Effect of different rare earths on microstructures and tensile strength of in situ hybrid reinforced (TiB2p + TiBw)/Cu composites

Hybrid reinforced (TiB2p + TiBw)/Cu composites were prepared via the double-beam mixed casting method. In order to improve the tensile strength of the composites, 0.04 wt% rare earths (La, Ce and Y) were separately added to the composites. The size, distribution and morphology of the reinforcements and the tensile strength of composites were studied, and the strengthening mechanism and failure behavior of the composites were discussed. Results indicate that the TiB2 particles with rare earths are refined and rounded, the average size are refined from 654 nm (without) to 515 nm (Ce), 567 nm (Y), 596 nm (La), respectively. TiB whiskers with rare earths also show different refinement effects in length and diameter directions. The effect of rare earths on the size and morphology of the reinforcements are mainly due to the promotion of the nucleation stage and the inhibition of segregation in the growth stage. After heat treatment and rolling, the tensile strength of the samples increased from 524 MPa without rare earth to 624 MPa (Ce), 606 MPa (La), and 595 MPa (Y). In particular, a remarkable change in the tensile strength appeared with 0.04 wt% Ce. The microcracks initiate at the interface between the reinforcements and the matrix, then propagate along the interface, and finally the reinforcements debond from the matrix.