite) type and the latter comprise the QP (quenching-partitioning) microstructure. At greatly reduced processing costs, properties comparable to tempered martensite can thus be attained.

Die Quench Process Sensitivity of AA7050

The current work investigates the sensitivity of AA7050 aluminum alloy sheet to the thermal cycle involved in the die quenching (DQ) process. This entailed the variation of three key parameters in the thermal cycle, namely solutionizing time, transfer time and quench rate, considering both water quenching (WQ) and die quenching (DQ) at various die pressures. Following a lab-grade T6 heat treatment, Vickers hardness (HV-1000) measurements of all test conditions and tensile testing on a reduced number of test conditions were completed. The results showed only limited sensitivity to solutionizing time for the range of conditions tested. Longer transfer times and slower cooling rates both negatively affected final hardness properties, with up to 4% reduction in final hardness relative to the water-quenched T6 condition. Higher cooling rates during die-quenching produced statistically similar final tensile properties to those achieved from water quenching, following a T6 heat-treatment; while slower cooling rates resulted in significant reductions in tensile strength and uniform elongation. Limiting dome height testing of a 101.6 mm dome sample under die-quench conditions produced a major true limit strain of 0.42. The die-quench limit strain compared favourably against the limit strains of the same geometry in the T6 condition at room temperature and 150 °C (isothermal), which were 0.12 and 0.18, respectively.

Numerical Simulation of Heat Treatment Process of Aluminium Profiles

Abstract The paper deals with the simulation of cooling processes of the aluminium profiles inside the water quench. Cooling of profile surfaces is performed by water spray, which is created by mixing a water and an air in a nozzles. Formulas were found in literature, modified and applied to a given problem that significantly simplified a solution. The task of numerical simulations was to determine temperature and velocity profile on aluminium profile surfaces for establishing of the heat transfer coefficient which was used as the convective boundary condition necessary to solve the heat transfer in the aluminium profile by finite element method. The difference between FEM and CFD results is up to 10%.

Precipitation in an extruded AA7003 aluminium alloy: Observations of 6xxx-type hardening phases

Precipitation behavior in an industrially extruded AA7003 alloy has been studied using Transmission Electron Microscopy (TEM) together with Differential Scanning Calorimetry (DSC). Air Cooling (AC) after solution heat treatment results in quench induced heterogeneous precipitation of both β-Mg2Si and η-MgZn2 phases. Detailed TEM characterisation of resulting nanoscale precipitates after AC, or Water Quenching (WQ), and subsequent artificial ageing demonstrate that η′ and η2 hardening precipitates dominate in T6, whereas the overaged T7 state contains η2 and η1, where the latter accounts for approximately 50% of the relative phase fraction. The T7 state in addition forms 6xxx-type hardening precipitates only after WQ. Results presented here are expected to be relevant for any Si containing 7xxx alloy and open new possibilities for development of hybrid 6xxx- and 7xxx series aluminium alloys. This is discussed with respect to potential influence on mechanical- and corrosion properties.

Effect of pre-weld heat treatment on the microstructure and mechanical properties of electron beam welded IN738LC joint

Influence of pre-weld heat treatment on the microstructure and mechanical properties of electron beam welded IN738LC superalloy was investigated systematically. The microstructure of as-cast base metal (BM) mainly consisted of “ogdoadically” diced cube γ′ particles, fanlike γ-γ′ eutectics, MC carbides, Cr–Mo borides and Ni–Zr intermetallics. Grain-boundary liquation cracking was observed in the HAZ of as-cast joint, resulting from the segregation of elemental boron. Pre-weld heat treatment had a significant influence on the size, volume fraction and distribution of γ′ particles. It also decreased the non-equilibrium segregation of boron during cooling, which inhibited the formation of grain-boundary liquid film and liquation cracking. The precipitation of MC carbides and nanoscaled γ′ particles in the fusion zone (FZ) improved the micro-hardness of the FZ. The micro-hardness of the BM and the HAZ were influenced by the volume fraction and the size of γ′ particles. All the joints fractured in the BM at RM and 900 °C. The as-cast and water quenched (WQ) joints failed with a quasi-cleavage fracture mode at RM and 900 °C while the tensile fracture of furnace cooled (FC) joint showed a ductile rupture at RM and 900 °C.

Comparison of multi-valent manganese oxides (Mn4+, Mn3+, and Mn2+) doping in BiFeO3-BaTiO3 piezoelectric ceramics

ABSTRACT Different manganese oxides-doping effects were compared in piezoceramic BiFeO3-BaTiO3 system. 0.67Bi1.05(Fe0.99Mnx0.01)O3-0.33BaTiO3 (valence state x = 4+, 3+, and 2+) ceramics were prepared via a solid-state reaction process followed by furnace-cooling (FC) or water-quenching (WQ) process. For the FC ceramics, the direct piezoelectric sensor coefficient (d33) was almost independent of valence state of doped Mn, while d33 depended on the fraction of Fe3+/Fe2+ in WQ ceramics. The d33 value was highest for the donor Mn4+-doped ceramic, among the FC ceramics, with 175 pC/N. However, acceptor-doping with Mn2+ prevented the transition of Fe ion valence state from 3+ to 2+ in the WQ ceramics, the Mn2+-doped WQ ceramic showed the largest d33 of 313 pC/N and converse piezoelectric actuator coefficient, d33* of 352 pm/V, with high Curie phase transition temperature (482 °C).

Realizing high figure of merit plateau in Ge1-xBixTe via enhanced Bi solution and Ge precipitation

We reported in this work that both a broad plateau (623–773 K) of high figure of merit ZT (over 1.8) and a decent peak ZT∼2.0 at 773 K can be simultaneously achieved in Bi-doped Ge1-xBixTe sample as x = 0.07 when it experienced a water quench process. Distinct from Bi2Te3 alloying, Bi-doping in GeTe not only produces Ge “neutral vacancies” which eventually evolve into planar van der Waals gaps, but also generate residual Ge atoms which precipitate intrinsically as secondary phase. Additional water quench process is concluded to be of two main functions: (i) increasing the solution of Bi in GeTe matrix, and (ii) suppressing the Ge phase aggregation. The former function further modulates the matrix structure and electronic band, resulting in an improved Seebeck coefficient; while the latter one results in increased Ge/GeTe phase boundaries hence enhanced phonon scattering. Besides, the structure of intrinsic Ge precipitation and enhanced Bi solution is thermally stable; the water quenched Ge0.93Bi0.07Te sample can retain the high thermoelectric performance after 2-days annealing at 773 K. Our finding in this work might shed light on future researches in GeTe and related thermoelectric material systems.

Effect of solution treatment on microstructure and corrosion behaviour of Mg-9Al-1Zn alloys

The effect of solution treatment on the microstructure and corrosion behavior of cast Mg-9Al-1Zn (AZ91) were studied by using electro-optical microscopy, X-ray diffraction (XRD) technique, and weight loss method. The solution treatment was done at 415°C for 2 h followed by a water quench. The as-cast AZ91 alloy composed of α-Mg phase and β-phase (Mg17Al12). Most of the β-phase was segregated along the grain boundaries. A significant reduction in the volume fraction of β-phase was obtained as a result of solution treatment. The β-phase precipitate was distributed randomly both at grain boundaries and in the grain interior as discrete particles of a few µm sizes. The solution treatment induced grain growth resulting in a significantly larger equiaxed grain in the range 100-500 µm. A higher corrosion rate was obtained for the solution treated alloy than the untreated one. The β-phase precipitate played a dual role in the corrosion of AZ91 alloy depending on its volume fraction in the alloy. A nearly continuous distribution of β-phase along grain boundaries in the as-cast alloy served as a barrier for corrosion across grain while the distribution of discrete particles in the solution-treated alloy accelerated corrosion in the surrounding matrix.

Effect of Heat Treatment on Microstructure and mechanical hardness of aluminum alloy AA7075

The mechanical properties of high strength aluminum alloy AA7075 were greatly affected by heat treatment. This paper was intended to clarify the effect of heat treatment on the microstructure and the mechanical hardness of commercial alloy AA7075-T651. Heat treatment was performed at a variation temperature of 300, 400, 500, and 600°C for 1 h in a vacuum furnace followed by a water quench. The surface observation was done by using optical and electron microscopy and the mechanical hardness was measured by the Vickers Hardness test. The XRD result on as-received alloy revealed the precipitates in the alloy was MgZn2, Al7Cu2Fe, and Al2CuMg. The average hardness of the as-received alloy was 136 HV. The hardness became significantly lower (78.5 HV) after heat treatment at 400°C while heat treatment at others temperature gave hardness in the range 116-122 HV. Heat treatment induced grain growth and dissolution of metastable precipitates. Reduction in the number of MgZn2 and Fe-rich phase decreased the hardness significantly. Heat treatment above 400°C promoted segregation of fresh precipitates which enhanced the metal hardness again. The metallic grain size increased with heat treatment temperature. At 600°C, most of the precipitates were segregated along the equiaxed grain boundaries.

Effect of Heat Treatment on the Al-Cu Feedstock Powders for Cold Spray Deposition

This paper examines the effects of heat treatment on the Al-Cu feedstock powders used for cold spray deposition. In particular, we relate improvement of the powder to changes in the spray characteristics and microstructure of cold-sprayed coatings. The inert-gas-atomized Al-Cu powders were solutionized at 535 °C for 2 hours using a rotary furnace, followed by a water quench. Heat treatment of the powders not only eliminated most of the cellular solidification structure generated by the gas atomization process but also resulted in significant grain growth in the powder particles. After solution treatment, the copper content in the α-aluminum matrix increased as expected. After heat treatment, the powders were immediately cold sprayed onto AA2024 substrates. Heat treatment of Al-Cu feedstock powders significantly increased the deposition efficiency for all compositions tested. For heat-treated powders, the deposition efficiency systematically decreased with the increasing copper content, while the coating hardness increased. The formation of GP zones or θ″/θ′ strengthening precipitates through natural aging was not generally observed in the powder particles, but θ″/θ′ precipitates were observed in some cases for the cold-sprayed material with higher copper content.

Characterization of mechanical and microstructural properties of constrained groove pressed nitinol shape memory alloy for biomedical applications

Among shape memory alloys, nitinol alloy is biocompatible in nature and thus widely used in bone tissue engineering, stents, dental and orthopedic implants. To improve mechanical properties and extend its application window, in this paper, the Ni50.5Ti49.5 (nitinol) sheets are processed by constrained groove pressing (CGP) process, which is one of the effective severe plastic deformation (SPD) techniques for refining microstructure and enhancing mechanical properties in sheet metals. The microstructure and X-ray diffraction studies of CGPed sheets show uniform grain refinement and increase in martensitic variant. Based on tensile and micro-hardness tests on water quenched (WQ) and CGPed nitinol alloy, the results show about up to 2.5 times increment in ultimate tensile strength and yield strength, significant enhancement in micro-hardness and change in strain hardening behavior. For characterizing the strain hardening behavior, Holloman and Voce models have been determined to have strong correlation with the experimental data for WQ and CGPed nitinol alloy respectively. Thus, nitinol alloy after CGP exhibits grain refinement and microstructural evolution, showing an increase in stress induced martensite phase which indicates superior mechanical properties such as high strength, uniform deformation regime and microhardness. These enhancements will help in reduction of other supporting materials generally used for improving structural integrity and load bearing capacity in biomedical applications of nitinol alloy.

X-ray Determination of Compressive Residual Stresses in Spring Steel Generated by High-Speed Water Quenching.

Automotive components manufacturers use the 5160 steel in leaf and coil springs. The industrial heat treatment process consists in austenitizing followed by the oil quenching and tempering process. Typically, compressive residual stresses are induced by shot peening on the surface of automotive springs to bestow compressive residual stresses that improve the fatigue resistance and increase the service life of the parts after heat treatment. In this work, a high-speed quenching was used to achieve compressive residual stresses on the surface of AISI/SAE 5160 steel samples by producing high thermal gradients and interrupting the cooling in order to generate a case-core microstructure. A special laboratory equipment was designed and built, which uses water as the quenching media in a high-speed water chamber. The severity of the cooling was characterized with embedded thermocouples to obtain the cooling curves at different depths from the surface. Samples were cooled for various times to produce different hardened case depths. The microstructure of specimens was observed with a scanning electron microscope (SEM). X-ray diffraction (XRD) was used to estimate the magnitude of residual stresses on the surface of the specimens. Compressive residual stresses at the surface and sub-surface of about −700 MPa were obtained.

A novel manufacturing process and validated predictive model for high-strength and low-residual stresses in extra-large 7xxx panels

A novel manufacturing process, enabling the production of high quality (i.e. with low and controllable residual stress (RS) distributions and good mechanical properties) T-section 7xxx panels, has been established. This process provides a solution to residual stress induced distortion problems, which greatly concerns a range of industries, especially the aircraft industry. This process consists of three sequential steps — water quenching (WQ), cold rolling (CR) and constrained ageing (CA). The effectiveness of this process was experimentally verified through applying this process to laboratory sized 7050 T-section panels. The RS was measured by neutron diffraction and X-ray techniques, in addition to deflections and hardness at each processing stage. An integrated Finite Element (FE) model, including all three steps, was developed to simulate this manufacturing process and predict both the RS and the final strength distributions. It has been concluded that this novel process can effectively reduce the residual stresses from ±300 MPa to within ±100 MPa and produce T-section panels with required mechanical properties (i.e. hardness: ~159 HV10). A cold rolling level of 1.5% was found most appropriate. The residual stress and yield strength distributions were accurately predicted by FE, providing a valuable prediction tool to process optimization for industrial applications.