Please consider attending the following: MATERIALS ENGINEERING SEMINAR "Segregated-Assister Shearing of the G'Phase in Ni-Based Superalloys" By Sae Matsunaga Purdue MSE Ph.D. Preliminary Exam Advisor: Professor Michael S. Titus ABSTRACT Ni-based superalloys have been developed and used for over 60 years for high temperature applications due to their superior material properties; such as, high temperature strength, resistance to creep, high thermal/mechanical fatigue strength, and excellent oxidation resistance. Much of the high temperature strength is due to the presence of a high volume fraction (~70%) of *'-(ordered fcc/L12) precipitates, which are embedded coherently in a ***fcc/A1) matrix. These materials are widely used in gas turbines for aircraft engines, land-based turbines for natural gas-operated power plants, rocket engines, and other applications where extreme environments are present. Over the decades, the high temperature deformation mechanisms of Ni-based superalloys have been studied, and it has been revealed that the deformation mechanisms of Ni-based superalloys strongly depend on certain microstructural features (*' volume fraction, size, and shape) and alloy composition. Recently, shearing of the *' precipitates by partial dislocations has been identified as the rate-limiting creep deformation mechanism at low temperature and high stresses in some Ni-based superalloys. The current understanding of *' shearing will be discussed with special focus on the planar defects in the *' phase such as superlattice intrinsic/ extrinsic stacking faults, antiphase boundaries, and microtwins. To understand the relationship between defects in *' phase and primary alloy elements, high resolution EDX would be carried out for further investigation of segregation at faults and microtwins. This would bring a more complete understanding of the deformation mechanisms and segregation behavior of essential alloying elements would bring new insight to guided alloy design and reveal the underlying mechanisms and driving forces responsible for shearing of the *' phase. Date: Monday, December 11, 2017 Time: 9:30 A.M. Place: ARMS 3115