Catalyst Project: Microstructural Evolution and Constitutive Modeling of Creep and Elevated Temperature Quasi-Static Tensile Deformation in Additively Manufactured Grade 91 Alloy

Tennessee State University, Nashville TN

Investigators

Abstract

Catalyst Projects provide support for Historically Black Colleges and Universities (HBCU) to work towards establishing research capacity of faculty to strengthen science, technology, engineering, and mathematics (STEM) undergraduate education and research. It is expected that the award will further the faculty member's research capability, improve research and teaching at the institution, and involve undergraduate students in research experiences. This award to Tennessee State University supports faculty and undergraduate research experiences in the development of phenomenological constitutive creep deformation models for Additively manufactured (AM) Grade 91 alloy. The proposed models will provide insights into the nature of the metallurgical processes taking place during hot deformation processes in AM Grade 91 alloy, which will ultimately determine the mechanical behavior of the material. Creep, the time-dependent deformation under statically applied load at high homologous temperature is detrimental, resulting in catastrophic failures and/or substantially reduced life of critical structural components in nuclear, aerospace, and microelectronic industries. Given that additive manufacturing (AM) is proliferating as a manufacturing technique across many industries, it is imperative to characterize creep mechanisms in AM ferritic steel alloys, a topic that has not been addressed in either the AM literature or the materials science literature. The goal of this research is to study the creep behavior of AM ferritic grade 91 steel alloys which are potential materials for high-temperature structural applications in the aerospace and nuclear energy industries. For this study, the test loads will range from 100 MPa to 300 MPa, while the test temperatures will range from 300⁰C – 700⁰C. The minimum creep rates obtained from the plots of creep strain against time provides a measure of the creep resistance. Creep testing will be complimented with microstructural study using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Rietveld refinement to gain insight into the fundamental mechanisms that control creep in AM ferritic grade 91 steels. The results of this study will aid the development of new generation of creep resistant superalloys, impacting the scholarly communities of AM and materials science, aerospace, and nuclear engineering industries. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.