Ting Ju Li

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.

Microstructure and Properties of Multi-Component AlxCoCrFeNiTi0.5 High-Entropy Alloys

The multi-component AlxCoCrFeNiTi0.5 (x=0, 0.2, 0.5, 0.8, 1.0) high-entropy alloys were prepared by vacuum arc melting. The microstructure and mechanical properties were studied. It was found that the structure transformed from FCC into FCC + BCC + Laves, and finally into BCC with the increase of Al content. The compress test results showed that with the addition of aluminium from 0 to 1.0, the fraction strength increased while plasticity reduced. In the stain rates of 5×10-3/s and 1×10-3/s, when x=0.8 the fraction strength achieved maximum and x=0 the plastic was best, the strength of 2879MPa and 2433MPa, the strain of 0.21 and 0.22, respectively. The hardness increased obviously (from Hv479.1 to Hv692.7) when Bcc phase and Laves phase appeared. The analysis revealed that the strengthen mechanism was mainly composed of solid solution strengthening and precipitation strengthening.

Microstructure and Mechanical Properties of VTaTiMoAlx Refractory High Entropy Alloys

A series of refractory high-entropy alloys VTaTiMoAlx with x=0,0.2,0.6,1.0 were designed and produced by vacuum arc melting. The effect of added Al elements on the microstructure and mechanical properties of refractory high-entropy alloys were investigated. The X-ray diffraction results showed that all the high-entropy alloys consist of simple BCC solid solution. SEM indicated that the microstructure of VTaTiMoAlx changes from equiaxial dendritic-like structure to typical dendrite structure with the addition of Al element. The composition of different regions in the alloys are obtained by energy dispersive spectroscopy and shows that Ta, Mo elements are enriched in the dendrite areas, and Al, Ti, V are enriched in inter-dendrite areas. The yield strength and compress strain reach maximum (σ0.2=1221MPa, ε=9.91%) at x=0, and decrease with the addition of Al element at room temperature. Vickers hardness of the alloys improves as the Al addition.

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.

Al/B4C Laminated Composite Fabricated by Powder Metallurgy Process and its Mechanical Property

A new type of laminated composite with B4C particle reinforced Al matrix composites as its inner layer and metal Al as outer layer was fabricated by powder metallurgy process. The effects of sintering time on the density and the mechanical properties of Al/B4C laminated composites were investigated. In the inner layer, Vicker’s hardness was enhanced with the addition of B4C. With the extension of sintering time from 2h to 4h at 300°C, aggregation of B4C particles reduced, while the density and Vicker’s hardness improved.

Study of the Grain Refinement Technology by Electromagnetic Stirring for IN100 Superalloy Vacuum Investment Casting

The effects of rotating electromagnetic stirring and inoculants on the solidification structures and properties of IN100 superalloy vacuum investment casting was studied with XRD, SEM and optical microscope. The results show that by initiating the 50Hz, 150A rotating electromagnetic stirring as soon as the molten metal was poured into the mould, which was coated with inoculant CoAl2O4, the average equiaxed grain size of IN100 superalloy vacuum investment casting can be refined to 95μm and the fraction of equiaxed grains can be increased to 99 %. On condition that the grain size of K417 superalloy vacuum investment casting were refined to 95μm, the tensile properties at room temperature, the morphology of （γ＋γ′）eutectic and the morphology of dendrites can be greatly improved.

Research on Effects of Rolling-Drawing Deformation on Performance of Cu-10Ni-1Fe-1Mn Alloy

Evolution laws of structure and performance of Cu-10Ni-1Fe-1Mn alloy in the process of continuous casting-planetary rolling-drawing deformation were studied by OM, SEM, TEM, Brinell Hardness tester and universal material testing machine. Results demonstrated that the alloy ingot is composed of thick dendrites. The ingot makes grain crushing and dynamic recrystallization after planetary rolling. The hot rolling samples still have abundant fine recrystallization textures after multi-pass drawings. Due to roller-core head or internal-external mold opposite pressure, dislocations in different regions of sample move along the glide plane, forming a macroscopic slip band. Two adjacent macroscopic slip zones which move toward opposite directions compose the folded structures after the deformation. Refined crystalline strengthening, solution strengthening of Fe, Ni and Mn, work hardening, and iron-containing particle precipitation are major causes of alloy strengthening. SEM analysis of tensile fracture demonstrated that the material still maintained good plasticity after rolling and drawing deformation. However, material plasticity declined with the increase of cold processing-induced deformation.

Microstructure and Properties of the Co2NiWV0.5Mo1.5, Co2NiWV0.5Mo2, and Co2NiWV1.0Mo2 Multi-Principal Elements Alloys

The Co2NiWV0.5Mo1.5, Co2NiWV0.5Mo2 and Co2NiWV1.0Mo2 multi-principal elements alloys were prepared by vacuum arc melting. The microstructure, compressive property and corrosion resistance of the alloys were investigated by means of X-ray diffraction, scanning electron microscope with energy dispersive spectroscopy, electrochemical workstation and material testing machine. Results indicated that all of these alloys were composed of primary dendrite with BCC structure. Inter-dendrite regions were filled with irregular and lamellar eutectics with a mixture of FCC solid solution and Co7Mo6-type μ phase. Compression tests indicated that fracture strength of Co2NiMo2V1.0W, Co2NiMo2V0.5W and Co2NiMo1.5V0.5W alloys was 2308MPa, 1983MPa and 1861MPa, respectively. The solid-solution strengthening of BCC matrix and μ phase were the two main factors to strengthen the alloys. Alloys corrosion resistance showed the alloy with higher Mo or lower V content has better corrosion resistance.

An Effective Method to Fabricate 5083 Aluminum Alloy with Excellent Corrosion Resistance

The 5083 aluminum alloy was prepared and subjected to cryogenic rolling (CR) after heat treatment. The samples were reduced from 15mm to 1.5 mm in the thickness direction and the amount of deformation was 90%. For comparison, samples with the same deformation amount were obtained by room temperature rolling (RTR). The corrosion behavior of CR and RTR samples was measured by electrochemical test, and their microstructures before and after corrosion had been studied through electron scanning microscopy (SEM) and optical microscope (OM). The influence of cryogenic rolling on the corrosion behavior of 5083 aluminum alloys was explored. The experiment results suggested that anti-corrosion ability of 5083 aluminum alloys could be enhanced through cryogenic rolling. The corrosion potential elevated and the corrosion current density reduced according to the electrochemical test. The primary reasons and corresponding mechanism were also discussed.