S. L. Semiatin

Bio: S. L. Semiatin is an academic researcher from Wright-Patterson Air Force Base. The author has contributed to research in topics: Microstructure & Hot working. The author has an hindex of 66, co-authored 406 publications receiving 16798 citations. Previous affiliations of S. L. Semiatin include Rockwell International & Ohio State University.

Thermomechanical processing of beta titanium alloys—an overview

Abstract: Thermomechanical processing (TMP) is associated with two major requirements: (i) to produce usable shapes through primary working (ingot breakdown) and secondary mill operations (hot rolling or forging) and (ii) to optimize mechanical properties through microstructure control during the different stages of the thermomechanical process. This paper reviews the thermomechanical processing of beta titanium alloys in general and high temperature deformation mechanisms, microstructure control during TMP, and final mechanical properties in particular.

Flow behavior and globularization kinetics during hot working of Ti–6Al–4V with a colony alpha microstructure

Abstract: The effect of process variables on flow response and microstructure evolution during hot working of Ti–6Al–4V with a colony alpha preform microstructure was established using isothermal hot compression tests. Testing was conducted on material with prior-beta grain sizes of 100 μm or 400 μm at strain rates of 0.001–10 s−1, test temperatures between 815 and 955°C, and height reductions of 40–80%. All of the flow curves exhibited a peak stress followed by moderate flow softening. The absence of a grain/colony size dependence of flow behavior, coupled with relatively low values of the strain rate sensitivity of the flow stress (∼0.05–0.30), led to the conclusion that deformation was controlled by dislocation glide/climb processes. Flow softening was interpreted in terms of deformation heating and substructure/texture evolution. The dependence on strain rate and temperature of the kinetics of dynamic globularization of the colony microstructure was complex and appeared to be of second-order importance compared to the effects of strain per se, thus suggesting the dominance of dislocation-type processes for the control of globularization as well.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Friction Stir Welding and Processing

Abstract: Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.