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The oxidation behavior of alloy 625 and 120 foils was studied at 650, 700 and 800 $$^\circ$$ C in dry air and flowing air + 10% H $$_2$$ O up to 10,000 h (alloy 625) or 30,000 h (alloy 120). The effect of water vapor on Cr loss was investigated. Manganese and iron in the 120 foil induced faster Cr depletion in the foil and breakdown of the Cr $$_2$$ O $$_3$$ scale into Fe and Cr-rich oxide compared to the alloy 625 foil. In the latter case, the presence of Nb led to the formation of Nb and Cr-rich oxide after breakdown of the Cr $$_2$$ O $$_3$$ scale. Simultaneous Cr loss due to oxidation and volatilization of the Cr $$_2$$ O $$_3$$ oxide scale was predicted and compared to experimental Cr loss measurements for exposures up to 30,000 h.

Oxide dispersion strengthened (ODS) FeCrAl alloy (Fe-12Cr-5Al wt%) was neutron irradiated to 1.8 displacements per atom (dpa) at 215, 357, and 557 °C to investigate (Y,Al,O) nano-oxide stability and Cr-rich α′ precipitate formation using atom probe tomography. The nano-oxide sizes remain unchanged after irradiation, but the compositions are dependent on irradiation temperature due to competition between ballistic dissolution and precipitate reformation. Cr-rich clusters observed after 357 °C irradiation have lower Cr contents (61 at.%) than equilibrium α′, with a lower number density than wrought FeCrAl alloys. This suggests a suppression of α′ precipitation due to the high sink strength of ODS FeCrAl.

Surface reliefs due to phase transformations in a 56.8Ni-5.6Pt-37.6Al at. pct alloy were characterized in situ using digital holographic imaging during thermal cycling from room temperature up to 405 K (132 °C). The 3D images of the surface revealed that the austenite plates formed during heating are exactly the same for each cycle, which is not the case for the martensite plates formed during cooling. The martensite start temperature was found to vary by up to ~ 20 K from one grain to another within the same specimen. The absence of Ni3Al γ′ precipitates, due to the relatively high Al content, results in the propagation of the martensitic transformation over grains up to a millimeter in size. Bright-field optical imaging showed the formation of large martensite plates in some grains, with cracks perpendicular to these plates, upon cycling. Cracks were also observed at grain boundaries and could be related to the height variations across the grain boundaries.

Low-Cr oxide dispersion strengthened (ODS) FeCrAl alloys were developed as accident tolerant fuel cladding because of their excellent oxidation resistance at very high temperature, high strength and improved radiation tolerance. Fe-12Cr-5Al wt.% gas atomized powder was ball milled with Y2O3+FeO, Y2O3+ZrO2 or Y2O3+TiO2, and the resulting powders were extruded at 950 °C. The resulting fine grain structure, particularly for the Ti and Zr containing alloys, led to very high strength but limited ductility. Comparison with variants of commercial PM2000 (Fe-20Cr-5Al) highlighted the significant impact of the powder consolidation step on the alloy grain size and, therefore, on the alloy mechanical properties at T

Increasing peak cylinder pressures and operating temperatures of turbo-charged internal combustion engines (ICEs) engines present new challenges for existing materials employed in engine exhaust valves. Oxidation induced degradation of current Ni based alloys for these components will be a life-limiting mechanism while strict cost margins in the automotive transportation industry further limit the choice of suitable candidate materials. Metallic diffusion aluminide coatings can provide a cost-effective way to improve the oxidation resistance of underlying materials. In this study, the high temperature oxidation behavior of diffusion nickel aluminide coatings on two Ni based alloys (commercially available alloy 31V and a developmental alloy) during cyclic oxidation behavior in air+10% H2O at 900 °C was investigated. A complete depletion of the beneficial Al-rich β-(NiFe)Al phase was observed in the coating on alloy 31V while a significant fraction of this phase was retained in the coating on the second alloy. A coupled thermodynamic-kinetic model showed that the disappearance of the Al-rich phase in the coating on 31V was mainly due to the combined effect of steeper chemical potential gradients of Al and Ti between the coating and the substrate and their faster diffusivities compared to the coated developmental alloy. A higher content of Fe was shown to support the retention of β-(NiFe)Al phase in the coating on the developmental alloy while the presence of Ti in the alloy was shown to be detrimental for long-term coating performance.

A new test rig was developed to conduct creep evaluation in steam. The isothermal creep performance for ferritic 9Cr and ferritic/martensitic Gr.91 steels was superior at 650 °C in steam than in air. Microstructure characterization revealed the presence of an adherent and continuous (Fe,Cr)-rich inner oxide layer because of crack healing by re-oxidation. Stress calculation based on a composite structure showed that the longer lifetimes in steam were likely due a transfer of load from the alloy to the inner scale. However, a significant decrease of the Gr91 creep lifetime was observed in steam at 650 °C when the specimens were thermally cycled every 10 h. This could be explained by localized cracking of the load-bearing inner layer.

s Burst behavior of austenitic and ferritic Fe-based alloy tubes has been examined under a simulated large break loss of coolant accident. Specifically, type 304 stainless steel (304SS) and oxidation resistant FeCrAl tubes were studied alongside Zircaloy-2 and Zircaloy-4 that are considered reference fuel cladding materials. Following the burst test, characterization of the cladding materials was carried out to gain insights regarding the integral burst behavior. Given the widespread availability of a comprehensive set of thermo-mechanical data at elevated temperatures for 304SS, a modeling framework was implemented to simulate the various processes that affect burst behavior in this Fe-based alloy. The most important conclusion is that cladding ballooning due to creep is negligible for Fe-based alloys. Thus, unlike Zr-based alloys, cladding cross-sectional area remains largely unchanged up to the point of burst. Therefore, for a given rod internal pressure, the temperature onset of burst in Fe-based alloys appears to be simply a function of the alloy's ultimate tensile strength, particularly at high rod internal pressures.

The effects of surface roughness on the high-temperature corrosion of nickel-based superalloy X produced through electron-beam melting (EBM) additive manufacturing were studied. Surface area of samples in the rough, as-fabricated condition was measured using a 2D cross-section image analysis technique and a 3D image analysis technique. To verify the accuracy of surface area measurements, oxidation testing of samples in the as-fabricated and polished conditions was performed; polished sample oxidation curves were then compared to the as-fabricated sample oxidation curves before and after being adjusted using obtained surface area measurements. It was found that the 2D technique accurately measured surface area and accounted for the overlapping features present on EBM sample surfaces, whereas the 3D technique did not. Further, it was also observed that oxidation kinetics were moderately faster on the alloy X samples in the as-fabricated condition than for the polished condition.

We have previously reported (Boatner et al., J. Alloys Compd. 691 (2017) 666–671) on the discovery, formation, processing, and application of a new decorative ternary steel. alloy and on its use in a wide range of practical applications including: custom and commercial knives, art objects, jewelry, electronics, and furniture. This decorative property results when polished single crystals of the 70 wt%Fe-15 wt%Ni-15 wt% Cr austenitic alloy are cryo-quenched into the martensitic phase resulting in the formation of a three-dimensional raised pattern of mixed austenitic/martensitic laths. These laths propagate across large dimensions of the material due to the absence of grain boundaries in the single crystal. The macroscopic optically reflective 3-D decorative pattern reproduces the structural symmetry inherent in the single-crystal orientation. This pattern results solely from the metallurgical phase properties of the ternary alloy and is completely distinct from the properties of Damascus steels or more modern so-called pattern-welded steels. Here we use X-ray diffraction, nanoindentation, hardness measurements/scratch testing, tribological measurements, and alloy resistivity and magnetization methods to obtain a more fundamental and comprehensive study of the effects of the austenitic/martensitic phase transition on the structural and physical properties of the 70 wt%Fe-15 wt%Ni-15 wt% Cr alloy. These results reveal new insight into irreversible phenomena that are associated with the inhibited phase transition on heating of the two-phase, mixed austenitic/martensitic structure that is formed subsequent to cryo-quenching the alloy crystal to 77 K.

Oxide dispersion strengthened (ODS) FeCrAl alloys are promising candidate materials for advanced nuclear reactor applications requiring high-temperature strength, corrosion resistance, and irradiation tolerance. As these alloys have increased in compositional complexity through attempts to use highly reactive elements such as Zr to refine particle sizes and optimize nanoprecipitate dispersion characteristics, much debate has ensued as to the effects of these alloying element additions on alloy properties. In an attempt to reconcile differences in nanoprecipitate distributions reported in the literature over the past decade, a detailed investigation of a recently developed ODS FeCrAl alloy with nominal composition Fe–10Cr-6.1Al-0.3Zr+0.3Y2O3 is presented using a combination of atom probe tomography (APT), scanning/transmission electron microscopy (S/TEM), and computational thermodynamics modeling. It is illustrated that based on the amount of Zr available in the lattice, Zr competes with Al and Cr to form carbides and nitrides as opposed to oxygen-rich precipitates. This alloy system has a high number density (>1023 m−3) of ∼2–4 nm diameter (Y,Al,O)-rich nanoprecipitates, but it is shown that due to the compositional spread and unknown partitioning of Al between the matrix and precipitates, significant challenges still exist for quantifying the exact compositions of these precipitates using APT. However, the noted compositional spread is supported by identified complex oxides yttrium aluminum monoclinic (YAM) and yttrium aluminum garnet (YAG) using S/TEM. As a result of these findings, researchers developing ODS FeCrAl with reactive element additions must pay careful attention to C and N impurities when optimizing reactive element additions.

The electron beam melting (EBM) process is an attractive additive manufacturing technology that can be applied to a number of different materials. However, fabrication of each material requires tweaking and identifying optimal processing parameters. In this study, process parameters were successively varied to identify a processing regime to fabricate the nickel-base (Ni-base) superalloy Haynes 282. Key parameters to minimize porosity and mitigate the potential for cracking were beam velocity, beam current, hatch spacing, line order, and beam focus. Overall, the EBM process window produced a combination of promising microstructure and 99.5% dense material with no observable cracking. Electron backscatter diffraction revealed a crystallographic texture along the [001] direction of the cube orientation aligned with the build direction. Within the grain interiors of the as-fabricated material were observed uniformly distributed γ′ precipitates with a size distribution ranging from ~80 nm spherical to ~190 nm cuboidal particles with an average particle size of ~128 nm. Grain boundary carbides were observed in two morphologies: blocky and thin film–like. Hardness and tensile testing of the as-fabricated EBM material indicated a 10% higher hardness and slightly lower tensile strength compared with the as-annealed wrought form of the Haynes 282 alloy. The EBM alloy exhibited pronounced ductility except at T > 600 °C perpendicular to the build direction. Annealing based on standard wrought heat treatments showed that γ′ precipitates measuring 20–30 nm in average size can be achieved to improve the alloy's high-temperature performance.

Increasing the efficiency of natural gas reciprocating engines will require materials with better mechanical and corrosion resistance at high temperatures. One solution to increase the lifetime of exhaust valves is to apply an aluminide coating to prevent corrosion assisted fatigue cracking, but the impact of the coating on the valve material mechanical properties needs to be assessed. In addition to cyclic oxidation testing in dry and humid air at 800°C, creep and high cycle fatigue (HCF) testing were conducted at 816°C on bare and slurry or pack-coated 31V alloy. The coated and bare creep specimens exhibited very similar creep rupture lives, as long as the specimens were annealed according to the 31V standard heat treatment before testing. The HCF behavior of the pack-coated alloy was close to the behavior of the bare alloy, but fatigue lifetimes of slurry-coated 31V specimens had higher variability. Aluminide coatings have the potential to improve the valve performance at high temperature, but the coating deposition process needs to be tailored for the substrate standard heat treatment.

Oxide dispersion strengthened (ODS) FeCrAl alloys with 12–15% Cr are being evaluated for improved compatibility with Pb-Li for a fusion energy application and with high temperature steam for a more accident-tolerant light water reactor fuel cladding application. A 12% Cr content alloy showed low mass losses in static Pb-Li at 700°C, where a LiAlO2 surface oxide formed and inhibited dissolution into the liquid metal. All the evaluated compositions formed a protective scale in steam at 1200°C, which is not possible with ODS FeCr alloys. However, most of the compositions were not protective at 1400°C, which is a general and somewhat surprising problem with ODS FeCrAl alloys that is still being studied. More work is needed to optimize the alloy composition, microstructure and oxide dispersion, but initial promising tensile and creep results have been obtained with mixed oxide additions, i.e. Y2O3 with ZrO2, HfO2 or TiO2.

The creep behavior of various pack cementation aluminide coatings on Grade 91 ferritic–martensitic steel was investigated at 650 °C in laboratory air. The coatings were fabricated in two temperature regimes, i.e., 650 or 700 °C (low temperature) and 1050 °C (high temperature), and consisted of a range of Al levels and thicknesses. For comparison, uncoated specimens heat-treated at 1050 °C to simulate the high temperature coating cycle also were included in the creep test. All coated specimens showed a reduction in creep resistance, with 16–51% decrease in rupture life compared to the as-received bare substrate alloy. However, the specimens heat-treated at 1050 °C exhibited the lowest creep resistance among all tested samples, with a surprisingly short rupture time of

A new, cast austenitic stainless steel, CF8C-Plus (CF8C-P), has been developed for a wide range of high temperature applications, including diesel exhaust components, turbine casings and turbocharger housings. CF8C-P offers significant improvements in creep rupture life and creep rupture strength over standard CF8C steel. However, at higher temperatures and in aggressive environments such as those containing significant water vapor, an oxidation-resistant protective coating will be necessary to extend service life. The oxidation behavior of alloys CF8C and CF8C-P with various aluminide coatings were compared at 800 °C in air plus 10 vol% water vapor. Due to their affordability, slurry aluminides were the primary coating system of interest, although chemical vapor deposition and pack cementation coatings were also compared. Additionally, a preliminary study of the low-cycle fatigue (LCF) behavior of aluminized CF8C-P was conducted at 800 °C. Each type of coating provided substantial improvements in oxidation behavior, with simple slurry aluminides exhibiting very good oxidation resistance after 3,000 h testing in water vapor. Preliminary LCF results indicated that thicker aluminide coatings degraded high temperature fatigue properties of CF8C-P, whereas thinner coatings did not. Results suggest that appropriately designed slurry aluminide coatings are a viable option for economical, long-term oxidation protection of austenitic stainless steels in water vapor.

Although expensive, Ni-based superalloys are of interest for the ultrasupercritical steam program because of their good creep and oxidation resistance at temperature above 700 C. However, the effect of steam oxidation on the alloy mechanical properties is unknown, and creep specimens of alloy CCA617, 740 and 230 were pre-oxidized for 2000 and 4000h in steam at 800 C before testing in air at the same temperature. Exposure in steam decreased the creep properties of alloy CCA617 compared with as fabricated material, had less of an effect on alloy 740, and did not affect alloy 230. Testing of a specimen repolished after steam exposure as well as microstructure observation indicate that the oxidation affected zone at the specimen surface is not responsible for the properties degradation. Surprisingly, a similar time anneal in an inert environment resulted in a drastic decrease of creep rupture life and an increase in the creep rate and elongation at rupture. TEM analysis revealed that the mechanical properties decrease for alloy CCA617 is related to the absence of precipitates in the grain.

The surface scale formed on specimens of a commercial oxide dispersion strengthened (ODS) FeCrAl alloy (PM2000) exposed for 1 and 500 h at 1050°C in dry O2, Air+10%H2O and Ar+10%H2O consisted of a two-layer α-Al2O3 structure with a columnar grain inner layer and a finer grain outer layer. The alumina scales formed in Air+10%H2O and Ar+10%H2O were slightly more than half of the thickness of the scale formed in dry O2. The same two-layer structure was also observed after exposure for 500 h at 1100°C in dry O2 and 50%CO2+50%H2O. The alumina scales formed in both atmospheres were similar in thickness. Oxides rich in Y and Ti at the gas – scale interface grew in size and number with time in each case. Using analytical transmission electron microscopy, alumina grain boundary segregation of both Y and Ti was evident near the gas interface but only Y segregation was detected near the metal interface. This difference was attributed to Ti depletion in the adjacent metal and the rapid outward flux of the sma...

The ductility of various coatings deposited by chemical vapor deposition, pack cementation and slurry processes on Fe- and Ni-based alloys was characterized by indentation at room temperature. A hot indentation apparatus has also been developed to more rapidly determine the ductile to brittle transition temperature of coated specimens. Creep testing has been conducted on bare and coated alloy 230 (NiCrW) specimens at 800 °C with a significant decrease in creep life observed. Based on the observed failure of coated 230 specimens, the impact of coating ductility on substrate creep properties is discussed.

Short cracks, extending to the interdiffusion zone, have been observed in platinum-modified nickel-aluminide diffusion coatings on single-crystal CMSX-4 superalloys after these have been subject to short (10 min) rapid thermal cycles. The cracks were revealed after removing the thermally grown oxide formed during cycling on the coating surfaces. Cracking was observed for coatings subject to thermal cycling between 1150 and 1050 °C, with and without an applied compressive stress, as well as on thermal cycling between 1150 °C and room temperature.

The evolution of the surface roughness of an initially flat platinum-modified nickel aluminide (NiPtAl) coating on a single crystal superalloy with cyclic oxidation has been measured by optical profilometry and correlated with the aluminide microstructure. The roughness evolution is dominated by the relative motion of individual grains on thermal cycling, with the larger sized grains moving up and the smaller grains moving down with respect to the average surface. Detailed crystallographic analysis indicates that the grains in the coating are randomly distributed and have no crystallographic relationship with the underlying single crystal superalloy. Furthermore, there is a correlation between the number of sides a grain has and the propensity for its center to move relative to the average surface plane: grains with six or more sides bow up, whereas the surfaces of those grains with fewer than six sides bow down. It is proposed that rumpling initiates due to the vertical displacement of the smaller grains having fewer than six sides. Once initiated, rumpling proceeds driven by the strain energy in the thermally grown oxide.

The evolution in surface morphology of platinum modified nickel aluminide (Ni,Pt)Al oxidation coatings during thermo-mechanical testing has been evaluated. One type of test consisted of cyclic oxidation between an upper temperature of 1150°C and a lower temperature varying from room temperature to 1050°C. The other type of test was cycling between 1000°C/1150°C under an applied compressive stress. Profilometry using optical interferometry was used to quantify the surface “rumpling”. First and second-order statistical parameters including RMS roughness and the auto-correlation function were calculated from the profilometry measurements. The results indicate that the grain structure of the aluminide coating plays a major role in the early stages of rumpling and set its wavelength. Also, the superimposed compressive stress during thermal cycling leads to an asymmetry in the rumpling pattern with respect with the loading axis as well as cracking along the applied stress direction.

Cast stainless steel CF8C-Plus (19wt%Cr/12%Ni) has excellent creep properties, but limited oxidation resistance above 700°C in environments containing H2O. One strategy to improve the alloy oxidation performance is to increase the Cr and Ni concentration. Two new alloys, with, respectively, 21wt%Cr–15wt%Ni and 22wt%Cr–17.5wt%Ni were therefore developed and their long-term oxidation behaviors in humid air were compared with the oxidation behavior of five other cast alloys. At 650°C and 700°C, all the alloys formed internal Cr-rich nodules, and outer nodules or layers rich in Fe and Ni, but they grew a protective Cr-rich inner layer over time. At 750°C, the lower alloyed steels such as CF8C-Plus showed large metal losses, but the two new alloys still exhibited a protective oxidation behavior. The 21Cr–15Ni alloy was severely oxidized in locations at 800°C, but that was not the case for the 22Cr–17.5Ni alloy. Therefore, the two new modified alloys represent a potential operating temperature gain of, respectively, 50°C and 100°C in aggressive environments compared with the CF8C-Plus alloy.

Alumina-forming austenitic (AFA) steels represent a new class of corrosion- and creep-resistant austenitic steels designed to enable higher temperature recuperators. Field trials are in progress for commercially rolled foil with widths over 39 cm. The first trial completed 3000 hrs in a microturbine recuperator with an elevated turbine inlet temperature and showed limited degradation. A longer microturbine trial is in progress. A third exposure in a larger turbine has passed 16,000 hrs. Furthermore, to reduce alloy cost and address foil fabrication issues with the initial AFA composition, several new AFA compositions are being evaluated in creep and laboratory oxidation testing at 650–800 °C and the results compared to commercially fabricated AFA foil and conventional recuperator foil performance.

Pack and chemical vapor deposited (CVD) aluminide coatings on commercial ferritic–martensitic Fe–9Cr–2W steel are being investigated by creep and corrosion testing at 650 °C. Results from different coating thicknesses show that the coated region makes no contribution to the creep strength. The creep behavior of uncoated material was studied after various heat treatments to simulate the coating process and typical secondary heat treatments. Alternating creep and corrosion exposures showed little effect on the creep strength of uncoated material but coated materials became progressively weaker. The coatings were protective in wet air at 650 °C after creep testing.

ODS FeCrAl alloys are being developed with optimum composition and properties for accident tolerant fuel cladding. Two oxide dispersion strengthened (ODS) Fe-15Cr-5Al+Y2O3 alloys were fabricated by ball milling and extrusion of gas atomized metallic powder mixed with Y2O3 powder. To assess the impact of Mo on the alloy mechanical properties, one alloy contained 1%Mo. The hardness and tensile properties of the two alloys were close and higher than the values reported for fine grain PM2000 alloy. This is likely due to the combination of a very fine grain structure and the presence of nano oxide precipitates. The nano oxide dispersion was however not sufficient to prevent grain boundary sliding at 800 C and the creep properties of the alloys were similar or only slightly superior to fine grain PM2000 alloy. Both alloys formed a protective alumina scale at 1200 C in air and steam and the mass gain curves were similar to curves generated with 12Cr-5Al+Y2O3 (+Hf or Zr) ODS alloys fabricated for a different project. To estimate the maximum temperature limit of use for the two alloys in steam, ramp tests at a rate of 5 C/min were carried out in steam. Like other ODS alloys, the two alloysmore » showed a significant increase of the mas gains at T~ 1380 C compared with ~1480 C for wrought alloys of similar composition. The beneficial effect of Yttrium for wrought FeCrAl does not seem effective for most ODS FeCrAl alloys. Characterization of the hardness of annealed specimens revealed that the microstructure of the two alloys was not stable above 1000 C. Concurrent radiation results suggested that Cr levels

The successful joining of oxide dispersion-strengthened (ODS) alloy PM2000 rods by pulsed plasma-assisted diffusion bonding is reported. During secondary recrystallization after joining, the alloy grains grew across the original interface, which was then marked by a row of remnant alumina particles. These did not appear to act as pinning sites for the alloy grain boundaries, which moved easily past them, leaving a strong diffusion bond.

During thermal cycling of nickel-aluminum-platinum (NiAlPt) and single crystal iron-chromium-nickel (FeCrNi) alloys, the structural changes associated with the martensite to austenite phase transformation were measured using dual-wavelength digital holography. Real-time in situ measurements reveal the formation of striations within the NiAlPt alloy at 70°C and the FeCrNi alloy at 520°C. The results demonstrate that digital holography is an effective technique for acquiring noncontact, high precision information of the surface evolution of alloys at high temperatures.

Alumina-forming austenitic (AFA) steels represent a new class of corrosion- and creep-resistance austenitic steels to enable higher temperature recuperators. Several commercial batches of the first AFA composition have been produced with different thicknesses and widths over 39cm. This commercial AFA foil was successfully folded by two manufacturers. Creep and laboratory oxidation results at 650°-800°C are presented to compare to conventional recuperator alloy performance. While this initial effort was successful, concerns with cost and ease of production suggested that a leaner AFA composition with a lower final annealing temperature would be more attractive for commercial applications. Therefore, several new AFA compositions are being evaluated in laboratory trials and compared to the initial material for down selection of a better AFA composition for commercialization.Copyright © 2013 by ASME

International audience; Cyclic oxidation testing was conducted on alloy MA956 and two different batches of alloy PM2000 at 1,100 and 1,200 °C in different atmospheres rich in O2, H2O and CO2. Compared to 1 h cycles in dry O2, exposure in air + 10 vol.% H2O resulted in an increase of the oxidation rate and a decrease of the time to breakaway for all alloys at 1,200 °C, and a faster consumption of Al in the MA956 alloy. One hour cyclic testing in 49.25 % CO2 + 50 % H2O + 0.75 % O2 had a smaller effect on the oxidation rate but led to increased formation of voids in alloy MA956, which had an impact on the alloy creep resistance. At 1,100 °C, exposure in 50 % CO2 + 50 % H2O resulted in significant oxide spallation compared with oxidation in air, but this was not the case when 0.75 % O2 was added to the CO2/H2O mixture as a buffer. The control of impurity levels drastically improved the oxidation resistance of PM2000.

Superalloys like 718 and its derivatives primarily rely on the formation of an external Cr-rich oxide layer or scale for environmental protection at high temperatures. Operating conditions where environmental resistance is more of a concern generally involve higher temperatures or more corrosive environments, especially where S is present, usually due to fuel impurities. With clean fuels, the presence of water vapor and oxygen, such as a combustion environment in a natural gas-fired turbine, chromia forms a volatile oxy-hydroxide leading to accelerated Cr loss. In laboratory experiments, mass losses are measured due to this volatilization. For sulfidizing or hot corrosion environments, the role of alloy and coating composition on corrosion resistance will be reviewed. An increasing area of interest is the interaction between environmental degradation and the stress-induced deformation of the superalloy including the influence of oxidation-resistant coatings on mechanical properties. Strategies to study this interaction will be discussed.