Method of Stray Grain Inhibition in the Platforms with Different Dimensions During Directional Solidification of a Ni-Ba
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DUE to the elimination of grain boundary (GB), single crystal turbine blades can be subjected to higher service temperature and possess superior mechanical properties. Therefore, in the past decades, Ni-base superalloy single crystal turbine blades have been widely used in the modern gas turbine for aircraft propulsion and power generation. However, owing to the complex geometry shape and intricate air-cooling channels of the turbine blades, the prevention of defect formation for the advanced turbine blades during the directional solidification (DS) process becomes increasingly challenging. One of the major defects encountered during the DS process is stray grain,[1–4] which is randomly oriented and easily forms high angle boundaries (HABs) with primary grain. Since GB strengthening elements are XIANGBIN MENG, Associate Professor, is with the Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China, is also Post-doctoral with the Aviation Industry Corporation of China (AVIC) Xi an Aero-engine (Group) Corporation LTD., Xi an 710021, People’s Republic of China. Contact e-mail: [email protected] JINGUO LI, TAO JIN, and XIAOFENG SUN, Professors, and ZHUANGQI HU, Academician, are with the Institute of Metal Research, Chinese Academy of Sciences. Contact e-mail: [email protected] SHIZHE ZHU and HONGQIANG DU, Engineers, are with the Aviation Industry Corporation of China (AVIC) Shenyang Liming Aero-Engine (Group) Corporation LTD., Shenyang 110043, People’s Republic of China. ZHONGHUA YUAN and JUNWU WANG, Engineers, are with the Aviation Industry Corporation of China (AVIC) Guiyang Liyang Aero-Engine (Group) Corporation LTD., Guiyang 550002, People’s Republic of China. Manuscript submitted February 28, 2013. Article published online November 9, 2013 1230—VOLUME 45A, MARCH 2014
nearly absent in single crystal, HABs are very harmful for the mechanical properties, and usually perform as the source for crack initiation. Therefore, many researches[1–25] have been carried out to study the formation of low-angle boundaries and stray grains as well as the corresponding methods of stray grain inhibition. The platform of turbine blade, which is considered as the most likely location to form the lowangle boundaries and stray grains, has been paid full attention to. Napolitano and Schaefer[5] investigated the dendrite growth and the low-angle boundary formation in the platform. They defined a connectivity parameter to predict the formation of low-angle boundary. Newell and D’Souza et al.[9,10] proposed the cumulative misorientation of low-angle boundary in the platform results from plastic deformation of dendrite stems in response to contraction stresses during the DS process. Yang et al.[14] simulated the formation of stray grains in the platform by cellular automaton finite difference (CAFD) model. It is found that decreasing either withdrawal velocity or isotherm inclination angle results in a decreased undercooling in the platform, which could reduce the formation and growth of stray grains. Ma
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