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The effects of cooling rate and pouring temperature on microstructure and fracture toughness of the induction melted Nb-16Si-22Ti-2Hf-2Cr-2Al alloy were extensively investigated. The results revealed that with the decrease of cooling rates, the Nb_ss exhibits the dendrite-like morphology, the primary Nb₅Si₃ blocks form and the mean sizes of Nb₅Si₃, Nb_ss and eutectic colonies increase; with the increase of the pouring temperature, the microstructure shows columnar structure and the particles of Nb₅Si₃ or Nb_ss become long and thin. Pouring temperature and cooling rate had little influence on the volume fractions of Nb_ss and Nb₅Si₃ and their compositions. The Nb₃Si phase eliminated in the case of high pouring temperature and slow cooling rate. Fracture toughness of the alloy prepared by induction melting is on the order of 13.7 to 15.3 MPa·m^1/2. Similar fracture toughness value of each slab may be ascribes to the same volume fraction of the Nb_ss.

Till now, the developed centimeter-sized Ti-based bulk metallic glasses (BMGs) always consist of at least five elements. We report that Ti₄₁Zr₂₅Be₂₈Fe₆ quaternary glassy alloy can be made up to 10 mm in diameter by water quenching, while only ϕ 8 mm fully glassy rod can be obtained by copper mould suction casting. This alloy possesses fewer constituent elements, wider supercooled liquid region and higher specific strength than other developed centimeter-sized Ti-based BMGs and has wide prospect for practical application. Our results also indicate that for Ti₄₁Zr₂₅Be₂₈Fe₆ alloy which possesses relatively strong glass-forming ability, reducing the heterogeneous impurities in the melt is more effective to obtain fully glassy samples than increasing the cooling rate merely.

This study reports the results of a finite element simulation of powder mixed electric discharge machining process for H11 Hot Die steel material using relevant boundary conditions and reasonable assumptions. The crater shape was developed using simulated temperature profiles to estimate the volume removed in a single crater. The temperature distribution on the workpiece was used to predict the cooling rate and calculate the stresses generated due to thermal loading. Subsequently, the simulation results were experimentally validated by physically measuring the crater shape and volume. From the results it was concluded that about 25% of heat is transmitted to the workpiece during machining at the process conditions used in the experiment. The microscopic pictures showed bigger craters with increase in current. The machined surface showed overlapping craters with surface cracks suggesting a high cooling rate.

Refrigeration and air conditioning cycles consume a large amount of electrical energy and the shortage in traditional sources of energy is the main reasons for governments to use renewable energy. The most power consuming part in the Vapor Compression Cycle (VCC) is the gas compressor. Therefore, the objective of this research is to increase the cooling rate of the VCC using the same compressor, and that is done by heating the refrigerant coming out from the compressor. The proposed cycle is similar to the VCC except that the compression processes is done in two stages, the first stage via a gas compressor and in the second stage by heating the refrigerant under constant volume. The heating process can be done using solar energy. An experimental setup has been developed to study the influence of heating the refrigerant on the cooling rate of the VCC. The heating process is performed after the compressor, and it is done under constant volume in order to increase the pressure of the refrigerant. Four experiments have been performed; the first experiment is a normal VCC, i.e., without heating, while in the second, third and fourth experiments, the refrigerant has been heated to 50^∘C, 100^∘C and 150^∘C, respectively. It has been found that the cooling power increases with the heating temperature. Heating increases the pressure of the refrigerant in VCC, and consequently increases the mass flow rate of the refrigerant that results in an increase in the refrigeration power for the same compressor power. However, the disadvantage of heating the refrigerant is that it increases the evaporator temperature, which limits the possibility of the VCC to be used in freezing applications.

The cooling system design is a crucial issue for hot stamping tool design which directly affects product's cooling rate and cooling uniformity. Then the cooling rate of blank sheet further affects the final strength of product parts. So, the design of cooling system for hot stamping process was studied in this paper. In this paper, the effects of cooling channel configuration were investigated by flat plate tool model. By the study of the flat plate model, the basic design method for hot stamping tool was constructed. It provides a method to pre design the cooling system to obtain the required cooling rate and cooling uniformity. Then, the effects of cooling channel configuration on cooling rate then investigated by the U-hat shaped tool model. In the study of U-hat shaped tool model, four types cooling channel design were applied and the influences of these cooling system design were also discussed. It finds that the cooling rate of blank is inverse linear to the length of product's surface for each cooling channel design. So, it provides a method to design a cooling system for U-hat shaped tool. In order to validate the accuracy of finite element analysis, the experiments of U-hat shaped model were conducted in this study. By comparing the tool's surface temperature between experiments and simulation, it founds that the simulation results are well consistent with experimental results.

Hot stamping parts have been widely used as re-enforcement for better crash safety and other attributes as well as in lightweight applications such as vehicle B-pillar, rocker and other structure parts. In this paper hot stamped torsion beam is studied as a function of product DVP and hot stamping process. Although hot-stamping process is fairly understood, the lightweight designed torsion beam’s property as a function of various parameters is not well studied. In order to study the temperature field, stress field, strain field, thinning rate and phase distribution in the hot forming process of torsion beam, the finite element software was used in this paper. The study found the maximum principal strained area appeared in the highest temperature region due to the different regions of part contact with the tool in the different order while the maximum principal stress area is located in the lower temperature region. In the process of hot forming, the slow cooling rate of the part is 77 °C/s, which is greater than critical cooling rate of martensitic transformation 30 °C/s; With the increase of the initial temperature of sheet metal, the maximum content of austenite and thinning rate of the parts increase, and the forming quality of the parts decreases; with the increase of stamping speed, the thinning rate of parts is violent fluctuation. When the stamping speed is too large, parts of the temperature of parts is greater than the martensite transformation temperature in some regions at the end of forming; with the increase of friction coefficient, the thinning rate and the minimum content of martensite firstly increase and then decrease; the maximum content of austenite decreases first and then increases. Research shows that: when the initial temperature of blank is 850, stamping speed is 75 mm/s, coefficient of friction is 0.45, the quality of the parts is the best and thinning rate is 5.804 %. At the end of forming, the minimum temperature of parts is 285 °C; minimum martensite content is 75.63 % and the maximum content of austenite is 24.36 %.

Fe₃Al intermetallics were solidified separately in sodium silicate sand mould and permanent mould to get different cooling rates. After heat treatment (1000°C/15h homogenizing annealing + furnace cooling + 600°C /1h tempering + oil quenching), the microstructure, mechanical properties and impact fracture of Fe₃Al intermetallics were investigated. The microstructure of Fe₃Al intermetallics is refined and the dispersive second phase is more at higher cooling rate (in permanent mould) than that at lower cooling rate (in sodium silicate sand mould). Compared to intermetallics solidified at lower cooling rate, the Fe₃Al intermetallics solidified at higher cooling rate has the higher tensile strength and good hardness. The impact power increases from 35.28J to 59.09J, while the impact fracture transforms from intercrystalline fracture to intercrystallin+transcrystalline mixed fracture.

Gleeble-3800 thermo-simulation system was used to study the effect of cooling rate on transformation of GCr15steel. The dynamic CCT diagram was established, microstructure and hardness of experimental specimens were analyzed. As the cooling rate lower than 5°C.s-1, the transformed microstructure is composed of pearlite colony and proeutectoid carbide precipitated on the grain boundary. The starting and finishing transformation temperature gradually decreased with the cooling rate increasing. Under higher cooling rate, partial austenite transformed to martensite as temperature lower than 187°C. Vickers hardness increases obviously with cooling rate increasing, which can be explained by the following reasons. The diameter of pearlite colony and the pearlite lamellar spacing becomes smaller at lower cooling rate, and martensite and retained austenite appears at higher cooling rate.