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

The age hardening precipitation reactions in a ZK60 matrix composite reinfo rced with 12 vol.% B4C particles and 12 vol.% SiC whiskers were investigate d using differential scanning calorimetry (DSC), Vickers hardness testiug a nd transmission electron microscopy (TEM). It was found that the addition o f the reinforcement did not change the hardening sequence observed in the m onolithic alloy, but the formation of the beta' phase is considerably accel erated. The peak temperature of the beta' phase precipitation in the compos ite was decreased by 15 degrees C and the time to peak hardness aged at 170 degrees C decreased from approximately 40 h in the monolithic alloy to abo ut 8 h in the composite. The amount, the growth rate and the stability of t he precipitates near the reinforcement/matrix interface were increased. Sig nificant dislocation hardening was produced in the composite which was reta ined 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 me chanism of the effect of reinforcement addition on aging response was propo sed in terms of the distinct aging behaviors near the reinforcement/matrix interface and within the matrix grains. (C) 1999 Elsevier Science S.A. All rights reserved.