Precipitation of γ′ Phase of DD6 at Unequal Service Temperatures

In this paper, the DD6 alloys after complete heat treatment were heat-treated at 900, 1000, 1100, 1200, 1300 °C for 1 h, then was air cooled. Microstructures treated by different temperatures were investigationed by OM and FESEM. The microstructures evolution of alloys were estimat using JMatPro software and Image-Pro Plus. Conclusion illustrates the size of γ′ phase increases gradually after the DD6 alloy heat-treated at 900, 1000, 1100 and 1200 °C for 1 h, and the size reaches the maximum after heat-treated at 1200 °C. Most of the γ′ phase dissolves and then precipitate the irregular small γ′ phase, about 0.20 nm after preservation at 1300 °C. The size distribution of the γ′ phase turned into more and more uniform, and the best distribution state is achieved after preservation at 1100 °C; The matrix channel of the microstructure of DD6 widens gradually with temperatures increasing and reaches a maximum value at 1100 °C, about 65 nm. The matrix channel is narrowed gradually, and the most part of γ′ phase has serrated γ/γ ′ phase surface after heat treatment at 1200 °C. After heat preservation at 900 °C, volume fraction of γ′ increases contrast that after complete heat-treatment; after heat-treatment at temperature degree of 1000-1200 °C, γ′ volume fraction decreases gradually; γ′ phase volume fraction increases again at 1300 °C. The different microstructure characteristics of DD6 after heat-treatment at unequal temperatures are obtained, indicating that the using temperature has a significant effect on the microstructure of DD6 alloy. (paper)