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Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.

Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

This report covers some of the results attained during the last year concerning attempts to elucidating the mechanisms(s) at hot corrosion processes. AC impedance tests and Wagner-Hebb type polarization measurements on pure Na2SO4 at 900 C were performed as a function of Na2O activities. These results, to be published in an Electrochem. Soc. Proceedings showed that the conductivties of the pure Na2SO4 were of the order of .257/ohm-cm and varied only slightly with Na2O activity changes. From the Wagner-Hebb type polarization measurements on the pure Na2SO4 it was found that electron conductivity was much higher than electron hole conductivity. Additional tests were conducted to determine (1) the effect of height of Na2SO4 melts, (2) the effect of electronic short circuiting the Na2SO4 melts with gold wires and (3) the effect of presaturating the salt melt with corrosion products in the hot corrosion process. However, the amount of Na2SO4 present, which is directly proportional to the height of the melt, does affect the rate of corrosion. This was demonstrated by the decrease in rate observed when the melt was pre-saturated with the corrosion products.

This report covers some of the results attained during the last year concerning attempts to elucidating the mechanisms(s) at hot corrosion processes. AC impedance tests and Wagner-Hebb type polarization measurements on pure Na2SO4 at 900 C were performed as a function of Na2O activities. These results, to be published in an Electrochem. Soc. Proceedings showed that the conductivties of the pure Na2SO4 were of the order of .257/ohm-cm and varied only slightly with Na2O activity changes. From the Wagner-Hebb type polarization measurements on the pure Na2SO4 it was found that electron conductivity was much higher than electron hole conductivity. Additional tests were conducted to determine (1) the effect of height of Na2SO4 melts, (2) the effect of electronic short circuiting the Na2SO4 melts with gold wires and (3) the effect of presaturating the salt melt with corrosion products in the hot corrosion process. However, the amount of Na2SO4 present, which is directly proportional to the height of the melt, does affect the rate of corrosion. This was demonstrated by the decrease in rate observed when the melt was pre-saturated with the corrosion products.

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

No Abstract Available

Hot corrosion is a form of accelerated oxidation of alloys which can occur in combustion gases in the presence of impurities. The characteristics of the reaction are defined by describing practical examples, and then the results of a variety of laboratory experiments are considered in relation to the practical process. The temperature dependence and kinetics of the corrosion are briefly presented, and the effect of alloying elements is discussed; high chromium contents are required for good corrosion resistance, but there is no general agreement on the effect of other alloy elements. A number of mechanisms for hot corrosion are described and discussed in relation to the practical results.

MATERIALS & STRESSES M&S DIVISION FACILITIES IN THE MATERIALS & STRESSES M&S BUILDING - MATERIALS PROCESSING LABORATORY MPL - SPECIAL PROJECTS LABORATORY SPL - HIGH TEMPERATURE EROSION CORROSION FACILITY

The high temperature oxidation and corrosion behavior of a number of direction-ally solidified eutectic alloys were studied in the temperature range 1600-2000 Degrees F; these include gamma/gamma prime-delta alloys and alloys containing Tantalum Carbide or Cr Sub 7 C sub 3 fibers. With all the alloys the important factor appears to be whether or not a fiber-free zone is established between the surface scale and the alloy eutectic structure, and this in turn depends in a complex way on temperature, the degree of alignment and spacing of the eutectic, and the composition of the alloy. Tantalum Carbide fibers are very oxidation prone, and alloys containing this phase have poor overall resistance; Cr sub 7 C sub 3 or delta (Ni sub 3 Nb) are not as detrimental. (Author)

The rolling element fatigue lives of AMS 5749 and AISI M-50 were compared in tests run in the five ball fatigue tester and the rolling contact fatigue tester. The effects of double vacuum melting and retained austenite on the life of AMS 5749 were determined in five ball fatigue tests. The double vacuum melting process consisted of induction vacuum melting followed by vacuum arc remelting (VIM-VAR). In the five ball tests, VIM-VAR AMS 5749 gave lives at least six times that of VIM-VAR AISI M-50. Similar tests in the rolling contact fatigue tester showed no significant difference in the lives of the two materials. The rolling element fatigue life of VIM-VAR AMS 5749 was at least 14 times that of vacuum induction melted AMS 5749. A trend toward increased rolling element fatigue life with decreased retained austenite is apparent, but the confidence that all experimental differences are significant is not great.

In order to aid in further understanding hot corrosion processes, investigations of the electrical behavior of molten Na2SO4 (Sodium Sulfate) have been undertaken. Wagner-Hebb type polarization experiments and total electrical conductivity measurements by an A.C. impedance technique were carried out on melts of Na2SO4. It was observed that the total electrical conductivity of pure Na2SO4 was of the order of 2.33 x .1 (ohm-cm)(-1) and varied only slightly with changes in the activity of Na2O. From the Wagner-Hebb type D.C. polarization experiments on pure Na2SO4, the electron conductivity was shown to be much greater than the electron hole conductivity over the entire range of Na2O activities. The partial conductivity of electrons in Na2SO4 was about two orders of magnitude less than the total electrical conductivity. Additionally, studies were conducted to examine the nature of vanadium hot corrosion on two ceramic coatings (alumina and zirconia). Experiments showed significant solubility of V2O5 in Al2O3 while apparently causing little surface corrosion of the alumina. Similar work with stabilized zirconia samples evidenced definite corrosive dissolution of the surface. Electrical conductivities of a variety of partially- densified stabilized zirconia samples were measured to determine the effect of porosity on electrical transport. Thermodynamic models of both the Al2O3-Na2SO4- V2O5 and the stabilized zirconia-Na2SO4-V2O5 systems were described and compared to experimental data. (kt)

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

Bibliography: p. 27-31

AD-A313 885

An improved micro oxidation-corrosion test method for the effective screening of candidate advanced gas turbine engine lubricants is presented. A method for the preparation of formulations (base fluid plus additives) is also discussed. Micro oxidation (without metals) and oxidation-corrosion (with metals) evaluation data were obtained for various fluids and compared with results at other laboratories incorporating different test methods. A brief description of several large scale oxidation-corrosion test methods and a miniature scale oxidation test method developed previously at various laboratories is given.

A new family of fluorocarbon polyether fluids were investigated. The results show that these fluids have potential for advanced lubricant and hydraulic fluid applications. The fluid class is thermally stable at 700 deg F, has good lubricating characteristics, and is nonflammable. A shortcoming of these fluids is their corrosive effect on ferrous and titanium alloys in oxidizing atmospheres above 500 deg F.

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

The effects of potential impurities in coal derived liquids such as Na, K, Mg, Ca and Cl on the accelerated corrosion of IN-100, U-700, IN-792 and Mar-M509 were investigated using a Mach 0.3 burner rig for times to 1000 hours in one hour cycles. These impurities were injected in combination as aqueous solutions into the combustor of the burner rig. The experimental matrix utilized was designed statistically. The extent of corrosion was determined by metal recession. The metal recession data were fitted by linear regression to a polynomial expression which allows both interpolation and extrapolation of the data. As anticipated, corrosion increased rapidly with Na and K, and a marked maximum in the temperature response was noted for many conditions. In contrast, corrosion decreased somewhat as the Ca, Mg and Cl contents increased. Extensive corrosion was observed at concentrations of Na and K as low as 0.1 PPM at long times.

The corrosion of Udimet-700, coated with different doses of Na2SO4, was studied in an isothermal thermogravimetric test in the temperature range 900 to 950 C. The weight gain curve is characterized by five distinct stages: an initial period of linear corrosion; an induction period; a period of accelerated corrosion; a period of decelerating corrosion; and a period of parabolic oxidation. The time required for the failure of the alloy increases with an increase in the amount of Na2SO4, reaches a peak and then decreases with further increase in the amount of Na2SO4. For low and intermediate doses (0.3 to 2.0 mg/sq cm), the catastrophic failure of the material occurs by the formation of Na2MoO4 and interaction of the liquid Na2MoO4 with the alloy. For heavy doses, the degradation of the material is due to the formation of large amounts of sulfides.

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.

Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.

Silver and copper were deposited by electroless deposition upon YBa2Cu3O7 (bulk pieces and fibers). The electrical properties of these coated materials were determined by the four-point resistivity method. Good electrical contact between electroless silver layers and the YBa2Cu3O7 substrate could be attained. Copper was electrodeposited on electroless silver layer provided excellent environment protection to the underlying YBa2Cu3O7. The stability of YBa2Cu3O(6.5+x) powder in various aqueous and nonaqueous environments was studied. The time dependence of sample weight and oxygen content, x, were determined for the samples exposed to atmospheres saturated with concentrated ammonium hydroxide, glacial acetic acid, acetone, hexane, toluene, ethanol and methanol. Little evidence for reaction was found for the latter five organic vapors, while substantial reaction was found for the first two vapors. YBa2Cu3O(6.5+x) powder was also suspended in deionized water and aqueous 1 molar solutions of NaCl, KCl, KNO3, and NaBr. The results suggest that reaction is minimal and probably involves only the surface of the powder.

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

A review of High Temperature Tribocorrosion is presented focussing attention on those contributions that illustrate the general principles, modelling and scientific theories of the processes of high temperature wear. A significant aspect of this chapter is the inclusion of new information on glaze formation, generated at the sub-microscopic and nano-scale level.

A review of High Temperature Tribocorrosion is presented focussing attention on those contributions that illustrate the general principles, modelling and scientific theories of the processes of high temperature wear. A significant aspect of this chapter is the inclusion of new information on glaze formation, generated at the sub-microscopic and nano-scale level.

The effects of trace metal impurities in coal-derived liquids on deposition, high temperature corrosion and fouling were examined. Alloys were burner rig tested from 800 to 1100 C and corrosion was evaluated as a function of potential impurities. Actual and doped fuel test were used to define an empirical life prediction equation. An evaluation of inhibitors to reduce or eliminate accelerated corrosion was made. Barium and strontium were found to limit attack. Intermittent application of the inhibitors or silicon additions were found to be effective techniques for controlling deposition without losing the inhibitor benefits. A computer program was used to predict the dew points and compositions of deposits. These predictions were confirmed in deposition test. The potential for such deposits to plug cooling holes of turbine airfoils was evaluated. Tests indicated that, while a potential problem exists, it strongly depended on minor impurity variations.

The effects of trace metal impurities in coal-derived liquids on deposition, high temperature corrosion and fouling were examined. Alloys were burner rig tested from 800 to 1100 C and corrosion was evaluated as a function of potential impurities. Actual and doped fuel test were used to define an empirical life prediction equation. An evaluation of inhibitors to reduce or eliminate accelerated corrosion was made. Barium and strontium were found to limit attack. Intermittent application of the inhibitors or silicon additions were found to be effective techniques for controlling deposition without losing the inhibitor benefits. A computer program was used to predict the dew points and compositions of deposits. These predictions were confirmed in deposition test. The potential for such deposits to plug cooling holes of turbine airfoils was evaluated. Tests indicated that, while a potential problem exists, it strongly depended on minor impurity variations.

The hot corrosion of five alloys was studied in cyclic tests in a Mach 0.3 burner rig into whose combustion chamber various aqueous salt solutions were injected. Three nickel-based alloys, a cobalt-base alloy, and an iron-base alloy were studied at temperatures of 700, 800, 900, and 1000 C with various salt concentrations and compositions. The relative resistance of the alloys to hot corrosion attack was found to vary with temperature and both concentration and composition of the injected salt solution. Results indicate that the corrosion of these alloys is a function of both the presence of salt condensed as a liquid on the surface and of the composition of the gas phases present.

* Corrosion research at the University of Wisconsin is focused on two areas (i) plasma-based surface treatments to reduce corrosion, (ii) high temperature corrosion in harsh environments. * Plasma-based surface treatments (10 to 2000nm depth) have involved ion implantation and thin film deposition and atomic mixing approaches to mitigate corrosion and wear. * Specific testing equipment for corrosion testing in high temperatures and harsh environments such as supercritical water, molten salts, supercritical carbon dioxide (KAPL), and helium have been designed and built. * Room temperature corrosion tests for potentiodynamic corrosion tests, impedance spectroscopy, and salt spray test facilities exists and are being used for research in conjunction with a suite of materials characterization techniques. * Research projects involve the development of a basic understanding of corrosion mechanisms as well as strategies such as surface treatments and grain boundary engineering to mitigate corrosion.

This report summarizes the results of a research effort aimed at identifying hot corrosion-resistant stabilizers for zirconia (ZrO2) which could be used in zirconia-based thermal barrier coatings (TBCs) for engines operating on marine fuel under sea-going conditions. Among the oxides investigated were TiO2, CeO2, Y2O3, MgO, Sc2O3, In2O3, and SnO2. A brief overview of the hot corrosion of zirconia TBCs is given to illustrate the rationale used in evaluating the hot corrosion performance of the candidate oxides. The most promising stabilizer found for hot corrosion resistance was Sc2O3, or perhaps mixtures of Sc2O3 and small amounts of Y2O3. It was also discovered that Sc2Os, Y2O3- stabilized ZrO2 (SYSZ), of approx. 7 mol% of total stabilizer of which 5-20% is Y2O3, shows improved 1400 deg C stability of the tetragonal (t') phase as compared to present-day Y2O3-stabilized ZrO2 TBC compositions. This new material may have potential for TBC use in future high temperature, high efficiency gas turbine engines.

This report describes the 1st years efforts upon a number of processes related to hot corrosion. Total conductivities of pure sodium sulfate, Na2SO4 doped with nickel oxide and Na2SO4 doped with ferric oxide were measured at 900 C as a function of the activity of sodium monoxide. Partial electronic conductivies were also measured for the same systems utilizing the Wagner-Hebb type polarization cell. It was found that the total D.C. conductivity of pure Na2SO4 was of the order of .05 (1/cc) and varied only slightly with changes in the activity of Na2O.

This report describes the 1st years efforts upon a number of processes related to hot corrosion. Total conductivities of pure sodium sulfate, Na2SO4 doped with nickel oxide and Na2SO4 doped with ferric oxide were measured at 900 C as a function of the activity of sodium monoxide. Partial electronic conductivies were also measured for the same systems utilizing the Wagner-Hebb type polarization cell. It was found that the total D.C. conductivity of pure Na2SO4 was of the order of .05 (1/cc) and varied only slightly with changes in the activity of Na2O.

The oxidation and corrosion behavior of SiC (in the form of a SiC powder) and hot-pressed and reaction-bound material were studied. The excellent stability of SiC in an oxidizing atmosphere is due to the development of protective SiO2 coatings. Any changes in these protective layers (e.g., due to impurities, reaction with corrosive media, high porosity of SiC, etc.) lead in most cases to increased rates of oxidation and thus restrict the field of SiC application.

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

This report summarizes the current view of the mechanisms of the phenomenon of hot corrosion, whereby the surface integrity of gas turbine superalloys is degraded, and also the principal types of protective coating applied to aerofoil components made of these materials to inhibit hot corrosion and extend their useful lives. A concept is presented that the high-temperature corrosion resistance of superalloys can be significantly enhanced by selective modification of the composition and structure of their parasurface zones, utilizing new methods of surface treatment such as ion implantation, laser alloying, and thermal passivation. (Author)

Alloy 600, the material used for pressurized water reactor steam generator tubing, is susceptible to environmentally assisted stress corrosion cracking. Intergranular stress corrosion cracking (IGSCC) attacks the tubes in areas of high residual stress, and in crevice regions. No method has been successfully developed to monitor steam generator tubing in-situ for crack initiation and growth. Essentially all available published IGSCC crack growth data for alloy 600 is based on non-tubing material. Although it is very likely that the current data base is applicable to tubing processing, differences between tube and other geometries make a comparison between tubing and other data important for verification purposes. However, obtaining crack initiation and growth data from tubing is difficult due to the geometry and the thin wall thickness

The effects of potential impurities such as Na, K, Mg, Ca, and Cl, in coal-derived liquid fuels on accelerated corrosion of IN-100, U-700, IN-792, and Mar M-509 were investigated using a Mach 0.3 burner rig for times to 200 hours in one hour cycles. These impurities were injected in combination as aqueous solutions into the combustor. Other variables were time, temperature, and fuel-to-air ratio. The experimental matrix was a central composite fractional fractorial design divided into blocks to allow modification of the design as data was gathered. The extent of corrosion was determined by metal consumption. The time exponent was near 1.0 for the least corrosion resistant alloys, U-700 and IN-100; near 0.8 for the moderately resistant IN-792; and close to Mar M-509, the most corrosion resistant alloy. As anticipated, corrosion rapidly increased with increasing temperature as well as Na and K concentrations, while corrosion decreased somewhat as the Ca concentration increased for all alloys. Mg was beneficial for the Ni-base alloys but had little effect on the Co-base alloy. Surprisingly, the effect of increasing Cl was to decrease the corrosion of all alloys. Little interaction among the dopants was noted.

Methods currently used to deposit protective coatings in gas turbines are reviewed, and the structure of the respective coatings is examined. The corrosion behavior of such coatings is discussed on the basis of experimental data. General trends in the preparation of protective coatings are noted.

Candidate alloys for the Shuttle Solid Rocket Booster (SRB) case were tested under simulated service conditions to define subcritical flaw growth behavior under both sustained and cyclic loading conditions. The materials evaluated were D6AC and 18 Ni maraging steel, both heat treated to a nominal yield strength of 1380 MN/sq m (200 ksi). The sustained load tests were conducted by exposing precracked, stressed specimens of both alloys to alternate immersion in synthetic sea water. It was found that the corrosion and stress corrosion resistance of the 18 Ni maraging steel were superior to that of the D6AC steel under these test conditions. It was also found that austenitizing temperature had little influence on the threshold stress intensity of the D6AC. The cyclic tests were conducted by subjecting precracked surface-flawed specimens of both alloys to repeated load/thermal/environmental profiles which were selected to simulate the SRB missions. It was found that linear removal operations that involve heating to 589 K (600 F) cause a decrease in cyclic life of D6AC steel relative to those tests conducted with no thermal cycling.

This report results from a contract tasking Institute for Problems of Materials Science as follows: In this Project the new composites of ZrB2-SiC system will be created, their structure and high-temperature mechanical and corrosion properties will be studied up to 1600 C. The effect of (Zr, Mo)Si2 additives on both high-temperature corrosion resistance and high-temperature strength of composites above will be investigated. The new technologies of protective coatings will be developed with the use of thermal-chemical and also electrochemical (polarization) methods. The results obtained will be used for the development of a model of high-temperature oxidation of chosen ceramic systems. We are planning in this Project the obtaining of dense composites by activated sintering under pressure (hot pressing) using nanosized row materials with MoSi2 additives. Low porosity, composition modification and protective coating formation at high-temperature treatment will provide high level of strength and enhanced corrosion resistance. This Project also supposes the development of theoretical speculation for high-temperature oxidation parameters determination using both specific models and experimental kinetic curves of oxide layer growth for the systems under study. Such modeling concerns the peculiarities of oxide layer formation at the scale-ceramic substrate boundary including the investigation of oxide layers stability as to pittings, voids and other real scale defects. As a result of Project fulfillment a new knowledge for structural state and properties of ceramic composites management techniques will be obtained. So, new structural ceramic materials with higher working temperatures will be developed and studied in details.

This report describes the interaction between perfluoroalkyl polyether linear and cyclic derivative fluids and a high temperature bearing steel, WD-65, among others, studied in a laboratory oxidation-corrosion environment. Temperature ranges of 500F to 700F were covered by this investigation.

Silicon carbide (SiC) and silicon nitride (Si3N4) are proposed for applications in high temperature combustion environments containing water vapor. Both SiC and Si3N4 react with water vapor to form a silica (SiO2) scale. It is therefore important to understand the durability of SiC, Si3N4 and SiO2 in water vapor. Thermogravimetric analyses, furnace exposures and burner rig results were obtained for these materials in water vapor at temperatures between 1100 and 1450 C and water vapor partial pressures ranging from 0.1 to 3.1 atm. First, the oxidation of SiC and Si3N4 in water vapor is considered. The parabolic kinetic rate law, rate dependence on water vapor partial pressure, and oxidation mechanism are discussed. Second, the volatilization of silica to form Si(OH)4(g) is examined. Mass spectrometric results, the linear kinetic rate law and a volatilization model based on diffusion through a gas boundary layer are discussed. Finally, the combined oxidation and volatilization reactions, which occur when SiC or Si3N4 are exposed in a water vapor-containing environment, are presented. Both experimental evidence and a model for the paralinear kinetic rate law are shown for these simultaneous oxidation and volatilization reactions.

This research has examined the transport mechanisms relevant to hot corrosion. Three different approaches were used to elucidate this problem: an examination of the corrosion of the base metal, an exploration of the transport properties in Na2SO4, and an investigation in the role of defects in the transport behavior of a protective coating. The transport properties of molten Na2SO4 have been investigated to aid further understanding of hot corrosion processes at 1173 K. Tests were conducted to determine: the effect of height of Na2SO4 melts, the effect of electronic short circuiting the Na2SO4 melts with gold wires, and the effect of presaturating the salt melt with corrosion products in the hot corrosion process. Basically, these tests showed that neither ionic nor electronic transport in the bulk melt controls the hot corrosion process. However, the amount of Na2SO4 present, which is directly proportional to the height of the melt, does affect the rate of corrosion. This was demonstrated by the decrease in rate observed when the melt was presaturated with the corrosion products. An A.C. impedance technique for the total electrical conductivity, the potentiostatic polarization method for ionic transport numbers, and the steady state polarization method of Wagner and Hebb for the electronic conductivity were employed as a function of Na2O activity in the melt by controlling the gas atmosphere. These results showed that the conductivities of the pure Na2SO4 were of the order of 0.232 (ohm-cm)-1 and varied only slightly with Na2SO4, activity changes. From the polarization measurements, on the pure Na2SO4, it was found that electron conductivity was much higher than electron hole conductivity. The transport numbers were t (sub e) = 7.0x10(exp -3) and t (sub o) = 5.7x10 (exp -5).

Alloy 600, the material used for pressurized water reactor steam generator tubing, is susceptible to environmentally assisted stress corrosion cracking. Intergranular stress corrosion cracking (IGSCC) attacks the tubes in areas of high residual stress, and in crevice regions. No method has been successfully developed to monitor steam generator tubing in-situ for crack initiation and growth. Essentially all available published IGSCC crack growth data for alloy 600 is based on non-tubing material. Although it is very likely that the current data base is applicable to tubing processing, differences between tube and other geometries make a comparison between tubing and other data important for verification purposes. However, obtaining crack initiation and growth data from tubing is difficult due to the geometry and the thin wall thickness.