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Lanthana precursor was coated on yttria-stabilized-zirconia (YSZ) powders by wet chemical infiltration, and was introduced to the crystalline structure and grain boundaries of YSZ after plasma spraying of thermal barrier coatings (TBCs). The microstructural stability and thermal barrier properties of this new kind of TBCs were studied under different annealing conditions. It demonstrates that the La2O3 surface coating restrains grain growth of YSZ during both deposition and post-annealing processes, compared to a TBC obtained from commercially available unmodified YSZ powders. According to the composition analysis, lanthana partially dissolved in the zirconia matrix after heat treatment. The thermal diffusivity of YSZ coating significantly decreased after lanthana modification, typically from 0.354 mm2 s− 1 for an unmodified sample to 0.243 mm2 s− 1, reflecting a decrease of 31%. Even after annealed at 1200 °C for 50 h, the thermal diffusivity of modified coatings still shows a reduction of 25% than unmodified samples. 相似文献
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S.P. Wen 《Surface & coatings technology》2008,202(10):2040-2046
The microstructure, hardness and thermal stability of Ni/Ru multilayers prepared by evaporation deposition were investigated by X-ray diffraction, transmission electron microscopy, vacuum annealing and nanoindenation. The hardness values of as deposited multilayers increase, while their elastic modulus values decrease, with decreasing periodicity. After annealing at low temperature (below 450 °C), the decrease in hardness of multilayers with larger periodicity is more remarkable than that of multilayers with smaller periodicity due to coarsening of the in-plane grain size. The higher temperature (600 °C) annealing results in the breakdown of the periodical structure and a significant drop in hardness for multilayers with smaller periodicity. The results were discussed according to Orowan-type single dislocation bowing mechanism. 相似文献
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This paper was aimed at providing the underlying thermo-mechanical mechanisms in relation to the residual stresses in surface coatings. Four different topics were involved, namely the analytical model for predicting the residual stress, the accuracy of Stoney's equation, the bifurcation behavior for a coating system, and the optimal design for improving the adhesion of a coating. All these topics were in relation to the curvature and the misfit strain created during the coating deposition process, the material properties and dimensions of the coating and substrate. 相似文献
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《中国铸造》2015,(2)
Soldering is a unique casting defect associated with die casting or metal mold casting of aluminum alloys. It occurs when molten aluminum sticks or solders the surface of the die steel and remains there after the ejection of the casting, causing a surface defect and dimensional inaccuracy of the castings and increased machine downtime. Soldering occurs easily when a bare die steel mold is used for die casting of aluminum alloys. When molten aluminum comes in contact with the die steel at a temperature higher than a critical temperature, the iron and aluminum atoms diffuse into each other, forming a series of intermetallic phases and a liquid aluminum-rich fcc phase. This liquid phase exists between intermetallic phases. On cooling, the liquid fcc phase solidifi es on the intermetallic phases and grows into the casting, resulting in soldering. The critical temperature is the eutectic temperature near the aluminum corner of the phase diagram. If the die is protected using a nonreactive ceramic coating, soldering starts at locations where local coating failure occurs. Molten aluminum comes into contact with die steel through the coating failure locations and eats into the steel matrix, forming small pits. As these small pits grow, the coating is gradually removed and soldering becomes more severe. Details of die soldering step on a bare steel die and on a coated die material are discussed. 相似文献
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Strengthening technology and mechanism for semi-solid die casting of aluminum alloy 总被引:10,自引:0,他引:10
Combined with theoretical evaluation,an optimized strengthening process for the semi-solid die castings of A356 aluminum alloy was obtained by studying the mechanical properties of castings solution treated and aged under different conditions in detail,then,the semi-solid die castings and liquid die castings were heat treated with the optimized process.The results show that the mechanical properties of semi-solid die castings of aluminum alloy are superior to those of the liquid die castings,especially the strengthening degree of heat treated semi-solid die castingsis much greater than that of liquid die castings with the tensile strength more than 330 MPa and the elongation more than 10%,and this is mainly contributed to the non-dendritic and more compact microstructure of semi-solid die castings.The strengthening mechanism of heat treatment for the semi-solid die castings of A356 aluminum alloy is due to the dispersive precipitation of the second phase(Mg2 Si) and formation of GP Zone. 相似文献
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During high-pressure die-casting (HPDC) of aluminium alloys, there is a tendency for the molten alloy to react with the tool steel die, core pins and inserts. This occurrence within the high pressure die casting (HPDC) industry is referred to as ‘soldering’. It is of concern to high-pressure die casters because of down-time due to the regular removal of the soldered layer and its detrimental affect on die life and casting quality. In this investigation, several physical vapour deposited (PVD) coatings, namely, TiN, CrN and TiCN, were evaluated for their ability to eliminate soldering during HPDC of aluminium alloys. Accelerated semi-industrial trials were carried out in a 250-t Toshiba HPDC machine using a specially designed die made of P20 tool steel with removable core pins. The results from these trials showed that PVD coatings can act as a physical barrier coating preventing any reaction between the molten aluminium alloy and the tool steel. Thus the problem of soldering on such tools as core pins can be eliminated in high HPDC of aluminium alloys. In the accelerated trials, it was found that soldering was replaced by a built-up layer of cast aluminium alloy, which was less detrimental to tool life and reduced machine down-time due to the reduced need for tool polishing. The experimental results were confirmed by conducting in-plant HPDC trials. 相似文献
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The residual stress distributions of ZrO2/NiCoCrAlY high-temperature coatings were analyzed using an analytical model and finite element analysis. Three different topics were involved, namely the effect of interlayer on the stress distribution, the zero-deflection design for typical duplex-layer thermal barrier coating-based system, and the edge effect on the residual stress distribution. These topics could provide some insights into the development of a fail-safe design methodology for high-temperature coating systems. 相似文献
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Soldering of cast alloys to the dies has been a continuing source of die surface damage in the aluminum die-casting industry. To reduce the repair and maintenance costs, an approach to modeling the damage and predicting the die lifetime is required. The aim of the present study is the estimation of the die lifetime based on a quantitative analysis of die soldering in the framework of the numerical simulations of the die-casting process.Full 3D simulations of the process, including the filling, solidification, and the die cooling, are carried out using the casting simulation software MAGMAsoft. The resulting transient temperature fields on the die surface and in the casting are then post-processed to estimate the die soldering.The present work deals only with the metallurgical/chemical kind of soldering which occurs at high temperatures and involves formation and growth of intermetallic layers. The die-soldering model combines two approaches available in literature, describing the two aspects of die soldering: the growth of the intermetallic layer, and the thermal and metallurgical conditions in the layer that lead to the die soldering. The theoretical model is then extended with the treatment of the intermetallic layer growth controlled by the idealized effective diffusivity and with the treatment of solder strength dependent on the temperature and liquid fraction within the layer. The solder strength locally on the die surface is calculated as a function of the number of die-casting cycles. This also provides the estimation of the die lifetime defined as the number of cycles until the critical solder strength level is reached.Proper validation of the model is required, and the model parameters (the critical solder strength value, among others) need to be calibrated by measurements and data from the die-casting industry.As an example, the model is applied to several cases of high pressure die casting (HPDC) where A380 alloy parts are cast in the H13 steel die. The predicted locations of the higher strength of soldering appear in the “hot spot” areas of the die surface in agreement with the reports in literature. The influence of several casting process parameters such as cooling/spraying efficiency and other parameters that control the thermal history of the die and the casting is in agreement with the expected behavior. 相似文献
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M. Okayasu S. Wu T. Hirayama Y.-S. Lee 《International Journal of Cast Metals Research》2018,31(5):308-316
To reduce the amount of casting defects in diecast components, a new shot-sleeve is proposed. Cold flakes are generated by solidification of the casting material in the shot-sleeve before the injection process. To solve this problem, a thermal insulation system is introduced on the inner shot-sleeve surface, with tiny grooves being machined to create an air gap between the melt and the sleeve surface. Various casting materials with different material properties are used to examine the insulating effect of the shot-sleeve. The degree of thermal insulation is found to be influenced by the material properties, with the surface tension being significant factors. This thermal insulation effect allows the production of high-quality samples and therefore with good mechanical properties. When casting materials with low surface tension are used, the melt is able to penetrate deeply into the grooves of the shot-sleeve, lessening the insulation effect and leading to the defect. 相似文献
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The feasibility of semi-solid die casting of ADC12 aluminum alloy was studied. The effects of plunger speed, gate thickness, and solid fraction of the slurry on the defects were determined. The defects investigated are gas and shrinkage porosity. In the experiments, semi-solid slurry was prepared by the gas-induced semi-solid (GISS) technique. Then, the slurry was transferred to the shot sleeve and injected into the die. The die and shot sleeve temperatures were kept at 180 °C and 250 °C, respectively. The results show that the samples produced by the GISS die casting give little porosity, no blister and uniform microstructure. From all the results, it can be concluded that the GISS process is feasible to apply in the ADC12 aluminum die casting process. In addition, the GISS process can give improved properties such as decreased porosity and increased microstructure uniformity. 相似文献
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《中国铸造》2019,(4)
The gating system and the overflow system were designed according to the casting structure during high pressure die casting(HPDC) process. The simulation was carried out by ProCAST software to visualize the injection chamber pre-crystallization and the flow of molten metal. The main work is to research four die casting process parameters, i.e. injection temperature, low-pressure velocity, high-and low-pressure velocity's switching position, and high-pressure velocity. Experimental results show that the higher injection temperature and lowpressure velocity can mitigate the pre-crystallization of the injection chamber. However, when the low-pressure velocity exceeds 0.2 m·s~(-1), the air entrapment in the chamber occurs. Besides, when the high-pressure velocity is greater than 2.5 m·s~(-1), the overflow channel at the final filling position is covered by the liquid metal too early. Finally, the injection temperature of 650 °C, the low-pressure velocity of 0.2 m·s~(-1), the high-and low-pressure velocity's switching position of 320 mm and the high-pressure velocity of 2 m·s~(-1) are obtained as the optimal parameters by the software simulation, which has been verified by actual production. 相似文献
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1 INTRODUCTIONCastaluminumalloysarewidelyusedinaerospace ,aeronautics,automobiles ,mechanicalmanufacturingindustries ,etc .,duetotheirdesirablefeaturessuchaslowdensity ,highspecificstrength .Withthedevelopmentofmodernindustriesandnewcastingtechnologies ,thed… 相似文献
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1 INTRODUCTIONIndiecastingprocess,thediesexperiencease riesofcomplicatechanges.Thetemperatureonthecavitysurfacesofdiesincreasesrapidlyduetocontact ingandwashingbetweenthemoltenmeltanddies,andthehot yieldstrengthincontactzoneofthecavi tyisreducedrapidly .I… 相似文献
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汽车压铸及铸造铝合金 总被引:1,自引:0,他引:1
介绍了汽车铝合金中压铸、铸造合金的比例,变化趋势,在某些国家地区的产量。详细介绍了日本和美国近些年来各类汽车铝材的发货量,中国和日本压铸、铸造铝合金的化学成分、性能、特点及应用,各种铸造铝合金的热处理规范,汽车用高强度铸造铝合金的特点,典型汽车铸造铝产品的选材、生产与性能。介绍了压力铸造、金属型低压铸造、科斯沃斯法、气化模铸造工艺,列出了低压铸造工艺生产的各类铸件特征、材料和工艺。预测了汽车用铝的前景。 相似文献