Effect Of Cooling Rate Research Articles

Effects of Cooling Rate on the Microstructure and Tensile Properties of Wire-Arc Additive Manufactured Ti–6Al–4V Alloy

Wire-arc additive manufacturing has emerged as a technology that could replace the conventional manufacturing process of titanium alloys. However, it produces a coarse β grain, which can accumulate via several deposited materials, resulting is strong texture and anisotropy. To investigate potential solutions, the effects of the cooling rate on the resulting microstructure and tensile properties were studied. The cooling rate of the deposited materials was adjusted by interpass temperature control. Under rapid cooling, fine α + α′ grain with a low aspect ratio were observed and tensile and hardness properties were also improved.

Combined Effects of High Undercooling and Large Cooling Rate on the Microstructure Evolution and Hardening Mechanism of Rapidly Solidified Ti-Al Alloys

Controlling the microstructure evolution of Ti-(47, 50, 54) at. pct Al alloys by combining the effects of high undercooling and large cooling rate has been investigated. The calculated undercooling and cooling rates of the three component alloy droplets increase as power functions with the decreasing alloy droplet diameter D. With decreasing D, the microstructure of Ti-47 at. pct Al alloy evolves from dendritic dendrites to equiaxed dendrites, and the main microstructure of Ti-50 at. pct Al alloy transforms from a lamellar microstructure to a non-lamellar microstructure, while that of Ti-54 at. pct Al alloy appears as an interweaving microstructure. The α2 phase with a superlattice structure and the α2n phase with a nonsuperlattice structure are confirmed by transmission electron microscopy, and the large difference of Al contents leads to formation of the α2 phase and the α2n phase. Atomic images show that the interface of the α2n phase and γ phase is coherent. The α2n phase precipitates from the γ phase during cooling. The combined effects of high undercooling and large cooling rate suppress the transformation of the α phase to (α2 + γ) phases. The Young’s modulus first increases and then decreases with decreasing D, while the nanohardness is controlled by the combined factors of the microstructure morphology, phase composition, phase ratio, and grain refinement. As for the microhardness, grain refinement dominates the hardening of the Ti-54 at. pct Al alloys, while the combined factors dominate the hardening of Ti-(47, 50) at. pct Al alloys.

Effects of Ti and High Cooling Rate on the Phase Equilibria and Properties of Ni3(Al,V) Alloys

Investigations of the Ni3(Al,V,Ti) alloys with 5 at.% Ti addition show that high quenching rates from the liquid state allow for the preservation of the metastable Ni(Al,V,Ti) solid solution at low temperatures as well as for the limitation of the eutectoid decomposition range. Annealing at the temperatures close to the eutectoid decomposition causes an increase in the amount of the Ni3Al and Ni3V equilibrium phases, as well as the precipitation of the Ni3Ti phase. The V addition reveals the ability to stabilize Ni solid solution, while Ti retards Ni3V phase precipitation but also supports the precipitation of the Ni3Ti phase, in spite of the higher than 5 at.% range of Ti solubility in the Ni3V phase. The increase in V and Ti content at the cost of a decrease in Al content strongly increases micro-hardness of the alloys crystallized at high rates. For the alloys containing predominantly V, increased ductility was noticed in the temperature range of the dissolution of Ni3V precipitates.

Effect of Cooling Rate After Heat-Treatment Simulated Brazing on Precipitation Hardening of Cu-0.93 mass%Ni-0.24 mass%P Alloy

Effect of Cooling Rate After Heat-Treatment Simulated Brazing on Precipitation Hardening of Cu-0.93 mass%Ni-0.24 mass%P Alloy

Effects of Cooling Rate and Joint Size on Sn Grain Features in Cu/Sn-3.5ag/Cu Solder Joints

In Sn-based micro solder joint s for fine pitch flip chip or 3D packaging technologies , the number of Sn grains is always limited and sometimes only one Sn grain exists in a joint, which inevitably causes anisotropy in the performance of micro interconnection. It is known that the parameters and reliability of solder joint structure and reflow process, especially cooling stage, have a great significance for regulating the features of Sn grain s after soldering. Hence, in the present paper, the Sn grain features of Cu/Sn-3.5Ag/Cu solder joints with different joint size s (300 μm, 100 μm and 50 μm) solidified under different cooling rate s (1.5 °C /s, 0.5 °C /s and 0.1 °C /s) were studied. Generally, the number of Sn grains decrease d as the joint size decrease d . When the joint size was 50 μm, the solder joints tended to contain only one or two Sn grains irrespective of the cooling rate. Furthermore, cooling rates greatly affected the number and orientation of Sn grains as well as the growth of large Ag3Sn intermetallic plates to varying degrees. The formation of Sn grains and Ag 3 Sn plates was discussed from the viewpoint of nucleation under different conditions.

Effect of Cooling Rate under Quenching on the Structure and Properties of Sheets Made of High-Tech Alloy V-1341 of the Al–Mg–Si System

Phase transformations for alloy V-1341 of the Al–Mg–Si system under cooling from quenching temperature are investigated by differential scanning calorimetry and by transmission electron microscopy. An isothermal phase transformation diagram is generated by a design-experiment method. It is shown that the proposed method developed according to quenching factor theory makes it possible to predict reliably the dispersion hardening as a function of cooling rate for sheets made of alloy V-1341.

Austenitizing Temperature and Cooling Rate Effects on the Martensitic Transformation in a Microalloyed-Steel

Abstract The effects of the austenitizing temperature and the cooling rate upon the kinetic of athermal martensitic transformation in a microalloyed steel were evaluated. Considering the studied steel, the knowledge about these effects on the martensitic transformation has a great relevance for naval manufacturers and steel researchers. In this study, computational simulation was performed aiming to evaluate the phase’s stability. Specimens were submitted to quenching simulations in a dilatometer, considering four different austenitizing temperatures and four cooling rates. The results shown that the austenite chemical composition was not significantly affected by the austenitizing temperatures. Both the austenitic grain size and the cooling rate affected the martensitic transformation kinetics. The larger the austenitic grain size, the higher the Ms. The austenitic grain growth promoted a decrease in the required chemical energy to compensate the free energy increase associated with the lattice strain and the creation of new interfaces, leading to a lower austenite undercooling. An extrinsic effect of the cooling rate on the Ms was observed. For lower cooling rates, the carbide precipitation modified que austenite chemical composition, changing its stability and increasing Ms. A predictability equation, correlating the MS with the austenite grain size and the steel cooling rate, was proposed.

Cooling rate effects on microstructure and mechanical behaviour of tungsten heavy alloys

Tungsten heavy alloy of composition 90W-7Ni-3Fe was consolidated by liquid phase powder metallurgy processing technique and subjected to heat treatments with varying cooling rates in order to explore the possibility of enhancing mechanical properties. The alloy following sintering was subjected to vacuum heat treatments at 1150 °C/1 h followed by cooling at different rates-furnace cooling at 3 °C/min, 6 °C/min and oil quenching. This was followed by a systematic examination of microstructure and tensile properties. Strain rate jump tests were also carried out to get an insight into the deformation behaviour. Tensile strength ranging from 880 to 900 MPa and elongation ranging from 23 to 28% were realized. Cooling rate did not affect the resultant properties, which was attributed to predominant intergranular failure in all cases. Strain rate jump test pointed towards a Peierls deformation mechanism at room temperature that remained unaffected by cooling rate.

Sintering and Wear Behavior of a FeCrCB Hardfacing Alloy Applied by Tape Casting: A Study of Cooling Rate Effect

This study presents a simple process to deposit a hardfacing coating on a steel substrate, based on the sintering of metallic powder applied by tape casting (by a slurry of metallic powder suspension onto a steel substrate) thus avoiding the use of traditional welding processes and their variants. The effect of the cooling of hardfacing after the sintering process, by air at room temperature or by quenching in water, was studied. This new method ensures a good metallurgical bonding between the substrate steel and the hardfacing layer and shows mechanical property improvement on coated pieces, similar to those exhibited by hardfacing coatings produced by several kinds of welding processes. The characterization of the hardfacing coatings was made by X-ray diffraction, optical microscopy, scanning electron microscopy, microhardness and wear resistance according to the ASTM G65 standard. The characterization results show that the presented faces are: M7C3, M3C, MC, M2B and M23B6; there are three different phases in the micrograph glass phase, eutectic phase and hard phase with a volumetric fraction of 0.14, 0.20 and 0.66, respectively, for the air cooled and 0.15, 0.16 and 0.69 when quenched in water. The average microhardness value for the parts cooled in air was 832.5 HV and for that cooled in water was 958.9 HV, and the wear resistance was a mass loss of 0.219 and 0.128 g for parts cooled in air and water, respectively. These results show that the hardfacing coating could have twice the hardness and wear resistance than that observed for the boron steel used as a substrate.

A comparative study of the cooling-rate effect on rock strength reduction after microwave irradiation

AbstractA variety of machines are currently being used for mechanical excavation in mining and civil industries. A series of research works have been conducted at McGill University in the past decade to study the effects of microwave (MW) irradiation on rock mechanical properties. The idea is to enhance the excavation performance by improving the rate of penetration and decreasing the wear rate on the cutting tools. These two effects would eventually translate into economic benefits for mine operators. The effectiveness of MW on weakening rocks is proven, however the most efficient method to employ MW in mines is still under investigation. This article presents some experimental results on the effects of cooling- rate on rock strength. Brazilian Tensile Strength (BTS) of microwave treated samples were compared in natural air-cooled and water rapid-cooled conditions.

An Experimental Investigation on the Effect of Cooling Rate During Combined Continuous Casting and Rolling Process on Mechanical Properties of 7075 Aluminum Alloy

When a combined continuous casting–rolling (CCCR) process is employed for making Al plates and sheets, considerable savings in both the cost and the production time are attained. In the present research, the variation and control of temperature of the material flowing through the cooling jacket during CCCR of 7075 aluminum alloy were investigated. Employing three temperature profiles for this passage, it was shown that the best mechanical properties and grain size of the finally rolled product could be attributed to the exponential profile. It was also found through a heat transfer analysis that the difference in the free convection heat transfer from the top and bottom surfaces of the slab exiting the cooling jacket can result in a temperature gradient through the thickness of the plate, and this can consequently lead to certain variations in the hardness through the thickness of the finally rolled 7075 Al plate.

Secular Variation of the Intensity of the Geomagnetic Field in Mexico During the First Millennium BCE

AbstractIn Western Eurasia, the first millennium BCE is characterized by the fastest secular variation of the Earth Magnetic Field observed over the last millennia and by a geomagnetic anomaly centered on the Middle East. On the global scale, the variation of the dipolar field during this period remains poorly constrained because of the lack of data in other geographical areas. Here, we presented 23 new mean archaeointensity data on ceramic sherds dated between 1500 BCE and 200 CE from Chalcatzingo archaeological site in Central Mexico. Archaeointensities were determined using the classical Thellier‐Thellier protocol with corrections for TRM anisotropy and cooling rate effects. Our work doubles the number of high‐quality archaeointensity data in Mexico during the considered period. Using a Bayesian approach, a new secular variation curve was calculated at Mexico City between 1500 BCE and 200 CE after selection of Mexican archaeointensity data. After a period of oscillations of the intensity between 20 and 40 μT from 1500 to 300 BCE, the curve shows a large maximum `~65 μT in the second century BCE. The corresponding VADM varied between ~4.0 and ~11.0 × 1022 Am2, which highlights further that the intensity of the geomagnetic field could vary at regional scale over a larger range as previously thought. However, this amplitude variation may be overestimated, as it does not take into account the fast directional variation observed at this time.

The Effect of Various Annealing Cooling Rates on Electrical and Morphological Properties of TiO2 Thin Films

This paper presents the effect of different cooling rate after annealing on structural and electrical properties of TiO2 thin films. Titanium dioxide thin film was deposited on a silicon substrate using DC magnetron technique. After annealing TiO2 thin films at 600oC, to investigate the effect of different cooling rates on TiO2 thin films, samples were cooled down from 600oC to the room temperature under 3 different rates: 2oC/min, 6oC/min and 8oC/min. The Surface morphology, crystal structure, and electrical property of samples were characterized by atomic force measurement (AFM), X-ray diffraction (XRD) and Four-point probe (FPP) technique. It is found that the rate of decreasing temperature after annealing can affect the morphology structure and electrical resistivity of titanium dioxide. Sample with 2oC/m has the biggest grain size, and more electrical resistivity while the smallest grain size and lowest electrical resistivity belong to sample with 8oC/m cooling rate.

Effect of Cooling Rate on the Microstructure of a Pressure Vessel Steel

The present article thoroughly explores the effect of cooling rate on various microstructural features of a reactor pressure vessel steel (20MnMoNi55). For this, dilatometric experiments were performed at different cooling rates. Optical microscopy and electron backscatter diffraction were used to measure different microstructural parameters. Continuous cooling from 0.15 to 0.3 °C/s revealed ferrite and bainite; only bainite is seen from 1 to 2 °C/s, both bainite and martensite were found in the regime 5 to 15 °C/s, and complete martensitic transformation was observed at cooling rate 20 °C/s and above. With increase in cooling rate, the fraction of low angle boundary decreased and that of high angle boundary increased. The nature of grain size distribution was found to be cooling rate sensitive.

Structural Mechanisms of the Cooling Rate Effect on the Deformation Behaviors in Metallic Glasses

In this work, the structural mechanisms of the cooling rate effect on the deformation behaviors in metallic glasses (MGs) is studied, by performing the synchrotron radiation-based experiments coupled with a series of simulations. It is found that a MG prepared at lower cooling rate has the higher yield strength and is more likely to soften itself, resulting in lower plasticity. This is because some atomic-to-cluster level structural factors, such as coordination numbers, atomic packing efficiencies, cluster concentrations and regularities. In addition, a quantitative analysis reveals that higher cooling rate leads to more free volumes, and significantly affect the evolution of free volumes during the compressive deformation, tuning the formation and the evolution of shear transformation zones, as well as the yield strength and the plasticity.

Effect of Cooling Rate on the Grain Refinement of Mg-Y-Zr Alloys

The grain refinement resulting from the addition of yttrium (Y) (1, 3 pct, and 9 wt pct) and zirconium (Zr) (0.1, 0.2, and 0.5 wt pct) to magnesium (Mg) under a wide range of cooling rates (0.8 to 160 K/s) has been investigated. This study quantifies the effect of Y and Zr on the grain size (dgs) of Mg-Y base alloys followed by examination of the effect of cooling rate on these alloys. The Interdependence Model was able to describe the reduction in grain size caused by the growth restriction provided by Y and soluble Zr, and the introduction of potent Zr particles. It is shown that by incorporating a term for cooling rate into the Interdependence model the effect of cooling rate on grain size can be assessed for the range of growth restriction values and cooling rates investigated.

Effect of Cooling Rate on AlN Precipitation in FeCrAl Stainless Steel During Solidification

The effect of cooling rate on the evolution of AlN inclusions precipitated during solidification in FeCrAl stainless steel was investigated using an experimental study and thermodynamic and kinetic calculations. The number and size of AlN inclusions precipitated under different cooling rates were examined with the feature function of the field-emission scanning electron microscope. A model combining micro-segregation and the diffusion-controlled growth model was set up to determine the mechanism of AlN particle growth. The results showed that AlN precipitates in the mushy zone. The size of AlN particles decreases and the number of AlN particles increases with increasing cooling rate, whereas the volume fraction is essentially unchanged. The AlN particles grow during solidification after the content of solutes in molten steel has exceeded the concentration in equilibrium with AlN. The nitrogen content varies significantly with the cooling rate during solidification. Increasing the cooling rate and reducing the nitrogen content in the molten steel can reduce the AlN particle size in FeCrAl alloys as the growth time decreases.

Solidification processing and cooling rate effects on hexagonal Co22Cr18Cu20Mn16Ti24 high-entropy alloys

The majority Laves-FCC Co22Cr18Cu20Mn16Ti24 high-entropy alloy (HEA) was studied via electromagnetic levitation processing (EML) to elucidate the effect of cooling rate on the solidification microstructures and phase formation in this alloy. The relationship between the secondary dendrite arm spacing (S-DAS) and cooling rate was utilized to characterize different regions of the solidification microstructures. The cooling rates were determined via the dendrite arm spacing (DAS) equation, DAS=kε−n, with k = 16. The Co22Cr18Cu20Mn16Ti24 alloys were initially made using arc-melting to produce spherical 1.5 g buttons, which were then processed via EML. The molten samples were dropped from either completely molten state, dropped during solidification, dropped during re-melting, or solidified in the magnetic field. Microstructural characterization indicated that depending on the cooling rate, the sample may contain two to four phases. It was found that high cooling rates (≳102 K/s) led to the suppression of the randomly dispersed CoTi-rich dendrites. At slow cooling rates, all four phases were present, while at cooling rates ≳102 K/s, hexagonal dendrites surrounded by FCC interdendritic matrix were seen. Differential scanning calorimetry (DSC) displayed three distinct peaks at 905 °C, 1205 °C, and 1295 °C corresponding to these phases.

An Investigation of Columnar to Equiaxed Transition and the Effect of Cooling Rate on Nucleus Density Distribution of an Industrial Ti and Nb-Stabilized Ferritic Stainless Steel

The heterogeneous nucleus distribution of an industrial Ti and Nb-stabilized ferritic stainless steel (FSS) with high-equiaxed zone ratio was investigated in detail. The heterogeneous nucleus is the complex nucleus mainly composed of central Ti-containing oxide and external (Ti,Nb)(CN). A “V” type distribution of complex nucleus was revealed in the thickness direction, indicating that the nucleus density decreases as the slab solidifies. A “W” type distribution of equiaxed crystals was also observed in the thickness direction. A linear relationship between equiaxed crystal density and nucleus density was obtained in the columnar to equiaxed transition (CET) and quarter position of the slab, indicating that the density of equiaxed crystals is significantly influenced by that of the complex nucleus. Theoretical analysis and confocal laser scanning microscopy experiments were carried out to reveal the distribution mechanism of the complex nucleus. The results showed that the cooling rate has a significant influence on the nucleation undercooling of FSS, which indirectly affects the formation of the complex nucleus. Based on these findings, a numerical model was established to investigate the CET of FSS, and the prediction was in good agreement with the experimental results. According to the numerical model, even if the nucleus density decreases during solidification, it is still sufficient for stimulation of CET.

Enhancement of electrochemically deposited pristine CdTe film electrode photoelectrochemical characteristics by annealing temperature and cooling rate

Photoelectrochemical (PEC) characteristics of CdTe film electrodes, known to have low conversion efficiency when used in their pristine form, can be significantly enhanced by carefully controlling their annealing temperature and cooling rate. Pristine CdTe films were electrodeposited onto FTO/Glass substrates which were used as anodes. To reach films with optimal characteristics, different applied preparation potentials were intentionally examined, namely 1.0, 1.1 and 1.2 V, vs. Ag/AgCl reference electrode (or 1.2, 1.3 and 1.4 V NHE, respectively) where the 1.1 V applied potential showed best PEC characteristics, and was thus followed unless otherwise stated. To study effect of annealing temperature, three temperatures (150, 200 and 250 ºC) were attempted to enhance PEC characteristics of the deposited films. Effect of cooling rate, on PEC performance of pre-annealed films, was also studied using quenching and slow cooling. Films quenched from annealing at all temperatures showed lower PEC performance compared to non-annealed electrode. Film electrodes slowly cooled from 150 or 200 ºC show enhanced PEC performance compared to quenched or non-annealed films. Film slowly cooled from 250 ºC exhibited lower PEC performance than the quenched counterpart. Annealing at 250 ºC lowered PEC for both quenching and slow cooling. As a low band gap semiconductor film electrode, it is recommended to slowly cool CdTe from low annealing temperatures, and to quickly cool them from relatively higher annealing temperature. The annealing temperature and cooling rate effects on CdTe film PEC performance are attributed to their effects on other physical characteristics, namely crystallinity, morphology and chemical composition. The optimal conversion efficiency (6.9%) was observed for film deposited at 1.1 V applied potential when annealed at 200 ºC and slowly cooled to room temperature.