1. Introduction 2. The physical metallurgy of nickel and its alloys 3. Single crystal superalloys for blade applications 4. Superalloys for turbine disc applications 5. Environmental degradation: the role of coatings 6. Summary and future trends.

The Superalloys: Fundamentals and Applications

The impact resistance of composite materials — a review

Zirconates with high melting points were investigated for
application as materials for thermal barrier coatings at operating temperatures >1300°C. SrZrO3, BaZrO3, and La2Zr2O7
powders were synthesized and sintered to compacts with
various levels of porosity. The sintering results indicated a promising low-sintering activity of the investigated materials. Thermal properties of these dense materials were determined. Thermal expansion coefficients were slightly lower than those of Y2O3-stabilized ZrO2 (YSZ); thermal conductivities of SrZrO3 and BaZrO3 were comparable or slightly higher than those of YSZ. La2Zr2O7 had a lower thermal conductivity. SrZrO3 was not suitable for application as a thermal barrier coating because of a phase transition at temperatures between 700° and 800°C. Mechanical properties (hardness, fracture toughness, and Young’s modulus) of dense BaZrO3 and La2Zr2O7 samples were determined by indentation techniques and showed lower hardness and Young’s modulus compared to YSZ. BaZrO3 and La2Zr2O7 powders were optimized for application as powders for plasma spraying. Plasma-sprayed coatings were produced and characterized. Thermal cycling with a gas burner at 1200°C showed a massive attack of the BaZrO3 coating, with loss of BaO. On the other hand, the La2Zr2O7 coating showed excellent thermal stability and thermalshock behavior.

Zirconates as New Materials for Thermal Barrier Coatings

▪ Abstract The emphasis in this short review is to describe the materials issues involved in the development of present thermal barrier coatings and the advances necessary for the next generation, higher temperature capability coatings.

Materials design for the next generation thermal barrier coatings

Proprietes mecaniques de melange resines epoxyde-caoutchoucs liquides (copolymeres d'acrylonitrile et de carboxybutadiene). Mecanisme etudie par dilatometrie en etirage uniaxial

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Toughening mechanisms in elastomer-modified epoxies Part 1 Mechanical studies

The fracture behavior of a piperidine/bisphenol A diglycidyl ether (A) resin has been determined in bulk and as an adhesive using the linear elastic fracture methods developed by Mostovoy1. The effect of adding carboxy-terminated butadiene–acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy () of resin A was 120 to 150 J/m2, and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow at the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5–15% CTBN to resin A produced minute elastomer particles which increased to ∼4000J/m2 (at 15%). Further CTBN addition resulted in an elastomer–epoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elastomer–epoxy was found to be strongly dependent on the crack-tip deformation zone size (ryc) in that was a maximum when bond thickness was equal to 2 ryc. At bond thicknesses less than 2 ryc, there was a restraint on the development of the plastic zone resulting in lower values.

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

This paper reviews the hot corrosion of zirconia-based thermal barrier coatings for engine applications. Emphasis is placed on understanding the chemical reactions, and such other mechanisms as can be iden-tified, that cause corrosive degradation of the thermal barrier coating. The various approaches taken to improve the hot corrosion resistance of thermal barrier coatings are also briefly described and critiqued.

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Some Aspects of the Hot Corrosion of Thermal Barrier Coatings

Sol-gel prepared plasma spray powders of Sc2O3, Y2O3-stabilized ZrO2 (SYSZ), where the total amount of stabilizer is ∼ 7 mol. %, and the stabilizer contains 2.5–20% Y2O3, have been found to give significantly better tetragonal (t′) phase stability at 1400°C than present-day Y2O3-stabilized ZrO2 thermal barrier coating (TBC) material. The results are discussed in the context of the ongoing effort to develop ZrO2-based (or other) ceramics suitable for ultra-high temperature TBC usage.

Improved tetragonal phase stability at 1400°c with scandia, yttria-stabilized zirconia

Seven Sc2O3, Y2O3-stabilized ZrO2 (SYSZ) powders having 7 wt.% stabilizer, which was varied from 0%–100% Sc2O3, were prepared by a sol-gel process and tested for resistance to destabilization by molten NaVO3 at 700 °C and 900 °C. The Y2O3-rich SYSZ powders were destabilized by chemical reaction with the NaVO3, with YVO4 being produced, while the Sc2O3-rich powders were destabilized by a mineralization effect (no chemical reaction) by the molten NaVO3. Aging at 1400 °C for 140 hrs substantially improved the vanadate resistance of the Sc2O3-rich, but not the Y2O3-rich, SYSZ powders. The SYSZ powders stabilized by Sc2O3 plus 10%–20% Y2O3, after 1400 °C aging, showed 5–10 times better resistance to vanadate-induced destabilization than the 100% Y2O3-stabilized SYSZ powder. In addition, the Sc2O3-( 10–20%)Y2O3 powders gave less monoclinic formation, and therefore evidenced better high temperature phase stability, than the 100% Y2O3-stabilized powder during the 140 h of 1400 °C aging.

Scandia, yttria-stabilized zirconia for thermal barrier coatings

The evolution in phase composition resulting from 1400°C ageing of ZrO 2 samples stabilized by ∼4–7 mol.% each of Y 2 O 3 (YSZ), Sc 2 O 3 (ScSZ), or a mixture of Sc 2 O 3 –Y 2 O 3 (SYSZ) was studied by synchrotron radiation X-ray diffraction (SR XRD) using whole powder pattern fitting (WPPF), a recently proposed Rietveld-based method for the simultaneous refinement of phase composition and crystal microstructure. The results suggest that SYSZ has better high temperature tetragonal phase stability than the current state-of-art YSZ. For example, a plasma-sprayed coating of SYSZ (6.57 mol.%Sc 2 O 3 –1.00 mol.%Y 2 O 3 ) remained 96.7% in its original tetragonal phase (presumably t′, c / a of 1.0058) after being aged 100 h at 1400°C and then 24 h at 1480°C, whereas a 4.5 mol.% YSZ coating was transformed into two new tetragonal phases, one a low-stabilizer phase with c / a of 1.0154 (44.8%) and the other a high-stabilizer zirconia phase with c / a of 1.003 (46.5%), with some monoclinic (8.7%) formed. The phase compositions found for the various powder and coating specimens, together with information regarding lattice parameters, crystalline domain size and microstrain, also obtained by WPPF, are discussed in terms of the high-temperature phase stability of the YSZ vs SYSZ systems.

Robert L. Jones

Papers

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

Some Aspects of the Hot Corrosion of Thermal Barrier Coatings

Improved tetragonal phase stability at 1400°c with scandia, yttria-stabilized zirconia

Scandia, yttria-stabilized zirconia for thermal barrier coatings

Phase stability of scandia–yttria-stabilized zirconia TBCs