High Temperature Oxidation in Multicomponent Nb Alloys

Menon, E. S. K.; Mendiratta, M. G.

doi:10.4028/0-87849-960-1.717

Cited by 10 publications

(26 citation statements)

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“…Figure 15 is the δ versus VEC map of Nb-silicide-based alloys with addition of Al, Cr, Ge, Hf, Sn, Ta, W. With the exception of the alloys JZ1, JZ2, JZ3 and JZ3+, all other alloys are Ti rich (Ti ≥ 24 at.%). Notice differences in the concentrations of Al, Cr, Ge, Hf and Sn in the alloys M1, M2 and M6 [ 9 , 31 , 46 ] compared with the other Ti rich alloys. The data show (i) a clear separation between Ti lean and Ti rich Nb-silicide-based alloys that are B free (this separation is different from that discussed in [ 19 ], where Ti-rich Nb-silicide-based alloys with B addition form their own separate group), (ii) that improvement in oxidation resistance (see [ 5 ] and the data in this work for JZ1 to JZ3+) goes together with the decrease and increase, respectively of the parameters VEC and δ, in agreement with NICE [ 4 ], (iii) that the addition of specific elements, e.g., Ge, Hf, Sn, Ta brings changes of the aforementioned parameters along “different routes” indicated by the arrows in Figure 15 , with Hf having a remarkable effect, particularly in synergy with Sn (iv) and that this map “pinpoints” an area that could be exploited by alloy design/development to meet property goals (see Section 6 ).…”

Section: Discussionmentioning

confidence: 99%

“…As regards the above constraints, the (a), (d) and (e) were related to the creep target and data about creep in [ 4 , 6 ], the constraints (b), (d), (e) and (g) were linked with (c), and the constraints (b), (f) and (g) were linked with oxidation resistance. The choice of the concentrations of Al, Cr, Ge and Sn, and thus constraints (f) and (g), were informed by recent literature about the effect of the synergy of Al and Cr with Sn or Ge on the oxidation behaviour of Nb-silicide-based alloys [ 4 , 7 , 8 , 9 , 10 , 11 , 24 , 31 ].…”

Section: Alloy Design and Selectionmentioning

confidence: 99%

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On the Microstructure and Properties of Nb-12Ti-18Si-6Ta-5Al-5Cr-2.5W-1Hf (at.%) Silicide-Based Alloys with Ge and Sn Additions

2020

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The microstructures and properties of the alloys JZ3 (Nb-12.4Ti-17.7Si-6Ta-2.7W-3.7Sn-4.8Ge-1Hf-4.7Al-5.2Cr) and JZ3+(Nb-12.4Ti-19.7Si-5.7Ta-2.3W-5.7Sn-4.9Ge-0.8Hf-4.6Al-5.2Cr) were studied. The densities of both alloys were lower than the densities of Ni-based superalloys and many of the refractory metal complex concentrated alloys (RCCAs) studied to date. Both alloys had Si macrosegregation and the same phases in their as cast and heat treated microstructures, namely βNb5Si3, αNb5Si3, A15-Nb3X (X = Al, Ge, Si, Sn), C14-Cr2Nb and solid solution. W-rich solid solutions were stable in both alloys. At 800 °C only the alloy JZ3 did not show pest oxidation, and at 1200 °C a thin and well adhering scale formed only on JZ3+. The alloy JZ3+ followed parabolic oxidation with rate constant one order of magnitude higher than the single crystal Ni-superalloy CMSX-4 for the first 14 h of oxidation. The oxidation of both alloys was superior to that of RCCAs. Both alloys were predicted to have better creep at the creep goal condition compared with the superalloy CMSX-4. Calculated Si macrosegregation, solid solution volume fractions, chemical compositions of solid solution and Nb5Si3, weight changes in isothermal oxidation at 800 and 1200 °C using the alloy design methodology NICE agreed well with the experimental results.

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Section: Discussionmentioning

confidence: 99%

Section: Alloy Design and Selectionmentioning

confidence: 99%

On the Microstructure and Properties of Nb-12Ti-18Si-6Ta-5Al-5Cr-2.5W-1Hf (at.%) Silicide-Based Alloys with Ge and Sn Additions

2020

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“…For example, some of these alloys can have compressive yield strength of about 1800 MPa at room temperature, 1200 MPa at Materials 2020, 13, 245 2 of 37 1000 • C and 500 MPa at 1200 • C [2]. The oxidation resistance of Nb-silicide based alloys was improved dramatically when the key alloying elements Al, Cr, Si, and Ti were in synergy with other transition and refractory metals, for example Hf, Mo, and simple metal and metalloid elements, e.g., Sn [1,[3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

“…In the case of Sn, the early research [3,4] concentrated on alloys where its concentration was low to avoid the formation of the A15-Nb 3 Sn compound. In 2007, Geng et al [5] reported that the addition of Sn in the Nb-24Ti-18Si-5Al-5Cr-5Hf-5Sn-2Mo alloy (i) suppressed pest oxidation at 800 • C and (ii) improved the adhesion of the scale that formed at 1200 • C, which did not separate from the substrate, and linked the improved oxidation with Sn enrichment of the substrate below the scale where at 1200 • C the Nb 3 Sn and Nb 5 Sn 2 Si intermetallics were observed.…”

Section: Introductionmentioning

confidence: 99%

A Study of the Effect of 5 at.% Sn on the Micro-Structure and Isothermal Oxidation at 800 and 1200 °C of Nb-24Ti-18Si Based Alloys with Al and/or Cr Additions

Utton

Tsakiropoulos

2020

Materials

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This paper presents the results of a systematic study of Nb-24Ti-18Si based alloys with 5 at.% Sn addition. Three alloys of nominal compositions (at.%), namely Nb-24Ti-18Si-5Cr-5Sn (ZX4), Nb-24Ti-18Si-5Al-5Sn (ZX6), and Nb-24Ti-18Si-5Al-5Cr-5Sn (ZX8), were studied to understand how the increased Sn concentration improved oxidation resistance. In all three alloys there was macrosegregation, which was most severe in ZX8 and the primary βNb5Si3 transformed completely to αNb5Si3 after heat treatment. The Nbss was not stable in ZX6, the Nb3Sn was stable in all three alloys, and the Nbss and C14-NbCr2 Laves phase were stable in ZX4 and ZX8. The 5 at.% Sn addition suppressed pest oxidation at 800 °C but not scale spallation at 1200 °C. At both temperatures, a Sn-rich area with Nb3Sn, Nb5Sn2Si, and NbSn2 compounds developed below the scale. This area was thicker and continuous after oxidation at 1200 °C and was contaminated by oxygen at both temperatures. The contamination of the Nbss by oxygen was most severe in the bulk of all three alloys. Nb-rich, Ti-rich and Nb and Si-rich oxides formed in the scales. The adhesion of the latter on ZX6 at 1200 °C was better, compared with the alloys ZX4 and ZX8. At both temperatures, the improved oxidation was accompanied by a decrease and increase respectively of the alloy parameters VEC (Valence Electron Concentration) and δ, in agreement with the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration). Comparison with similar alloys with 2 at.% Sn addition showed (a) that a higher Sn concentration is essential for the suppression of pest oxidation of Nb-24Ti-18Si based alloys with Cr and no Al additions, but not for alloys where Al and Cr are in synergy with Sn, (b) that the stability of Nb3Sn in the alloy is “assured” with 5 at.% Sn addition, which improves oxidation with/out the presence of the Laves phase and (c) that the synergy of Sn with Al presents the “best” oxidation behaviour with improved scale adhesion at high temperature.

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“…However the Nb-Si binary composites consist of a bcc niobium solid solution, Nb 3 Si and/or Nb 5 Si 3 , and exhibit excellent creep strength but poor oxidation resistance and fracture toughness. The potential application of these composites at very high temperatures requires a balance of high creep resistance, good anti-oxidation performance, and sufficiently enough low-temperature damage tolerance or fracture toughness [4][5][6]. To achieve such a property balance, the elements such as Ti, Hf, Cr, and Al are added to the composites and the significant progress has been made in improving the properties of the materials [7][8][9][10].…”

Section: Introductionmentioning

confidence: 98%