Effects of reinforcements on the aging response of a ZK60-based hybrid composite

The age hardening precipitation reactions in a ZK60 matrix composite reinforced with 12 vol.% B 4C particles and 12 vol.% SiC whiskers were investigated using differential scanning calorimetry (DSC), Vickers hardness testing and transmission electron microscopy (TEM). It was found that the addition of the reinforcement did not change the hardening sequence observed in the monolithic alloy, but the formation of the β′ phase is considerably accelerated. The peak temperature of the β′ phase precipitation in the composite was decreased by 15°C and the time to peak hardness aged at 170°C decreased from approximately 40 h in the monolithic alloy to about 8 h in the composite. The amount, the growth rate and the stability of the precipitates near the reinforcement/matrix interface were increased. Significant dislocation hardening was produced in the composite which was retained during the whole aging process. The aging hardening efficiency of the composite, about 200 MPa, is the same as that of the monolithic alloy. A mechanism of the effect of reinforcement addition on aging response was proposed in terms of the distinct aging behaviors near the reinforcement/matrix interface and within the matrix grains.