Papers by Keyword: Hot-Pressing

Abstract: ZrB₂-Cu composite is a new electrical contact materials in the integration of high conductivity, high wear resistance and good mechanical strength. In this paper, ZrB₂-Cu composites were prepared by hot-pressing sintering at 800~900 °C under a pressure of 20 MPa.The densification of ZrB₂-Cu composites was improved by the addition of nickel using an electroless metal plating technique. X-ray diffraction and scan electron microscopy were used to analyze the phase and microstructure of ZrB₂-Cu composites. The results showed that ZrB₂-Cu composites with 60 vol % Cu which was sintered at 900 °C had a higher relative density, highest flexural strength of 381 MPa and higher hardness of 2.16 GPa(HV). ZrB₂-Cu composites with 50 vol % Cu which was sintered at 900 °C had higher flexural strength of 297 MPa and the highest hardness of 2.66 GPa.

Abstract: As the new structural material, TiAl intermetallic compound has great potential application in aerospace engine, energy and automotive fields. But the bottleneck problems including poor room temperature ductility and high-temperature oxidation resistance limit its application. Ti₂AlC possesses an unusual combination of the merits of both metals and ceramics, which is considered the best reinforcement for TiAl intermetallic compound. In the present work, Ti₂AlC/TiAl matrix intermetallic compound was successfully fabricated by in situ hot pressing method from the mixture of Ti/Al/TiC. The phase transitions were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The microstructure of the product was studied by scanning electron microscopy (SEM). Ti reacted with Al liquids to form Ti-Al intermetallics below 900 °C firstly. With increasing temperature (above 900 °C), a part of TiAl intermetallics reacted with TiC to form Ti₂AlC reinforcement. The as-sintered product presented dense and typical lamellar structure. The in-situ synthesized fine Ti₂AlC contributed to improve the strength of TiAl matrix intermetallic compound.

Abstract: The upper part and lower part of rice straw were respectively used as raw materials to prepare composites with poly (vinyl alcohol) (PVA) by hot-pressing at 140°C for 10 min. The performance differences of two kinds of composites were studied. Results showed that composites prepared with upper-part rice straw had higher tensile strength, strength at tensile break and hardness than that with lower-part rice straw. But the tensile elongation of composite prepared with upper-part rice straw was lower than that with upper-part rice straw. Difference ratio of tensile strength is higher than 6% and difference ratio of tensile elongation is higher than 16%. These differences were related to morphology and structure of upper-part rice straw and lower-part rice straw. Two parts of rice straw are both hollow, but upper-part rice straw has thinner holes. So the defect ratio of composite prepared with upper-part rice straw was low.

Abstract: This paper presents the manufacturing process of scrimber by using mulberry branches and urea-formaldehyde. The effect of density, hot-pressing conditions and resin content on scrimbers mechanical properties was conducted. The results showed that the mechanical properties of the scrimber met the relative requirements in the density of 0.8 g/cm³ while the resin content was 12% and the hot-pressing conditions were in 1.5MPa, 100°C and 1.4min/mm. The MOR, MOE and IB of samples had reached 40.14MPa, 5024.20MPa and 0.44MPa under the best process condition. The MOR and MOE had achieved the standard of LY/T 1655-2006 and the surface of scrimber had natural textures which could be used as decorated materials for building.

Abstract: This study describes the principles of synthesis and technological features of composition ceramics formation on the basis of silicon carbide and aluminum nitride by hot-pressing. The structural properties and composition of the ceramics were investigated by scanning electron microscope and the formation of the solid solution is confirmed. The elements distribution on the surface of failure pattern is shown. The results of the study are useful for optimization of manufacturing process of structural and functional high-density ceramics.

Abstract: TiB2-TiC0.8-40vol%SiC multiphase ceramics were prepared by in-situ hotpressing sintering. The phase composition and microstructures of the materials were characterized by optical mic- oscope, X-ray diffraction and scanning electron microscopy. The effects of sintering temperature on the phases, microstructures and mechanical properties of the ceramics were investigated. The results show that density, bending strength and fracture toughness of the ceramics are increased with the elevation of sintering temperature (1800-1950°C). High densified TiB2-TiC0.8-40vol%SiC multipha- se ceramics and optimized microstructure is obtained by sintering at 1900°C, in which the uniform distribution of lath-shape TiB2 and bulk TiC0.8 grains can be observed obviously. Nano-SiC particles distributed dispersively in the TiB2 and TiC0.8 grains and at boundaries. The Vickers hardness, fract- ure toughness, flexural strength and electrical conductivity of the TiB2-TiC0.8-40vol%SiC multipha- se ceramics sintered at 1900°C are 24.055GPa, 8.27±1.0MPa∙m1/2, 516.69MPa and 2.2×106S∙m-1, respectively. However, up to 1950°C, TiB2 and TiC0.8 grains gradually grew up, the bending stren- gth of multiphase ceramics was decreased greatly. In addition, TiB2, TiC0.8 and SiC particles were incorporated together to improve the particulate strength and toughness of composite material by the synergistic mechanism effects among the crystal phases in the multiphase ceramics, such as crack deflection, grain’s pull-out and fine-grain toughening.

Abstract: Titanium is characterised by an outstanding combination of properties like high strength, low density, good corrosion resistance and biocompatibility. Nonetheless, widespread employment of titanium at the industrial level, especially in the automotive industry, has not been achieved yet because of its high extraction and production costs. Consequently, titanium finds applications mainly in high demanding sectors, such as the aerospace industry or to produce biomedical devices, where the final high cost is not the principal issue. The processing of titanium and its alloys by means of powder metallurgy (PM) techniques is claimed to be a suitable way to reduce the fabrication cost of titanium products as well as offering the possibility to design new alloys which are difficult to obtain using the conventional metallurgical route, for example due to segregation of heavy alloying elements. This work deals with the processing of hydride-dehydride elemental titanium powder by means of different PM methods and aims at investigating the processing of near net-shape, chemically-homogeneous and fine-grained titanium-based components. In particular, properties achievable (i.e. relative density, microstructure and mechanical properties) and problems related to the processing of elemental titanium, by both the conventional PM route of pressing and sintering and the advanced PM method of hot-pressing, are presented.

Abstract: To improve the way of efficient recycling of waste Tetra Pak package, save wood materials and develope new packaging materials, this article studied on the optimum hot-pressing process and surface decoration of waste Tetra Pak/sawdust composite board. Using the orthogonal experimental method, we studied the effect of that four factors, such as resin content, hot-pressing temperature, hot-pressing time and Tetra Pak/sawdust mass ratio, on MOR, MOE, TS for 2h of waste Tetra Pak/sawdust composite board. And according to the measurement and analysis of these three test indicators of the board, we obtained the optimum hot-pressing process of waste Tetra Pak/sawdust composite board. The results showed the optimization of process parameters for the board was that: resin content for 14%, hot-pressing temperature for 150°C, hot-pressing time for 420s and Tetra Pak/sawdust mass ratio for 4:6 were suitable to product this board. At this point, the maximum MOR of the board was up to 23.1MPa, the maximum MOE of the board was up to 2917MPa, the minimum TS for 2h of the board was down to 6.1%. In the processing of PVC surface decoration, by using comparison tests, the results figured out that hot-pressing temperature for 50°C-60°C, hot-pressing time for 10s-20s, hot-pressing pressure beyond 0.02MPa were good for PVC to decorate this kind of board. The formaldehyde emission of this veneer composite board was 0.3mg/L, the surface abrasion resistance of it could reach 900r, besides, its performance of surface pollution resistance has reached the national standard.

Abstract: Particleboard is a widely used panel material because of its physical properties and low cost, the hot-pressing operation is the one of the most important stages of the whole particleboard production in which many physical processes are involved, such as mat moisture content and distribution, heat transfer. A number of factors are involved including resin type, press temperature, wood species and press closing time, pressure during pressing, Considering coupled heat transfer with resin release ,we presented a mathematical model have been given and solve the modeling with the method of variable separation characteristics and function expansion method. The model has described the relation of center layer temperature changes with pressing times. It is helpful for further research of Internal change in hot-pressing

Abstract: In this work, we perform a post hot-pressing on the pre-sintered Nd-Fe-B magnet, and investigate its influences. The results show that the main influence on the magnetic characteristics is that it deteriorates the rectangularity of the demagnetization curves. Further investigations on density, grain size and crystal alignment show that the increases of density and grain size, and the decrease of crystal alignment with the hot-pressing. The discussion indicates that at the temperature higher than the melting point of boundary phase, the liquefying of boundary under uniaxial external pressure brings about the grain growth, the density increase, and the deviation of crystal alignment from the pre-aligned optimum position.