Structural Properties and Phase Stability of Primary Y Phase (Ti(2)SC) in Ti-Stabilized Stainless Steel from Experiments and First Principles

The morphology and microstructural evaluation of Y phases in AISI 321 (a Ti-stabilized stainless steel) were characterized after hot deformation. The electronic structure and phase stability of titanium carbosulfide were further discussed by first-principle calculations. It was found that Y phases, like curved strips or bones in AISI 321 stainless steel, mostly show a clustered distribution and are approximately arranged in parallel. The width of the Y phase is much less than the length, and the composition of the Y phase is close to that of Ti(2)SC. Y phases have exceptional thermal stability. The morphology of Y phases changed considerably after forging. During the first calculations, the Ti(2)SC with hexagonal structure does not spontaneously change into TiS and TiC; however Ti(4)S(2)C(2) (Z = 2) can spontaneously change into the two phases. The Ti–S bonds are compressed in Ti(4)S(2)C(2) cells, which leads to poor structural stability for Ti(4)S(2)C(2). There is a covalent interaction between C/S and Ti, as well as an exchange of electrons between Ti and S/C atoms. Evidently, the mechanical stability of Ti(4)S(2)C(2) is weak; however, Ti(2)SC shows high stability. Ti(2)SC, as a hard brittle phase, does not easily undergo plastic deformation.