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High Temperature Strain of Metals and Alloys Part 9

Tham khảo tài liệu 'high temperature strain of metals and alloys part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 118 I 7 Single Crystals of Superalloys amount of primary creep 10 to 20 is exhibited. The extent of the primary creep is found to vary with temperature and deviation of the orientation from the 001 direction. A long steady-state stage is typical. This constitutes a considerable proportion of the available rupture life of the material. The research group from the University of Cambridge and Rolls-Royce University Technology Center have been carried out investigations on the problem of deformation of the single-crystal superalloys in detail 37 38 41 42 using the CMSX-4 superalloy see the chemical composition in Table S1 Supplement 3 . The obtained creep data for CMSX-4 superalloy are shown in Fig. 7.5 41 . The orientations of the tested single crystals were found to lie within 10 of the 001 direction. The test results are plotted in two forms strain versus time A and strain rate versus strain B . At 1023K 750 C the usual creep curve with primary steady-state and tertiary stages is observed Fig. 7.5 a . At 1223K 950 C the tertiary deformation begins almost at once Fig. 7.5 b . One can see in the inset of Fig. 7.5 b that to a good approximation the creep strain rate can be taken to be proportional to the accumulated creep strain. At higher temperature 1423K 1150 C and under a lower stress a small amount of strain is accumulated but there exists a plateau where the creep strain is almost constant in time. Later the creep strain dramatically increases with rupture eventually occurring the typical curve is Fig. 7.5 c . The dependence of the creep on the orientation of the CMSX-4 single crystals is shown in Fig. 7.6 42 . The orientations of the specimens after the creep tests are plotted in the standard stereographic triangle in Fig. 7.7. 0 50 100 150 200 250 300 Time hr Fig. 7.6 Creep curves from CMSX-4 superalloy single crystals tested at temperature 1023Kand stress 750MPa. The test temperature belongs to the lower temperature interval. Orientations of specimens are .