Materials Science Forum Vol. 724

Abstract: FeCoNi system equimolar alloys were fabricated by a vacuum arc melting. The phase constitution of FeCoNi system alloys was determined by XRD analysis and the microstructure was observed by OM. The comprehensive atomic radius δ, the mixing enthalpy ΔH_mix and the mixing entropy ΔS_mix of alloys were also calculated according to relevant equations. The results show that the addition of Ti, Al and Cu has an obvious influence on the microstructure and phase constitution of FeCoNi system equimolar alloys. Single Ti addition resulted in almost entire solid solution with a typical dendrite growth character and a little unknown phase. However, further addition of Al, Cu or Al+Cu into the FeCoNiTi equimolar alloys led to the occurrence of an entire solution phase with dendrite, coarse dendrite, and rosette dendrite respectively. Such a phenomena suggested that the mixing entropy caused by the increase of components number rather than the comprehensive atomic radius between the elements or the mixing enthalpy of the alloy systems might be responsible for the formation of almost entire solid solution in FeCoNi system equimolar alloys.

Abstract: The slurry erosion wear performances of the SiC_p/cast iron surface composite, which was prepared by infiltrating molten cast iron into SiC particles preforms, were studied on self-made slurry inject erosion wear machine. The results show that the erosion wear rate of the SiC_p/cast iron surface composite would be the lowest at impact angle of 30°, and the largest at impact angle of 60°. The erosion wear rate increases gradually when impact angle is changed from 30° to 60°, and then decreased with increasing the impact angle. The erosion wear mechanism of the SiCp/cast iron surface composite is dominated by cutting and grooving at low impact angle, and by fatigue spalling and cutting at high impact angle. For the gray cast iron, the erosion wear rate of would be increased gradually with the increase of impact angle, reaching the peak value at 90°, which indicates the typical characteristics of brittle material in slurry erosion wear process.

Abstract: Silicon was infiltrated into B₄C preforms to fabricate B₄C based composites ceramics at 1600 °C under vacuum circumstance. In this paper, silicon infiltration process was discussed by theoretical calculation. The volume expansion caused by reactions between silicon and boron carbide was about 89.1% from the calculation. In our study, the maximum density of B₄C preform for the infiltration of silicon was about 1.5g/cm³ which was larger than theoretical result. The results of mechanical behavior showed that B₄C based composites had excellent mechanical properties with a density lower than 2.6g/cm³, Vickers-hardness of this material was 27.2GPa, and this material showed a flexural strength of 349MPa and fracture toughness of 3.8 MPa*m^1/2.

Abstract: Porous SiC/SiAlON ceramics were fabricated by carbothermal reduction method from raw materials of fly ash and semi coke in nitrogen atmosphere. The results showed that composites were composed by multi-structure of SiC, Ca-SiAlON and AlN phases. With the increase of semi coke contents, the contents of Ca-Sialon increased. The fracture mode of this material was intergranular. The results also showed that micro area hereditary of semi coke particles was observed in the morphology of this material. The morphology of this material was composed by nanosized SiC and plate like Ca-SiAlON. The median pore diameter was affected by the contents of semi coke and increased with the increase of semi coke content.

Abstract: The high temperature flow behavior of as-cast 904L austenitic stainless steel was studied using artificial neural network (ANN). Isothermal compression tests were carried out at the temperature range of 1000°C to 1200°C and strain rate range of 0.01 to 10s¹. Based on the experimental flow stress data, an ANN model for the constitutive relationship between flow stress and strain, strain rate and deformation temperature was constructed by back-propagation (BP) method. Three layer structured network with one hidden layer and nine hidden neurons was trained and the normalization method was employed in training process to avoid over fitting. Modeling results show that the developed ANN model exhibits good performance for predicting the flow stresses of the 904L steel. Therefore, it can be used to reflect the hot deformation behavior in a wide working window.

Abstract: The wet technology for vanadium extraction from the complex refractory vanadium ores was studied as a preferred approach with phosphoric acid as helper leaching agent. The results showed that the addition of phosphoric acid could improve the vanadium leaching rate significantly. Combination with sulfuric acid, high amount of phosphoric acid and high leaching temperature can promote the leaching of vanadium. With the sulfuric acid concentration of 425.6 g/L, leaching temperature of 90 °C, leaching time of 4 h and liquid-solid mass ratio 2:1, the vanadium leaching rate of 90 wt.% can be achieved. Meanwhile, about 15% of the consumption of sulfuric acid could be reduced with 39 wt.% phosphoric acid.

Abstract: The precipitation behavior of nitrides and carbides occurred in aging process for 10Cr21Mn16NiN austenitic stainless steel at intermediate temperature was investigated by use of thermodynamic calculation, metallography and electron microscopy analysis. The precipitates evolved from chain-like initiatively along grain boundaries at lower aging temperature, to that along grain boundaries and inside the grain of austenite with more content as the temperature rising gradually. When aging at 800 °C, precipitates became layered tablet shaped and the composition was ascertained the mixture of Cr₂N and M₂₃C₆. At a certain temperature, the volume fraction of precipitates for the aged testing steel by air cooling was slightly higher than that by water quenching.

Abstract: The CBN grinding wheels with different porosity, which used 100/120 CBN grind grain and 15μm glass powder as main starting materials, pore creating material as auxiliary material, were prepared by conventional sintering technology; Used GCr15 bearing steel which quenching hardness was 60HRC as ground materials, investigated the effect of porosity of CBN wheel on its cutting ability. In this paper , the metal removal rate was measured by electronic analytical balance, surface roughness of GCr15 was analyzed used LEXT laser scanning confocal microscope and the surface topography of grinding face was observed used scanning electron microscope. The investigated results showed that the metal removal rate acutely increasing with the porosity of wheels increasing in same loading weight, it reached 0.445g/min with 41% porosity in 3500g loading weight, at the same time, the difference of surface roughness caused by variation of porosity of CBN grinding wheel was slight, it did not severely lower machining precision of workpiece.

Abstract: Sodium hydroxide was used to modify distillers' grains (DG) assisted by microwave in order to comprehensive utilization of distillers' grains (DG). The property of distillers' grains (DG) before and after modified was investigated as well as modified conditions. 0.1g of different modified distillers' grains (MDG) was, respectively, used as the absorbents for removal of heavy metal Cu²⁺ ions from aqueous solution at pH 7 and 25°C for 10h. The results show that the modification temperature, time and liquid to solid ratio has little effect on absorption of the modified distillers' grains (MDG) for Cu²⁺ except for concentration of alkali, 5% (wt/v) is the optimum concentration. 5% (wt/v) of the alkali concentration, the hydrolysis temperature of 20°C and the hydrolysis time of 30min and the ratio of liquid to solid ratio of 5:1 were, respectively, used as the optimized conditions to modified distillers' grains (MDG). The removal efficiency of the modified distillers' grains (MDG) for Cu²⁺ (20.00 mg·L¹) is 98.11% under optimized conditions.

Abstract: We carried out a reaction in which glycerol carbonate was synthesized by using glycerol and urea. The physical properties of the prepared catalysts were investigated by BET surface area, X-ray diffraction, temperature programmed desorption, and Field-emission scanning electron microcopy. In addition, we confirmed the conversion of the glycerol and the yield of the glycerol carbonate according to calcination temperature. From XRD results, the crystalline of prepared ZnAl₂O₄ was slowly increased with an increasing of the calcination temperature. When the calcination temperature of ZnAl₂O₄ was 500 , the conversion of the glycerol was 74.4% and the yield of the glycerol carbonate was 73.3%. The conversion of the glycerol and the yield of the glycerol carbonate can be obtained higher when acid/base ratio is approx. 1. From this result, we may conclude that the acid & base site density and ratio of catalysts were very important parameters in the synthesis of glycerol carbonate from urea and glycerol.