Temperature dependence of strengthening mechanisms in the nanostructured ferritic alloy 14YWT: Part I—Mechanical and microstructural observations

Grain size and particle dispersion effects on the tensile behavior of friction stir welded MA956 oxide dispersion strengthened steel from low to elevated temperatures

“…16 which suggests that FSW causes the complete loss of particle strengthening even for the low heat input condition. This overall conclusion is also strongly supported by research by Kim on 14YWT which concluded that oxide particles greater than 100 nm in size (comparable to all oxide particles following FSW in this research) would result in s P being less than 50 MPa [53,54]. It is worth noting that particles in 14YWT are Y-Ti-O particles as opposed to the Y-Al-O particles in MA956 and the work by Kim did not include any conditions that would cause a comparable degree of particle coarsening as that seen here, but the calculation method used by Kim is very similar to that presented by Wang and used here in Eq.…”

Nanoprecipitation of oxide particles and related high strength in oxide-dispersion-strengthened iron–aluminium–chromium intermetallics

“…5 times finer particles and 100 times more particles), the athermal Orowan strengthening at low temperatures can be as much as 5 times larger than for the present alloys. This very fine microstructure means, however, that strength is more temperature dependent than for the present alloys as thermally activated deformation processes, such as Coble creep in grain boundaries or dislocation activation over particles, operate more easily [3,4,6,7]. It is well known, for example, that coarse particles lead to less Orowan strengthening, since their separation is large, but thermal activation of dislocations over obstacles is too easy when excessively fine particles, e.g.<2-20 nm, are present [49].…”

“…The rapid loss of strength of finegrained 14YWT from 500°C means that this material has similar strength to the present alloys in the most-relevant 600-800°C range. Nanocluster-strengthened alloys such as 14YWT have very fine grain size, 100-500 nm [3,4,6,7] and very large numbers of 2-5 nm sized dispersoids [1][2][3][4]. Since these nanodispersion-strengthened alloys contain many more oxide particles than the present materials (e.g.…”

“…The Fe20Cr-base PM2000 alloy [6,7] is weaker at all temperatures, even in the fine-grained state. Nanodispersion-strengthened 14YWT (Fe-14Cr-base ODS alloy with small additions of Y, W and Ti) [3,4,6,7] is very strong at low temperatures in the fine-grained state, but is much weaker after recrystallization to a coarse grain. The rapid loss of strength of finegrained 14YWT from 500°C means that this material has similar strength to the present alloys in the most-relevant 600-800°C range.…”

“…Such materials show outstanding high-temperature strength [3,4] and creep resistance [5][6][7][8], and are stable at high temperatures as well as under irradiation [1,9,10]. The high strength has been explained by contributions of matrix and grain boundaries and by strong dislocation-particle pinning [3][4][5][6][7][8]. It is believed that the milling process used to prepare the alloys leads to the dissolution of the Y 2 O 3 , which then precipitates out as nanosized oxides during subsequent processing or annealing [2,11,12].…”