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Solid particle erosion (SPE) is a common phenomenon observed in gas turbine engines. Particles entrained in the gas flow impact engine hardware, resulting in micro-scale damage that leads to deleterious effects such as material removal. For protective coatings, damage due to SPE is a key concern, since it can negatively affect the durability of the coating and subsequently the life of the underlying component. In this work, the high-temperature SPE behavior of two state-of-the-art environmental barrier coatings (EBCs) deposited via air plasma spray (APS) is investigated using alumina erodent to understand the effect of particle kinetic energy, impingement angle, and temperature. The SPE behavior of the EBCs is also compared to APS and electron beam–physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs) to elucidate similarities and differences in the erosion response. The EBCs were more susceptible to SPE than the EB-PVD TBC but had greater SPE resistance compared to the APS TBC. Coating microstructure and porosity were shown to have a strong influence on the observed behavior. [ABSTRACT FROM AUTHOR]

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The erosion behavior of N720/Alumina oxide/oxide composite was investigated under a combustion environment to better represent particle ingestion of a jet engine. The effect of particle velocity, particle size, temperature and impingement angle were investigated. In addition, room temperature studies were also conducted for comparison. Eroded sites were investigated using optical and scanning electron microscopy to understand the extent of erosion and erosion mechanisms. The results indicate that erosion rate increased with an increase in particle velocity and particle size. Also, erosion rate increased from room temperature to 815 °C and then decreased from 815 °C to 1200 °C. Brittle fracture is the predominant mode under normal impacts and as the impact angle is decreased increased ploughing/wear is evident. [ABSTRACT FROM AUTHOR]

In this work, the kinetic behaviors and thermodynamic characteristics of aged refuse (AR) and municipal solid waste (MSW) under distinguishing conditions (blending ratios, heating rates, oxygen concentrations) had been investigated. Combining a low proportion of AR would promote the combustion of MSW, and 10%AR presented the best activation energy Eexp (166.62 kJ/mol). For the 10%AR, the heating rate of 40°C/min can reach the best comprehensive combustibility S (29.14%2°C−3min−2) and the burning temperature range had increased to 270.6°C727.6°C. When the oxygen concentration changed from 10% to 30%, the residual mass Mf dropped from 29.52% to 14.24%. This paper proposes a recycling strategy of AR by mixing combustion with MSW. [ABSTRACT FROM AUTHOR]

An environmental barrier-coated Sylramic-iBN/pyrolytic carbon/chemical vapor infiltration silicon carbide ceramic matrix composite was characterized in a harsh combustion environment under two conditions; (i) with a coating surface temperature of 1480℃, and (ii) with a combustion flame distance of 120 mm (constant flux). Three coating systems were evaluated; Coating “A” (ytterbium silicate using hafnium–silicate bond), Coating “B” (ytterbium silicate using alumina bond), and Coating “C” (ytterbium–silica compounds using alumina bond). All three coatings survived with essentially no mass loss up to 25 h when tested at 1480℃. At a flame distance of 120 mm coatings “A” and “B” experienced extensive degradation and strength loss while coating “C” had practically no degradation in retained strength. Coating “C” outperformed the other two coatings exposed to the harsh combustion environment. It performed best in terms of material loss, thermal barrier capability, and residual tensile strength. [ABSTRACT FROM AUTHOR]

Early stage oxidation behavior of SiSiC cellular lattices with different cell types was studied at 1400 °C in two different environments: a porous burner and an electric furnace with stagnant air. Oxidation and silicon alloy bead formation were observed and identified as the most important factors affecting the integrity of the structures. Low melting temperature silicon-based alloys formed from the material due to presence of impurities. Having lower melting point than the thermal tests temperature, the beads exuded from the microstructure leaving pores in the substrate material and leading to enhanced oxidation on the surface. Moreover, it was observed that different lattice architectures lead to different oxidation behavior on the struts as a result of the changing gas flow paths inside each ceramic architecture. [ABSTRACT FROM AUTHOR]

Abstract: The monotonic tension and creep loading behavior of single crystal nickel-base superalloy, CMSX-486 was investigated at 1093°C under ambient laboratory and simulated combustion environments. There was degradation in tension and creep performance under combustion environment. A reduction of about 30% in yield strength and ultimate tensile strength and 75% reduction in strain-to-failure were observed in combustion environment relative to laboratory environment. The creep rupture life reduced in combustion environment in comparison to laboratory environment. The creep rupture occurred at a lower strain level in the combustion environment when compared to laboratory environment. The laboratory environment tested specimens experienced higher % neck area reduction, exhibiting more ductility relative to the combustion tested specimens. The mass loss in combustion environment was about 3 times larger than in laboratory environment. The microstructure showed different distribution patterns of γ/γ′ phases. The combustion environment resulted in relatively more contiguous regions of γ phase which presented favorable condition for faster propagation of defects resulting in creep rupture over shorter time span. The subcritical crack growth regions on the fracture surface of the laboratory environment tested specimens were relatively much rougher with more number of craters/voids resulting in longer creep rupture life. [Copyright &y& Elsevier]

Ferritic - martensitic steels are of high interest as superheater materials or as materials for interconnectors in solid oxide fuel cells. In comparison to austenitic steels and nickel base alloys they offer much better heat transfer behaviour and a lower coefficient of thermal expansion, as well as lower costs. Modern 9% Cr-steels have sufficient creep strength however their corrosion resistance particularly in H2O containing oxidising environments (e.g. up to 25% H2O in the combustion of biomass or the oxyfuel process) needs further improvement. A large number of studies have shown that the corrosion resistance of 9% Cr-steels in water vapour containing combustion environments is inferior to that in dry atmospheres, due to the formation of a volatile Cr-species of the type CrO2(OH)2. This investigation starts from the idea of a shift of partial pressure of CrO2(OH)2 to lower values if the solid oxide phase on the alloy surface is a manganese - chromium - spinel scale, so that at 630°C the formation of volatile chromium species can be suppressed. Therefore, the metal subsurface region was enriched with manganese and chromium via a diffusion coating (pack cementation) to promote the formation of Cr - Mn - spinel during oxidation. In the course of the project it was observed that the diffusion treatment can lead to the formation of a chromium carbide surface layer. The surface treated alloys show extreme stability under oxidising water vapour containing environments, as illustrated by oxidation exposures in a simulated combustion environment (N2+1%O2+10%H2O) at 650°C for 800 h. [ABSTRACT FROM AUTHOR]

Abstract: Performance of three kinds of continuous fiber reinforced SiC matrix composites prepared by chemical vapor infiltration (CVI) method, i.e. 2D C/SiC, 3D C/SiC and 3D SiC/SiC composites, have been investigated in the high temperature combustion environment gas with various creep stresses. The relationship between the life time of composite and the normalized peak strength, defined by the ratio of the test stress to the material strength, was studied. The life time of composites decreased with increasing the normalized peak strength following an exponential relationship. The oxidation resistance of the SiC/SiC composite was the best and that of the 2D C/SiC composite was the worst in the high temperature combustion environment with an applied stress. The experimental results suggested that there was a critical normalized peak strength which controls the oxidation mechanism of C/SiC. Below the critical normalized peak strength, the degradation of C/SiC in the combustion environment was controlled by the diffusion of oxygen and water vapor through the cracks in the composite. Above the critical normalized peak strength, the degradation was controlled by the oxidation of C fibers. [Copyright &y& Elsevier]