A Discrepancy in Thermal Conductivity Measurement Data of Quantum Spin Liquid β′-EtMe3Sb[Pd(dmit)2]2 (dmit = 1,3-Dithiol-2-thione-4,5-dithiolate)

A molecular Mott insulator β′-EtMe3Sb[Pd(dmit)2]2 is a quantum spin liquid candidate. In 2010, it was reported that thermal conductivity of β′-EtMe3Sb[Pd(dmit)2]2 is characterized by its large value and gapless behavior (a finite temperature-linear term). In 2019, however, two other research groups reported opposite data (much smaller value and a vanishingly small temperature-linear term) and the discrepancy in the thermal conductivity measurement data emerges as a serious problem concerning the ground state of the quantum spin liquid. Recently, the cooling rate was proposed to be an origin of the discrepancy. We examined effects of the cooling rate on electrical resistivity, low-temperature crystal structure, and 13C-NMR measurements and could not find any significant cooling rate dependence.

A Comparative Study on the Microstructures and Mechanical Properties of Al-10Si-0.5Mg Alloys Prepared under Different Conditions

Fabrication condition greatly influences the microstructures and properties of Al alloys. However, most of the available reports focus on a single fabrication technique, indicating there is still a lack of systematic comparisons among wider ranges of fabrication methods. In this paper, with conventional casting (via sand/Fe/Cu mold) and additive manufacturing (AM, via selective laser melting, SLM) methods, the effects of cooling rate (Ṫ) on the microstructures and mechanical properties of hypoeutectic Al-10Si-0.5Mg alloy are systematically investigated. The results show that with increasing cooling rate from sand-mold condition to SLM condition, the grain size (d) is continuously refined from ~3522 ± 668 μm to ~10 μm, and the grain morphology is gradually refined from coarse dendrites to a mixed grain structure composed of columnar plus fine grains (~10 μm). The eutectic Si particles are effectively refined from blocky shape under sand/Fe-mold conditions to needle-like under Cu-mold conditions, and finally to fine fibrous network under SLM condition. The tensile yield strength and elongation is greatly improved from 125 ± 5 MPa (sand-mold) to 262 ± 3 MPa (SLM) and from 0.8 ± 0.2% (sand-mold) to 4.0 ± 0.2% (SLM), respectively. The strengthening mechanism is discussed, which is mainly ascribed to the continuous refinement of grains and Si particles and an increase in super-saturation of Al matrix with increasing cooling rate.

Phase Transformation of M2 High Speed Steel during Semi-Solid Cooling and Conventional Cooling

In this paper, the fundamental microstructure evolution of M2 high speed steel was investigated during semi-solid controlled cooling and conventional cooling, respectively. Semi-solid controlled cooling was conducted at 1260 °C with cooling rates from 0.1 to 10 °C/s, while conventional cooling was conducted at 1200 °C and 890 °C with different cooling rates. The continuous cooling transformation curves were plot according to the microstructure evolution. The results showed that microstructure transformation behavior of cooling structure in semi-solid temperature range was different from that of conventional process. For semi-solid specimen, the solid austenite dissolved more alloy elements, and the austenite stability was increased. The solid matrix was pearlite structure in the samples with cooling rate of 0.1 °C /s. When the cooling rate reached 1 °C/s, the granular pearlite disappeared and martensite lath was formed. The structure was relatively uniform, on which there were large carbide with regular shape. The solidified liquid phase showed a network shape surrounding the solid particles. The size of solid particles showed a decreasing trend with the increase of cooling rates. For conventional cooling process, the large eutectic M6C carbide and the small precipitated MC carbide could not be dissolved by austenitized at 890 °C. Increasing the austenitization temperature helped dissolving part of the carbides. The hardenability of M2 steel was high. The hardness has increased to a high level for both semi-solid and conventional specimens when cooling rate reached 1 °C/s. No obvious increase happened when cooling rate continued increasing.

Analysis of combined radiation and convection heat transfer inside a porous medium with heat source electronic devices

In this study, a numerical study is performed on the cooling phenomenon of three heat source electronic devices. The electronic devices are cooled in the form of natural heat transfer by the airflow in a porous medium. Electronic devices are installed on the boundary walls of a square environment. Cooling simulations are performed by drawing flow lines and constant temperature lines. Our main goal is to find the highest cooling rate in different Darcy numbers and different Rayleigh numbers in our investigation. The range of Darcy numbers and Rayleigh numbers is between 0.0001 to 0.01 and 1000 to 100,000, respectively. Our investigation showed the maximum cooling is obtained at the Darcy number of about 0.01. And also, by decreasing the value of Darcy number, a higher cooling rate for the hot boundary walls is achieved.

Influence of Cooling Scenarios on the Evolution of Microstructures in Nickel-Based Single Crystal Superalloys

The reprecipitation and evolution of γ’ precipitates during various cooling approaches from supersolvus temperature are studied experimentally and via phase field simulation in nickel-based single crystal superalloys. The focus of this paper is to explore the influence of cooling methods on the evolution of the morphology and the distribution of γ’ precipitates. It is demonstrated that small and uniform spherical shape γ’ particles formed with air cooling method. When the average cooling rate decreases, the particle number decreases while the average matrix and precipitate channel widths increase. The shape of γ’ precipitates which changed from spherical to cubic and irregular characteristics due to the elastic interaction and elements diffusion are observed with the decrease of the average cooling rate. The phase field simulation results are in good agreement with the experimental results in this paper. The research is a benefit for the study of the rejuvenation heat treatment in re-service nickel-based superalloys.

Effect of Cooling Rate on the Microstructure Evolution and Mechanical Properties of Iron-Rich Al–Si Alloy

The mechanical properties of iron-rich Al–Si alloy is limited by the existence of plenty of the iron-rich phase (β-Al5FeSi), whose unfavorable morphology not only splits the matrix but also causes both stress concentration and interface mismatch with the Al matrix. The effect of the cooling rate on the tensile properties of Fe-rich Al–Si alloy was studied by the melt spinning method at different rotating speeds. At the traditional casting cooling rate of ~10 K/s, the size of the needle-like β-Al5FeSi phase is about 80 μm. In contrast, the size of the β-Al5FeSi phase is reduced to 500 nm and the morphology changes to a granular morphology with the high cooling rate of ~104 K/s. With the increase of the cooling rate, the morphology of the β-Al5FeSi phase is optimized, meanwhile the tensile properties of Fe-rich Al–Si alloy are greatly improved. The improved tensile properties of the Fe-rich Al-Si alloy is attributed to the combination of Fe-rich reinforced particles and the granular silicon phase provided by the high cooling rate of the melt spinning method.

Study on the Solidification Behavior of Inconel617 Electron Beam Cladding NiCoCrAlY: Numerical and Experimental Simulation

To better control the Inconel617 electron beam cladding solidification process, a three-dimensional temperature field model was built to simulate the temperature gradient, cooling rate, and solidification rate in the solidification process and take a deep dive into the solidification behavior, as well as the calculation of the solidification characteristic parameters at the edge of the molten pool and then predict the solidification tissue structure. The study shows that the largest temperature gradient occurred in the material thickness direction. The self-cooling effect of the material dominated the solidification of the alloy layer; the cooling rate depended on the high-temperature thermal conductivity of the material and the self-cooling effect of the matrix, and the maximum cooling rate in the bonding zone was 1380 °C/s. The steady-state solidification rate was equal to the moving speed of the heat source; the solidification characteristics of the solidification process at the edge of the molten pool increased with the distance from the surface: the cooling rate decreased from 1421.61 to 623 °C/s, the temperature gradient increased from 0.0723 × 106 to 0.417 × 106, and the solidification rate decreased from 0.01 to 0 m/s. The prediction was made that the small and thin equiaxed crystals are on the top, a thin and short dendritic transition structure in the middle, and relatively coarse dendrites at the bottom. Experiments confirmed that the solidification tissue structure is basically consistent with the simulation law.

Continuous Cooling Transformation Behavior of High Carbon Pearlitic Steel

The continuous cooling transformation behavior of high-carbon pearlitic steel was studied by employing optical microscopy, scanning electron microscopy, and the Vickers hardness test. The results show that the microstructure of the test steel is composed of proeutectoid cementite and lamellar pearlite in the cooling rate range of 0.05–2 °C/s and lamellar pearlite in the range of 2–5 °C/s. Further, martensite appears at 10 °C/s. With the increase in the cooling rate, the Vickers hardness of the test steel first decreases and then increases. In the industrial production of high-carbon pearlite steel, the formation of proeutectoid cementite at a low cooling rate needs to be avoided, and at the same time, the formation of martensite and other brittle-phase at a high cooling rate needs to be avoided.