Effect of a High Magnetic Field on Microstructures of Ni-Based Single Crystal Superalloy During Seed Melt-Back
- PDF / 2,653,805 Bytes
- 6 Pages / 593.972 x 792 pts Page_size
- 105 Downloads / 237 Views
alloy single crystal turbine blade has been widely used in air-engines and land-based gas turbines due to its excellent high-temperature strength and creep durability. These single crystal turbine blades are usually obtained using directional solidification technique. The aims of preparing single crystal blades are to eliminate grain boundaries and to impose an elastically soft [001] orientation.[1–3] Some studies indicated that the misorientation of primary dendrite in single crystal blades is seriously deleterious to mechanical performance.[4,5] Therefore, primary dendrite orientation plays a main role in determining mechanical properties of single crystal turbine blades.[4–6] In industrial production, a single crystal casting of Ni-based superalloy is usually obtained by a grain selector method, while an off-axial orientation dendrite may be formed, which usually deviates from [001] to 12 through 15 deg because of random characteristic of grain
WEIDONG XUAN, Materials Research Engineer, HUAN LIU, Ph.D. Student, CHUANJUN LI, Lecturer, and ZHONGMING REN, YUNBO ZHONG, XI LI, and GUANGHUI CAO, Professors, are with the State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200072, P.R. China. Contact e-mail: wdxuan@ shu.edu.cn Manuscript submitted August 23, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS B
selector during directional solidification.[7] The deviation of crystal orientation significantly affects mechanical properties. In general, the misorientation of crystal less than 10 deg is acceptable by many engineers.[7] Recently, crystal orientation is controlled through seeding technology as the seed is a single crystal with desired orientation.[1,8] However, one of major problems encountered during directional solidification is the formation of stray grains on the edge of sample from melt-back period to initial withdrawal stage.[8,9] Due to random orientations of stray grains, high-angle boundaries may be formed and lead to the decrease of mechanical properties. Therefore, many scientific researchers have investigated the formation of stray grains during directional solidification by seeding method.[1,8–17] It is found that the convex melt-back interface shape of seed induces the sudden change of local solidification conditions, which may lead to the heterogeneous nucleation of stray grains. Moreover, It is also found that the pinching-off dendrite fragments are transferred to the interface front while being subjected to thermal-solutal convection, and then stray grains are formed ahead of the dendrite tips. In order to avoid the formation of stray grains, some methods are applied, such as optimization of cooling rate[18,19] and application of spiral grain selector between the blade and the seed.[1,9] However, these methods have still not effectively solved the problem of stray grain formation. In the recent years, with the development of superconducting magnets, a high magnetic field has been extensively used to improve material properties during solidification. Some reports show that a high magneti
Data Loading...
