Papers by Keyword: Microstructure

Abstract: The influence of the eutectoid structure of hypoeutectic Fe-C alloys by applying electric current pulse (ECP) is carried out. The experiment results show that ECP treatment can produce Joule heating. Joule heating increases the diffusion capability of atoms and the driving force of austenite growth, which promotes austenite crystal growth and accelerate cementite dissolution. In view of the influence of the electron-wind-force made by ECP, it can increase the quantity of moving dislocation. The dislocation pile-up which made by the dislocation motion lead to cementite dissolution. Cementite dissolution can lead to concentration fluctuation in Austenite. ECP can also make the phase transformation barrier and the phase transition drive force of graphite formation decrease. As the result, these phenomena can make cryogenic ledeburite become less and graphite increase. Furthermore, it can also increase the nucleation rate and growth rate of ferrite, which can make the relative amount of ferrite increase and the relative amount of pearlite decrease. Based on our experiments, the effect becomes more obvious with the pulse width increase.

Abstract: The mixture powder of Cr, Ni, Mo and Cu were deposited evenly on a ductile iron with ferrite matrix and treated by plasma transferred arc (PTA). The microstructure and hardness distribution of the PTA-alloyed layers were investigated by using scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and microhardness tester, respectively. Results show that the cross-section consists of four regions: alloyed zone, melted zone, heat affected zone and unaffected substrate. The maximum microhardness of PTA-alloyed sample is measured to be as high as 1077 HV_0.2, which is approximately 4.4 times higher than that of substrate. The improvement is attributed to the formation of mixed hard-phases such as Cr₇C₃, C₂₃C₆, martensite, cementite under nonequilibrium solidification, and the solution strengthening by the alloying elements as well as grain refining via the rapid cooling.

Abstract: The research progress of homogenization, solution and aging heat treatment processes and their effects on microstructure and properties of 7000 series aluminum alloy was reviewed in this paper. The solution and aging process were analysed mainly. The problems existing in the industrialization application of heat treatment of the alloy and the demanding problems to be solved in research and development in the future were described.

Abstract: The method to analysis the rheological property of the crosslinked polymer microspheres is presented in this paper. The flow curves and hysteresis loop areas of different swelling time and different mass concentrations of microspheres gotten. Through the above experimental data, the flow pattern and the time-dependent property are judged. Combined with the environmental scanning electron microscope images of microspheres, we can draw the conclusion that the concentration has obvious effects on the rheological property of the microspheres.

Abstract: In this study, a combination of a two-step sintering and a particle size gradation technique was used to prepare cermet samples. We focused on the impact of the AlF₃ additive on the performance of the cermet. We found that the addition of AlF₃ doesnt significantly improve the density and porosity of Ag-NiFe₂O₄, since the addition of the AlF₃ did not reduce the particle size, nor did it promote the tight packing of NiFe₂O₄ in a spinel-based cermet. However, we did observe a significant enhancement in its conductivity. The sample with 3% additive has the highest conductivity at 22.53S·cm^-1 at 900°C, nearly 3.8 times better than the pure sample. An Analysis of the cermet microstructure showed that adding AlF₃ can improve wetting between the ceramic phase and the silver metallic phase. It also facilitates the distribution of silver along the contour of the ceramic particles, which contributes to the improved conductivity of the nickel-based cermet.

Abstract: In this paper, in situ TiB reinforced Ti-3Al, Ti-6Al and Ti-6Al-4V matrix composites were prepared by arc-melting technique utilizing the reaction between Ti and TiB₂, and then forged in the α+β phase field. Phase identification was carried out via X-ray diffraction. Microstructure of the composites was studied by optical microscopy (OM) and scanning electron microscopy (SEM). Mechanical properties of the composites after forging were measured at various temperatures by tensile experiment. The results showed that Ti-6Al-4V-2TiB composite exhibits fine equiaxed matrix microstructure with a grain size of 5-10μm. The tensile strength and elongation of the composite at room temperature reached 1069MPa and 10.0%, respectively.

Abstract: Porous silica ceramics were prepared from rice husk ash with a small amount of soft clay as workability agent by the in situ combustion pore-forming technique. Then, the effects of the forming pressures on the linear shrinkage, density, porosity, absorption of water and mechanical strength were investigated. The results showed that the pores in the samples consisted of two groups. One was original porous texture from rice husk silica, which ranged from 1-10 μm. The other was formed by burning of carbon and grain packing. Obviously, the greater the forming pressure, the denser the sample. Especially, the amounts of the pores with bigger diameter dropped significantly when the forming pressure was greater than 25KN. Porous ceramics with density 1.07g/cm³ have high porosity and excellent comprehensive properties up to 10MPa.The preparation of porous ceramics utilizing high content rice husk would provide advantages of economical and ecological aspect.

Abstract: The in-situ synthesized TiB reinforced titanium matrix composites have been prepared by spark plasma sintering technique at 950–1250°C, using mixtures of 10wt% TiB2 and 90wt% Ti powders. The effects of the sintering temperature on the mechanical properties (Vickers microhardness, yield strength and Young`s modulus) of the composites were investigated. SEM was used to analyze the reaction process and the microstructure of the compacts synthesized at different sintering temperatures. The results indicated that the in situ synthesized TiB grow rapidly with increasing sintering temperature. The composite sintered at 1250°C have the highest relative density of 99.2%. However, the composite sintered at 950°C exhibits the best Vickers microhardness of 4.64GPa and yield strength of 989MPa, respectively.

Abstract: The microstructure and mechanical properties of magnesium alloy AZ61wtih1% Sn addition has been studied in this paper. The results show that the addition of 1% Sn can refine the grain size and improve the microstructure morphology of β-Mg₁₇Al₁₂ phase. The addition of Sn can cause the formation of Mg₂Sn phase in AZ61 alloy, which can effectively enhance the mechanical properties of magnesium alloy AZ61 at room temperature and 150°C.

Abstract: Based on the fatigue crack propagation experiments did by A.-L. Gloanec et al., the fatigue crack propagation rates of TiAl alloy of two processing routes, namely casting and PM, and stress ratios had been tested, in order to find out the effects of microstructure and stress ratio. An improved fatigue crack propagation formula for region Ⅱ (the expansion region) was derived according to Paris formula. The specific values of the constants in the formula were calculated. Fatigue crack propagation resistance of nearly fully lamellar microstructure is superior to that of equiaxed γ grain. The experimental results present that both microstructure and stress ratio has a significant influence on fatigue crack growth rate.