Decrease In Cooling Rate Research Articles

Effect of the track length and track number on the evolution of the molten pool characteristics of SLMed Al alloy: Numerical and experimental study

The effect of the track length and track number on the evolution of the thermal variables and molten pool characteristics of selective laser melting alumunum alloy has been studied numerically and experimentally in this paper. It is found that as the track length increases, the maximum temperature, maximum heating rate and maximum cooling rate decrease first and then become stable. Both molten pool width and depth increase first, then keep stable and then increase a little at the end of the track. The molten pool lifetime increases first, then becomes stable, and then decreases at the end of the track. With the increase of the track’s number, the maximum temperature decreases first and then becomes stable. While, the molten pool width, depth and lifetime increase first and keep almost constant, the maximum heating rate and cooling rate are nearly same.

Experimental study on powdered expansion of barium hydroxide octahydrate crystal

Barium hydroxide octahydrate (BHO) will randomly pulverize and expand into a white powder during phase transformation, causing the container to deform or even rupture. This phenomenon seriously affects the practical application of BHO, but there is no research on the powdery expansion of BHO in the existing literature. In order to study the causes and influencing factors of the powdered expansion of BHO, the white powder, BHO and Barium carbonate (BC) were characterized by microscopic morphology and infrared spectrum, and the effect of additives on BHO crystallization was also investigated. The results show that the powdered expansion of BHO is its physical property, and no new substance will be produced during the expansion process, the expansion rate of BHO is 25%, as the cooling rate decreases, the probability of BHO powdered expansion increases; when the melting temperature of BHO reaches above 90 °C, the degree of undercooling will increase significantly, and the probability of powdered expansion increases. By adding hydroxyethyl cellulose, soluble starch and sodium dodecyl sulfonate, the radial expansion of BHO could be reduced to some extent, but it could not be prevented from happening.

Stochastic deformation and shear transformation zones of the glassy matrix in CuZr-based metallic-glass composites

The incipient plasticity of an amorphous solid represents the onset of shear deformation, which is a stochastic progress closely related to microstructure evolution. It is well known that the cooling rate plays a crucial role in the microstructure evolution of a glass. Nevertheless, how the cooling rate affects the incipient plasticity is still unclear. In this work, the incipient plastic deformation of the amorphous phase in Cu47.5Zr48Al4Nb0.5 bulk metallic glass composites (BMGCs) cast with different cooling rates is systematically studied. The incipient plasticity of the glassy matrix of the BMGCs is found to occur via a first displacement burst, the occurrence of which is more stochastic as the cooling rate decreases. According to the auto-correlation functions and cooperative shear model, the stochastic behavior is attributed to the effects of the cooling rate on the initial free volume and subsequent activated shear transformation zones (STZs). A higher content of free volume is present in the glassy matrix of the studied samples cooled at a faster rate, which facilitates the operation of STZs. Moreover, the larger incipient burst size is correlated with the higher content of free volume and larger STZs in the glassy matrix. The larger STZs result in more preferable propagation of multiple shear bands, leading to less stochastic deformation and more obvious plastic deformation. This study provides further understanding on the incipient plasticity of glassy matrix in BMGCs.

Effect of cooling rate and resulting microstructure on tensile properties and deformation mechanisms of an advanced PM nickel-based superalloy

The powder metallurgy (PM) nickel-based superalloy FGH98 was subjected to solution treatment followed by cooling at three different rates, and the effects of the cooling rate on the microstructure and tensile properties of the alloy at 750 °C were investigated. The results show that as the cooling rate decreases, the average size of secondary γ′ precipitates increases, and the morphology of the secondary γ′ precipitates changes from a near-cuboidal shape to a butterfly shape. As the size of the γ′ precipitates increases, the localized slip occurs more difficultly resulting in improved plasticity. It is found that stacking fault (SF) shearing and microtwinning are the dominant mechanisms of 750 °C tensile deformation for the FGH98 alloy with fine and coarse γ′ precipitates respectively. The increase of γ′ precipitates size is suggested to promote the mechanism transition from SF shearing to microtwinning.

Exergoeconomic analysis of a novel trigeneration system based on organic quadrilateral cycle integrated with cascade absorption-compression system for waste heat recovery

The present research proposes a novel trigeneration system for cooling, heating, and power generation which is consisted of organic quadrilateral cycle (QLC) and cascade absorption – compression system. The system is simulated and studied from energy, exergy, and exergoeconomic viewpoints. Cyclohexane, LiBr-H2O, and R410a are respectively used as working fluids for QLC, Absorption refrigeration system (ARS), and Compression refrigeration system (CRS) in the combined system. Using QLC instead of simple organic Rankine cycle (ORC) in the combined system makes it possible to generate electricity besides improvement of total system performance from energy and exergy viewpoints for the same input values. According to the base case results, the unit cost of electricity is 36.9 $/GJ and it has much less value compared with unit cost of heating and cooling which are equal to 101 $/GJ and 84.7 $/GJ, respectively. Therefore, more electricity production by employing QLC instead of ORC is economical. The results of system parametric analysis show that by variation of QLC expander inlet temperature and QLC condensation temperature while cooling rate decreases, the other output parameters such as output electricity, heating rate, exergy efficiency, and total cost rate improve. Selection of these two input parameters depends on demands. On the other hand, less ARS evaporation temperature and higher CRS evaporation temperature in the allowed range lead to better performance of the system.

Correlation of Cooling Rate, Microstructure and Hardness of S34MnV Steel

A study of the hardenability, the microstructure and the phase transformations as a function of the cooling rate, of a marine crankshaft S34MnV steel has been performed using a Jominy end-quench test and dilatometry tests. The cooling rate has a distinct influence on the hardness and microstructure characteristics. As the cooling rate decreases, the hardness drops from HRC53 at the quenched end to HRC22 at the top end of the Jominy bar. The corresponding microstructures change from hard martensite to bainite, then soft pearlite and ferrite. The critical temperatures Ac1, 740 °C and Ac3, 830 °C were determined, and a continuous cooling transformation diagram was constructed from the dilatometric data. The important role of cooling rate on final hardness, phase transformation and microstructures are analyzed.

Cooling of Al-Cu-Fe-Cr-Ni high entropy alloy with different size

Cooling rate is critical in synthesizing nanoparticles (NPs), which determines the microstructure and the corresponding mechanical, thermal and electrical properties. This research, as the most initiative one, studies microstructure formation of three different sized high entropy alloy (HEA) NPs under three different cooling rates, employing molecular dynamics (MD). Through analysis of potential energy, “common neighbor analysis”, radial distribution function, and also the mean square displacement, it is found that phase transition temperature is independent of HEA NP size, and as cooling rate decrease, more amorphous atoms transform to fcc and hcp orders, which can alternate the mechanical and thermodynamic properties of the final structure. The Cr atoms are found to aggregate into one cluster inside the NP and also try to migrate to the surface of the HEA NP, due to the large diffusivity. This research provides new insights in the size dependency of the nanoparticles, which may motivate more applications in which the strong size dependency is not desirable.

Effect of Welding Process on Microstructure and Properties of High Strength Steel Joints

S900MC high strength steel was selected as the research object, and different MAG welding processes were designed according to the practical application of construction machinery. The microstructure, tensile test and impact test of the welded joints were carried out under different conditions. The effects of welding heat input, preheating temperature and cooling time t8/5 on the tensile strength and impact toughness of welded joints were studied. The results show that the microstructure of the welded joint is composed of weld, fusion zone, superheated zone, fine grain zone and incomplete recrystallization zone. When the welding line energy or preheating temperature is increased, the cooling rate decreases, the strength of the welded joint decreases. The impact absorption energy of the weld is about 50% higher than that of HAZ. With the increase of t8/5, the impact absorption energy of the weld and HAZ increases first and then decreases. When t8/5 is 15-20s, the impact absorption energy is the largest.

Non-isothermal crystallization kinetics of waxy crude oil

The crystallization behavior of Shengli waxy crude oil from the sol state to gel state was studied by the microscopic observation and DSC curve. The study shows that as the cooling rate decreases, the number of wax grains becomes smaller, the area is larger and the morphology of wax crystals is more irregular. Moreover, under different cooling rates, wax crystals were homogeneous transient nucleation, but the growth mode of wax crystals was different. When the cooling rate is between 1–4 °C/min, Crystallization Peak 1 wax crystal grows according to the mixed crystal mode of one-dimensional rod crystal and two-dimensional discoid crystal; When the cooling rate is between 6–8 °C/min, Crystallization Peak 1 wax crystal grows according to the mixed crystal mode of two dimensional discoid crystal and three-dimensional spherical crystal; Crystallization Peak 2 wax crystal grows according to the mixed crystal mode of two dimensional discoid crystal and three-dimensional spherical crystal at different cooling rates. Crystallization activation energy of crystallization Peak 1 and Peak 2 are 556.91 kJ/mol and 299.62 kJ/mol, respectively.

Molecular dynamics study of size and cooling rate effects on physical properties of Niobium nanoclusters

Using Molecular Dynamics (MD) Simulations, based on the embedded atomic method (EAM), we have investigated the effect of cooling rate and nanocluster size on thermophysics properties of supercooled liquid niobium. Simulations of Nb nanoclusters with sizes 125, 343, 1000, 1728 and 2744 nm3 have been carried out at various cooling rates. Thermophysical properties of Nb system, during quenching process, have been quantifying in terms of radial distribution function, thermal capacity and self-diffusion coefficients. Simulations results show that the crystallization of supercooled liquid Nb occurred at a critical cooling rate of about 7 × 1012 K/s for all nanocluster sizes. Moreover, our results show that for Nb nanocluster sizes equal or higher than 1000 nm3, the transition temperature increases as the cooling rate decreases. Finally, it is found that the pre-exponential factor and activation energy for self-diffusion in niobium are in good agreement with previous work.

Effect of cooling rate on microstructure, mechanical properties and residual stress of 7075 aluminum alloy

Abstract In this study, the effect of cooling rate on microstructure, mechanical properties and residual stress of 7075 aluminum alloy was investigated. The influence of cooling rate on microstructure, hardness, electrical conductivity of 7075 aluminum alloy was investigated using a Jominy end quench test. Water at three different temperatures (20 °C, 50 °C, 75 °C) and polymer solutions of varied concentrations (5vol.-% and 25vol.-%) were used as a quenching medium. The changes of hardness, electrical conductivity and microstructure properties of the specimens with an increase in distance from the quenched surface were investigated comparatively for different quenching mediums. Tensile tests were applied to determine the effect of the quenching rate on mechanical properties of the specimens. Residual stress was measured using the ESPI hole drilling technique to understand the influence of cooling rate. The results show that the cooling rate decreases as the distance from the quenched surface, water temperature and polymer concentration increases. The changes in material properties such as hardness, electrical conductivity along the material profile decrease as water temperature and polymer concentration increase. Although the hardness and mechanical properties of the material decrease as the cooling rate decreases, the values obtained are convenient for conditions of industrial usage. Residual stress was significantly eliminated by quenching in hot water or polymer solution at a high concentration.

Effect of Cooling Rate on Microsegregation During Solidification of Superalloy INCONEL 718 Under Slow-Cooled Conditions

The solidification sequence, microstructural evolution, solid-liquid interface variation, interdendritic segregation, and elemental distribution of as-cast IN718 alloy at three slow-cooling rates (5, 10, and 20 °C/min) were investigated by differential scanning calorimetry (DSC), confocal laser scanning microscopy (CLSM), optical microscopy (OM), field-emission scanning electron microscopy (FESEM), and electron-probe microanalysis (EPMA) techniques. The results indicate that as the cooling rate decreases, the constitutional supercooling at the solidification front affects the solid-liquid interface more significantly, and the size and quantity of the Laves phase increase. However, the composition of the Laves phase is insensitive to the cooling rate in the range of conditions studied here. In dendrite core, the contents of Ni, Cr, Fe, and Al follow a slight downward trend with an increasing cooling rate, whereas the Nb, Mo, and Ti contents show an upward trend. Additionally, Mo shows a stronger propensity to segregate under slow-cooling conditions because its effective partition coefficient almost linearly decreased with decreasing cooling rate, which is same as Nb. Using the parameters experimentally determined in this study and the Clyne–Kurz equation, we achieved reasonable agreement between the calculated and measured liquid composition change during the solidification process at different cooling rates. All experimental and theoretical programs in this research were undertaken with the aim of gaining further understanding of the microsegregation behaviors in large-scale IN718 ingots, whose cooling rates are within a lower range.

Structural and bonding transformation of Al0.67CrCoCuFeNi high-entropy alloys during quenching

Structural and bonding transformation of the Al0.67CrCoFeNi high-entropy alloys (HEA) during quenching is investigated by molecular dynamics simulations. At a high cooling rate, some short-ranged ordered clusters, such as FCC, HCP and BCC crystalline clusters are already present in the almost amorphous HEAs. When the cooling rate decreases, the atoms become packed more orderly and ultimately form a nano-polycrystalline structure dominated by FCC structures. The BCC structures appear only as an intermediate state acting on the course of crystallization, while the HCP structure can be viewed as the precursor of the malposed FCC structure due to the identical first neighbor distances. In liquid HEAs, the low-symmetry and low-coordination bond pairs, either transform to high-symmetry and high-coordination 1551 bond pairs, or transform to 1(5,4)41 bond pairs for FCC structure and 1661 bond pairs for an HCP structure, depending on the cooling rates. This study will contribute to a better understanding of the essential phase change in HEAs.

Study of the Boron Distribution and Microstructure of Solidified Al-Si Alloy During the Process of Silicon Purification

AbstractThe Al-Si melts that contain different silicon contents were solidified with a series of cooling rates, and the boron contents in primary silicon phases and eutectic silicon phases were measured and discussed. The results indicate that the boron content in the eutectic silicon phases is higher than that in the primary silicon phases when the cooling rate is constant. When the cooling rate decreases, the boron content in the primary silicon phases decreases, but the boron content in the eutectic silicon phases increases. The microstructure observations of solidified ingots show that there is an interface transition layer beside the primary silicon phase, and the average width of the interface transition layer increases with decreasing cooling rate.

Effects of cooling methods on the occurrence of sulfur in the low-titanium slag

The distribution of sulfur existence in the mineral phase and occurrence in the low-titanium slag with different cooling methods (water cooling, air cooling, crucible cooling, and furnace cooling) were studied by XRD, EPMA and XPS. The results show that with the cooling rate decrease, the distribution of S changes from clustering dots to large sheet or surface, and the occurrence of S in the mineral phase transfers gradually from the vitreous, perovskite, merwinite and the intertwined phase of some mineral phases to the gehlenite. During the transfer, the velocity decreases with the increasing of the cooling rate. The S in the water cooling slag only exists in the form of SO32−and SO42−, while the occurrences of S in the air cooling slag, crucible cooling slag, and furnace cooling slag are S2−, SO32−and SO42−.

Cooling rate effects in sodium silicate glasses: Bridging the gap between molecular dynamics simulations and experiments.

Although molecular dynamics (MD) simulations are commonly used to predict the structure and properties of glasses, they are intrinsically limited to short time scales, necessitating the use of fast cooling rates. It is therefore challenging to compare results from MD simulations to experimental results for glasses cooled on typical laboratory time scales. Based on MD simulations of a sodium silicate glass with varying cooling rate (from 0.01 to 100 K/ps), here we show that thermal history primarily affects the medium-range order structure, while the short-range order is largely unaffected over the range of cooling rates simulated. This results in a decoupling between the enthalpy and volume relaxation functions, where the enthalpy quickly plateaus as the cooling rate decreases, whereas density exhibits a slower relaxation. Finally, we show that, using the proper extrapolation method, the outcomes of MD simulations can be meaningfully compared to experimental values when extrapolated to slower cooling rates.

Numerical and experimental investigation into the subsequent thermal cycling during selective laser melting of multi-layer 316L stainless steel

Subsequent thermal cycling (STC), as the unique thermal behavior during the multi-layer manufacturing process of selective laser melting (SLM), brings about unique microstructure of the as-produced parts. A multi-layer finite element (FE) model was proposed to study the STC along with a contrast experiment. The FE simulational results show that as layer increases, the maximum temperature, dimensions and liquid lifetime of the molten pool increase, while the heating and cooling rates decrease. The maximum temperature point shifts into the molten pool, and central of molten pool shifts backward. The neighborly underlying layer can be remelted thoroughly when laser irradiates a powder layer, thus forming an excellent bonding between neighbor layers. The contrast experimental results between the single-layer and triple-layer samples show that grains in of latter become coarsen and tabular along the height direction compared with those of the former. Moreover, this effect become more serious in 2nd and 1st layers in the triple-layer sample. All the above illustrate that the STC has an significant influence on the thermal behavior during SLM process, and thus affects the microstructure of SLMed parts.

Tuning the Mechanical and Antimicrobial Performance of a Cu-Based Metallic Glass Composite through Cooling Rate Control and Annealing.

The influence of cooling rate on the wear and antimicrobial performance of a Cu52Z41Al7 (at. %) bulk metallic glass (BMG) composite was studied and the results compared to those of the annealed sample (850 °C for 48 h) and to pure copper. The aim of this basic research is to explore the potential use of the material in preventing the spread of infections. The cooling rate is controlled by changing the mould diameter (2 mm and 3 mm) upon suction casting and controlling the mould temperature (chiller on and off). For the highest cooling rate conditions CuZr is formed but CuZr2 starts to crystallise as the cooling rate decreases, resulting in an increase in the wear resistance and brittleness, as measured by scratch tests. A decrease in the cooling rate also increases the antimicrobial performance, as shown by different methodologies (European, American and Japanese standards). Annealing leads to the formation of new intermetallic phases (Cu10Zr7 and Cu2ZrAl) resulting in maximum scratch hardness and antimicrobial performance. However, the annealed sample corrodes during the antimicrobial tests (within 1 h of contact with broth). The antibacterial activity of copper was proved to be higher than that of any of the other materials tested but it exhibits very poor wear properties. Cu-rich BMG composites with optimised microstructure would be preferable for some applications where the durability requirements are higher than the antimicrobial needs.

Effect of Solidification Behavior on Microstructures and Mechanical Properties of Ni-Cr-Fe Superalloy Investment Casting.

The effect of solidification behavior on the microstructures and mechanical properties of Ni-Cr-Fe superalloy investment casting is given. Metallographic and image analysis have been used to quantitatively examine the microstructures’ evolution. For the parts with the thickness of 3 mm and 24 mm, the volume fraction and maximum equivalent radius of the Laves phase increases from 0.3% to 1.2%, from 11.7 μm to 23.4 μm, respectively. Meanwhile, the volume fraction and maximum equivalent radius of carbides increase from 0.3% to 0.5%, from 8.1 μm to 9.9 μm, respectively. In addition, the volume fraction of microporosity increases from 0.3% to 2.7%. As a result, the ultimate tensile strength is reduced from 1125.5 MPa to 820.9 MPa, the elongation from 13.3% to 7.7%, and the quality index from 1294.2 MPa to 954.0 MPa, respectively. A typical brittle fracture is observed on the tensile fracture. As the cooling rate decreases, the microstructures become coarser.

Effect of Cooling Rate on Modification and Grain Refinement of 4032 Aluminum Alloy

Effect of cooling rate on modification and refinement of 4032 aluminum alloy has been investigated at cooling rates of 0.7~4.5 K/s. Sr is used to modify eutectic silicon and B is used to refine primary α-Al grains. Modification level of eutectic silicon and refining results of primary α-Al are characterized quantitatively by Lp based on the perimeter of eutectic silicon particles and the maximum grain length D, respectively. As the cooling rate decreases, the needle-like eutectic silicon particles increases and the modification level reduces with a constant Sr content. Influenced by alloying elements such as Mg, Cu and Ni, the modification level is very low at the lowest cooling rate of 0.7 K/s, but properly increasing Sr content in the melt can improve the modification. At the cooling rates of 0.7~4.5 K/s, the element B can transform coarse columnar dendritic α-Al grains to equiaxed ones, and controlling the ratio of Sr and B is a valid technique to avoid mutual poisoning. On the conditions of present experiments, the Sr content of 350 ppm and Sr:B ratio of about 1.1 are rational to modify eutectic silicon and refine primary α-Al grains simultaneously.