Papers by Author: Wei Ping Chen

Abstract: Ti₃AlC₂/TiAl₃ composite was successfully fabricated by ball milling and in-situ reaction/hot-pressing of Ti, Al and graphite powders mixture at 1200 °C and 30 MPa for 30 min. The phase composition and microstructure of the milled powders and synthesized composite were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), the mechanical properties and the toughening mechanism of 20%vol Ti₃AlC₂/TiAl₃ composite was also studied. The results show that no new phase is detected during 50 h of milling process. The in-situ synthesized samples are fully dense and composed of 72%vol TiAl₃, 24%vol Ti₃AlC₂ and 4%vol Al₂O₃/TiC. The Vickers Hardness, three-point bending strength and fracture toughness of the composite is ~5.2 GPa, ~243 MPa and ~4.3 MPa/m^1/2, respectively. Analysis of microstructure reveals that crack deflection, crack bridging and delamination of Ti₃AlC₂ are the main mechanism responsible for the toughening.

Abstract: A heavy section ductile casting (HSDIC) with dimensions of Φ590 mm×800 mm was prepared. Cooling curves at the center, at 85 mm from the center, at 170 mm from the center and at 255 mm from the center of the casting were recorded and analyzed. The results show that the precipitation of initial graphite, nucleation of eutectic cell and mass eutectic reaction at 255 mm from the center were all earlier than the other three locations. Moreover, it takes the longest time of 53 minutes of recalescence at 170 mm from the center with the highest temperature rise of 7 °C, though the cooling rate at this location is not the lowest in the casting, the mechanical properties are the worst. In addition, the largest amount of chunky graphite appears at 170 mm from the center.

Abstract: Strain-rate sensitivities of 55-65vol.% aluminum 2024-T6/TiB₂ composites and the corresponding aluminum 2024-T6 matrix were investigated using split Hopkinson pressure bar. Results showed that 55-65vol.% aluminum 2024-T6/TiB₂ composites exhibited significant strain-rate sensitivities, which were three times higher than that of the aluminum 2024-T6 matrix. The strain-rate sensitivity of the aluminum 2024-T6 matrix composites rose obviously with reinforcement content increasing (up to 60%), which agreed with the previous researches. The aluminum 2024-T6/TiB₂ composites showed hybrid fracture characteristics including particle cracking and aluminum alloy softening under dynamic loading. The flow stresses predicted by Johnson-Cook model increased slowly when the reinforcement volume fraction ranged in 10%-40%. While the reinforcement volume fraction was over 40%, the flow stresses of aluminum matrix composites increased obviously and the strains dropped sharply. Keywords: Composite materials; Dynamic compression; Stress-strain relationship

Abstract: A new model for energy-saving in cast irons production introduced technology contribution has been developed. According to the analysis model, in case of keeping same energy efficiency of device, the higher technological level increases, the easier the R increases; even if keep the same melting and heat treatment devices, significant reduction of production energy consumption would be implemented just depending on the production yield increase. A case study results show that technology measurements which has no direct effect on energy consumption play an important role in energy conservation, where the contribution rates of lost-foam casting and computer technology are 20% and 17%. The technological measurements play an important role in cast irons production which cannot be ignored.

Abstract: Ductile iron specimen with dimensions of Φ590mm×800mm were prepared by treating the melt with an yttrium-containing nodulizer. Cooling curves at four locations____the center location, the location 85mm distant from the center, the location 170mm distant from the center and the location 255mm distant from the center of the heavy ductile iron casting Φ590mm×800mm was obtained. The effect of yttrium and magnesium on microstructure and mechanical properties was investigated, and the factors on the distribution of chunky graphite in the specimen were discussed as well. The results show that the largest amount of chunky graphite and the lowest mechanical properties appear at the location 170mm distant from the center. Excessive yttrium and magnesium content at the location 170mm distant from the center is the main factor for the large amount of chunky graphite. The characteristics of the solidification mode^____pasty solidification and the considerably long solidification of the casting are the basic reasons for the distribution of chunky graphite of the heavy ductile iron casting Φ590mm×800mm.

Abstract: Ti₆₆V₁₃Cu₈Ni_6.8Al6.2 bulk composites with high strength were fabricated by spark plasma sintering of amorphous Ti₆₆V₁₃Cu₈Ni_6.8Al_6.2 powder synthesized by mechanical alloying. X-ray diffraction (XRD), differential scanning calorimeter (DSC), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to investigate the synthesized amorphous powder and the fabricated composites. Results show that the supercooled liquid region ΔT_x and the crystallization enthalpy DH_x of the synthesized amorphous powder decrease, in relative with amorphous Ti₆₆Nb₁₃Cu₈Ni_6.8Al_6.2 powder, indicating that the thermal stability and glass forming ability of the synthesized amorphous powders decreases with vanadium element substituted for niobium element. And particle size of the synthesized amorphous powder also decreases. In addition, the fabricated alloys also consist of body-centered cubic β-Ti (V) and face-centered cubic (Cu, Ni)-Ti₂ regions, similar to Ti₆₆Nb₁₃Cu₈Ni_6.8Al_6.2 bulk alloys. The alloys exhibit a high fracture strength around 1966 MPa but limited plasticity.

Abstract: Six groups of castings which solidified at different cooling rates with or without addition of 0.03%Sb were fabricated. The effects of the melt holding time, cooling rate, and Sb on the microstructure of ductile iron were studied. Results show that as for the other three blocks with addition of 0.03%Sb, reducing the length of eutectic plateau could improve the graphite morphology, and sufficient residual contents of spheroidizing elements REE and Magnesium could also lead to small and diffuse globular graphite particles no matter what the cooling rate is. As for the other three blocks with addition of 0.03%Sb, no matter what the cooling rate is, the nodularity index values are all about 90%. The main difference among the three blocks is just the size of nodular graphite. And even if two of the blocks solidified at different cooling rates, they own nearly identical NI value and globular graphite average diameter value, which is because they both possess the tolerated rare-earth elements/antimony ratio for spheroidal graphite formation.

Abstract: To describe surface shape of the dust particle comprehensively, uses the bidirectional CCD to shoot picture of dust particle, through recognizing the bidirectional particle picture, matching the particle, computing the fractal results of identical particle in two pictures, and integrating two fractal results, obtains the dust particle bidirectional fractal. The results indicated that three fractal dimensions of spherical particle are quite closed, but the three fractal dimensions of flat type particle are significantly different.

Abstract: The massive dust is produced in the casting process, need to control. This paper takes electric arc furnace dust collection way as an example, where is in Guangdong Shaoguan Foundry and Forging Group Co., Ltd., establishes the conflict matrix about selection of the dust collection way, uses the TRIZ theory to solve, and obtains the standard solution, the results should provide the reference for collection way design of the electric arc furnace dust. The structure of half airtight cover is optimized by used of CFD, and the curve type is suitable shape to collect the dust.

Abstract: High plastic Ti66Nb13Cu8Ni6.8Al6.2 composites with in situ precipitated ductile -Ti phase were firstly synthesized by mechanical alloying and subsequent consolidation by spark plasma sintering with crystallization. Microstructure analysis indicated that all composites contain soft (Cu, Ni)-Ti2 regions and hard -Ti regions, but the two regions have different scale and distribution. The synthesized composites exhibit high fracture strength of 2415 MPa and large plasticity as high as ~31.8%. The large plastic deformability was well explained based on the distinctive microstructure by a developed “hard-soft model”.