Grain refinement in titanium prevents low temperature oxygen embrittlement

Chong, Y.*; Gholizadeh, R.*; Tsuru, Tomohito; Zhang, R.*; Inoue, Koji*; Gao, W.*; Godfrey, A.*; Mitsuhara, Masatoshi*; Morris, J. W. Jr.*; Minor, A. M.*; et al.

Nature Communications (Internet), 14, p.404_1 - 404_11, 2023/02

https://doi.org/10.1038/s41467-023-36030-0

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 77K, the uniform elongation of an ultrafine-grained (UFG) microstructure (grain size 2.0 m) in Ti-0.3wt.%O was 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 was achieved via the combined effects of diluted grain boundary segregation of oxygen that helps to improve the grain boundary cohesive energy and enhanced dislocation activities that contribute to the excellent strain hardening ability. The present strategy could not only boost the potential applications of high strength Ti-O alloys at low temperatures, but could also be applied to other alloy systems, where interstitial solution hardening results into an undesirable loss of ductility.

Origin of dramatic oxygen solute strengthening effect in titanium

Yu, Q.*; Qi, L.*; Tsuru, Tomohito; Traylor, R.*; Rugg, D.*; Morris, J. W. Jr.*; Asta, M.*; Chrzan, D. C.*; Minor, A. M.*

Science, 347(6222), p.635 - 639, 2015/02

https://doi.org/10.1126/science.1260485

Given that solute atoms interact weakly with the long-range elastic fields of screw dislocations, it has long been accepted that solution hardening is only marginally effective in materials with mobile screw dislocations. This accepted wisdom has recently been questioned by first-principles calculations suggesting that solutes may interact much more strongly with the screw dislocation core. We report here the results of a combined experimental and computational study undertaken to elucidate the profound hardening effect of oxygen in pure hexagonally-close-packed structured -Ti. High resolution and in situ transmission electron microscopy nanomechanical characterization establish that the strengthening is due to the strong interaction between oxygen and the core of screw dislocations that mainly glide on prismatic planes. First-principles calculations of the screw dislocation core reveal a simple crystallographic source for the oxygen-dislocation interaction that is consistent with experimental observations. The distortion of the interstitial sites at the dislocation core creates a very strong but short-range repulsion for oxygen atoms. These mechanisms effectively pin the dislocation near the oxygen interstitial. These results establish a highly effective mechanism for strengthening by interstitial solutes that, contrary to prior understanding, may be significant in many structural alloys.

Influence of self-irradiation on the magnitude of the superfluid density in PuCoGa probed by muon spin rotation

Oishi, Kazuki; Heffner, R. H.; Ito, Takashi; Higemoto, Wataru; Morris, G. D.*; Bauer, E. D.*; Graf, M. J.*; Zhu, J.-X.*; Morales, L. A.*; Sarrao, J. L.*; et al.

Physica B; Condensed Matter, 403(5-9), p.1013 - 1014, 2008/04

https://doi.org/10.1016/j.physb.2007.10.079

PuCoGa has attracted much interest because it is the first Pu-based superconductor, having an order of magnitude higher transition temperature K than the isostructural heavy fermion superconductor CeCoIn (K). The mechanism of the superconductivity in PuCoGa is still under investigation, though recent experiments and theory suggest a magnetic origin. A unique aspect of this compound is the self-irradiation damage because Pu (Pu, = 24,000 years) creates lattice defects which scatter electrons and, hence, break superconducting pairs. In order to elucidate the magnitude and temperature dependence of the magnetic penetration depth , we have performed SR measurements in the same PuCoGa single crystals after 25 and 400 days of aging. We found that decreased from 18.5K to 15K for the aged sample, yet a quasi-linear temperature dependence was found for the low-temperature in both the fresh and aged sample, consistent with -wave pairing symmetry. The magnitude of the muon spin relaxation rate in the aged sample, , where and are the superfluid density and the effective mass, respectively, is reduced by about 70% compared to fresh sample. This indicates that the scattering from self-irradiation induced defects is not in the limit of the conventional Abrikosov-Gor'kov pair-breaking theory, but rather in the limit of short coherence length (about 2nm in PuCoGa) superconductivity.

The Search for magnetic order in -Pu metal using muon spin relaxation

Heffner, R. H.; Oishi, Kazuki; Fluss, M. J.*; Morris, G. D.*; MacLaughlin, D. E.*; Shu, L.*; Chung, B. W.*; McCall, S. K.*; Bauer, E. D.*; Sarrao, J. L.*; et al.

Journal of Alloys and Compounds, 444-445, p.80 - 83, 2007/10

https://doi.org/10.1016/j.jallcom.2006.12.026

We summarize the results of muon spin relaxation (SR) measurements carried out in- and -Pu and in the superconducting state ofPuCoGa. In Pu metal, interest has centered on whether or not magnetic order exists in the hightemperature fcc phase,The Pu metal studies were designed to search for evidence of magnetic ordering, andhave set the most stringent limits to date for the ordered moment. In PuCoGa the temperature dependence of themagnetic penetration depth (T) was investigated in a fresh sample and again in the same sampleafter 400 days of aging. We find (T) T for T Tc/2, indicating a line of nodes in thesuperconducting order parameter. Remarkably, the temperature dependence of (T) is littlechanged even after significant radiation damage.

Magnetic penetration depth and self-induced irradiation effects in superconducting PuCoGa probed by muon spin rotation

Oishi, Kazuki; Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Bauer, E. D.*; Morales, L. A.*; Sarrao, J. L.*; MacLaughlin, D. E.*; Shu, L.*; Ito, Takashi; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.566 - 568, 2007/03

no abstracts in English

New limits on the ordered moments in -Pu and Ga-stabilized -Pu

Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Chung, B.*; MacLaughlin, D. E.*; Shu, L.*; Anderson, J. E.*

Physica B; Condensed Matter, 374-375, p.163 - 166, 2006/03

https://doi.org/10.1016/j.physb.2005.11.042

The SR measurements in pulutonium metals are reported for the first time. The ground-state properties of Pu metal is not understood clearly. We found the upper limits of the ordered moment in -Pu and -stabilized Pu is at 4K.

Evolution of the heavy fermion state in CeIrIn

Heffner, R. H.; Morris, G. D.*; Bauer, E. D.*; Sarrao, J. L.*; Thompson, J. D.*; MacLaughlin, D. E.*; Shu, L.*

Physica B; Condensed Matter, 375-375, p.184 - 187, 2006/03

https://doi.org/10.1016/j.physb.2005.11.048

Limits for ordered magnetism in Pu from muon spin rotation spectroscopy

Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Chung, B.*; McCall, S.*; MacLaughlin, D. E.*; Shu, L.*; Oishi, Kazuki; Bauer, E. D.*; Sarrao, J. L.*; et al.

Physical Review B, 73(9), p.094453_1 - 094453_5, 2006/03

https://doi.org/10.1103/PhysRevB.73.094453

no abstracts in English

Penetration depth study in the heavy-fermion superconductor PrOsSb

Shu, L.*; MacLaughlin, D. E.*; Heffner, R. H.; Callaghan, F. D.*; Sonier, J. E.*; Morris, G. D.*; Bernal, O. O.*; Bosse, A.*; Anderson, J. E.*; Yuhasz, W. M.*; et al.

Physica B; Condensed Matter, 374-375, p.247 - 250, 2006/01

https://doi.org/10.1016/j.physb.2005.11.066

Quasiparticle excitations in PuCoGa probed by muon spin rotation

Oishi, Kazuki; Heffner, R. H.; Higemoto, Wataru; Ito, Takashi; Morris, G. D.*; Bauer, E. D.*; Morales, L. A.*; Sarrao, J. L.*; Fluss, M. J.*; MacLaughlin, D. E.*; et al.

no journal, , 

The discovery of the first Pu-based superconductor PuCoGa ( = 18.5 K) demonstrates the rich and complex nature of Pu-based materials. The mechanism of the superconductivity in PuCoGa is still under investigation, though recent experiments and theory suggest a magnetic origin. For example, the electronic structure of this material was investigated theoretically, and spin-fluctuation mediated superconductivity was suggested. NMR results also suggest that the superconducting order parameter of this Pu-based superconductor has d-wave symmetry. We note that Pu is a radioactive nucleus (Pu, = 24000 years), thus PuCoGa suffers self-induced radiation damage. Previous SR results performed at 600 Oe in a 25-day old single crystalline sample show a linear temperature dependence for the muon spin relaxation rate (, : magnetic penetration depth) for 0.5, suggesting d-wave pairing symmetry. We have performed SR experimentes on the same sample after 400 days of aging in order to obtain more detailed information on the order parameter, i.e., T-dependence of at several magnetic fields, as well as the effects of aging. We found that Tc decreased from 18.5 K to 15 K for the 25-day and 400-day samples, respectively, yet the linear temperature dependence remains, consistent with a line of nodes (and suggesting d-wave pairing symmetry). These results indicate that the temperature dependence of does not depend on accumulated radiation damage over the span of time measured.