Papers by Keyword: Sintering Mechanism

Abstract: Ti-6Al-4V compact bulk was fabricated by Spark plasma sintering (SPS) with initial pressure of 1.7 MPa, holding pressure of 50 MPa, heating rate of 100 °C/min, and holding time of 5 min at different sintering temperature. The fracture morphology of the specimen sintered at different temperatures was observed to investigate the sintering mechanism. It can be concluded that there are four stages in the SPS process: activation and rearrangement of particles, connection of particles, growth of sintering neck and bulk deformation. The high-quality bulk compact can be obtained when the above mentioned four sintering stages proceed in turn and are all fully completed. The compact bulk has the best mechanical properties when the sintering temperature was 1050°C. The relative density of the bulk Ti-6Al-4V exceeds 99.5%. The tensile strength and the elongation of Ti-6Al-4V obtained by SPS process are 901 MPa and 13.9%, respectively.

Abstract: The SmCo₅ has three sintering stages using spheres (0.6 – 1.0 mm diameter) at temperatures between 1030 and 1200 °C. During the first stage the neck radius increases as X² ~ t for less than 1200 °C temperature, the exponent is 3 at 1200 °C. Interdiffusion is sintering mechanism for exponent of 2. Sm diffuses from inside to the surface, where it is oxidized and oxides fills the neck between the spheres. Co diffuses through the oxides. At 1200 °C the sintering mechanism is evaporation-condensation of Sm. The activation enthalpy of the first stage is 582 kJmol^-1 for temperatures above 1130 °C and 210 kJmol^-1 bellow 1130 °C, respectively. The second stage is characterized by a plateau where the neck growth is arrested. The small pores in the neck and in the sphere surface layer (formed during the first stage) shrink. When these pores disappear a continuous α-Co layer forms and the third stage starts. It is essential growth of the neck formed by dense Co layer. The law of sintering is X⁴ ~ t. The activation enthalpy (276 kJmol^-1 at temperatures above 1130 °C) closes the activation enthalpy of Co self-diffusion. This (together with the exponent of 4) suggests that the Co layer plays a role similar to that of a liquid film. Making slight changes in the chemical composition of the alloys and substituting an argon atmosphere to vacuum have no influence or stages and sintering mechanisms.

Abstract: Metal/ceramic composite materials with micro-cellular structure which is Al₉₀Mn₉Ce₁ micron powders coated by 10 wt% ZrO₂ nanosized powder is prepared by spark plasma sintering. Effects of the SPS pulse current on the sintering behavior and the composite interface structure is investigated via SEM, XRD, TEM and EDS. The experimental results show that the pulse current is the key factor to the formation of micro-cellular structure. When the Al₉₀Mn₉Ce₁/ZrO₂ composites are sintered by a large pulse current, the hot focus on ZrO₂ nanopowder among Al₉₀Mn₉Ce₁ alloy particles as well as Al₉₀Mn₉Ce₁ alloy particle surface, because of the effect of spark plasma and the concentration of the skin effect in short-term. Dividing temperature field on the interface of micro-cellular structure is benefit for the local high-temperature sintering of the ceramic cell walls layer, and also for the diffusion and interfacial bonding between Al₉₀Mn₉Ce₁ alloy cell body and the ZrO₂ nanosintered cell wall, so as to achieve good sintering.

Abstract: The Pr₂O₃ doped SnO₂ dense ceramic was prepared by co-precipitation method and further sintering. Through the micrograph of the cross-sectional microstructure of the electrodes, the sintering process was analyzed and discussed. Results showed that the solid phase sintering was exhibited at the early stage; when sintering was kept going on, the instant liquid phase could be emerged due to the rich dopants in the grain boundary. Finally, there would be much secondary phase existe as the concentration of dopants reached to a certain value.

Abstract: his paper studies the feasibility of preparation high strength fired bricks from iron tailings with addition of clay and coal gangue. The results indicated that the optimum conditions were found to be that the hematite tailings content were 35%–50%; the firing temperature was 1000 °C. Under these conditions, the mechanical strength, the water absorption and the bulk density of the fired bricks were 21.17–26.14 MPa, 14.55–15.47% and 1.648–1.629g/cm³, respectively, these were well conformed to standards MU20 of Chinese Fired Common Bricks Standard (GB/T5101-2003).The phase composition and microstructure of the fired specimen were characterized by XRD and SEM. The results showed that the major crystalline phases present in fired brick were quartz, albite, amphibole, hematite and muscovite, and glass phase encapsulated and cement the crystalline phases forming strong entirety which promoted the strength of bricks.

Abstract: As vapor grown carbon fiber (VGCF) possesses the good mechanical properties, high thermal conductivity, high electrical conductivity and low thermal expansion, VGCF/ Al composites are expected to be suitable materials for a high performance radiator. In this study, VGCF were dipped and treated with ultrasonic vibration in some kinds of solution at first. Then, the mixed powders including three kind of average particle size of Al (1, 3 and 30µm) was milled by wet process with three kinds of solution, which are acetone, ethanol and butanol. Ethanol is most suitable for mixing solution because of homogeneous distribution of VGCF and Al powders. The mixed powders were spark-sintered in order to obtain dense VGCF/Al composites. The densification mechanism of VGCF/Al composites was divided into the plastic deformation (2nd stage) and creep deformation (3rd stage) after the 1st stage of rectangular wave pulse discharge. The densification rate of VGCF/Al composite powder depended on Al powder for matrix, but independent on VGCF. VGCF are dispersed uniformly in the VGCF/1 µm Al composite. But the aggregations of VGCF exhibited a preferential orientation in VGCF/30 µm Al composite, which results from the deformation of Al powders under the uniaxial pressure during the hot pressing in sintering process.

Abstract: A multi-component polymer-coated molybdenum powder was chosen for selective laser sintering (SLS). A novel preparing method of polymer-coated molybdenum powder was presented. The effect of the process parameters on the part’s characteristics is investigated. Based on our study for dynamic laser sintering process of polymer-coated molybdenum powder, its laser sintering mechanism was reported as follows: at the early stage of laser sintering, the viscous flow is the major mechanism; during the laser sintering, the melting/solidification is the major mechanism. Furthermore, a model corresponding to the mechanism was discussed schematically, which could be used to explain the material migrating mode during laser sintering process.

Abstract: Microstructure is the key scale to understand and describe sintering mechanisms and their consequences at the macroscopic level. As modeling techniques are continuously developing, the need for input data and comparison with more and more accurate descriptions of the evolution is expected to create a growing demand for quantitative microstructure data. Image analysis is the classic way to get these data. This paper reviews the practical use and progresses of this old technique in the sintering literature during the past and recent years. The place of basic tools and more recent ones, such as 3D imaging, are discussed from a practical point of view accounting from sintering models needs: mean size and size distributions in pores and grains, homogeneity, sintering trajectories…