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It is well established that hydrogen derived from water vapor can penetrate oxidizing alloys with detrimental effect. However, the complexities of tracking hydrogen in these materials have prevented the direct profiling of hydrogen ingress needed to understand these phenomena. Here we report hydrogen profiles in industrially-relevant alumina- and chromia-forming steels correlated with the local oxide-metal nano/microstructure by use of SIMS D 2 O tracer studies and experimental protocols to optimize D retention. The D profiles unexpectedly varied markedly among the alloys examined, which indicates mechanistic complexity but also the potential to mitigate detrimental water vapor effects by manipulation of alloy chemistry.

A family of alumina-forming austenitic (AFA) stainless steels is under development for use in aggressive oxidizing conditions from ~600–900 °C. These alloys exhibit promising mechanical properties but oxidation resistance in air with water vapor environments is currently limited to ~800 °C due to a transition from external protective alumina scale formation to internal oxidation of aluminum with increasing temperature. The oxidation behavior of a series of AFA alloys was systematically studied as a function of Cr, Si, Al, C, and B additions in an effort to provide a basis to increase the upper-temperature oxidation limit. Oxidation exposures were conducted in air with 10% water vapor environments from 800–1000 °C, with post oxidation characterization of the 900 °C exposed samples by electron probe microanalysis (EPMA), scanning and transmission electron microscopy, and photo-stimulated luminescence spectroscopy (PSLS). Increased levels of Al, C, and B additions were found to increase the upper-temperature oxidation limit in air with water vapor to between 950 and 1000 °C. These findings are discussed in terms of alloy microstructure and possible gettering of hydrogen from water vapor at second phase carbide and boride precipitates.

This study investigated the effects of a reading intervention that integrated vowel pattern analysis and children’s literature on the word decoding performance of second graders with reading disabilities. The intervention evaluated students’ abilities to decode a set of training words using 3 common vowel patterns (syllable types), in isolation and in context. Additional sets of novel words and nonsense words using the same vowel patterns were presented to evaluate generalization of the reading intervention. A multiple-baseline design across vowel patterns was used to analyze the experimental effects of the decoding performance of 5 students. All 5 second graders demonstrated substantial gains in their ability to decode words with the 3 vowel patterns. The students increased their accuracy reading words in isolation, as well as in context. In addition, all students increased their decoding accuracy of both novel and nonsense generalization words. These increases in decoding accuracy were maintained during follow-up observations. The effects suggest the value of integrating code-based and meaning-based teaching strategies when designing interventions for students with reading disabilities.

The authors explored Itchy's Alphabet as an innovative approach to teaching letter–sound connections through multisensory cues. This is the initial demonstration of this instructional method for increasing students’ sublexical skills (letter identification, letter–sound knowledge, and phonological awareness). To examine the effectiveness of the program, the authors chose 3 kindergarten classrooms as intervention and comparison classes. The authors chose the Dynamic Indicators of Basic Early Literacy Skills (R. H. Good, D. Simmons, E. Kame'enui, R. A. Kaminski, & J. Wallin, 2002) to monitor early decoding progress because of its unique ability to assess and monitor young children's acquisition of early reading skills. Results show that Itchy's Alphabet, combined with hands-on manipulatives, was strongly connected to children's grasp of sublexical skills. Test scores indicated gains for all children including those who were at risk, children who received special education services, and typically developing ...

Response to Intervention (RtI) is a general education initiative that takes place prior to evaluation for placement in special education. Essentially, the first two tiers of RtI require general education teachers to use research-based instruction with all students and then to evaluate the effectiveness of that instruction. Given that the use of RtI as an assessment tool begins in the general education classroom, the following question remains: Are general educators aware of the development and implementation of RtI as a process for assessing and, eventually, possibly placing students into special education? The purpose of this study was to review the literature to answer the following two questions: To what extent is RtI evident in the professional literature of educator groups (teachers, administrators, and teacher educators) who will be responsible for implementing these school practices? What is the nature of the published literature (concept papers, assessment practices, instructional practic...

Thermal (gas) nitridation of stainless steel alloys can yield low interfacial contact resistance (ICR), electrically conductive and corrosion-resistant nitride containing surface layers (Cr2N, CrN, TiN, V2N, VN, etc.) of interest for fuel cells, batteries, and sensors. This paper presents results of proton exchange membrane (PEM) single-cell fuel cell studies of stamped and pre-oxidized/nitrided developmental Fe–20Cr–4V weight percent (wt.%) and commercial type 2205 stainless steel alloy foils. The single-cell fuel cell behavior of the stamped and pre-oxidized/nitrided material was compared to as-stamped (no surface treatment) 904L, 2205, and Fe–20Cr–4V stainless steel alloy foils and machined graphite of similar flow field design. The best fuel cell behavior among the alloys was exhibited by the pre-oxidized/nitrided Fe–20Cr–4V, which exhibited ∼5–20% better peak power output than untreated Fe–20Cr–4V, 2205, and 904L metal stampings. Durability was assessed for pre-oxidized/nitrided Fe–20Cr–4V, 904L metal, and graphite plates by 1000+ h of cyclic single-cell fuel cell testing. All three materials showed good durability with no significant degradation in cell power output. Post-test analysis indicated no metal ion contamination of the membrane electrode assemblies (MEAs) occurred with the pre-oxidized and nitrided Fe–20Cr–4V or graphite plates, and only a minor amount of contamination with the 904L plates.

Thermal (gas) nitridation of stainless steel alloys can yield low interfacial contact resistance (ICR), electrically conductive and corrosion-resistant nitride containing surface layers (Cr 2 N, CrN, TiN, V 2 N, VN, etc.) of interest for fuel cells, batteries, and sensors. This paper presents results of scale-up studies to determine the feasibility of extending the nitridation approach to thin 0.1 mm stainless steel alloy foils for proton exchange membrane fuel cell (PEMFC) bipolar plates. Developmental Fe–20Cr–4V alloy and type 2205 stainless steel foils were treated by pre-oxidation and nitridation to form low-ICR, corrosion-resistant surfaces. As-treated Fe–20Cr–4V foil exhibited target (low) ICR values, whereas 2205 foil suffered from run-to-run variation in ICR values, ranging up to 2× the target value. Pre-oxidized and nitrided surface structure examination revealed surface-through-layer-thickness V-nitride particles for the treated Fe–20Cr–4V, but near continuous chromia for treated 2205 stainless steel, which was linked to the variation in ICR values. Promising corrosion resistance was observed under simulated aggressive PEMFC anode- and cathode-side bipolar plate conditions for both materials, although ICR values were observed to increase. The implications of these findings for stamped bipolar plate foils are discussed.

PurposeThe purpose of this paper is to examine the use of Section 1031 of the Internal Revenue Code (IRC), a piece of US tax law that allows for tax‐deferred exchanges of like‐kind property.Design/methodology/approachThe paper derives a theoretical premium value for exchanges and presents the first national level analysis of Federal tax data on the use of like‐kind exchanges involving farmland between 1999 and 2005.FindingsThere is significant interest in Section 1031 from stakeholders in rural communities because there is widespread belief that the recent growth in farmland values may have, in part, been stimulated by Section 1031 exchanges of farmland. Despite these concerns, little is known about the extent of such exchanges.Originality/valueThis paper provides insight into the value and use of the IRC's Section 1031 provision. Based on simulations of a theoretical model using plausible assumptions about asset growth, the paper shows how proposed tax changes will affect the tax value of the deferral.

The importance of employment in society is unmistakable, but for many people sustained employment remains elusive. The unemployment rate for individuals with disabilities is staggering, and the consequences of being unemployed affects those individuals, their families, and society. The effects of performance feedback delivered via covert audio coaching on the job performance of supported employees were examined in this investigation. A multiple baseline design across employees and work tasks was used to evaluate the effects of the intervention on work performance. Supported employees made substantial improvements on their work performance, and the improvements maintained for 4 to 5 weeks following the removal of the intervention. The results have implications for the use of covert audio coaching in employment and other settings.

Short-term sulfidation–oxidation exposures were conducted under high pS2 and low pO2 conditions for TiCrAl and FeCrAl alloys at 600 and 800 °C. Low mass gains and submicron Al-and Ti-rich oxide scales were formed on TiCrAl at 600 °C, while high mass gains and FeS-based scale formation were observed for FeCrAl. Based on the good behavior of TiCrAl, third-element effect additions of Cr are not inherently detrimental under sulfidation–oxidation conditions. Rather, differences in the mechanistic action of the third-element addition of Cr between FeCrAl and TiCrAl alloys and its relevance to low oxygen potential sulfidation–oxidation environments were the key factors in determining whether or not a protective alumina scale was established.

Isothermal aging and tensile evaluation were conducted for recently developed alumina-forming austenitic stainless steels (AFAs). Microstructural observation reveals that NiAl-type B2 and Fe 2 (Mo,Nb)-type Laves phase precipitates form as dominant second phases in the austenitic matrix during aging at 750 °C. At room temperature these precipitates increase the strength but decrease the ductility of the AFA alloys. However, when tested at 750 °C, the AFA alloys did not show strong precipitation hardening by these phases, moreover, the elongation to fracture was not affected by aging. Fracture surface and cross-sectional microstructure analysis after tensile testing suggests that the difference of mechanical behaviors between room temperature and 750 °C results from the ductile–brittle transition of the B2 precipitates. At room temperature, B2 precipitates are strong but brittle, whereas they become weak but ductile above the ductile–brittle transition temperature (DBTT).

There has been increasing interest in the substitution of low-cost Mn for Ni in austenitic stainless steels due to the rising price of Ni. This paper investigates the possibility of such a substitution approach for the recently developed alumina (Al2O3)-forming austenitic (AFA) class of heat-resistant stainless steels. Computational thermodynamic tools were utilized to predict the alloy composition range to maintain an austenitic matrix microstructure when Mn is substituted for Ni in the presence of Al, which is a strong body-centered-cubic (BCC) phase stabilizer. Phase equilibria, oxidation behavior, and creep properties of Fe–(10–14)Cr–(5–15)Mn–(4–12)Ni–(2.5–3)Al–Cu–Nb–C–B (in weight percent) based alloys were studied. The alloys based on Fe–14Cr–2.5Al–(5–9)Mn–(10–12)Ni exhibited the best balance of oxidation and creep resistance, which represents approximately 50% reduction in Ni content compared to previously developed AFA alloys. These low-Ni, high-Mn AFA alloys formed protective Al2O3 scales up to 973–1073 K in air and at 923 K in air with 10% water vapor. Creep-rupture lives of the alloys under a severe screening condition of 1023 K and 100 MPa were in the 7.2 × 105–1.8 × 106 s (200–500 h) range, which is comparable to or somewhat improved over that of type 347 stainless steel (Fe–18Cr–11Ni base).

A family of creep-resistant austenitic stainless steels based on alumina (Al2O3) scale formation (AFA alloys) for superior high-temperature oxidation resistance was recently identified. Excellent oxidation behavior was observed at 650 and 700 °C in air with 10% water vapor. However, particularly at 800 °C, the presence of water vapor greatly increased the tendency for internal oxidation of Al. Water vapor also enhanced subscale Al depletion in some AFA alloys relative to dry air exposure. Increased levels of Nb additions were found to significantly improve oxidation resistance, as were reactive element additions of Hf and Y. Computational thermodynamic calculations of the austenitic matrix phase composition and the volume fraction of MC, B2-NiAl, and Fe2Nb base Laves phase precipitates were used to interpret oxidation behavior in terms of two-phase oxidation theory, reservoir effect, and the third-element effect of Cr. Of particular interest was the enrichment of Cr in the austenitic matrix phase by additions of Nb, which aided the establishment and maintenance of alumina. Higher levels of Nb additions also increased the volume fraction of B2-NiAl precipitates, which served as an Al reservoir during long-term oxidation. Implications of these findings for the design of AFA alloys with increased upper use temperature limits are discussed.

The high-temperature creep properties of a series of alumina-forming austenitic (AFA) stainless steels based on Fe-20Ni-(12-14)Cr-(2.5-4)Al-(0.2-3.3)Nb-0.1C (weight percent) were studied. Computational thermodynamics were used to aid in the interpretation of data on microstructural stability, phase equilibria, and creep resistance. Phases of MC (M: mainly Nb), M23C6 (M: mainly Cr), B2 [β-(Ni,Fe)Al], and Laves [Fe2(Mo,Nb)] were observed after creep-rupture testing at 750 °C and 170 MPa; this was generally consistent with the thermodynamic calculations. The creep resistance increased with increasing Nb additions up to 1 wt pct in the 2.5 and 3 Al wt pct alloy series, due to the stabilization of nanoscale MC particles relative to M23C6. Additions of Nb greater than 1 wt pct decreased creep resistance in the alloy series due to stabilization of the Laves phase and increased amounts of undissolved, coarse MC, which effectively reduced the precipitation of nanoscale MC particles. The additions of Al also increased the creep resistance moderately due to the increase in the volume fraction of B2 phase precipitates. Calculations suggested that optimum creep resistance would be achieved at approximately 1.5 wt pct Nb in the 4 wt pct Al alloy series.

Involvement of students and adult employees into the decisions that affect their education and employment can improve their transition into supported employment. One means for increasing involvement into these decisions is to gain their input into performance evaluations and support needs. The Job Observation and Behavior Scale: Opportunity for Self-Determination is an assessment designed to obtain such input from the perspective of students preparing for, and employees participating in, supported employment. This article presents the role of the scale in obtaining student and employee input into their own work performance and support needs; it summarizes the development and technical properties of the instrument; and it describes how this instrument can promote the self-determination of students and adult employees with disabilities.

Supervision and coaching strategies that provide immediate feedback can help improve instruction for novice teachers. In this study, feedback was provided to teachers using “bug-in-ear” technology to coach them to deliver effective instructional interactions: “learn units.” Three novice teachers in K—8 classrooms with students with disabilities including emotional disorders, autism, attention-deficit/hyperactivity disorder, and developmental delays participated in the study. Results from the multiple-baseline design showed that the rate and accuracy of effective teaching behaviors increased when in-class feedback was delivered via the electronic “bugs.” For two of the three teachers, these increases maintained when the instructional feedback was faded. This study extends previous research and suggests an effective coaching supervision strategy for novice teachers.

Interdiffusion in Fe-Ni-Cr (fcc γ phase) alloys with small additions of Si and Ge at 900°C was studied using solid-to-solid diffusion couples. Alloy rods of Fe-24 at.%Ni, Fe-24 at.%Ni- 22at.%Cr, Fe-24 at.%Ni-22at.%Cr-4at.%Si and Fe-24 at.%Ni-22at.%Cr-1.7at.%Ge were cast using arc-melt, and homogenized at 900°C for 168 hours. Sectioned alloy disks from the rods were polished, and diffusion couples were assembled with in Invar steel jig, encapsulated in Argon after several hydrogen flushes, and annealed atz 900°C for 168 hours. Polished cross-sections of the diffusion couples were characterized to determine experimental concentration profiles using electron probe microanalysis with pure elemental standards. Interdiffusion fluxes of individual components were calculated directly from the experimental concentration profiles, and the moments of interdiffusion flux profiles were examined to determine the average ternary and quaternary interdiffusion coefficients. Effects of alloying additions on the interdiffusional behavior of Fe-Ni- Cr-X alloys at 900°C are presented with due consideration for the formation of protective Cr2O3 scale.

A family of creep-resistant, Al2O3-forming austenitic (AFA) stainless steels was recently developed. The alloys exhibit excellent oxidation resistance up to ∼800°C, but are susceptible to internal attack of Al at higher temperatures. In the present work, higher levels of Ni, Cr, Al, and Nb additions were found to correlate with improved oxidation behavior at 900°C in air. The alloys generally appeared to be initially capable of external Al2O3 scale formation, with a subsequent transition to internal attack of Al (internal oxidation and internal nitridation) that is dependent on alloy composition. Compositional profiles at the alloy/scale interface suggest that the transition to internal oxidation is preceded by subsurface depletion of Al in the lower-Al compositions. In higher Al-containing compositions, NiAl second-phase precipitates act as an Al reservoir, and Al depletion may not be a key factor. Alloy design directions to increase the upper-temperature limit of protective Al2O3 scale formation in these alloys are discussed.

A new family of alumina-forming austenitic stainless steels is under development at Oak Ridge National Laboratory for structural use in aggressive oxidizing environments at 600–900°C. Data obtained to date indicate the potential to achieve superior oxidation resistance compared to conventional Cr2O3-forming iron-and nickel-based heat-resistant alloys, with creep strength comparable to state-of-the-art advanced austenitic stainless steels. A preliminary assessment also indicated that the newly developed alloys are amenable to welding. Details of the alloy design approach and composition-microstructure-property relationships are presented.

The continuing shortage of special education teachers, combined with increased ideological critiques of teacher education programs, has spurred the growth of alternative models of teacher preparation. Only recently have professional standards for alternative models been proposed. This paper summarizes two years of a program based on professional standards. External influences, internal design, and implementation elements are presented. Results suggest that there is value in distinguishing between the effectiveness of alternative programs and their success.

Microstructure evolution during creep testing at 750 C and 100 MPa of Fe-20Cr-30Ni-2Nb (at.%) alloys with and without 0.4 Si, 0.2 Zr or 5.0 Al additions has been studied, in order to explore the viability of Fe-rich austenitic stainless alloys strengthened by intermetallic phases. Fine Fe{sub 2}Nb Laves phase dispersions with the size of less than 1 {micro}m within the {gamma}-Fe matrix were obtained in the base and Si-modified alloys after aging at 800 C. The addition of Si helped to refine and stabilize the size of particles, resulting in finer and denser Fe{sub 2}Nb dispersion than that in the base alloy. The alloys with only solution heat-treatment exhibited superior creep resistance to the aged ones, which is due to dynamic precipitation of the Fe{sub 2}Nb Laves phase during creep testing with a size of 300-400 nm, resulting in more effective pinning of dislocations. The base alloy also showed the meta-stable {gamma}*-Ni{sub 3}Nb phase with a size of 50 nm during the transient state of the creep testing. The Zr-modified alloy achieved significant improvement of creep properties. This is hypothesized to be due to the stabilization of {delta}-Ni{sub 3}Nb phase relative to Fe{sub 2}Nb, resulting in the formation of multiplemore » fine dispersions of stable intermetallic compounds of {delta} and Fe{sub 2}Nb within the {gamma}-Fe matrix. A small amount of a (Ni, Zr and Nb)-enriched unidentified phase was also observed. The addition of Al significantly improved the oxidation resistance because of the formation of protective alumina scales on the surface. The alloy also showed superior creep resistance to that of the base alloy due to the formation of a dense dispersion of spherical Ni{sub 3}Al, typically 30 nm in diameter. Collectively, these findings provide the alloy design basis for creep and oxidation-resistant austenitic stainless steel alloys via intermetallic precipitates.« less

Niobium was found to be beneficial for alumina scale formation in newly developed creep-resistant austenitic stainless steels. Additions of both Ti and V degraded alumina scale formation, whereas alloys with individual additions of Ti or V were able to form protective alumina scales. The ability to form external alumina scales was lost in the lower Al- and Nb-containing alloys between 800 and 900 °C. Compositions with the potential to form alumina at 900 °C were identified.

Gas nitridation has shown excellent promise to form dense, electrically conductive and corrosion-resistant Cr-nitride surface layers on Ni-Cr base alloys for use as proton exchange membrane fuel cell (PEMFC) bipolar plates. Due to the high cost of nickel, Fe-base bipolar plate alloys are needed to meet the cost targets for many PEMFC applications. Unfortunately, nitridation of Fe-base stainless steel alloys typically leads to internal Cr-nitride precipitation rather than the desired protective surface nitride layer formation, due to the high permeability of nitrogen in these alloys. This paper reports the finding that it is possible to form a continuous, protective Cr-nitride (CrN and Cr{sub 2}N) surface layer through nitridation of Fe-base stainless steel alloys. The key to form a protective Cr-nitride surface layer was found to be the initial formation of oxide during nitridation, which prevented the internal nitridation typically observed for these alloys, and resulted in external Cr-nitride layer formation. The addition of V to the alloy, which resulted in the initial formation of V{sub 2}O{sub 3}-Cr{sub 2}O{sub 3}, was found to enhance this effect, by making the initially formed oxide more amenable to subsequent nitridation. The Cr-nitride surface layer formed on model V-modified Fe-27Cr alloys exhibited excellent corrosion resistancemore » and low interfacial contact resistance under simulated PEMFC bipolar plate conditions.« less

A new low thermal expansion, low-Cr, Fe–Co–Ni base alloy was developed and evaluated as interconnect for intermediate-temperature solid oxide fuel cells (SOFCs). This alloy demonstrated good oxidation resistance, low oxide scale area specific resistance and a reasonable match in coefficient of thermal expansion with adjacent cell components. A double-layer oxide structure with an highly conductive, Cr-free (Fe,Co,Ni) 3 O 4 spinel outer layer and a thin protective Cr 2 O 3 inner layer was formed on the alloy surface upon thermal exposure in air at 800 °C. The existence of the Cr-free (Fe,Co,Ni) 3 O 4 outer layer effectively reduced the Cr evaporation and in transpiration testing resulted in a six-fold decrease in Cr evaporation as compared to a state-of-the-art ferritic interconnect alloy. The new low-Cr alloy also exhibited good scale spallation resistance and adequate compatibility with the cathode material La 0.8 Sr 0.2 MnO 3 (LSM).

Creep strengthening of Al-modified austenitic stainless steels by MC carbides or Fe2Nb Laves phase was explored. Fe-20Cr-15Ni-(0–8)Al and Fe-15Cr-20Ni-5Al base alloys (at. pct) with small additions of Nb, Mo, W, Ti, V, C, and B were cast, thermally-processed, and aged. On exposure from 650 °C to 800 °C in air and in air with 10 pct water vapor, the alloys exhibited continuous protective Al2O3 scale formation at an Al level of only 5 at. pct (2.4 wt pct). Matrices of the Fe-20Cr-15Ni-5Al base alloys consisted of γ (fcc) + α (bcc) dual phase due to the strong α-Fe stabilizing effect of the Al addition and exhibited poor creep resistance. However, adjustment of composition to the Fe-15Cr-20Ni-5Al base resulted in alloys that were single-phase γ-Fe and still capable of alumina scale formation. Alloys that relied solely on Fe2Nb Laves phase precipitates for strengthening exhibited relatively low creep resistance, while alloys that also contained MC carbide precipitates exhibited creep resistance comparable to that of commercially available heat-resistant austenitic stainless steels. Phase equilibria studies indicated that NbC precipitates in combination with Fe2Nb were of limited benefit to creep resistance due to the solution limit of NbC within the γ-Fe matrix of the alloys studied. However, when combined with other MC-type strengtheners, such as V4C3 or TiC, higher levels of creep resistance were obtained.

Interdiffusion at 700°C for Ni-22at.%Cr (fcc γ phase) alloys with small additions of Al, Si, Ge, or Pd was examined using solid-to-solid diffusion couples. Rods of Ni-22at.%Cr, Ni- 21at.%Cr-6.2at.%Al, Ni-22at.%Cr-4.0at.%Si, Ni-22at.%Cr-1.6at.%Ge and Ni-22at.%Cr-1.6at.%Pd alloys were cast using arc-melt and homogenized at 900°C for 168 hours. The diffusion couples were assembled with alloy disks in Invar steel jig, encapsulated in Argon after several hydrogen flushes, and annealed at 700°C for 720 hours. Experimental concentration profiles were determined from polished cross-sections by using electron probe microanalysis with pure standards of Ni, Cr, Al, Si, Ge and Pd. Interdiffusion fluxes of individual components were calculated directly from the experimental concentration profiles, and the moments of interdiffusion fluxes were examined to determine average ternary interdiffusion coefficients. Effects of ternary alloying additions on the interdiffusional behavior of Ni-Cr-X alloys at 700°C are presented in the light of the diffusional interactions and the formation of protective Cr2O3 scale.

Ti2AlC ternary carbide is being explored for various high temperature applications due to its strength at high temperatures, excellent thermal-shock resistance, and high electrical conductivity. A potential advantage of Ti2AlC over conventional Al2O3-forming materials is the near-identical coefficient of thermal expansion (CTE) of Ti2AlC and α-Al2O3, which could result in superior spallation resistance and make Ti2AlC a promising option for applications ranging from bondcoats for thermal barrier coatings to furnace heating elements. In this study, isothermal and cyclic oxidation were performed in air to examine the oxidation behavior of Ti2AlC. Isothermal oxidation was performed at 1000, 1200 and 1400 °C for up to 25 h and cyclic oxidation consisted of 1,000 1-hour cycles at 1200 °C. Characteristics of the oxide scale developed in air, including mass change, residual stress in the α-Al2O3 scale, phase constituents and microstructure, were examined as functions of time and temperature by thermogravimetry, photostimulated luminescence, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy via focused ion beam in situ lift-out. Above a continuous and adherent α-Al2O3 layer, a discontinuous-transient rutile-TiO2 scale was identified in the oxide scale developed at 1000 and 1200 °C, while a discontinuous-transient Al2TiO5 scale was identified at 1400 °C. The continuous α-Al2O3scale thickened to more than 15 μm after 25 h of isothermal oxidation at 1400 °C, and after 1,000 1-hour cycles at 1200 °C, yet remained adherent and protective. The compressive residual stress determined by photoluminescence for the α-Al2O3 scale remained under 0.65 GPa for the specimens oxidized up to 1400°C for 25 hours. The small magnitude of the compressive residual stress may be responsible the high spallation-resistance of the protective α-Al2O3 scale developed on Ti2AlC, despite the absence of reactive element additions.

A family of inexpensive, Al 2 O 3 -forming, high–creep strength austenitic stainless steels has been developed. The alloys are based on Fe-20Ni-14Cr-2.5Al weight percent, with strengthening achieved through nanodispersions of NbC. These alloys offer the potential to substantially increase the operating temperatures of structural components and can be used under the aggressive oxidizing conditions encountered in energy-conversion systems. Protective Al 2 O 3 scale formation was achieved with smaller amounts of aluminum in austenitic alloys than previously used, provided that the titanium and vanadium alloying additions frequently used for strengthening were eliminated. The smaller amounts of aluminum permitted stabilization of the austenitic matrix structure and made it possible to obtain excellent creep resistance. Creep-rupture lifetime exceeding 2000 hours at 750°C and 100 megapascals in air, and resistance to oxidation in air with 10% water vapor at 650° and 800°C, were demonstrated.

Iron and Fe–10 wt.% Ge alloy were exposed at 680 °C to reducing, carbon-supersaturated CO–H2–H2O gas (ac = 2.9). Iron grew into a cementite scale which disintegrated into nanoparticles as graphite deposited from the gas and grew into the Fe3C. The Fe–Ge alloy formed no Fe3C, and carbon deposited directly on the metal surface. As the graphite grew into the metal, ferrite nanoparticles were dislodged from the surface into the carbon. Metal consumption and carbon nanotube growth were more rapid in the latter case.

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.

International audience; Fe- and Ni-base alloys including an alumina-forming austenitic alloy were exposed for 500h under metal dusting environments with varying temperature, gas composition and total pressure. For one H2–CO–CO2–H2O environment, the increase in temperature from 550 to 750°C generally decreased metal dusting. When H2O was added to a H2–CO–CO2 environment at 650°C, the metal dusting attack was reduced. Even after 5000h at a total pressure of 9.1atm with 20%H2O, the higher alloyed specimens retained a thin protective oxide. For gas mixtures containing little or no H2O, the Fe-base alloys were less resistant to metal dusting than Ni-base alloys.

Interdiffusion in nickel (Ni)-chromium (Cr) (face-centered cubic γ phase) alloys with small additions of aluminum (Al), silicon (Si), germanium (Ge), or palladium (Pd) was investigated using solid-to-solid diffusion couples. Ni-Cr-X alloys having compositions of Ni-22at.% Cr, Ni-21at.%Cr-6.2at.%Al, Ni-22at.%Cr-4.0at.%Si, Ni-22at.%Cr-1.6at.%Ge, and Ni-22at.%Cr-1.6at.%Pd were manufactured by arc casting. The diffusion couples were assembled in an Invar steel jig, encapsulated in Ar after several hydrogen purges, and annealed at 900 °C in a three-zone tube furnace for 168 h. Experimental concentration profiles were determined from polished cross sections of these couples by using electron probe microanalysis with pure element standards. Interdiffusion fluxes of individual components were calculated directly from the experimental concentration profiles, and the moments of interdiffusion fluxes were examined to determine the average ternary interdiffusion coefficients. The effects of ternary alloying additions on the diffusional behavior of Ni-Cr-X alloys are presented in the light of the diffusional interactions and the formation of a protective Cr2O3 scale.

The relationships between nitridation, microstructure and corrosion were studied for a thermally nitrided model Ni–50Cr (wt.%) alloy to gain insight into the protection of metallic bipolar plates in proton exchange membrane fuel cells (PEMFCs). Surface layers containing CrN, Cr2N or ternary Cr–Ni–N π phase nitride were formed, dependent on the nitridation conditions. Studies in aerated pH 3 sulfuric acid at 80 °C indicated that the best corrosion resistance was exhibited by CrN + Cr2N surface layers, which were more corrosion resistant than Ni–50Cr metal, Cr metal, and nitrided Cr. X-ray photoelectron spectroscopy (XPS) analyses indicated oxygen enrichment of the polarized surfaces in the form of Cr-oxide and Cr-oxynitride species. Such oxygen enrichment does not appear to result in detrimental increases in interfacial contact resistance/electrical properties of the surface.

The goal of this paper was to determine if NiO-forming alloys are a viable alternative to Cr2O3-forming alloys for solid-oxide fuel-cell (SOFC) metallic interconnects. The oxide-scale growth kinetics and electrical properties of a series of Li- and Y2O3-alloyed, NiO-forming Ni-base alloys and La-, Mn-, and Ti-alloyed Fe–18Cr–9W and Fe–25Cr base ferritic Cr2O3-forming alloys were evaluated. The addition of Y2O3 and Li reduced the NiO scale growth rate and increased its electrical conductivity. The area-specific-resistance (ASR) values were comparable to those of the best (lowest ASR) ferritic alloys examined. Oxidation of the ferritic alloys at 800°C in air and air+10% H2O (water vapor) indicated that Mn additions resulted in faster oxidation kinetics/thicker oxide scales, but also lower oxide scale ASRs. Relative in-cell performance in model SOFC stacks operated at 850°C indicated a 60–80% reduction in ASR by Ni+Y2O3, Ni+Y2O3, Li, and Fe–25Cr+La,Mn,Ti interconnects over those made from a baseline, commercial Cr2O3-forming alloy. Collectively, these results indicate that NiO-forming alloys show potential for use as metallic interconnects.

The selective gas nitridation of model nickel-based alloys was used to form dense, electrically conductive and corrosion-resistant nitride surface layers, including TiN, VN, CrN, Cr2N, as wellas a complex NiNbVN phase. Evaluation for use as a protective surface for metallic bipolar plates in proton exchange membrane fuel cells (PEMFC) indicated that CrN/Cr2N based surfaces holdpromise to meet U.S. Department of Energy (DOE) performance goals for automative applications. The thermally grown CrN/Cr2N surface formed on model Ni−Cr based alloys exhibited good stability and low electrical resistance in single-cell fuel cell testing under simulated drive-cycle conditions. Recent results indicate that similar protective chromium nitride surfaces can be formed on less expensive Fe−Cr based alloys potentially capable of meeting DOE cost goals.

This article illustrates (a) 2 recent innovations in the changing criterion research design, (b) how these innovations apply to research and practice in special education, and (c) how clinical needs influence design features of the changing criterion design. The first innovation, the range-bound changing criterion, is a very simple variation of the classic changing criterion design. The classic version uses a single criterion for each stepwise intervention phase, whereas the range-bound version uses a range criterion—that is, an upper and lower limit for each intervention phase. The second innovation, the distributed criterion, combines elements of the changing criterion, multiple-baseline, and ABAB designs. It is well suited to contexts where students must multitask—that is, allocate, prioritize, and adjust time and effort to complete multiple tasks in response to changing environmental demands. These two innovations expand options available to researchers who use single-case research designs to investigate questions of interest in special education.

This paper discusses strategies for controlling the surface chemistry and microstructure of materials to form protective and functional surfaces through controlled gas-metal reactions. Potential applications range from oxidation, corrosion, and wear resistance to electrochemical devices such as fuel cells to catalysts. Phenomenological examples are presented for coatings designed to self-grade under oxidizing conditions, and for the growth of simple and complex (binaryand ternary) nitride and carbide phase surface layers by nitridation and carburization reactions. Specific systems discussed include environmental barrier coatings (EBCs) for Si-based ceramics such as Si 3 N 4 and SiC, the growth of continuous, protective CrN/Cr2N, TiN, VN, NiNbVN, and related simple nitride layers on Fe- and Ni-base alloys, the possible formation of ternary nitride and carbide surface phases (e.g. Ti3AlC2 and related MAX-phases) on intermetallic surfaces to improve oxidation resistance, and the formation of composite near-surface structures in Ag-SiO 2 and Co(Mo)-Co6Mo6C2 systems.

Microstructural and optical spectroscopic analyses were carried out on as-received and used spark plugs after field service in natural gas (NG) reciprocating engines. The objective of this work was to examine the corrosion and erosion mechanisms of natural gas engine spark plug as well as identify the primary life limiting processes during field operation. The optical emission spectroscopic analysis showed a strong Ca signal in the exposed spark plugs and scanning electron microscopy showed substantial formation of Ca-enriched glassy oxide phase(s) on the electrode surfaces. In addition, intergranular cracking was observed in the subsurface region of both iridium (Ir) and platinum-tungsten (Pt-W) alloy electrode insert tips. The coalescence and subsequent growth of these cracks would accelerate the wear of the electrodes and shorten the lifetime of the spark plugs. Also, extensive internal oxidation and subsequent crack generation occurred along the interface between Ni-base alloy electrode and Pt-W alloy tip insert during field service, which would result in substantial degradation in the ignitability and performance of the electrodes, and thus spark plug failure.

In a 1967 patent, D. M. Scruggs found that the room temperature ductility of molybdenum is improved by adding several volume percent of MgAl2O4 spinel particles. The present work substantiates Scruggs' claim – with increasing MgAl2O4 volume fraction the ductility of Mo–MgAl2O4 is found to pass through a maximum near 2.5 vol%. Scruggs postulated that gettering of detrimental impurities was responsible for this effect. In the present work, fracture initiated at microcracks that formed on the Mo–MgAl2O4 specimen surfaces during tensile testing. The ductility maximum is interpreted in terms of the change in the microcrack size (which is assumed to scale with the grain size) and the ultimate tensile stress, as the MgAl2O4 volume fraction increases. Fracture occurs once a critical local stress-intensity factor, which is approximately independent of the MgAl2O4 volume fraction, is reached.

The addition of Fe to Cr–Cr2Ta eutectic alloys increased ambient fracture toughness from a maximum of 12–14 to 18–21 MPa m1/2. The elevated-temperature yield strength was depressed, but still reached >250 MPa at 1000 °C. The Fe additions also resulted in a potentially beneficial change in oxidation mechanism from Cr2N subscale formation to internal oxidation.

The addition of Fe to Cr and to oxide dispersion ductilized Cr alloys modified, but did not eliminate subscale internal nitridation on oxidation in air. The addition of 45 wt.% Fe increased the room-temperature tensile yield strength of Cr–6MgO from ∼225 MPa to ∼650 MPa, while still exhibiting 1–1.5% tensile elongation.

A sputtered {gamma} (TiAl)+Laves TiAlCr coating formed an adherent Al{sub 2}O{sub 3} scale on SN 282 Si{sub 3}N{sub 4} when oxidized. A Ti-N rich layer was formed at the TiAlCr-Si{sub 3}N{sub 4} interface, which effectively resulted in beneficial local Al enrichment underneath the growing Al{sub 2}O{sub 3} scale, rather than detrimental Al loss to the substrate.

Thermal nitridation of a model Ni–50Cr alloy at 1100 °C for 2 h in pure nitrogen resulted in the formation of a continuous, protective CrN/Cr2N surface layer with a low interfacial contact resistance. Application of similar nitridation parameters to an austenitic stainless steel, 349™, however, resulted in a discontinuous mixture of discrete CrN, Cr2N and (Cr,Fe)2N1−x (x = 0–0.5) phase surface particles overlying an exposed γ austenite-based matrix, rather than a continuous nitride surface layer. The interfacial contact resistance of the 349™ was reduced significantly by the nitridation treatment. However, in the simulated PEMFC environments (1 M H2SO4 + 2 ppm F− solutions at 70 °C sparged with either hydrogen or air), very high corrosion currents were observed under both anodic and cathodic conditions. This poor behavior was linked to the lack of continuity of the Cr-rich nitride surface formed on 349™. Issues regarding achieving continuous, protective Cr-nitride surface layers on stainless steel alloys are discussed.

This paper highlights some evolving new design approaches to developing intermetallic alloys capable of protective scale formation and/or for their use as precursors for functional complex ceramic phase surface synthesis. The unique characteristics of intermetallics present challenges to achieving protective scale formation, but also offer the potential for leveraging novel phenomena not generally observed in conventional alloys. Examples will be drawn from the oxidation of aluminides (Fe{sub 3}Al, Nb{sub 2}Al, NbAl{sub 3}, Ti{sub 3}Al, TiAl), silicides (MoSi{sub 2}, Mo{sub 5}Si{sub 3}, Mo-Si-B, Ti{sub 5}Si{sub 3}), and Laves phases (Cr{sub 2}Nb, Cr{sub 2}Ta, Nb(Cr,Al){sub 2}, Ti(Cr,Al){sub 2}). Recent work also suggests that intermetallics can be used as precursors for the synthesis of functional complex ceramic phase surfaces by gas-metal reactions (oxidation, nitridation, carburization, etc.). The potential for using such reaction phenomena to synthesize layered or composite surfaces of ternary nitrides (carbides, borides, etc.) of technological interest such as Ti{sub 3}AlC{sub 2}, bimetallic nitride and carbide catalysts (e.g. Co{sub 3}Mo{sub 3}N or Co{sub 3}Mo{sub 3}C), and magnetic rare earth nitrides (Fe{sub 17}Sm{sub 2}N{sub x} or Fe{sub 17}Nd{sub 2}N{sub x}), from intermetallic precursors is discussed.

A series of single-phase Cr(X), single phase Cr 2X Laves phase, and two-phase Cr(X) + Cr2 X alloys (X = Nb or Ta) were thermally nitrided for 24 hr at 1100°C in N2--4H2 and then oxidized for 2 hr at 1100°C in air. The Cr(X) phase nitrided to form Cr2N while the Cr2X phases nitrided to form a complex local mixture of Cr2N/Cr and CrNbN/CrTaN, Cr3Nb3N/Cr3Ta3N phases depending on the depth in the nitrided zone. The Ta only slightly increased the isothermal oxidation rate of nitrided Cr(Ta) and Cr2Ta-reinforced Cr alloys, compared with nitrided, unalloyed Cr. Further, the nitrided two-phase alloys Cr--9.5Ta and Cr--20Ta exhibited improved Cr2O3 scale adherence relative to nitrided unalloyed Cr and Cr--1Ta. In contrast, Nb was detrimental to the oxidation resistance of the nitrided Cr(Nb) and Cr2Nb-reinforced Cr alloys, resulting in the formation of nonprotective Cr--Nb oxides rather than continuous Cr2O3. A phenomenological explanation for these effects based on phase chemistry and microstructural distribution is presented. Implications of these results for understanding the oxidation behavior of developmental high-temperature, Laves-strengthened Cr alloys, as well as possible applications as oxidation and wear-resistant coatings are discussed.

The use of intermetallic alloy precursors is explored as a new means to synthesize complex transition and refractory metal nitrides, carbides, and related phases. The conditions under which model single-phase Cr3Pt and two-phase Cr3Pt-dispersed Cr alloys form Cr3PtN antiperovskite when thermally nitrided were studied. Phenomenological experiments suggest that the key variable to achieving single-phase Cr3PtN surface layers is the Cr3Pt phase composition. In two-phase β-Cr−Cr3Pt alloys, the formation of single-phase Cr3PtN at Cr3Pt precipitates by in-place internal nitridation was found to be a strong function of the size of the Cr3Pt dispersion in the microstructure. Nanoscale Cr3Pt dispersions were readily converted to near single-phase Cr3PtN, whereas nitridation of coarse Cr3Pt particles resulted in a cellular or discontinuous-type reaction to form a lath mixture of Cr3PtN and a more Cr-rich Cr3Pt or β-Cr. The potential for using such external/internal oxidation phenomena as a synthesis approach to lay...

Preferential thermal nitridation was used to form a pin-hole defect free CrN/Cr2N surface on a model Ni–Cr alloy. Excellent corrosion resistance and negligible contact resistance increase was observed over a 4100 h exposure in 80 °C sulfuric acid and when used as a metallic bipolar plate in a 1000 h proton exchange membrane (PEM) fuel cell test.