Tong Min Wang

Surface Pretreatment and Fabrication Technology of Woven Carbon Fiber Cloth Aluminium Alloy Matrix Composite

Carbon fiber is mainly distributed in the shape of short fibers and unidirectional fibers as the reinforcing phase in metal matrix composites, and it is seldom studied as woven-cloth shaped to reinforce the matrix. In this paper, the pretreatment and the surface metallization of the woven carbon fiber were studied. Besides, the casting experiment without external pressure was carried out under the application of magnetic field. The result shows that when burning about 45mins at 500°C in the atmospheric environment, the pretreatment can achieve the best result according to differential thermal analysis and weight-time variation curve. Meanwhile the surface wettability between the carbon fiber and the matrix is greatly improved after the surface treatment and at the same time the reaction between the carbon fiber and molten aluminium alloy matrix is necessarily avoided, and it can consequently achieve an excellent bonding between the woven carbon fiber and aluminium alloy matrix. The application of magnetic field also provides magnetic force to promote the penetration of the molten matrix into the carbon fiber bundles.

Influence of Pulsed Electric Current on Dendrite Growth of Sn-Bi Alloy via Real-Time Observation

External fields (e.g. electromagnetic field, electric field, etc.) are often applied to modify the solidification structure of metallic alloys. The dynamic process of structure modification is invisible because of the opacity of metallic alloys. To understand the modification mechanism, it is necessary to discover the microstructure evolution during solidification. In present paper, we focus on studying the influence of pulsed electric current (PEC) on dendrite growth of Sn-Bi alloy by insitu and real time observation using the third synchrotron X-ray source at Shanghai Synchrotron Radiation Facility (SSRF) in China. The modification mechanism of PEC on solidification structure is analyzed based on a series of real time observations.

Microstructure Evolution and Hardness of AlCrFeNixMo0.2 High Entropy Alloy

The microstructures, phase composition and hardness of the AlCrFeNixMo0.2 high entropy alloy (x=0.5, 0.8, 1.2 and 1.5, the x values refer to molar ratio) were reported. When the value of x was smaller than 1.2, the alloys consisted of BCC and B2 structures. The BCC and B2 phases were identified to be (Cr, αFe) solid solution and NiAl intermetallic compound, respectively. With the increase of x from 0.5 to 1.2, the microstructure transformed from dendrite/inter-dendrite to eutectic microstructures. When the x was equal to 1.5, besides BCC and B2 phases, another CrFe2.32MoNi phases formed and Net-like (Cr, αFe) phases distributed in the NiAl intermetallic compound matrix. The hardness first decreased then increased with the increase of Ni content. Generally, Ni element is a FCC stabilizer. However, in AlCrFeNixMo0.2 alloys, Ni element promoted the formation of B2 and CrFe2.32MoNi phases. The influence mechanism of Ni element was discussed systematically.

Microstructure and Mechanical Properties of the W-Ni-Co System Refractory High-Entropy Alloys

The elements Mo, Cr and V were added to the W-Ni-Co system high entropy alloys, the effects of these added elements on microstructure and mechanical properties of these alloys were studied. The alloys were produced by vacuum arc melting. The compositions were W0.5Ni2Co2VMo0.5, W0.5Ni2Co2VCr0.5 and W0.5Ni2Co2CrMo0.5 (denoted as Alloy 1, Alloy 2 and Alloy 3) respectively. The theoretical melting temperatures were higher than 2000 K. X-ray diffraction, SEM and energy dispersive spectroscopy (EDS) results indicated that the matrix of the alloys is face-centered cubic (FCC) solid-solution, the alloys showed dendrite crystal structure. Ni, Co elements were enriched in the dendrite areas, the W, Mo were enriched in the inter-dendrite regions ,while V, Cr elements were uniform distribution. The Vickers hardness of these alloys was 376.1 HV, 255.88 HV and 306.8 HV, respectively. The yield strength values (σ0.2) of Alloy 1, Alloy 2 and Alloy 3 were approximately 1000MPa, 750MPa, 250MPa, respectively. The alloys show good compression plasticity deformation capacity at RT.

Effect of Sr and La on the In Situ A356-TiB2 Composite Fabricated via Remelting and Diluting Approach

In this paper, a remelting and diluting (RD) approach was used to fabricate in situ A356-3wt.%TiB2 composites and the effect of Sr and La on the modification of the composites is investigated in comparison with the conventional flux assisted synthesis (FAS) approach. The microstructure was examined and tensile properties were tested to evaluate the modification efficiency on the composites. The results demonstrated that composites fabricated via RD approach achieve preferable modification by Sr and La due to the higher level of melt cleanliness so as to minimize the Sr-B interaction, in which the eutectic Si which displays a microstructure with globular-fibrous eutectic Si particles. Superior mechanical properties are obtained in the RD composites (especially the elongation) after modified by Sr and La.

Effect of addition of elements on two-glass-forming ability of Zr–Ce–Co–Cu immiscible alloys

ABSTRACT The effects of Al element addition and partial substitution of Ce with La, Pr, and Nd on the two-glass-forming ability of the phase-separating Zr–Ce–Co–Cu alloy system have been studied. The distribution of the additions in the two coexistent immiscible liquids was analysed thermodynamically. The results indicate that Al almost equally distributes in the two liquids, whereas the elements La, Pr, and Nd are predominantly found in the Ce–Cu-rich liquid. X-ray diffraction analysis reveals that these additions obviously enhance the two-glass-forming ability of the coexisting liquids. This work presents a strategy for improving the two-glass-forming ability of immiscible alloys to obtain phase-separated bulk metallic glasses.

In Situ Observation of Diffusion Behavior and Microstructural Evolution on Interfaces in Al/Cu Bimetal

Synchrotron X-ray radiography was used to in situ study the diffusion behavior and microstructural evolution of Al/Cu bimetal. The interface diffusion, dendritic/eutectic growth and the formation of intermetallic compounds around the Al/Cu bimetal interface were analyzed. During the isothermal diffusion process, a liquefied transition zone at the interface with a concentration gradient was formed when the Cu concentration exceeded eutectic composition of Al-Cu alloy. During the solidification of transition zone, the growth sequence of α-Al dendrites and eutectic structure were mainly dominated by the variation of Cu concentration and thermal field according to the temperature of the liquidus line of the equilibrium phase diagram. Finally, the transition zone around the interface were identified to be I (α-Al), II (Al+Al2Cu), III (Al2Cu) and IV (Al2Cu, AlCu and Al4Cu9), respectively.

Growth of Equiaxed Dendrite in Al-20wt.%Cu Alloy by Synchrotron X-Ray Radiography

Synchrotron X-ray radiography was used to in-situ study the growth of equiaxed dendrite during the solidification of Al-20 wt.% Cu alloy. Equiaxed dendrites with two different morphologies were formed in nearly isothermal conditions. The image processing was used to improve the image quality. The time evolution of the primary dendrite arm length and the corresponding growth rates were analyzed. The experimental results indicated that the solute interaction was the main factor to influence the equiaxed dendrites growth. Besides, the rotation and floating of the dendrites were also observed during the early growth phase.

Study on the Solidification of Sn-Pb Alloy under Direct Current Field by Synchrotron X-Ray Radiography

In this paper, synchrotron X-ray radiography was used to study the grain refining performance of direct current (DC) during the solidification of Sn-50 wt.% Pb alloy. Based on the radiographs, the variations of equiaxed grain number and dendrite growth rate with time were measured and analyzed. It is shown that DC mainly affects the microstructure formation through changing the nucleation behavior and the dendrite growth rate. When DC was applied during the whole process of solidification, the nucleation was enhanced and the dendrite growth was suppressed, which resulted in significant grain refinement.

In Situ Synchrotron X-Ray Diffraction Study of a Deformed Cu-Fe-P Alloy during Heating

In situ synchrotron X-ray diffraction was used to study a deformed Cu-0.88 Fe-0.24 P alloy during heating process. The measurements were performed at room temperature and also at high temperatures up to 893 K in order to determine the recovery, ageing and recrystallization process. With the increase of temperature, the angles of copper matrix peaks moved left and the FWHM (full width at half maximum) decreased slightly. Fe3P precipitates were first detected at 533 K, reached the maximum at 673 K, and re-dissolved into matrix at 853 K. A dramatic decrease in FWHM was observed accompanied by the precipitation of Fe3P phases, indicating the reduction of lattice distortion of copper matrix.