Effect of ball milling process on the mechanical and thermal properties of the nanodiamond/2024Al composites

In this study, 5 wt.% nanodiamond (ND) reinforced 2024Al matrix composites (ND/2024Al) were fabricated with various ball milling processes. The microstructure, compressive yield strength (sigma(yc)) and coefficient of thermal expansion (CTE) of ND/2024Al composites were investigated. It is found that the addition of 5 wt.% NDs significantly increases the sigma(yc) and decreases the CTE of 2024Al. High energy ball milling further increases sigma(yc) and decreases CTEs of ND/2024Al composite due to it enhances the fine grain strengthening of alpha-Al matrix and the dispersion strengthening of NDs, decreases the thermal mismatch stress at the ND/alpha-Al matrix interface, and increases the constraint of NDs on alpha-Al. The composites fabricated by the combinations of ball milling speeds and times of (5 7) hx(200 250)rpm and 9 hx300 rpm have the highest sigma(yc) and the lowest CTE respectively. Considering the different influence of ball milling parameters on sigma(yc) and CTEs, a evaluation coefficient alpha = sigma(ycC.)epsilon(kcC)/sigma(ycM.)epsilon(kcM)center dot CTEM/CTEC is proposed to evaluate the synergistic influence of mechanical properties and CTEs on the dimensional stability of ND/2024Al composites. Large value of alpha may lead to high dimensional stability of material, hence the alpha can be used to determine the ball milling parameters.The ball milling process of 250 300 rpm ball milling speeds and 5 7 h ball milling times are recommended based on alpha, which causes a 95-100 % increase in sigma(yc) and a 30-35 % decrease in CTE compared with 2024Al alloy, respectively.

Automated summary

The addition of 5 wt.% nanodiamond significantly increases the compressive yield strength and decreases the coefficient of thermal expansion of 2024Al. High energy ball milling further enhances these properties due to the strengthening effects on the alpha-Al matrix and nanodiamond dispersion. The optimal ball milling parameters are 250-300 rpm speed and 5-7 hours time.