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DOE OSTI2020

Materials Data on Y2S3 by Materials Project

Y2S3 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. there are three inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Y–S bond distances ranging from 2.73–3.20 Å. In the second Y3+ site, Y3+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Y–S bond distances ranging from 2.76–3.01 Å. In the third Y3+ site, Y3+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Y–S bond distances ranging from 2.77–3.08 Å. There are three inequivalent S2- sites. In the first S2- site, S2- is bonded in a 6-coordinate geometry to six Y3+ atoms. In the second S2- site, S2- is bonded to five Y3+ atoms to form a mixture of distorted edge, face, and corner-sharing SY5 trigonal bipyramids. In the third S2- site, S2- is bonded to five Y3+ atoms to form a mixture of distorted edge, face, and corner-sharing SY5 square pyramids.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Y2S3 by Materials Project

Y2S3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are six inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to seven S2- atoms to form distorted YS7 pentagonal bipyramids that share corners with two YS6 octahedra, corners with two equivalent YS7 pentagonal bipyramids, edges with two equivalent YS6 octahedra, edges with six YS7 pentagonal bipyramids, and a faceface with one YS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 33–34°. There are a spread of Y–S bond distances ranging from 2.74–2.99 Å. In the second Y3+ site, Y3+ is bonded to seven S2- atoms to form distorted YS7 pentagonal bipyramids that share corners with five YS6 octahedra, edges with four YS6 octahedra, edges with four equivalent YS7 pentagonal bipyramids, and a faceface with one YS6 octahedra. The corner-sharing octahedra tilt angles range from 31–49°. There are a spread of Y–S bond distances ranging from 2.70–2.94 Å. In the third Y3+ site, Y3+ is bonded to six S2- atoms to form YS6 octahedra that share corners with four YS6 octahedra, corners with three YS7 pentagonal bipyramids, edges with three YS6 octahedra, and edges with four YS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–68°. There are a spread of Y–S bond distances ranging from 2.65–2.84 Å. In the fourth Y3+ site, Y3+ is bonded to six S2- atoms to form YS6 octahedra that share corners with four YS6 octahedra, corners with two YS7 pentagonal bipyramids, edges with three YS6 octahedra, and edges with four YS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–63°. There are a spread of Y–S bond distances ranging from 2.70–2.87 Å. In the fifth Y3+ site, Y3+ is bonded to six S2- atoms to form YS6 octahedra that share corners with four YS6 octahedra, corners with five YS7 pentagonal bipyramids, edges with four equivalent YS6 octahedra, and a faceface with one YS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 63–68°. There are a spread of Y–S bond distances ranging from 2.70–2.85 Å. In the sixth Y3+ site, Y3+ is bonded to seven S2- atoms to form distorted YS7 pentagonal bipyramids that share corners with three YS6 octahedra, corners with two equivalent YS7 pentagonal bipyramids, edges with two equivalent YS6 octahedra, edges with six YS7 pentagonal bipyramids, and a faceface with one YS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 49–51°. There are a spread of Y–S bond distances ranging from 2.74–2.95 Å. There are nine inequivalent S2- sites. In the first S2- site, S2- is bonded to four Y3+ atoms to form distorted SY4 tetrahedra that share a cornercorner with one SY5 square pyramid, corners with two equivalent SY4 tetrahedra, corners with four equivalent SY5 trigonal bipyramids, corners with four SY4 trigonal pyramids, edges with two equivalent SY5 square pyramids, edges with two equivalent SY4 tetrahedra, and an edgeedge with one SY5 trigonal bipyramid. In the second S2- site, S2- is bonded to four Y3+ atoms to form distorted SY4 trigonal pyramids that share corners with two equivalent SY5 square pyramids, a cornercorner with one SY4 tetrahedra, corners with two equivalent SY5 trigonal bipyramids, corners with eight SY4 trigonal pyramids, and edges with three equivalent SY5 trigonal bipyramids. In the third S2- site, S2- is bonded to five Y3+ atoms to form distorted SY5 trigonal bipyramids that share corners with seven SY4 trigonal pyramids, edges with four equivalent SY5 trigonal bipyramids, and edges with six SY4 trigonal pyramids. In the fourth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to four Y3+ atoms. In the fifth S2- site, S2- is bonded to five Y3+ atoms to form SY5 square pyramids that share a cornercorner with one SY4 tetrahedra, corners with seven SY4 trigonal pyramids, edges with two equivalent SY5 square pyramids, edges with two equivalent SY4 tetrahedra, edges with two equivalent SY5 trigonal bipyramids, and an edgeedge with one SY4 trigonal pyramid. In the sixth S2- site, S2- is bonded to five Y3+ atoms to form distorted SY5 trigonal bipyramids that share corners with four equivalent SY4 tetrahedra, corners with five SY4 trigonal pyramids, edges with two equivalent SY5 square pyramids, an edgeedge with one SY4 tetrahedra, edges with two equivalent SY5 trigonal bipyramids, and edges with three equivalent SY4 trigonal pyramids. In the seventh S2- site, S2- is bonded to four Y3+ atoms to form distorted SY4 trigonal pyramids that share corners with two equivalent SY5 square pyramids, corners with five SY5 trigonal bipyramids, corners with six SY4 trigonal pyramids, an edgeedge with one SY5 trigonal bipyramid, and edges with four SY4 trigonal pyramids. In the eighth S2- site, S2- is bonded to four Y3+ atoms to form distorted SY4 trigonal pyramids that share corners with two equivalent SY5 square pyramids, corners with three SY5 trigonal bipyramids, corners with six SY4 trigonal pyramids, an edgeedge with one SY5 square pyramid, edges with two equivalent SY5 trigonal bipyramids, and edges with two equivalent SY4 trigonal pyramids. In the ninth S2- site, S2- is bonded to four Y3+ atoms to form SY4 trigonal pyramids that share a cornercorner with one SY5 square pyramid, corners with three equivalent SY4 tetrahedra, corners with two equivalent SY5 trigonal bipyramids, corners with two equivalent SY4 trigonal pyramids, edges with three equivalent SY5 trigonal bipyramids, and edges with two equivalent SY4 trigonal pyramids.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Y2S3 by Materials Project

Y2S3 is Stibnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to seven S2- atoms to form a mixture of distorted edge and corner-sharing YS7 pentagonal bipyramids. There are a spread of Y–S bond distances ranging from 2.76–2.82 Å. In the second Y3+ site, Y3+ is bonded in a 7-coordinate geometry to eight S2- atoms. There are a spread of Y–S bond distances ranging from 2.83–3.35 Å. There are three inequivalent S2- sites. In the first S2- site, S2- is bonded to five Y3+ atoms to form a mixture of distorted edge and corner-sharing SY5 trigonal bipyramids. In the second S2- site, S2- is bonded to five Y3+ atoms to form a mixture of distorted edge and corner-sharing SY5 square pyramids. In the third S2- site, S2- is bonded in a 4-coordinate geometry to five Y3+ atoms.

36 MATERIALS SCIENCE↗

NASA NTRS2007

Sulfur and Moisture Effects on Alumina Scale and TBC Spallation

It has been well established that a few ppmw sulfur impurity may segregate to the interface of thermally grown alumina scales and the underlying substrate, resulting in bond degradation and premature spallation. This has been shown for NiAl and NiCrAl-based alloys, bare single crystal superalloys, or coated superalloys. The role of reactive elements (especially Y) has been to getter the sulfur in the bulk and preclude interfacial segregation. Pt additions are also very beneficial, however a similar thermodynamic explanation does not apply. The purpose of the present discussion is to highlight some observations of these effects on Rene'142, Rene'N5, PWA1480, and PWA1484. For PWA1480, we have mapped cyclic oxidation and spallation in terms of potential sulfur interfacial layers and found that a cumulative amount of about one monolayer is sufficient to degrade long term adhesion. Depending on substrate thickness, optimum performance occurs if sulfur is reduced below about 0.2-0.5 ppmw. This is accomplished in the laboratory by hydrogen annealing or commercially by melt-fluxing. Excellent 1150 C cyclic oxidation is thus demonstrated for desulfurized Rene'142, Rene'N5, and PWA1484. Alternatively, a series of N5 alloys provided by GE-AE have shown that as little as 15 ppmw of Y dopant was effective in providing remarkable scale adhesion. In support of a Y-S gettering mechanism, hydrogen annealing was unable to desulfurize these alloys from their initial level of 5 ppmw S. This impurity and critical doping level corresponds closely to YS or Y2S3 stoichiometry. In many cases, Y-doped alloys or alloys with marginal sulfur levels exhibit an oxidative sensitivity to the ambient humidity called Moisture-Induced Delayed Spallation (MIDS). After substantial scale growth, coupled with damage from repeated cycling, cold samples may spall after a period of time, breathing on them, or immersing them in water. While stress corrosion arguments may apply, we propose that the underlying cause is related to a hydrogen embrittlement reaction: Al alloy + 3 H2O = Al(OH)3 + 3H(+) + 3e(-). This mechanism is derived from an analogous moisture-induced hydrogen embrittlement mechanism originally shown for Ni3Al and FeAl intermetallics. Consequently, a cathodic hydrogen charging technique was used to demonstrate that electrolytic de-scaling occurs for these otherwise adherent alumina scales formed on Y-doped Rene'N5, in support of hydrogen effects. Finally, some TBC observations are discussed in light of all of the above. Plasma sprayed 8YSZ coatings, produced on PWA1484 without a bond coat, were found to survive more than 1000 1-hr cycles at 1100 C when desulfurized to below 0.1 ppmw. At higher sulfur (1.2 ppmw) levels, moisture sensitivity and delayed TBC failure, referred to as Desk Top Spallation, occurred at just 200 hr. Despite a large degree of scatter, a factor of 5 in life improvement is indicated for desulfurized samples in cyclic furnace tests, confirming the beneficial effect of low sulfur alloys on model TBC systems. (DTS and moisture effects are also observed on commercially applied PVD 7YSZ coatings on Rene'N5+Y with Pt-aluminide bond coats). These types of catastrophic failure were subverted on the model system by segmenting the substrate into a network of 0.010 high ribs, spaced in. apart, prior to plasma spraying. No failures occurred after 1000 cycles at 1150 C or after 2000 cycles at 1100 C, even after water immersion. The benefit is described in terms of elasticity models and a critical buckling stress.

Smialek, James L.↗