Synergistic effect of ball milling time and nano-sized Y2O3 addition on hardening of Cu-based nanocomposites

A fruitful combination of powder metallurgy and the mechanical alloying route is one of the most promising process for producing advanced Cu-based nanocomposites. In this study, three different material systems, namely, pure copper (Cu), 5 wt% Cr reinforced Cu matrix composites, and 1 wt% Y2O3 reinforced Cu–Cr matrix nanocomposites were synthesized by ball milling method at different milling times. The influence of different ball milling times (0.5, 2, and 4 h) and different types of reinforcements (Cr and Y2O3) on the powder and sintered parts properties were thoroughly analyzed with a holistic approach. The milled powders were then consolidated using a cold press followed by a liquid phase sintering process. Results revealed that the Cr and Y2O3 particles were fractionally dispersed and imbedded in the ductile Cu matrix with respect to increasing milling time. Milling for 4 h of Cu–Cr–Y2O3 powders produced the lowest level of particle size (28 µm) with reduced and flattened and uniformly distributed reinforcement phases due to intense plastic deformation induced shearing effect and dominant powder-ball-jar collisions. Besides, the ball milling process of the same powders concluded a decrement of crystallite size to 35 nm in concomitant with an increase of lattice strain and dislocation density ⁓ % 0.3 and 0.8 × 1015 line/m2, respectively. Brinell hardness of the sample produced by these powders increased from 39 to 95 HB. A ⁓%145 striking increase of hardness could be attributed to the strong hindrance of high-dense dislocations triggered by several concurrent strengthening mechanisms. Nevertheless, relative density results of sintered samples revealed that the addition of Cr and Y2O3 along with increasing milling time deteriorated the density due to the higher hardness and brittleness of milled powders and accompanying worsened compressibility and sinterability. The source of noticed differences between hardness and density results were discussed within the process-structure-performance framework.