A sulfur segregation study of PWA 1480, NiCrAl, and NiAl alloys Download PDF EPUB FB2
Sulfur surface segregation was similar for PWA and NiCrAl and reached a maximum of 30 at% at to C. Above C the sulfur surface concentration decreased to about 3 at% at C.
The segregation of sulfur to the oxide-metal interface is believed to effect oxide adhesion, since low sulfur alloys exhibit enhanced adhesion. X ray Photoelectron Spectroscopy (XPS) was combined with an in situ sample heater to measure sulfur segregation in NiCrAl, PWAand NiAl : D.
Jayne and J. Smialek. Jayne, D. T., and Smialek, J. L.,“A Sulphur Segregation Study of PWANiCrAl, and NiAl Using X-ray Photoelectron Spectroscopy with In-Situ sample Heating,” Microscopy of Oxidation 2, S. Newcomb and M. Bennett, eds., Institute of Metals, London, pp.
– by: A commercial superalloy, PWAwas annealed in hydrogen at ° to ° in order to remove a 10 ppmw sulfur impurity. This treatment was very successful above °, resulting in residual sulfur contents below by: Auger electron spectroscopy (AES), low‐energy electron diffraction (LEED) and X‐ray photoelectron spectroscopy (XPS) data on the segregation of sulphur at the surface of an NiAl() single crystal and at the interface with alumina thin films are reported.
The results show that sulphur segregates at the free metallic surface. In Part II of this study, the characterization by TGA, SEM and AFM of the oxidation behavior at °C of NiAl() samples with various sulfur concentrations is reported. The formation of interfacial cavities is observed for all samples.
The simultaneous reduction of other impurities has now been reexamined for up to 20 impurity elements, in the case of five different alloys (NiCrAl, FeCrAl, PWARenand Ren N5. P.Y. Hou, K. PriimakInterfacial segregation, pore formation, and scale adhesion on NiAl alloys Oxid.
Met., 63 (), pp. CrossRef View Record in Scopus Google Scholar. Microstructure and segregation The microstructures of specimens in this study varied ition, with the P, S and Si contents in- creasing in the alloy. The amount of Laves phase precip- itating from liquid increased, especially for P-doped al- loys and Si-doped alloys, giving the alloys a tendency to.
A fundamental study was conducted on segregation behavior of alloying elements in titanium alloys to clarify the formation mechanism of "beta-flecks", melt-related defects enriched in beta stabilizing elements, which can cause a decrease in mechanical performance. Commercial titanium alloys, which are prone to the beta-fleck formation.
D.T. Jayne and J.L. Smialek, “A Sulfur Segregation Study of PWA NiCrAl and NiAl Alloys,” Microscopy of Oxidation II, ed. S.B. Newcomb and M.J.
Bennett (London: Institute of Metals, ), pp. –; also NASA TM (). Google Scholar. A sulfur segregation study of PWANiCrAl, and NiAl alloys. Article. The oxidation of Ni-Al intermetallic alloys in the beta-NiAl phase field and in the two phase beta-NiAl/gamma'-Ni3Al.
Cast nickel aluminum bronze (NAB) alloy is widely used for large engineering components in marine applications due to its excellent mechanical properties and corrosion resistance.
Casting porosity, as well as coarse microstructure, however, are accompanied by a decrease in mechanical properties of cast NAB components. Although heat treatment, friction stir processing, and fusion welding were. A recent comprehensive study of the effects of water vapor on the oxidation of PWAPWACMSX-4, aluminide coatings and CoCrAlY showed that moisture had little effect on scale growth rate, but dramatically increased the rate of spallation in cyclic tests.
In general, alloys which did not form strongly adherent scales were adversely. Segregation in cast products 9 and km is mass transfer coefficient. If R /km Ú 1, i.e. for slow solidification and/or vigorous stirring, K eff ≈ K e (Scheil’s equation).
If R /km ä 1, K eff ≈ 1, i.e. C L ≈ C O and there is almost no segregation. This is t he situation in rapid solidification. Application to. The cooling curves of these alloys were obtained by solidifying the alloy melts in a preheated graphite mold (°C, cooling rate ∼°C/s). From these the first derivate curves were plotted and used to determine the effect of the additives on the precipitation temperature of the Al-CuAl2 eutectic reaction.
these alloys. This problem is even more acute when trying to optimize the structures of cast versus wrought versions of the same alloy.
The development of such alloys as or modified alloy called PWA make use of the Nb rich phases to either control the grain size during processing or to.
However, addition of a similar amount of Ti to Ni base alloy, such as PWAdoes not have a comparable effect. Ti is known to increase the growth rate of Al 2 O 3 and has a detrimental effect on scale adherence on Ni base alloys.
For Ni–Cr alloys, on the other hand, Ti promotes Cr 2 O 3 formation. Experimental results on S segregation at growing Al 2 O 3 /alloy interfaces are reviewed for binary FeAl, NiAl alloys, and ternary alloys with additions of Cr, Pt, or a reactive element, such as Zr, Hf, or Y.
The segregation behavior is thermodynamic in nature, but the segregation energy can change not only with alloying elements but also with oxidation time and temperature as the oxide growth. The Lubrizol Corporation.
Contact. The bulk sulfur content of these 4 alloys was 36 ppm, 26 ppm, 7 ppm, and 32 ppm S, respectively. A second FeCrAl alloy with 2 ppm bulk S exhibited 1 ML of sulfur segregation. (The higher levels observed for NiCrAl and FeCrAl were associated with thick surface layers caused by Cr–C–S cosegregation effects.).
Simple-NiAl, Hf-modified-NiAl, Pt-diffused, Pt-modified-(Ni,Pt)Al +-PtAl2, and Hf-Pt-modified-(Ni,Pt)Al were cyclic oxidation tested at °C in air on Inconel substrates for up to h. Oxidation resistance is an important property for alloys to be used in power plants.
It can be qualitatively evaluated by computational thermodynamics. The microstructures of oxide scales that form on FM steels, austenitic stainless steels, and Ni-base superalloys exposed to supercritical water were evaluated by Tan and co-workers [–] by simulating the oxide phases that form at.
A method coupling electronic structure calculations with Monte Carlo simulations has been developed to determine surface compositions in Cu-Ni alloys. The calculations are based on an effective Ising model with parameters as defined within the framework of the generalized perturbation method and as calculated by means of the tight-binding version of the linear-muffin-tin-orbital method.
AbstractThis study first examined segregation behaviour in the alumina scale formed after h at °C on bare and MCrAlYHfSi-coated single-crystal superalloys with ~10 ppma La and Y. For the ba. AbstractThree dual alloy ingots were processed by electroslag remelting with A, A and A.
The compositions and inclusions of ingots were analyzed by means of various analytical techniques. The results show that the segregation becomes severer with the increase of current.
With the current increasing, the proportion of inclusions with large size, the T.[O] and sulfur content in. A correlation between sulfur and antimony grain boundary segregation has been observed on inter-granular surfaces of iron by Auger electron spectroscopy (AES).
The slope of a plot of S/Sb indicated a ratio of two antimony atoms per sulfur atom arriving at the grain boundary, while the ratio for the total S/Sb at the grain boundary was about Surface segregation and ordering of alloy surfaces in the presence of adsorbates B. Han,1 A. Van der Ven,2 G.
Ceder,1,* and Bing-Joe Hwang3 1Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MassachusettsUSA 2Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan.
Stability is an important aspect of alloys, and proposed alloys may be unstable due to unfavorable atomic interactions. Segregation of an alloy may occur preferentially at specific exposed surfaces, which could affect the alloy's structure since certain surfaces may become enriched in certain elements.
Using. fore. Although the segregation of P and S during isothermal heat treatment has been recently studied (Ref. 5), no differ-entiation between the individual roles of P and S was established.
Fu r t h e r m o r e, there has not been a systematic study of the segregation and redistribution of P and S in the weld HAZ of austenitic stain. the segregation of sulfbr to such an interface seems impr~bable.~ Furthermore, the amount of sulfur found at interfaces that appeared to have good scale-to-alloy contact could be a result of interface sweeping, where sulfur in the alloy is accumulated at the moving interface as a result of scale growth.Segregation of metalloid impurities to grain boundaries of iron and its alloys can produce brittle intergranular cracking under a variety of external conditions.
This set of phenomena is reviewed in terms of: segregation in dilute iron–metalloid binary alloys, interactions of metalloid elements with other solutes to enhance or retard segregation, the thermodynamics of segregation in binary.the equilibrium segregation and negative impact of impurities, such as Si and P in tested platinum alloys.
Bismuth can some-what neutralize the negative impact and accumulation of impurities such as Fe, Cu, Cr, Co, As and Ni.
Also, the presence of Ca, Ba and K in platinum alloys .