Miscibility gap in Fe-Ni-Al and Fe-Ni-Al-Co systems

Hao, Sancun; Takayama, Takemori; Ishida, K.; Nishizawa, Tsutomu

doi:10.1007/bf02664895

Cited by 93 publications

(46 citation statements)

References 11 publications

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“…3b, c). The same features are also peculiar for multicomponent alloys and were reported for the Fe-Ni-Ta and Fe-Ni-AlTa [35] and for the Al-Fe-Ti systems [17,36] (Fig. 3d, e) on the basis of experimental data as well as by means of Fig.…”

Section: Chemical Ordering In Alloyssupporting

confidence: 64%

Phase Equilibria in Binary and Ternary Systems with Chemical and Magnetic Ordering

Witusiewicz

Bondar

Hecht

et al. 2011

J. Phase Equilib. Diffus.

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Univariant and invariant phase equilibria for systems that display second-order transformations such as chemical and magnetic ordering are arranged consistently aiming to construct complete Scheil's reaction schemes. For this purpose it is assumed that univariant phase boundaries representing second-order (or higher-order) transformations are nothing else than phase fields collapsed into infinitely thin thickness. This implies that second-order transformations can be formally treated like first-order transformations. Adequate notations and representation guidelines are proposed for the Scheil's scheme. Examples are given for binary Al-Fe and ternary Al-Fe-Ta systems using recently obtained thermodynamic descriptions.

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Section: Chemical Ordering In Alloyssupporting

confidence: 64%

Phase Equilibria in Binary and Ternary Systems with Chemical and Magnetic Ordering

Witusiewicz

Bondar

Hecht

et al. 2011

J. Phase Equilib. Diffus.

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“…Therefore, this feature reveals a possibility of a small amount of α Fe transforming to γ Fe. However, it was reported that this transformation can be suppressed by the small addition of Al [2.5 atomic percent (at.%)] in the Fe-NiAl pseudo-binary phase diagram [105]. The difference might be due to the much complex alloy systems in our study.…”

Section: B331 Phase Transformationcontrasting

confidence: 42%

Computational Design and Prototype Evaluation of Aluminide-Strengthened Ferritic Superalloys for Power-Generating Turbine Applications up to 1,033 K

Liaw¹,

Ghosh²,

Asta³

et al. 2010

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The objective of the proposed research is to utilize modern computational tools, integrated with focused experiments, to design innovative ferritic NiAl-strengthened superalloys for fossil-energy applications at temperatures up to 1,033 K. Specifically, the computational alloy design aims toward (1) a steady-state creep rate of approximately 3 x 10 -11 s -1 at a temperature of 1,033 K and a stress level of 35 MPa, (2) a ductility of 10% at room temperature, and (3) good oxidation and corrosion resistance at 1,033 K.The research yielded many outstanding research results, including (1) impurity-diffusion coefficients in α Fe have been calculated by first principles for a variety of solute species; (2) the precipitates were characterized by the transmission-electron microscopy (TEM) and analytical-electron microscopy (AEM), and the elemental partitioning has been determined; (3) a bending ductility of more than 5% has been achieved in the unrolled materials; and (4) optimal compositions with minimal secondary creep rates at 973 K have been determined. Impurity diffusivities in α Fe have been calculated within the formalisms of a harmonic transition-state theory and Le Claire nine-frequency model for vacancy-mediated diffusion. Calculated diffusion coefficients for Mo and W impurities are comparable to or larger than that for Fe self-diffusion. Calculated activation energies for Ta and Hf impurities suggest that these solutes should display impurity-diffusion coefficients larger than that for self-diffusion in the body-centered cubic Fe. Preliminary mechanical-property studies identified the alloy Fe-6.5Al-10Ni-10Cr-3.4Mo-0.25Zr-0.005B (FBB-8) in weight percent (wt.%) for detailed investigations. This alloy shows precipitation of NiAl particles with an average diameter of 130 nm.In conjunction with the computational alloy design, selected experiments are performed to investigate the effect of the Al content on the ductility and creep of prototype Fe-Ni-Cr-Al-Mo alloys. Three-point-bending experiments show that alloys containing more than 5 wt.% Al exhibit poor ductility (< 2%) at room temperature, and their fracture mode is predominantly of a cleavage type. Two major factors governing the poor ductility are (1) the volume fraction of NiAl-type precipitates, and (2) the Al content in the α-Fe matrix. A bend ductility of more than 5% can be achieved by lowering the Al concentration to 3 wt.% in the alloy.The alloy containing about 6.5 wt.% Al is found to have an optimal combination of hardness, ductility, and minimal creep rate at 973 K. A high volume fraction of precipitates is responsible for the good creep resistance by effectively resisting the dislocation motion through Orowan-bowing and dislocation-climb mechanisms. The effects of stress on the creep rate have been studied. With the threshold-stress compensation, the stress exponent is determined to be 4, indicating power-law dislocation creep. The threshold stress is in the range of 40 ~ 53 MPa. The addition of W can significantly reduce the secondary c...

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“…The results of XRD and EPMA analysis are summarized in Table 1. Note that the composition of the [6] and Jia et al [7] to yield the partial isothermal sections at 900-1200°C (Fig. 1).…”

Section: Resultsmentioning

confidence: 98%

“…3). The three-phase field [a + B2 + c], which is connected with the miscibility gap between disordered a and ordered B2-type phases, was detected [6] ; white triangles: phase compositions in diffusion couples from Jia et al [7] ; hatched-full lines: second-order phase boundaries investigated by Hao et al [6] ; hatched-dashed lines: second-order phase boundaries extrapolated from the limiting binary Fe-Al Section I: Basic and Applied Research only at 900 and 1000°C. This result confirms the assumption of Eleno et al [3] that the miscibility gap closes between 1050 and 1150°C.…”

Section: Resultsmentioning

confidence: 98%

“…[2] The most recent critical assessment of the Fe-Ni-Al phase diagram was carried out by Eleno et al [3] Isothermal sections of the Fe-Ni-Al phase diagram below 50 at.% Al were investigated long ago by Bradley [4,5] using x-ray powder diffraction and optical microscopy. Hao et al [6] later reexamined the miscibility gap in Fe-Ni-Al by a diffusion couple technique. Jia et al [7] examined the c/c¢ and c¢/B2 phase boundaries in Fe-Ni-Al, also by means of a diffusion couple method.…”

Section: Introductionmentioning

confidence: 98%

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