scholarly journals 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

Materials ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 245 ◽  
Author(s):  
Zhen Xu ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Design Methodology ◽  
Isothermal Oxidation ◽  
Oxidation Behaviour ◽  
Laves Phase ◽  
Valence Electron Concentration ◽  
Micro Structure ◽  
Scale Spallation ◽  
Intermetallic Composite ◽  
The Stability ◽  
Al Additions

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.

scholarly journals On the Microstructure and Isothermal Oxidation at 800 and 1200 °C of the Nb-24Ti-18Si-5Al-5Cr-5Ge-5Sn (at.%) Silicide-Based Alloy

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 722 ◽  
Author(s):  
Ofelia Hernández-Negrete ◽  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Oxidation Resistance ◽  
Volume Fraction ◽  
Coefficient Of Thermal Expansion ◽  
Cast Alloy ◽  
Isothermal Oxidation ◽  
Valence Electron Concentration ◽  
Scale Spallation ◽  
Substrate Interface ◽  
Oxidation In Air

The research presented in this paper aspired to understand how the simultaneous addition of Ge and Sn in an Hf-free Nb-silicide-based alloy affected its oxidation resistance. Results are presented for the Nb-24Ti-18Si-5Al-5Cr-5Ge-5Sn alloy (at.%) which was studied in the as-cast and heat-treated (1400 °C/100 h) conditions and after isothermal oxidation in air at 800 and 1200 °C. There was macrosegregation in the cast alloy, in which the Nbss formed at a low volume fraction and was not stable after heat treatment at 1400 °C. The βNb5Si3, A15-Nb3Sn, and C14-NbCr2 were stable phases. The alloy did not undergo pest oxidation at 800 °C, and there was no spallation of its scale at 1200 °C. There was enrichment in Ge and Sn in the substrate below the scale/substrate interface, where the compounds Nb3Sn, Nb5Sn2Si, (Ti,Nb)6Sn5, and Nb5Ge3 were formed. After the oxidation at 1200 °C, the solid solution in the bulk of the alloy was very Ti-rich (Ti,Nb)ss. Improvement of oxidation resistance at both temperatures 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). The elimination of scale spallation at 1200 °C was attributed (a) to the formation of Ti-rich (Ti,Nb)ss solid solution and (Ti,Nb)6Sn5, respectively, in the bulk and below the scale, (b) to the low concentration of Cr in the scale, (c) to the absence of GeO2 in the scale, (d) to the formation of αAl2O3 in the scale, and (e) to the presence (i) of Nb5Ge3 below the scale/substrate interface and (ii) of oxides in the scale, namely, SiO2, Al2O3, TiO2, and SnO2, and Ti2Nb10O29,TiNb2O7, and AlNbO4, respectively, with a range of intrinsic thermal shock resistances and coefficient of thermal expansion (CTE) values that reduced stresses in the scale and the substrate below it.

scholarly journals Effective Design of Cr-Co-Ni-Ta Eutectic Medium Entropy Alloys with High Compressive Properties Using Combined CALPHAD and Experimental Approaches

2021 ◽  
Vol 11 (13) ◽  
pp. 6102
Author(s):  
Taiwen Huang ◽  
Jiachen Zhang ◽  
Jun Zhang ◽  
Lin Liu
Keyword(s):  
Solid Solution ◽  
Plastic Strain ◽  
Compression Strength ◽  
Volume Fraction ◽  
Laves Phase ◽  
Valence Electron Concentration ◽  
Solid Solution Strengthening ◽  
Binary Diagram ◽  
High Plastic Strain ◽  
The Stability

Alloy design of Cr-Co-Ni-Ta eutectic medium entropy alloys (EMEAs) was performed through a CALPHAD method coupled with experimental study, with the aim to attain high phase stability as well as excellent mechanical properties. Based on calculated pseudo-binary diagram, CrCoNiTax (x = 0.1, 0.3, 0.4, 0.5, 0.7) medium entropy alloys were investigated. Two phases, FCC solid solution and Laves phase, were identified in the alloys. With increasing Ta content, the volume fraction of hard and brittle Laves phase increased, microstructure changed from hypoeutectic (Ta0.1, Ta0.3) to eutectic (Ta0.4) and then to hypereutectic (Ta0.5, Ta0.7). The stability of phases was assessed by considering the thermodynamic parameter Ω and valence electron concentration (VEC). The eutectic phases become stable when 1.42 < Ω < 0.74 and 7.5 < VEC < 8.25. In addition, based on nanoindentation, the results indicated that solid solution strengthening in γ phase was significantly enhanced, eutectic phase in CrCoNiTa0.4 EMEA was found to process the highest microhardness and elastic modulus. Finally, the hardness of alloys was positively correlated with the content of Ta and the plastic strain of alloys obviously decreased, while the compression strength firstly increased and then decreased. CrCoNiTa0.4 was the most promising alloy with the highest compression strength (2502 MPa) and high plastic strain (20.6%).

scholarly journals Refractory Metal (Nb) Intermetallic Composites, High Entropy Alloys, Complex Concentrated Alloys and the Alloy Design Methodology NICE—Mise-en-scène † Patterns of Thought and Progress

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 989
Author(s):  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Refractory Metal ◽  
Design Methodology ◽  
Alloy Design ◽  
High Entropy Alloys ◽  
Laves Phases ◽  
High Entropy ◽  
High Temperature Materials ◽  
Mise En Scene ◽  
Intermetallic Composite

The paper reflects on the usefulness of the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration) for the development of new Nb-containing metallic ultra-high-temperature materials (UHTMs), namely refractory metal (Nb) intermetallic composites (RM(Nb)ICs), refractory high entropy alloys (RHEAs) and refractory complex concentrated alloys (RCCAs), in which the same phases can be present, specifically bcc solid solution(s), M5Si3 silicide(s) and Laves phases. The reasons why a new alloy design methodology was sought and the foundations on which NICE was built are discussed. It is shown that the alloying behavior of RM(Nb)ICs, RHEAs and RCCAs can be described by the same parameters. The practicality of parameter maps inspired by NICE for describing/understanding the alloying behavior and properties of alloys and their phases is demonstrated. It is described how NICE helps the alloy developer to understand better the alloys s/he develops and what s/he can do and predict (calculate) with NICE. The paper expands on RM(Nb)ICs, RHEAs and RCCAs with B, Ge or Sn, the addition of which and the presence of A15 compounds is recommended in RHEAs and RCCAs to achieve a balance of properties.

Effect of the Superalloy Composition on the Isothermal Oxidation Behaviour of TBC Systems

2013 ◽  
Vol 81 (1-2) ◽  
pp. 57-67 ◽  
Author(s):  
Marion Chieux ◽  
Cécilie Duhamel ◽  
Régine Molins ◽  
Luc Rémy ◽  
Jean-Yves Guédou
Keyword(s):  
Isothermal Oxidation ◽  
Oxidation Behaviour ◽  
Tbc Systems

Isothermal Oxidation of René N5 at 1150°C

2018 ◽  
Author(s):  
Megan Walker ◽  
Xiao Huang
Keyword(s):  
Single Crystal ◽  
Exposure Time ◽  
Bond Coat ◽  
Isothermal Oxidation ◽  
Oxidation Behaviour ◽  
Single Crystal Superalloy ◽  
Short Term ◽  
Alumina Layer ◽  
Spinel Layer ◽  
Oxide Spallation

In this study, single crystal superalloy René N5 was exposed in air at 1150 °C for up to 16 hours to evaluate the alloy’s short-term oxidation behaviour and the potential for developing a no-bond coat TBC system. The results showed that after 1 hour of exposure, a three layered oxide developed on the surface, consisting of spinel, Ta-containing oxide and alumina just above the substrate. After 4 hours of exposure, oxide spallation occurred; this became more pronounced after 16 hours. The oxide spallation took place between the top spinel layer and alumina layer, where Ta-rich oxide was more abundant. All samples tested for 0.5, 1, 2, 4 and 16 hours developed alumina near the substrate while the occurrence of NiO, spinel and Ta-oxides varied, depending upon the exposure time.

scholarly journals Isothermal Oxidation Behaviour of NiCoCrAlYTa Coatings Produced by HVOF Spraying and Tribomet™ Process

2013 ◽  
Vol 81 (1-2) ◽  
pp. 105-113 ◽  
Author(s):  
Raphaël Goti ◽  
Marie Bétaille-Francoual ◽  
Elodie Hourcastagné ◽  
Bernard Viguier ◽  
Fabrice Crabos
Keyword(s):  
Isothermal Oxidation ◽  
Oxidation Behaviour ◽  
Hvof Spraying

Commitment among adjunct faculty

2020 ◽  
Vol 12 (5) ◽  
pp. 1209-1220
Author(s):  
Heidi Reeder
Keyword(s):  
Adjunct Faculty ◽  
Self Efficacy ◽  
Design Methodology ◽  
Predictive Power ◽  
Adjunct Instructors ◽  
Content Type ◽  
Part Time ◽  
Time Position ◽  
The Stability ◽  
Practical Implications

PurposeWithout the stability of tenure, adjunct faculty have few barriers to leave their position. The purpose of this article is to understand the variables that predict commitment among adjunct instructors.Design/methodology/approachThis paper statistically analyzed data from a survey completed by adjunct instructors at two 4-year universities. The survey included scales on commitment, satisfaction, investments, alternatives and the psychological concepts of grit and self-efficacy. In addition, a qualitative analysis was conducted on supplemental open-ended questions that allowed participants to describe the basis of their commitment.FindingsSatisfaction and investments were the main predictors of commitment and those together accounted for just over 50 percent of the variance. Grit and self-efficacy did not correlate with commitment, but did correlate with satisfaction and investments.Practical implicationsGiven the predictive power of satisfaction to explain commitment, understanding the specific rewards and costs experienced by this population can give administrators ideas for making the part-time position more appealing. Similarly, given the predictive power of investments, administrators might consider identifying avenues for adjunct faculty to contribute to the department and university in a meaningful and rewarding way.Originality/valueUniversities are increasingly dependent on adjunct instructors, so it is worthwhile to understand the experience of such faculty. This is best done through research, rather than relying on assumptions, stereotype or anecdotes.

Towards greater supply chain stability

2019 ◽  
Vol 35 (6) ◽  
pp. 33-35
Keyword(s):  
Supply Chain ◽  
Design Methodology ◽  
Bullwhip Effect ◽  
Global Supply Chain ◽  
Global Supply Chains ◽  
Content Type ◽  
Pertinent Information ◽  
The Stability ◽  
Practical Implications ◽  
Chain Increase

Purpose This paper aims to review the latest management developments across the globe and pinpoint practical implications from cutting-edge research and case studies. Design/methodology/approach This briefing is prepared by an independent writer who adds their own impartial comments and places the articles in context. Findings Building a regional rather than a global supply chain can help firms guard against the damaging impact of the bullwhip effect and increase the stability of their supply chain. The possibility of better communication, greater flexibility, and ability to respond more quickly are factors that can appease the bullwhip severity. The benefits of a regional supply chain increase further in times of economic certainty, when the risk to global supply chains intensifies. Originality/value The briefing saves busy executives and researchers hours of reading time by selecting only the very best, most pertinent information and presenting it in a condensed and easy-to-digest format.

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

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3719
Author(s):  
Jiang Zhao ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Design Methodology ◽  
Isothermal Oxidation ◽  
Chemical Compositions ◽  
Weight Changes ◽  
Parabolic Oxidation ◽  
Goal Condition ◽  
Heat Treated ◽  
Order Of Magnitude ◽  
Solution Volume

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.

Isothermal Oxidation Behavior of a New Directionally Solidified Ni-Base Superalloy in Air at Different Temperature

2010 ◽  
Vol 654-656 ◽  
pp. 538-541
Author(s):  
Lei Wang ◽  
Yan Huang ◽  
Zhuo Zhao ◽  
Yang Liu ◽  
Jian Tao Wu ◽  
...  
Keyword(s):  
Oxidation Resistance ◽  
Oxidation Behavior ◽  
Isothermal Oxidation ◽  
Oxidation Behaviour ◽  
Diffusion Activation Energy ◽  
Directionally Solidified ◽  
Temperature Range ◽  
Parabolic Law ◽  
Diffusion Activation ◽  
Base Superalloy

The isothermal oxidation behaviour under static atmosphere of a new directionally solidified Ni-base superalloy was investigated. The results showed that the oxidation kinetics curves of the alloy follow parabolic law in the temperature range of 750-950°C. The diffusion activation energy Q is to be about 244.86 kJ•mol-1 and the oxidation within this temperature range is mainly controlled by Cr3+ diffusion among Cr2O3 oxidation film. The oxidation resistance grade of the alloy is perfect anti-oxidation within 750-850°C, and anti-oxidation within 900-950°C. The oxidation film can be divided into TiO2, Cr2O3+TiTaO4+NiCr2O4, Al2O3 and TiN layers, from the surface to inside. Priority oxidation and the inside oxidation of Al are considered with the oxidation of Ti and the depletion of Cr, and it is the key point for the improving of oxidation resistance.

Sign in / Sign up

Export Citation Format

Share Document