To obtain high performance composites for thermal management fields, we adopt a new route to prepare the graphite flakes (Gf)/aluminum (Al) composites via vacuum pressure infiltration process. In this study, aluminum nitride (AlN) particles were used as supporting particles to obtain infiltration pathways for the penetration of the molten Al matrix. Gf, starch , urea and AlN were mixed evenly in the mass ratio of 1: 0.035: 0.058: 0.3 and then sintered at 330 °C to prepare porous preforms. It was observed that these substances had excellent chemical compatibility using characterization equipment. The improvement of the thermal transfer and mechanical properties of the composites for silicon coating was also studied. When the volume fraction of graphite was about 54%, compared with the samples without coating, the samples with SiC coating displayed an excellent thermal conductivity (TC) of 467.8 W/m·K and a promising bending strength of 58.8 Mpa, which increased about 82.1 and 238.0%, respectively. The coefficient of thermal expansion (CTE) of composites also decreased about 23.3% from 2.19 × 10 −5 K −1 to 1.68 × 10 −5 K −1 from room temperature to 380 °C.
Chuandong Wu,Yuehui Lu,Guoqiang Luo,Qiang Shen,Zhanghua Gan,Jing Liu
We reported the influence of particle size (micro-B 4 C and nano-B 4 C) on microstructural evolution and mechanical properties in nanostructured Al matrix during heat treatment. The results indicated the incorporation of nano-B 4 C could significantly inhibit the grain growth of Al during heat treatment. The segregation layer in Al/B 4 C interface increased after heat treatment for all the composites samples. High density of Guinier-Preston (GP) zones and platelet η' could be observed in grain interior of all samples, while some coarse η phases (MgZn 2 ) could be only detected in grain boundaries of AA7075 alloys and the composites with micro-B 4 C. The yield strength of the composites with the incorporation of nano-B 4 C could reach up to 958 ± 28 MPa after heat treatment, which could be ascribed to the Hall-Petch strengthening and dislocation strengthening.
Al 2 O 3 /MoS 2 /CePO 4 composite ceramic layer was in-situ prepared on aluminum alloy by micro-arc oxidation. The results show that the content of (CH 3 CO 3 ) 3 Ce·xH 2 O has a great influence on the microstructure of the ceramic layer. When the addition amount is 7.5 g/L, the surface hardness of the ceramic layer is 961.97 HV 1 , which is 1.8 times that of the unadded and 8.36 times that of the matrix. Tribological tests show that the moderate addition of (CH 3 CO 3 ) 3 Ce·xH 2 O also significantly improves the wear resistance of the ceramic layer. Composite layer research can be developed and applied to other alloys to improve their friction properties.
In this work, the Nextel 720 continuous fiber reinforced alumina ceramic matrix composites (CMCs) were prepared by an improved prepreg process. The alumina matrix was derived from aqueous slurry, which consisted of organic glue, alumina sol, nanometer alumina powders, and micrometer alumina powders. This design provided a densely packed matrix for the CMC, and made the whole process relatively simple. The ratio of different alumina components in aqueous slurry was optimized to obtain good sintering activity, high thermal resistance, and excellent mechanical properties simultaneously. Furthermore, a preceramic polymer of mullite was used to strengthen the ceramic matrix through a multiple infiltration process. The final CMC sample achieved a high flexural strength of 255 MPa and a good high-temperature stability. After 24 h of heat treatment at 1100°C, 85% of the maximum flexural strength still had been retained.
Zhichao Yang,Dehui Zheng,Zhen Wang,Tingbin Liang,Shuangbao Wang
Twin-jet electropolishing (TJE) is a well-known method to prepare Cu-containing Al alloys for transmission electron microscopy (TEM) observation. Previous studies have reported a Cu-rich layer usually formed between Al matrix and outermost alumina layer at the electropolished Al surface. However, characteristics and formation mechanisms of the Cu-rich layer remain largely unexplored. Herein, configurations, formation process and property of the Cu-rich layer formed during TJE of Al alloys are revealed detailly employing aberration-corrected scanning TEM (STEM), STEM image simulations and first-principles calculations. The results reveal a new orientation relationship between the Cu-rich layer (θ’-Al 2 Cu) and Al matrix, which produces a low interfacial Al strain field. Formations of ∼2-nm-thick θ’ layer and its beneath ∼6-nm-thick Cu diffusion zone at the electropolished Cu-containing Al surface are mainly associated with traces of Cu in the electrolyte and anodization. Selective oxidation of elements, Cu-emitting alumina layer and spontaneous solute Cu segregation at the Al surface are also responsible for formations of the θ’ layer and Cu diffusion zone. Further study reveals that the θ’ layer behaves a strong self-healing ability after damaged by high-energy electron beam. The obtained results provide a potential insight into the surface modification of metals and alloys using electrochemical method.
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