The conclusions that can be reached from this are (a), Alloy 3 displays a greater flaw size distribution (i.e., lower Weibull modulus) than Alloys 1 and 2 when produced at 26 m/s;


and (b), both Alloys 2 and 3 display superior quality (higher Weibull modulus) to Alloy 1 when cast at 82 m/s. As a result, it may be concluded that the higher alloying contents do have


Figure 8. A sample of Alloy 2 showing several large oxide defects (in the mm range), on the fracture surface. Views (a) secondary electron mode, (b), backscattered electron (BSE) mode showing the oxide films, (c & d)) BSE at higher magnification. Note in (d), the material still shows a small amount of the foam-like shrinkage defect cluster in the centre of the image and hard, Fe-bearing particles showing white contrast. (0.2% proof stress, 182 MPa, UTS 302 MPa, 1.9% Ef


.) (a) (b)


Figure 9. Two Weibull distributions for the three alloys at (a) 26 m/s, or (b) 82 m/s. Note the differences which exist at 26 m/s are reduced at 82 m/s.


International Journal of Metalcasting/Summer 2011 47


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