Papers by Keyword: Hot-Pressing

Abstract: Dense Y³⁺-dopted α-SiAlON/BN composition ceramics was fabricated by hot pressing at 1900 °C for 60 min, and flextural strength at room and 1000 °C was investigated through three-point bending test. The results show that h-BN contribute to the densification of powder body, but h-BN have little affect on the key temperature region of sintering densification of α-SiAlON ceramics. When content of BN is lower, which didn’t affect on the phase transformation of α-SiAlON, but when content of BN is higher, besides of major phase α-SiAlON, a little of β-SiAlON was also formed. For the α-SiAlON/BN composite ceramics content of 20 wt.% h-BN, the higer flexural strength( room-temperature and 1000 °C) were abtained, the formation of β-SiAlON should be an important resonon for the higher strentgh, more important is , whose flexural strength at 1000 °C is higher 50 MPa than at room temperature, the differnce of thermal properties between SiAlON and BN should contribute to the improve of high-temperature flextural strength.

Abstract: The SiCp/Al-30Si composite material was prepared by hot-pressing. The microstructure was characterized by means of optical microscope and SEM, the thermal expansion performance was tested by PYC-Ⅲ Thermal Expansion Coefficient Tester. It was researched that the influence of SiC particle size and manufacture technology on the microstructure and thermal expansion coefficient. Results show that shortening soaking time decreases the number and the size of the nascent and precipitating Si particles, enlarges the CTE of the composite; lager pressure is beneficial to reduce the CTE of the composite, and the larger the pressure is, the more compact microstructure is and the less number of holes are. Thermal expansion performance of the composite was influenced by SiC particle size, distribution of matrix phase, trait of interface combination and the holes.

Abstract: In traditional processing technology for easy tear lid, punching and hot-pressing are separated. They are finished by different mechanisms. There are some producing problems because of separated processing stages. In order to solve the problems, an innovated processing technology and the related mechanism for easy tear lid's forming are proposed in this paper. The new processing technology combines punching with hot-pressing; it can raise the rate of production. The related mechanism not only assures the accuracy of the lid’s forming, but also simplifies the structure of forming machine, making overall arrangement of machine become more reasonable.

Abstract: During hot pressing of the wood-based panels, the technological conditions, environment noises and performance of the sensors often result in errors in the temperature measurement. To improve the precision and reliability of data, multi-sensor technology is used for measurement data processing. The data consistency checking is performed by computing the confidence distance between adjacent sensors, and therefore the valid data fusion collection is determined. The weighted least square algorithm is applied to acquire high accuracy of overall estimation value by determining the information weight coefficient with the corresponding measurement variance of each sensor. The results of experiment demonstrate that the precision of overall estimation value is preferable than the partial estimation of each sensor and show the effectiveness and reliability of the algorithm.

Abstract: WC matrix composites toughened by commercial Al₂O₃composed of AlOOH, χ-Al₂O₃and amorphous Al₂O₃ were prepared by high energy ball milling and then hot pressed at 769°C, 984°C, 1100°C, 1540°C for 90min, respectively, to investigate the phase transformation process. Microstructure and mechanical properties of WC-40vol.%Al₂O₃ composites were studied as well. The results showed that, with the increasing hot pressing temperature, the commercial Al2O3 transformed to α-Al₂O₃ completely through γ-Al₂O₃. WC could be oxidized and decarburized to W, C and W₂C at low temperature when the vacuum degree was very low. The existence of W in the composites sintered at 1540°C for 90min could contribute to a metal particle toughening effect to the composites, resulting in the achievement of an excellent fracture toughness of 10.43MPa•m^1/2, combining a Vickers hardness of 18.65GPa with a relative density of 97.98% for WC-40vol.%Al₂O₃ composites.

Abstract: To enhance the mechanical properties of Mg alloys, powders of pure Mg (Al₂O₃/Mg) dispersed with over 10 vol% Al₂O₃ particles were formed by ball milling powder mixtures of pure Mg and Al₂O₃ particles with particle sizes of 0.3 and 1 μm. The effect of the Al₂O₃ content of hot-pressed discs of Al₂O₃/Mg powders on the mechanical properties was investigated. The hardness increased sharply at certain Al₂O₃ content. This is considered to be because of the development of Al₂O₃ particle strengthening due to the excellent interfacial bonding between Mg and Al₂O₃ particles when the Al₂O₃/Mg discs contain a sufficient amount of Al₂O₃ particles and have a sufficient interparticle distance. The maximum hardness was 220 HV. The tensile strength increased as Al₂O₃ content was increased. The Al₂O₃/Mg plate with Al₂O₃ particles sizes of 0.3 and 1 μm indicated maximum values of the bending strength at 10 and 14vol%Al₂O₃ content, respectively.

Abstract: One of the most challenging areas in engineering of composite materials is the fabrication of high quality microstructures. This issue is complicated for tungsten composites due to its high melting temperature and this leads to limitations in terms of possible processing techniques. This research investigates the fabrication of W-12%wtCu composites based on powder metallurgy techniques. Due to the very large difference between the melting point of tungsten and copper, there is no common sintering temperature range for them. In this work, 0.5%Wt nickel was added as an activator to decrease the sintering temperature of tungsten using an activated sintering effect. The effects of pressure, sintering time and temperature in solid state and liquid phase conditions were also investigated. While solid state hot pressing did not result in appropriate microstructures, the liquid phase hot pressing provided high quality samples with a relative density of 98.0%.

Abstract: Pure MoSi₂ and MoSi₂ composites with different volume fraction of SiC particles were prepared by the technology of in situ reaction and hot pressing the pure powder of Mo, Si and C after alcohol mixing. The effects of in situ formed SiC particles on the microstructure, the flexural strength and fracture toughness of SiC_P/MoSi₂ composites were studied. The research shows the relative density, flexural strength and fracture toughness of the composites are increased compared with those of the pure MoSi₂ material. It is found that the in–situ formed SiC particles refine the MoSi₂ grains and eliminate the brittle SiO₂ glass phase. The strengthening mechanism of the composites is of the refinement of MoSi₂ grains,dispersion strengthening of the in–situ formed SiC particles and elimination of the brittle SiO₂ glass phase.

Abstract: The Fe₃Al/Al₂O₃ composites were fabricated by hot-pressing process in this research. The Fe₃Al intermetallics compounds powders were fabricated by mechanical alloying and heat treatment, then the Fe₃Al powders and Al₂O₃ powders were mixed and the Fe₃Al/Al₂O₃ composite powders were prepared, so the Fe₃Al/Al₂O₃ composites were fabricated by hot-pressing process at 1300°C for 2h under the pressure of 35MPa. The phase composition and microstructure of the Fe₃Al intermetallics compounds powders produced by mechanical alloying and heat treatment were investigated. The phase composition, microstructure and mechanical properties of the Fe₃Al/Al₂O₃ composites sintered bulks were investigated. The XRD patterns results showed that there existed Fe₃Al phase and Al₂O₃ phase in the sintered composites. The Fe₃Al/Al₂O₃ composites sintered bulks exhibited the homogenous and compact microstructure, the Fe₃Al particles were homogenously distributed in the Al₂O3 matrix, the mean particles size of Fe₃Al intermetallics compounds was about 3-4μm. The Fe₃Al/Al₂O₃ composites exhibited more homogenous and compact microstructure with the increase of Fe₃Al content in the Al₂O₃ matrix. The density and relative density of the Fe₃Al/Al₂O₃ composites increased gradually with the increase of Fe₃Al content. The fracture strength and fracture toughness of the Fe₃Al/Al₂O₃ composites increased gradually with the increase of Fe₃Al content. The elastic modulus and hardness (HRA) of the Fe₃Al/Al₂O₃ composites decreased gradually with the increase of Fe₃Al content.

Abstract: The composite materials with a nominal composition of Cr₂Nb-24wt.%Ti were fabricated by mechanical alloying followed by hot pressing. The microstructures and properties were investigated on the composites contained with Laves phase prepared through 20 hours mechanical alloying of chromium, niobium and titanium elemental powders and hot pressing at 1250°C for half an hour. The results indicate that the near full-dense Laves phase Cr₂(Nb,Ti) based alloy with homogeneous composition and microstructure is obtained by mechanical alloying and hot pressing techniques. The dispersed soft second phase Nb solid solutions with the fine grain size less than 1μm are distributed uniformly on the matrix. The sample has a relative density of 99%, fracture toughness of 5.32MPa•m^1/2 and compress strength of 2080MPa. Due to the effect of fine-grain and alloying addition, the toughening of the Cr₂(Nb,Ti) based alloy has been fully realized.