| Title |
Studies on Time-Temperature-Dependent Fracture Behavior of a RS/PM Al-Fe-V-Si Alloys |
| Abstract |
Fracture toughness of RS/PM Al-8.5%Fe-1.3%V 1.7%Si alloy decreases with increasing temperature and decreasing loading rate. Low toughness cracking is associated with single size of shallow dimples, while that with high toughness case is associated with bimodal distribution of dimples. Thermomechanical processing (TMP) has been performed on extruded Al-Fe-V-Si alloys to improve elevated temperature fracture toughness and toughness isotropy. Substantial improvement in toughness isotropy is obtained with TMP by homogenization of microstructure. K_k, however, tends to decrease with rolling reduction at 25 and 175℃. A decrease in fracture toughness with TMP is believed to be related to the microstructural changes occurred during rolling reduction. Fracture is by microvoid processes at all temperature ; reduced toughness correlates with changed void shape from spherical to irregular. It is believed that increased temperature reduces work and strain rate hardening between growing primary voids, leading to intravoid instability and coalescence at lowered strain. Decreased strain rate hardening is attributed to increased mobile dislocation density due to dislocation emission and detrapping from dispersoids in dynamically recovered dislocation-source-free grains. |