Grain refinement in titanium prevents low temperature oxygen embrittlement

Abstract

Interstitial oxygen embrittles titanium, particularly at cryogenic temperatures, which necessitates a stringent control of oxygen content in fabricating titanium and its alloys. Here, we propose a structural strategy, via grain refinement, to alleviate this problem. Compared to a coarse-grained counterpart that is extremely brittle at 77 K, the uniform elongation of an ultrafine-grained (UFG) microstructure (grain size ~ 2.0 µm) in Ti-0.3wt.%O is successfully increased by an order of magnitude, maintaining an ultrahigh yield strength inherent to the UFG microstructure. This unique strength-ductility synergy in UFG Ti-0.3wt.%O is achieved via the combined effects of diluted grain boundary segregation of oxygen that helps to improve the grain boundary cohesive energy and enhanced <c + a> dislocation activities that contribute to the excellent strain hardening ability. The present strategy will not only boost the potential applications of high strength Ti-O alloys at low temperatures, but can also be applied to other alloy systems, where interstitial solution hardening results into an undesirable loss of ductility.

Dual-scale chemical ordering enables exceptional cryogenic mechanical properties of medium-entropy alloys

“…hydrogen, methane, ammonia) which serve as global energy carriers in fields like marine, aerospace, grids, transport, chemical conversion and power plants [4,5] . Yet, most alloys and their microstructures have been developed over the past decades for providing the desired mechanical performance at room and elevated temperatures, and fewer material design options exist for strong and damage-tolerant cryogenic applications, despite the less severe cost restrictions in this field [3] . The reason for the steep and often abrupt decay in system-critical mechanical properties at low-temperatures is the ductile-to-brittle transition of many alloys [6][7][8] .…”

“…11). This effect releases local stress concentrations that would otherwise build up due to deformation localization [3,37] . Further gliding of these dislocations will eventually trigger their mutual interactions as well as the interaction with the existing slip bands, resulting in a high density of dislocation networks between the dislocation bands (as shown in the microstructure at 30% strain demonstrated in Figs.…”

“…Yet, safe and lasting lowtemperature infrastructures are needed to realize the growing global demand for liquid energy carriers such as hydrogen [1] . Traditional microstructure strategies designed for high strength and ductility at room temperature often fail when exposed to such low temperatures due to the unresolved conflict between strength and damage tolerance under such conditions [2,3] . Here we introduce a new type of dual-scale atomic ordering nanostructure embedded in a massive metallic solid solution matrix to overcome this challenge.…”

Achieving excellent strength-toughness combination in hexagonal closed-packed multi-principle element alloys via 〈c + a〉 slip promotion

“…The homogeneous stress distribution and high work hardening rate, induced both by the modified dislocation plasticity, are considered as the primary reason responsible for the best-ever strength-toughness combination reported in coarse-grained HCP materials. Yet, it's important to recognize that beyond the nucleation/gliding resistance gap among the soft and hard slip modes, which typically dominates in HCP materials, other factors can significantly influence the mechanical behavior as well [18,85]. For instance, comparing the ductile fracture of T1.2 to the brittle fracture of similarly strong, cold-rolled pure Ti (Supplementary Materials) reveals the former's better grain boundary cohesion, which also contributes to strength-toughness.…”