High-Throughput Creep Testing for Additively Manufactured 316H SS by Using Microstructurally-Graded Specimen

Laser additive manufacturing (AM) is being considered by the nuclear industry to manufacture net-shape components for advanced reactors and micro reactors. Part-to-part and vendor-to-vendor variations in part quality, microstructure, and mechanical properties are common for additively manufactured components, attributing to the different processing conditions. On a single component, microstructural variation also exists due to the local changes in thermal history. This work demonstrates the ability of additive manufacturing (AM) to induce microstructurally gradient specimen as a high throughput means to establish the relationship between process-microstructure-creep properties. Through gradient specimen manufacturing, multiple microstructures, correlated to the processing conditions, can be produced in a single specimen. To produce multiple microstructures within a single part, the AM processing parameters are changed at finite height intervals so that a specified region will manifest a uniform microstructure. Using digital image correlation (DIC), the creep strain can be calculated in these gradient regions, allowing for multiple microstructures to be probed in a single creep test. Employing DIC allows for local and global strain measurements to be identified within each region. The total creep strain in a gradient region can be tracked while also allowing for various points on the bar to be examined, showing a direct correlation between creep strain and microstructure during characterization. Using these techniques, strain development’s effect on microstructure within crept specimen is investigated to reveal the deformation mechanisms during creep as well as determine the effects of cellular structures on creep performance. This work will present the gradient microstructure manufacturing and validation as well as microstructural evolution during creep, emphasizing the effects of cellular structures on creep deformation.