Abstract: Metastable phase was observed in as-solidified microstructure of undercooled Fe-Co alloy, provided that the initial undercooling (T) of the melt exceeds the critical value. On this basis, the forming mechanism and stability of metastable phase were investigated. The forming mechanism of metastable phase in undercooled Fe-Co alloy was concluded as cooperative effect of “competitive nucleation—remelting—extensive growth—incomplete solid-state transformation” in this work. With the increase of annealing time, the number and dimension of metastable phase decreased at the same time. Moreover, metastable phase was transformed to stable phase completely when annealing time increased to three hours.
Abstract: The surfaces of carbon black were modified by nitric acid oxidation. The surface structures of the original and oxidized carbon black were investigated by means of FT-IR and XPS, respectively. Furthermore, the oxidized carbon black and distilled water were mixed to form the self-dispersal nanometer carbon black pigment. The particle size distribution and dispersion stability of the carbon black pigment were investigated by means of particle-size analyzer and spectrometer, respectively. The results showed that some highly marked hydrophilic character functional groups on carbon black surfaces were increased greatly by nitric acid oxidation.
Abstract: Directional solidification (DS) of FeCoNiCrAl high entropy alloy is carried out to investigate the microstructures and microsegregation under controlled solidification conditions. With an increasing solidification rate, the interface morphology grows in a planar, cellular and dendritic manner. The microstructures of the dendritic and interdendritic segregation areas are found to be spherical precipitates and basket-weave structures, respectively. With the help of an electron microprobe, microsegregation is determined in directionally solidified FeCoNiCrAl high entropy alloys. In contrast to the as-cast condition, directional solidification can refine microstructures of FeCoNiCrAl high entropy alloy dramatically and reduce microsegregation effectively.
Abstract: The solidification and process optimization for twin-roll casting of magnesium alloys have been studied. Effects of roll speed, roller diameter, setback length and strip thickness on the position of the solidification front and the surface quality of strip were analyzed through experiments. A kiss-point model which considers the strip thickness, set-back length and roll speed was established to optimize process and enhance the surface quality of magnesium alloy strip. Results showed that the twin-roll casting process could be effectively stabilized and optimized under the direction of the model, and the defectless magnesium alloy strip was obtained.
Abstract: The impeller is an important component applied in airplanes, ships and weapons. It is difficult to form the complicated geometry of the impeller by using the conventional forging and casting technology. Semi-solid forming is a promising forming process that can produce complicated and high-quality components of wrought aluminum alloys. In this paper, the formability of the impeller was investigated by using advanced semi-solid forming technology and self-designed combined die, as well as quick forging hydraulic press. Experimental results show that the formability of the impeller increases with the increase of reheating temperature and holding time of the billet. When heating temperature and holding time during the pretreatment of the billet were 620°C and 25 min respectively, reheating temperature and holding time of the billet before thixoforging were 600°C and 90 min respectively, preheating temperature of the die was 320°C , the impeller was formed perfectly on the quick forging hydraulic press.
Abstract: The quality and properties of steels may be affected due to the segregation of the alloying elements, even though the properties of steels can be improved by adding appropriate amount of alloying elements. Rapid solidification was regarded to be an effective method to reduce or eliminate the segregation of alloying elements. While the segregation of C, P and Mn was also observed in rapid solidified (in silicone oil) droplet carbon steels in this paper. The microstructures of rapid solidified droplets were rather fine. When the P content was less than about 0.09% (in mass) in low carbon steels, P did not show obvious segregation in rapid solidified droplet samples; when the P content raised up to about 0.5% in the samples, both P and Mn showed center segregation even though the content of Mn kept unchanged. So the alloying elements can segregate and even effect the distribution of other elements in rapid solidified steel samples. When the C content increased, the segregation of C was observed in high-C samples, while the segregation tendency is opposite to that of P in high-P samples. For all the droplet samples, the micro-hardness of high-P samples was also much higher than those samples with less P content.
Abstract: This paper studied the effects of inclusion and slag on properties of a die cast A356 alloy wheel. The result showed that the rate of defect is important for the mechanical properties. The tensile strength and extension was not dropped but the rate of defect is increased about 2%. The variation trend of tensile strength and extension is linear, while the area of porosity on tensile fracture is between 2% and 6%. However, the tensile strength and extension was dropped with the increasing rate of defect. The variation trend of mechanical properties of the sample with inclusion is stable, but the sample with slag is not stable. The mechanical properties of samples with inclusion are drastically changed, while the rate of defect is increased. The mechanical properties of samples with slag are smoothly. The EDS analysis indicated that the defects consist of Al-Ti-B compound, α-phase (Al12FeSi), β-phase (Al9Fe2Si2) and Al2O3. These oxides form the compact composite oxide film expand into first cracks. The fracture mode of sample with defects is brittle fracture. The values of the Secondary dendrite arm spacing (DAS) in the inclusion and the matrix are the same, while the values of DAS in the slag and the matrix are different.
Abstract: In this paper pure carbon, pure iron and single crystall silicon were firstly loaded into a pure graphite crucible to obtain a hypereutectic Fe-C melt by carburizing at high temperatures. The powder Ce2S3 was added to the melt with different proportion under the same process conditions and cast iron samples were obtained. The graphite morphology of the samples was observed under optical microscope. Then matrix of the samples was etched by electrolysis way. At last the non-ferrous residue gathered from the surface of cast iron sample after electrolysis process was calcined and analysed with BEI and EDS to find the trace of Ce2S3. The results showed that the powder Ce2S3 was really added into the melt but did not make any change in graphite morphology.The only effect of Ce2S3 was to make the amount of graphite increase slightly.All results of this paper indicat that the additive Ce2S3 is only the base for graphite flake to precipitate but is not a sufficient condition for graphite to nodularize.
Abstract: Thermal expansion mismatch is the most important which leads to the film/substrate interface damage and destruction. In this paper, the interface stresses analyses was conducted using Airy functions for the diamond-like carbon (DLC) film/ tungsten cobalt alloy(WC-Co) substrate structure; according to stress-strain relation, obtain the interface stress expression by substituting into the boundary conditions for giving parameter. The calculation results were analyzed and compared with the FEM simulation.
Abstract: Numerical simulation based on a new regularized phase field model was performed to describe the dendritic growth of an isothermal alloy with a strong anisotropy in the presence of a forced flow. These results indicate that a crystal grow into an equiaxial facet dendritic in the absence of a forced flow and into an asymmetrical facet dendritic in the presence of a forced flow. With increasing a flow velocity, the tip steady velocity of upstream dendritic arm increases, that of the downstream arm decreases, and that of the perpendicular arms increases at first, and then decreases, the perpendicular arms gradually grow toward the incoming flow direction. In the certain range of anisotropy parameter, when γ is larger than 0.14, dendritic tip steady velocities in all direction are expected to reach their own saturation values. In addition, the effect of a compound forced flow on an isothermal facet dendritic is similar to experimental results.