Investigation on material's fatigue property variation among different regions of directional solidification turbine blades-Part I: Fatigue tests on full scale blades

At present, directional solidification (DS) made blades are commonly used in high performance turbine for their better high temperature mechanical, especially in creep properties compared with the equiaxed grain (EG) blades made by conventional casting method. To predict DS blades' fatigue life accurately, one of the practical ways is to conduct tests on full-scale blades in a laboratory/bench environment. In this investigation, two types of full scale turbine blades, which are made from DZ22B by DS method and K403 by conventional casting method, respectively, were selected to conduct high temperature combined low and high cycle fatigue (CCF) tests on a special design test rig, to evaluate the increase of fatigue life benefitted from material change. Experimental results show that different from EG blades, DS blades' fracture section is not located on the position where the maximum stress point lies. By comparing fatigue test results of the two types of blade, it can be found that the fatigue properties among different regions of the DS blade are different, and its fatigue damage is not only related to the stress field, but also affected by different parts material's fatigue properties.