Effect of Nanoscale W Coating on Corrosion Behavior of Diamond/Aluminum Composites

The stability of diamond/aluminum composite is of significant importance for its extensive application. In this paper, the interface of diamond/aluminum composite was modified by adding nanoscale W coating on diamond surface. We evaluated the corrosion rate of nanoscale W-coated and uncoated diamond/aluminum composite by a full immersion test and polarization curve test and clarified the corrosion products and corrosion mechanism of the composite. The introduction of W nanoscale coating effectively reduces the corrosion rate of the diamond/aluminum composite. After corrosion, the bending strength and thermal conductivity of the nanoscale W-coated diamond/aluminum composite are considerably higher than those of the uncoated diamond/aluminum composite. The corrosion loss of the material is mainly related to the hydrolysis of the interface product Al4C3, accompanied by the corrosion of the matrix aluminum. Our work provides guidance for improving the life of electronic devices in corrosive environments

Tunable nonlinear conductive behavior without percolation threshold and high thermal conductivity of epoxy resin/SiC ceramic foam co-continuous phase composites

Smart dielectrics with self-adaptive capabilities can exhibit desirable electric field-grading performance as the applied electric field exceeds a critical value. However, the conventional approaches to such dielectrics need heavy doping rate, which will not only increase the interface thermal resistance and limit the improvement of thermal conductivity, but also severely sacrifice the mechanical property. In this contribution, a new type of electric field-grading co-continuous phase composite (EP/SiCcf) composed of epoxy resin and SiC ceramic foam was prepared to realize tunable nonlinear conductive performance, while simultaneously improving thermal and mechanical properties. Results show that there is no percolation threshold for all EP/SiCcf composites. The volume loadings of EP/SiCcf composites range from 8.7 vol% to 15.6 vol%, while the nonlinear coefficient subjected to potential barrier height increases from 2.1 to 4.5 and the switching field tuned by barrier width decreases from 1008 kV/mm to 686 kV/mm. The EP/SiCcf40 still exhibits sharp thermal conductivity enhancement of about 1000% and glass transition temperature enhancement of 10.8 °C. The surface temperature fluctuation over time during heating and cooling has illustrated the prospective application of thermal management capability. In addition, the dynamic mechanical analysis reveals that all EP/SiCcf composites have the significantly improved storage modulus and crosslinking density ascribed to the intact SiC skeleton. The novel co-continuous phase composite provides a new approach for global enhancement of smart dielectric composites in potential applications.This work was supported by the National Natural Science Foundation of China (No. 51977084)

Ablation Mechanism of AlSiB-C/C Composites under an Oxy-Acetylene Torch

In order to improve the ablation resistance of C/C composites, an AlSiB alloy (mass ratio of Al/Si/B = 2:4:1) was used as a dissipative agent to fill the pores of a C/C composites matrix by reactive melt infiltration to prepare AlSiB-C/C composites. The microstructure evolution and ablation behavior of the obtained AlSiB-C/C composites (mass ratio of Al/Si/B = 2:4:1) under oxy-acetylene flame were investigated by SEM after ablating for 25 s, 50 s, 100 s and 150 s. At the beginning of the ablation process, thermal chemical erosion played a leading part. By using the heat-absorption effect of sweating and the sealing protection effect of the oxide layer, AlSiB-C/C composites significantly reduced the ablation surface temperature, and the linear ablation rate was 4.04 μm/s. With the process of ablation, thermal mechanical erosion tended to dominate. The specimen surface could not form a continuous covering of oxide film to slow down the flame scour, resulting in non-uniform ablation and further expansion of the ablation pit. The self-transpiration cooling behavior and the self-sealing of the ablation products of the dissipative agent played an important role in reducing the extent of thermal chemical erosion and preventing matrix ablation