Localized Deformation in Ni-base Superalloys Under Severe Microstructural Gradients

Materials joining science and technology are critical to the overall cost and performance of manufactured goods in industry.  As in the broader materials universe, significant progress has been made in computationally modeling joining processes such as welding; however, contemporary weld process models are not capable of predicting final mechanical properties (i.e, tensile strength, ductility, impact toughness, and creep strength) without employing semi-empirical methods or significant calibration.  This severely limits their long-term predictive capability, particularly for next-generation materials relevant to industry and the Center for Integrative Materials Joining Science for Energy Applications (CIMJSEA). 

Despite the clear need for models informed by fundamental physical processes, development has been complicated by a lack of data for welded components with severe gradients in crystallography, composition, and microstructure.  These variations profoundly affect the deformation mechanisms and mechanical behavior of welded parts; however, accurate mechanical data generation at the micron scale will push the science and technology of small-scale property measurements to its limits.  The objective of this work is to develop and apply emerging experimental techniques for the measurement of local (μm to mm scale) mechanical properties to the heterogeneous microstructures developed in association with welds.  This will lead to new insights to inform the development of “digital apps” that will predict the final mechanical properties of a weld as a function of microstructural gradients. 

Preliminary experiments will focus on mechanical testing and grain-scale analysis of autogenous welds in alloy 740H prepared at Lehigh University and tested at Ohio State University.  Model alloy systems will subsequently be prepared and characterized at Lehigh University with light optical microscopy (LOM) and orientation imaging microscopy (OIM).  Property measurement will be performed at OSU with conventional creep testing, high resolution strain mapping, and micropillar/nanoindentation tests.