DECHEMA

About: DECHEMA is a nonprofit organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Corrosion & Oxide. The organization has 756 authors who have published 1307 publications receiving 25693 citations.

Microstructural evolution of silicon-platinum modified aluminide coatings on superalloy GTD-111

Abstract: The microstructure evolution of (Si,Pt)-modified aluminide coatings has been investigated. Coatings were prepared by slurry silico-aluminizing of different thicknesses of platinum-electroplated GTD-111 Ni-based superalloy. Microstructure and phase characterizations were conducted by means of SEM, EDX, XRD and EPMA. The composition of the coating's outer layer altered from single β-(Ni,Pt)Al phase to two phase β-NiAl + PtAl 2 by increasing the initial Pt thickness. Silicon diffusion into the coating is shown to be less in the presence of the PtAl 2 phase. Furthermore, refractory metal-containing precipitates in the outer two phase layer of the platinum modified coating were replaced by silicides in the corresponding (Si,Pt)-modified aluminide coating.

Corrosion of alloys and their diffusion aluminide coatings by KCl:K2SO4 deposits at 650 °C in air

Abstract: P91 ferritic-martensitic steel, 17Cr-13Ni and alloy 800 austenitic stainless steels and Inconel 617 alloy have been aluminised to form Fe 2 Al 5 , (Fe,Ni)Al and N1 2 A1 3 aluminide coatings. These alloys and their corresponding coatings were subjected to corrosion in air by 50:50 mol/mol K 2 SO 4 /KCl deposits at 650 °C for 300 h. With the exception of the Inconel 617 alloy, significant metal losses (>180 (Ji m) were recorded. These losses were planar for P91 alloy but involved internal corrosion for the two austenitic steels. The (Fe,Ni)Al and NiAl coatings on the austenitic steels and the Inconel 617 alloy were significantly corroded via intergranular and internal chloridation-sulphidation-oxidation. In contrast, the Fe 2 Al 5 coating on the P91 alloy coating was virtually unattacked. For the alloys, the relative extents of corrosion damage can be explained in terms of the stability and volatility of metal chlorides formed. For the coatings, STEM/EDS analyses enable clear linkages to be made between the presence and number of Cr-rich particles on coating grain boundaries and the corrosion damage observed for the coatings.

Thermochemistry and phase stability of the polymorphs of yttrium tantalate, YTaO4

Abstract: Thermodynamic parameters of the three fergusonite-related polymorphs M’, M and T of YTaO4 and their phase stabilities were investigated experimentally. The debate on the relative stability of the M and M’ phases was resolved, and it was shown that the compound does not transform to a cubic polymorph prior to melting. The enthalpies of formation of M and M’ were determined using high temperature oxide melt solution calorimetry, and the heat capacities and heat contents were measured. The enthalpy of the M’ to T phase transition was measured by differential thermal analysis. The stability of the T phase up to its melting at 2090 °C was demonstrated using high temperature X-ray diffraction and thermal analysis. Its enthalpy of fusion was determined using drop-and-catch calorimetry. The thermodynamic properties of YTaO4 assessed in this study enable the thermodynamic modeling of its polymorphs and related materials systems of technological importance.