Partitioning behavior of platinum group metals on the γ and γ′ phases of Ni-base superalloys at high temperatures

Yokokawa, Toshio; Osawa, Makoto; Nishida, Kenji; Kobayashi, Toshiharu; Koizumi, Yutaka; Harada, Hiroshi

doi:10.1016/s1359-6462(03)00437-8

Cited by 123 publications

(62 citation statements)

References 4 publications

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“…It was early reported that Ru additions induced the reverse partitioning behavior of alloying elements between the γ and γ phases and then suppressed the formation of TCP phases [7]. However, later studies provided contradictory results about the effect of Ru additions on the elemental partitioning behavior [8,15,22,23]. In the current study, increasing Ru addition from ∼ 2.5 wt.% to ∼ 4.0 wt.% decreased the partitioning ratio of those TCP-forming elements to different degrees (Fig.…”

Section: Discussionmentioning

confidence: 99%

Compositional effect on TCP phase formation in Ru-containing Ni-based single crystal superalloys

Shi

Huo

Cao

et al. 2014

MATEC Web of Conferences

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Abstract. Microstructural instability involving the formation of topologically close-packed (TCP) phases is restricted during the alloy development of Ni-based single crystal superalloys. In this study, the effects of alloying elements including Co, Cr, Mo and Ru on the formation of different TCP phases were investigated in a series of single crystal superalloys. Experimental results showed that more additions of Cr and Mo promoted the TCP phase formation, while Co and Ru played a positive role in improving microstructural stability. It is indicated that σ , P and R phases existed with various morphology and compositions in different experimental alloys during thermal exposure at 1100• C. The content of Co, Cr and Mo in those alloys affected the types of TCP phases significantly, while Ru additions showed a negligible effect. R phase was prone to form in alloys containing high level of Co addition. Meanwhile, the ratio of Cr and Mo content had strong influence on the formation of σ and P phases in alloys containing low level of Co addition. The effects of alloying additions on the elemental partitioning ratios between γ and γ phases contributed to their corresponding influence on TCP phase formation.

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Section: Discussionmentioning

confidence: 99%

Compositional effect on TCP phase formation in Ru-containing Ni-based single crystal superalloys

Shi

Huo

Cao

et al. 2014

MATEC Web of Conferences

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“…These observations indicate that the contributions of Cr and Ru in solution strengthening are very small, although Cr and Ru are respectively effective elements in improving oxidation resistance and in suppressing TCP formation by expanding the solubility limit [10,15]. Ru also makes a small contribution to increasing creep-rupture life by changing the lattice misfit toward a negative value by the partitioning of Ru in the  phase.…”

Section: Resultsmentioning

confidence: 99%

Quantitative Analysis of Creep Strengthening Factors in Ni-base Single Crystal Superalloys

Yokokawa¹,

Harada²,

Kawagishi³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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Ni-base single-crystal (SC) superalloys with superior mechanical properties are being developed to improve the thermal efficiency of jet engines and land-based gas turbines. In this study, we investigate the relationships among alloy compositional factors, structural factors, and the creep-rupture life of Ni-base SC superalloys by multi-regression analysis with creep-tested data for 75 alloys. We also obtain three equations to predict creep-rupture lives at 900 ºC/392 MPa, 1000 ºC/245 MPa, and 1100 ºC/137 MPa with excellent multi-correlation coefficients from 0.94 to 0.98. The ' phase composition, ' volume fraction, and lattice misfit were used as explanatory variables. The regression coefficients of the refractory elements including W, Ta, and Re were comparatively large at 900 ºC/392 MPa and they decreased with an increase in temperature and decrease in stress. The coefficient for negative lattice misfit increased at higher temperatures and lower stresses, especially at 1100 ºC/137 MPa. The coefficient of Ru showed a small value for all the conditions in this study. Consequently, it is clear that solution strengthening is effective in the lower-temperature and higher-stress regions, and that a larger negative misfit leads to a quicker formation of the rafted /' structure with a finer interfacial dislocation network. The finer dislocation network assures superior creep resistance by preventing glide dislocation from cutting the rafted /' structure. The addition of Ru in alloys is effective in suppressing topologically close packed (TCP) phases formation by expanding the solubility limit. The lattice misfit shifts toward a slightly negative value with the addition of Ru, but this effect was small with respect to the enhancement of creep strength.

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“…For example, adding Mo to third generation alloys deteriorates their oxidation resistance because of the formation of Mo oxide, which is more prone to volatilization. In addition, each alloying element, consisting of Ni-base superalloys, has a different partition behavior [24], which would also affect the initial oxidation resistance of Ni-base superalloys. The complexity of the alloy composition of Ni-base superalloys increases the difficulty in estimating the oxidation behavior of current Ni-base superalloys with conventional Ni-AlCr ternary diagrams [8].…”

Section: Discussionmentioning

confidence: 99%

Prediction of Initial Oxidation Behavior of Ni-base Single Crystal Superalloys: A New Oxidation Map and Regression Analysis

Suzuki¹,

Kawagishi²,

Yokokawa³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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Predictions for oxidation behavior of Ni-base superalloys are becoming increasingly difficult because of the complex alloy composition. In this study, we focus on the initial oxidation behavior of Ni-base superalloys, and suggest a new oxidation map with using Al and Cr chemical potentials to distinguish the initial oxide type of Ni-base superalloys with seventy binary, ternary, and multicomponent Ni-base single crystal superalloys at 1100 °C. As a comparison of observed and calculated weight changes after one cycle at 1100 °C obtained by a regression analysis, seventy alloys demonstrated two distinct behaviors, which are divided heretofore into group A and group B. Microstructural observation revealed that an oxide layer in the group A alloys consists of Al 2 O 3 and/or spinel or complex oxide, whereas an oxide layer in the group B alloys consists of a thick NiO layer with an Al 2 O 3 internal subscale. Thermodynamic properties can reflect more effects of alloy elements in Ni-base superalloys, and Al and Cr activities, calculated by Thermo-Calc, were used as factors to distinguish the type of initial oxides. Group A and B alloys can clearly be divided according to Al and Cr activities. This was suggested as a new oxidation map to distinguish the initial oxide type of Ni-base superalloys, and possibly it can apply for any generation of Ni-base superalloys. In addition, empirical equations obtained from regression analysis were suggested to be used for predicting the weight change of alloys after one cycle at 1100 °C, and these could also be applied to all generations of Nibase superalloys. One equation exhibited excellent agreement between observed and calculated weight changes. The alloys that were applicable for this equation therefore had a compositional dependence.

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Partitioning behavior of platinum group metals on the γ and γ′ phases of Ni-base superalloys at high temperatures

Cited by 123 publications

References 4 publications

Compositional effect on TCP phase formation in Ru-containing Ni-based single crystal superalloys

Compositional effect on TCP phase formation in Ru-containing Ni-based single crystal superalloys

Quantitative Analysis of Creep Strengthening Factors in Ni-base Single Crystal Superalloys

Prediction of Initial Oxidation Behavior of Ni-base Single Crystal Superalloys: A New Oxidation Map and Regression Analysis

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