Stablization of Nanotwinned Microstructures in Stainless Steels Through Alloying and Microstructural Design

In this STIR we proposed to investigate the microstructure and alloy composition on the formation and stability of nanotwinned microstructures. The long-term alloy design strategy focuses on microalloying additions to 1) reduce the stacking fault energy (SFE), enhance twinning formation, and increase twin volume fraction; 2) reduce the twin size via increasing interstitial content while also taking into account solid solution hardening in twin size; 3) form high temperature, mainly intergranular, carbides, nitrides, carbonitrides to pin twin boundaries, increasing their high temperature stability; 4) form nano-scale intermetallic precipitates in the presence of Co and refractory elements for creep resistance and high temperature strength. Microstructural design strategy would concentrate on twinning-induced grain boundary engineering and distribution of nano-precipitates/carbides. In the present STIR project focused mainly on the formation and stability of deformation nano-twins in the single crystals of low SFE austenitic stainless steels , experimentally. We did some preliminary investigation on the phase stability of precipitate phases likely to stabilize twinned structure at elevated temperatures. This computational work was accompanied by few experimental validation cases through microstructural investigations and thermo-mechanical testing. The experimental work was performed in collaboration with Prof. Ibrahim Karaman (a) Papers published in peer-reviewed journals (N/A for none) Enter List of papers submitted or published that acknowledge ARO support from the start of the project to the date of this printing. List the papers, including journal references, in the following categories: