Orientation dependence of microfracture behavior in a dual-phase high-strength low-alloy steel
- PDF / 1,731,787 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 34 Downloads / 289 Views
Fig. 3—The solidification curve of the Rene N4 superalloy determined in this study superimposed with those calculated by Chen et al.[4] using Kohler approximation.
respectively. These two temperatures are about 50 K lower than the value 1626.5 K, which is determined experimentally by using DTA. One advantage of this proposed DTA method is the direct measurement of the solidification temperatures, and thus, the results are more precise than those found by model prediction. Due to the effect of undercooling, in most cases, the liquidus temperature determined in the cooling mode is lower than the equilibrium temperature and that determined in the heating mode. The degree of undercooling varies with samples, so its quantitative prediction is difficult. For this specific superalloy, it has been found that the effect of undercooling is negligible. The liquidus temperatures of the superalloy determined at 40 K/min scanning rate in the cooling mode and heating mode are identical. However, under the same experimental condition, the degrees of undercooling are 10 and 33 K for Ni and Au, respectively. Chen et al.[4] assumed three different mixing conditions in calculating the solidification curves, i.e., 100, 80, and 60 pct mixing, and it was also pointed out that in realistic freezing, 60 to 80 pct rejected solute was mixed in the liquid alloy. It is interesting to notice that the slope of the experimentally determined solidification curve for most courses during solidification is similar to the calculated curves with 60 to 80 pct mixing, but the slopes become different in the final part of solidification. The possible reason for the deviation is also given in Chen et al.’s[4] article: their phase equilibria models consider only the solid and liquid phases and do not include other phase equilibria existing in the lower temperature. However, as mentioned previously, much work is required if a complete thermodynamic modeling is to be carried out. The thermodynamic descriptions provide useful information that is difficult to obtain by using other methods, such as tie-line that can be used in computing compositional variations of the solidified alloy. For the purpose of solidification curve determination, this proposed DTA method is certainly an alternative that has been found to be much more simplistic and reliable.
The authors would like to thank Professor Y.A. Chang and Dr. S.-L. Chen for providing the superalloy. The financial assistance of the National Science Council of Taiwan (Taiwan, Republic of China), through Grant No. NSC 85-2216E-007-042, is also appreciated. 504—VOLUME 28A, FEBRUARY 1997
1. S.-W. Chen and Y.A. Chang: Metall. Trans. A, 1991, vol. 22A, pp. 267-71. 2. S.-W. Chen, Y.Y. Chuang, Y.A. Chang, and M.G. Chu: Metall. Trans. A, 1991, vol. 22A, pp. 2837-48. 3. S.-W. Chen and Y.A. Chang: Metall. Trans. A, 1992, vol. 23A, pp. 1038-43. 4. S.-L. Chen, W. Oldfield, Y.A. Chang, and M.K. Thomas: Metall. Mater. Trans. A, 1994, vol. 25A, pp. 1525-33. 5. S.-W. Chen, C.-C. Huang, and J.-C. Lin: Chem. Eng. Sci., 1995, vo
Data Loading...
