Copper precipitation in cobalt-alloyed precipitation-hardened stainless steel

Murthy, Arpana S.; Medvedeva, Julia E.; Isheim, Dieter; Lekakh, Semen Naumovich; Richards, Von; Aken, David C. Van

doi:10.1016/j.scriptamat.2012.02.039

Cited by 36 publications

(17 citation statements)

References 22 publications

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“…We found, however, that the interfacial segregation energy calculated with respect to random cobalt distribution in bulk Fe becomes negative, E segr (Co) \ 0, for concentration less than 2.4 at.% Co. This means that at the low concentration, cobalt prefers to [17]. It should be noted that the surface segregation energy for Co on the (110) Fe surface is known to have a small negative value [62,63].…”

Section: Cobalt Segregationmentioning

confidence: 71%

“…Previously [16,17], we studied three bcc-based alloys with 0, 3, and 7 wt% Co and observed that Co addition increases the strength and toughness. By means of atom probe tomography, a decrease in Cu precipitate radius and a narrowed size distribution was observed with addition of Co.…”

Section: Cobalt-induced Strengthening In Fe/cumentioning

confidence: 97%

“…Recently, it was observed that cobalt addition improves the room temperature strength as well as the toughness of precipitation hardened steel; however, the mechanism of additional cobalt-induced strengthening was not established [16,17]. In multi-component alloys, the effect of additions on the properties of precipitated steel strongly depends on their interaction with matrix and precipitate, as well as on the aging stages.…”

Section: Introductionmentioning

confidence: 99%

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First principle study of cobalt impurity in bcc Fe with Cu precipitates

et al. 2012

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The addition of cobalt was experimentally observed to increase the strength and impact toughness of Cu precipitation hardened steel. In order to understand the mechanism of this strengthening, we studied the effect of cobalt in the bulks and surfaces of bcc Fe and bcc Cu, as well as at the Fe/Cu interface by ab initio density-functional approach. We investigated the cobalt distribution between the Fe matrix and Cu precipitate, and found that cobalt is rejected from the core of the Cu particle. The calculated elastic constants and stacking fault energies show that cobalt does not produce any solid solution softening or hardening in bcc Fe. However, cobalt segregated in the interfacial region increases the cleavage fracture energies and cleavage stress of the Fe/Co/Cu interface. The compressive stress, which arises near the interface due to strong Fe-Co bonds, may serve as a barrier for dislocation motion through the interface resulting in additional hardening.

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Section: Cobalt Segregationmentioning

confidence: 71%

Section: Cobalt-induced Strengthening In Fe/cumentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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First principle study of cobalt impurity in bcc Fe with Cu precipitates

et al. 2012

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“…Atom-probe tomography (APT) allows the accurate determination of compositions as small as 50 ppm at interfaces with subnanometer resolution, [20] and details of the APT method have been described in several review publications. [21][22][23] Local-electrode APT, LEAP, has been used to characterize precipitation in a variety of age-hardenable alloys including stainless steels, [24] Al-Sc alloys, [25] and Ni-based superalloys. [23] This technique has also been used to measure the extent of spinodal decomposition in Ti-Al-N thin films, [26] Fe-Cr binary alloys, [27] as well as in Fe-Ni-Mn-Al Fig.…”

Section: Introductionmentioning

confidence: 99%

An Atom Probe Study of Kappa Carbide Precipitation and the Effect of Silicon Addition

Bartlett

Aken

Medvedeva

et al. 2014

Metall Mater Trans A

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The influence of silicon on j-carbide precipitation in lightweight austenitic Fe-30Mn-9Al-(0.59-1.56)Si-0.9C-0.5Mo cast steels was investigated utilizing transmission electron microscopy, 3D atom-probe tomography, X-ray diffraction, ab initio calculations, and thermodynamic modeling. Increasing the amount of silicon from 0.59 to 1.56 pct Si accelerated formation of the j-carbide precipitates but did not increase the volume fraction. Silicon was shown to increase the activity of carbon in austenite and stabilize the j-carbide at higher temperatures. Increasing the silicon from 0.59 to 1.56 pct increased the partitioning coefficient of carbon from 2.1 to 2.9 for steels aged 60 hours at 803 K (530°C). The increase in strength during aging of Fe-Mn-Al-C steels was found to be a direct function of the increase in the concentration amplitude of carbon during spinodal decomposition. The predicted increase in the yield strength, as determined using a spinodal hardening mechanism, was calculated to be 120 MPa/wt pct Si for specimens aged at 803 K (530°C) for 60 hours and this is in agreement with experimental results. Silicon was shown to partition to the austenite during aging and to slightly reduce the austenite lattice parameter. First-principles calculations show that the Si-C interaction is repulsive and this is the reason for enhanced carbon activity in austenite. The lattice parameter and thermodynamic stability of j-carbide depend on the carbon stoichiometry and on which sublattice the silicon substitutes. Silicon was shown to favor vacancy ordering in j-carbide due to a strong attractive Si-vacancy interaction. It was predicted that Si occupies the Fe sites in nonstoichiometric j-carbide and the formation of Si-vacancy complexes increases the stability as well as the lattice parameter of j-carbide. A comparison of how Si affects the enthalpy of formation for austenite and j-carbide shows that the most energetically favorable position for silicon is in austenite, in agreement with the experimentally measured partitioning ratios.

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“…Despite intensive investigations of Fe-Cu alloys (see [4][5][6][7]), the composition of the precipitates and their stability against coarsening remain subjects of debate [4,8,9]. As revealed by 3D atom probe tomography [8], the bcc Cu-rich precipitates also contain Fe, Ni, Mn, and Al.…”

mentioning

confidence: 99%