Yi Ping Lu

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.

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.

Effect of Ta Addition on Structural Evolution and Mechanical Properties of the CoFeNi2W0.5 High Entropy Alloy

A series of CoFeNi2W0.5Tax (x = 0-0.6) high entropy alloys (HEAs) were synthesized by arc melting to investigate the alloying effect of Ta element on the microstructure and mechanical properties of the CoFeNi2W0.5 alloy system. Phase constitution, microstructure and mechanical properties of the alloys were analyzed by X-ray diffraction (XRD), scanning electron microscopes (SEM), Vickers hardness and compressive test. It was found that when x = 0, the alloy consists of a single-phase face-centered cubic (FCC) solid solution structure and exhibit excellent ductility, the compressive plastic elongation of which can reach 80% without fracture. While with increasing Ta content, the brittle Co2Ta-type Laves phase appears which leads to a decrease of the plastic strain and an increase of the yield strength, and the Vickers hardness shows an obvious increase from HV 179.5 to HV 753.2.

Effect of Annealing Time on the Microstructure and Mechanical Properties of the AlCrFeNi2Ti0.5 High Entropy Alloys

As-cast AlCrFeNi2Ti0.5 high entropy alloy was annealed at 600 °C and 800 °C for 6 h, 12 h and 24 h, respectively. The effect of annealing time on the microstructure and mechanical properties were investigated intensively. The as-cast sample showed a fine and homogeneous microstructure, and owned an excellent ductility of 16.3%. While the 600 °C, 12 h annealed sample showed the highest compressive strength of 2658 MPa and yield strength of 2046 MPa. The mechanical properties of the samples after 800 °C annealed for 12 h and 24 h deteriorated obviously. High annealing temperature promotes the growth of the crystal grains, and the new generated FeCr-type intermetallic phase leads to the embrittlement of the alloy.

Microstructure and Properties of Ni70.2Si29.8 Eutectic Alloy Produced by Directional Solidification

The directional solidification of Ni70.2Si29.8 eutectic alloy was carried out, and the solidification microstructure and compression properties of Ni2Si – Ni31Si12 eutectic composite were systematically studied. Directional solidification samples were obtained by induction heating and down – draw process. During directional solidification, well-aligned lamellar structure with a micron scale was obtained in directional solidified Ni70.2Si29.8 eutectic alloy. Despite it is a kind of faceted – faceted eutectic alloys, highly regular and homogeneous structure was obtained through directional solidification. Compared with other methods, the compress test results showed that fracture strength of Ni70.2Si29.8 eutectic alloy obtained through directional solidification was improved obviously, reaching 2100 MPa.

Effect of Aging Temperature on Microstructure and Hardness of CoCrFeNiTi0.5 High Entropy Alloy

A bulk casting ingot (Ø70 × 150mm) of CoCrFeNiTi0.5 high entropy alloy was prepared by vacuum medium frequency induction melting. The samples from the ingot were aged for 12h in the temperature range of 900-1100°C and then quenched in water to investigate the effect of aging temperature on the microstructure and hardness of CoCrFeNiTi0.5 alloy. The crystalline structure of as-cast CoCrFeNiTi0.5 alloy consisted of the principal face-centered cubic (FCC) dendrite phase plus (Ni, Ti)-rich R phase, (Fe, Cr)-rich σ phase, (Co, Ti)-rich Laves phase within the inter-dendrite area. The dendrite contained approximately equivalent amount of Co, Cr, Fe, Ni and a smaller amount of Ti element. After aging treatment in the temperature range of 900-1000°C, the (Co, Ti)-rich phase disappeared while the amount of (Ni, Ti)-rich phase and (Fe, Cr)-rich phase increased. But the volume fraction of FCC dendrite phase increased and the intermetallic phases decreased after aging at 1100°C. The micro-hardness and the macro-hardness of the as-cast CoCrFeNiTi0.5 alloy were HV616.8 and HRC52, respectively. After heat treatment at 1000°C, the micro-hardness and macro-hardness decreased from HV616.8 to HV386.8 and from HRC52 to HRC42.7, respectively.