The role of (FeCrSi)2(MoNb)-type Laves phase on the formation of Mn-rich protective oxide scale on ferritic stainless steel

Ali‐Löytty, Harri; Hannula, Markku; Juuti, Timo; Niu, Yuran; Zakharov, Alexei; Valden, M.

doi:10.1016/j.corsci.2017.12.026

Cited by 21 publications

(9 citation statements)

References 37 publications

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“…Interconnects for SOFC stacks are another application of high-Cr stainless ferritic steels containing Laves phase [758][759][760][761][762][763][764][765][766][767][768][769][770][771]. Alloying elements and concentrations are similar to those in steels for automotive exhaust systems, C contents are \ 0.01 wt% and Cr contents are in the range 18 to 22 wt% to ensure formation of protecting chromia scales.…”

Section: Ferritic 15-22% Cr Steelsmentioning

confidence: 99%

“…Interconnect materials must not only have good high-temperature mechanical properties, but also a low electrical resistivity, high thermal conductivity, and very good corrosion resistance and chemical stability in both anode and cathode gases, i.e., in reducing and oxidizing atmosphere [762]. The role of Laves phase is mainly to provide good mechanical properties [759,763,764], but there is also a complex interplay between Laves phase precipitation and the formation of different types of surface oxides [771].…”

Section: Ferritic 15-22% Cr Steelsmentioning

confidence: 99%

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Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

2020

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Laves phases with their comparably simple crystal structure are very common intermetallic phases and can be formed from element combinations all over the periodic table resulting in a huge number of known examples. Even though this type of phases is known for almost 100 years, and although a lot of information on stability, structure, and properties has accumulated especially during the last about 20 years, systematic evaluation and rationalization of this information in particular as a function of the involved elements is often lacking. It is one of the two main goals of this review to summarize the knowledge for some selected respective topics with a certain focus on non-stoichiometric, i.e., non-ideal Laves phases. The second, central goal of the review is to give a systematic overview about the role of Laves phases in all kinds of materials for functional and structural applications. There is a surprisingly broad range of successful utilization of Laves phases in functional applications comprising Laves phases as hydrogen storage material (Hydraloy), as magneto-mechanical sensors and actuators (Terfenol), or for wear- and corrosion-resistant coatings in corrosive atmospheres and at high temperatures (Tribaloy), to name but a few. Regarding structural applications, there is a renewed interest in using Laves phases for creep-strengthening of high-temperature steels and new respective alloy design concepts were developed and successfully tested. Apart from steels, Laves phases also occur in various other kinds of structural materials sometimes effectively improving properties, but often also acting in a detrimental way.

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Section: Ferritic 15-22% Cr Steelsmentioning

confidence: 99%

Section: Ferritic 15-22% Cr Steelsmentioning

confidence: 99%

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

2020

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“…Precipitation of cubic C15 (metastable phase) and hexagonal C14 (stable phase) (Nb,Mo)(Cr,Si,Al) 2 Laves phases in the bcc phase of a Nb–27Mo–27Cr–9Al–9Si (at %) alloy during heat treatment has been reported [ 20 ]. The precipitation of a (Nb,Mo)(Cr,Fe,Si) 2 Laves phase in a ferritic stainless steel contributed to its improved oxidation resistance [ 21 ].…”

Section: Introductionmentioning

confidence: 99%

Alloying and Properties of C14–NbCr2 and A15–Nb3X (X = Al, Ge, Si, Sn) in Nb–Silicide-Based Alloys

Tsakiropoulos

2018

Materials

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The oxidation of Nb–silicide-based alloys is improved with Al, Cr, Ge or Sn addition(s). Depending on addition(s) and its(their) concentration(s), alloyed C14-AB2 Laves and A15-A3X phases can be stable in the microstructures of the alloys. In both phases, A is the transition metal(s), and B and X respectively can be Cr, Al, Ge, Si or Sn, and Al, Ge, Si or Sn. The alloying, creep and hardness of these phases were studied using the composition weighted differences in electronegativity (∆χ), average valence electron concentrations (VEC) and atomic sizes. For the Laves phase (i) the VEC and ∆χ were in the ranges 4.976 < VEC < 5.358 and −0.503 < ∆χ < −0.107; (ii) the concentration of B (=Al + Cr + Ge + Si + Sn) varied from 50.9 to 64.5 at %; and (iii) the Cr concentration was in the range of 35.8 < Cr < 51.6 at %. Maps of ∆χ versus Cr, ∆χ versus VEC, and VEC versus atomic size separated the alloying behaviours of the elements. Compared with unalloyed NbCr2, the VEC decreased and ∆χ increased in Nb(Cr,Si)2, and the changes in both parameters increased when Nb was substituted by Ti, and Cr by Si and Al, or Si and Ge, or Si and Sn. For the A15 phase (i) the VEC and ∆χ were in the ranges 4.38 < VEC < 4.89 and 0.857 < ∆χ < 1.04, with no VEC values between 4.63 and 4.72 and (ii) the concentration of X (=Al + Ge + Si + Sn) varied from 16.3 to 22.7 at %. The VEC versus ∆χ map separated the alloying behaviours of elements. The hardness of A15-Nb3X was correlated with the parameters ∆χ and VEC. The hardness increased with increases in ∆χ and VEC. Compared with Nb3Sn, the ∆χ and hardness of Nb3(Si,Sn) increased. The substitution of Nb by Cr had the same effect on ∆χ and hardness as Hf or Ti. The ∆χ and hardness increased with Ti concentration. The addition of Al in Nb3(Si,Sn,Al) decreased the ∆χ and increased the hardness. When Ti and Hf, or Ti, Hf and Cr, were simultaneously present with Al, the ∆χ was decreased and the hardness was unchanged. The better creep of Nb(Cr,Si)2 compared with the unalloyed Laves phase was related to the decrease in the VEC and ∆χ parameters.

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“…In the last 20 years, X‐ray photoelectron spectroscopy and photoemission electron microscopy (XPS and XPEEM) were used in several studies of the surface of stainless steel 8–17 . XPS was used to reveal the spatially averaged surface elemental and sometimes chemical composition 8–12 .…”

Section: Introductionmentioning

confidence: 99%

“…Although sputtered surface allows a clear interpretation of the XPS data, it makes it difficult to directly relate to the diffusion conditions in the presence of the native Cr surface oxides. With the advent of XPEEM, it has become possible to combine the spectroscopic information from photoemission with lateral imaging down to tens of nanometers 13–17 . A particular advantage of XPEEM is that the (potentially significant) variations in the chemical composition due to the grain structure of the metal and presence of inclusions become directly visible.…”

Section: Introductionmentioning

confidence: 99%

Surface chemistry and diffusion of trace and alloying elements during in vacuum thermal deoxidation of stainless steel

Zhu

Al-Sakeeri

Lenrick

et al. 2021

Surface & Interface Analysis

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Removal of the native surface oxide from steel is an important initial step during vacuum brazing. Trace and alloying elements in steel, such as Mn, Si, and Ni, can diffuse to the surface and influence the deoxidation process. The detailed surface chemical composition and grain morphology of the common stainless‐steel grade 316L is imaged and spectroscopically analyzed at several stages of in‐vacuum annealing from room temperature up to 850°C. Measurements are performed using synchrotron‐based X‐ray photoemission and low‐energy electron microscopy (XPEEM/LEEM). The initial native Cr surface oxide is amorphous and unaffected by the underlying Fe grain morphology. After annealing to ~700°C, the grain morphology is seen at the surface, persisting also after the complete oxygen removal at 850°C. The surface concentration of first Mn and then Si increases significantly when annealing to 500°C and 700°C, respectively, while Ni and Cr concentrations do not change. Mn and Si are not located only in grain boundaries or clusters but are distributed across over the surface. Both Mn and Si appear as oxides, while Cr oxide becomes metallic Cr. Annealing from 500°C up to 850°C leads to the removal of first the Mn and then Si oxides from the surface, while Cr and Fe are completely reduced to metals. Deoxidation of Cr occurs faster at the grain boundaries, and the final Cr metal surface content varies between the grains. The findings are summarized in a general qualitative model, relevant for austenite steels.

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The role of (FeCrSi)2(MoNb)-type Laves phase on the formation of Mn-rich protective oxide scale on ferritic stainless steel

Cited by 21 publications

References 37 publications

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

Alloying and Properties of C14–NbCr2 and A15–Nb3X (X = Al, Ge, Si, Sn) in Nb–Silicide-Based Alloys

Surface chemistry and diffusion of trace and alloying elements during in vacuum thermal deoxidation of stainless steel

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