Sulfidation Resistance Research Articles

High Temperature Corrosion Behaviour of Intermetallic Phases based on Ni3Al

ABSTRACTNickel aluminides based on Ni3Al were continuously cast into 12.4 mm diameter wire in an industrial production machine. Cyclic corrosion tests were carried out on this material in oxidizing, carburizing, sulfidizing and chloridizing atmospheres at temperatures between 750°C and 1100 °C in order to study the time and temperature dependence of high temperature corrosion. The results show, that Ni3Al has a very good oxidation resistance up to 1000 °C. The sulfidation resistance is poor, while resistance against carburization and chlorination is significantly better than that of the commercial alloy 800H andalloy 617.

Effects of ion implantation on the mixed gas corrosion of a chromia former

The objective of this research was to understand the physical effects of the implantation process and the chemical effects of implanted species on the formation and breakdown of chromia scales in an oxidizing-sulfidizing atmosphere. Coupons of Fe25Cr and AISI 446 were polished metallographically on both sides up to 1 μm alumina and implanted on both sides with cerium. The energy and the fluence of implantation were about 160 keV and about 10 16 ions cm −2, respectively. A few coupons were implanted with xenon to isolate the effects of physical defects introduced by the implantation process on the corrosion behavior. Implanted and unimplanted coupons were exposed to a mixed gas environment at 700–850°C for times of up to 100 h. The breakdown of preoxidized scales by sulfur was also studied. The scales and the substrates were characterized by scanning electron microscopy combined with energy dispersive X-ray analysis, sputter Auger electron spectroscopy, Rutherford backscattering and transmission electron microscopy. The results showed that there was no significant change in the oxidation kinetics of cerium-implanted Fe25Cr from that of the unimplanted alloy at 700–850°C. Further, the presence of cerium did not enhance the sulfidation resistance at 700°C in a mixed gas environment.

Kinetics and mechanism of the sulfidation of Fe-Mo alloys

Iron-molybdenum alloys containing up to 40 wt.% molybdenum were exposed to sulfur vapor at a partial pressure of 0.01 atm at temperatures of 600–900°C. Sulfidation kinetics were measured over periods of up to 8 hr using a quartz-spring thermogravimetric method. The sulfidation kinetics of all alloys studied obeyed the parabolic rate law. The sulfidation rate of iron was found to be reduced by factors of 60 at 900°C and 120 at 600°C by the addition of 40 wt.% molybdenum. Duplex sulfide scales formed on all alloys at all temperatures, the scales consisting of an inner layer of mostly MoS2 and an outer layer of FeS. Platinum markers were located at the interface between the outer and inner scales, showing that outward iron diffusion and inward sulfur diffusion through the inner layer occurred. The improved sulfidation resistance was attributed to the formation of the MoS2, which acted as a partially protective barrier to the diffusion of the reacting species. Sulfidation activation energies were found to range from 24.3 to 28.5 kcal mole for the alloys compared to 20.6 kcal/mole, for pure iron. The rate-controlling step was outward iron diffusion through the outer iron sulfide layer.

Microstructural aspects of low-pressure plasma-sprayed CoNiCrAlY coating on Hastelloy X

A Co-32Ni-21Cr-8Al-0.5Y alloy coating was plasma sprayed on Hastelloy X. The microstructure of the coating layer consists of γ phase solid solution, γ′ phase, and Y-rich intermetallic phase. This coating exhibits excellent oxidation and sulfidation resistance after exposure in air and in sodium sulfate at 1,000°C for 60 h, due to the formation of α-Al 2O 3 oxide scale. However, the presence of chloride in the sodium sulfate leads to rupture of the aluminium oxide scale, and this results in the precipitation of chlorides and sulfides within the coating layer.

Oxidation-sulfidation behavior of nickel-base superalloys and MCrAl coatings

The oxidation-sulfidation behavior of several nickel-base superalloys and a number of MCrAl coatings on an IN-738 substrate has been examined after exposure to ten different O 2S 2 mixed gas environments. Selected alloys have been tested in a thermogravimetric system in which the mass change of the specimens was continuously monitored. Extensive metallurgical analyses of the exposed specimens were performed and the results were used to develop generalized maps that depict the corrosion product morphologies as a function of the exposure environment. The results, in general, showed that nickel-base superalloys are susceptible to sulfidation attack and undergo breakaway corrosion in low O 2 environments that contained sulfur. Of several MCrAl coatings that were tested, CoCrAlY and NiCoCrAlY compositions showed superior sulfidation resistance over a wide range of S 2 partial pressures at the test temperatures of 1144 and 923 K. Other MCrAl coatings examined in this study showed promise at low to intermediate S 2 partial pressures.

High temperature corrosion of Fe‐Cr‐Mn‐alloys in H2‐H2S and H2‐H2O‐H2S gas mixtures

AbstractThe sulfidation of Fe‐20% Cr‐30% Mn, Fe‐25%Cr‐20%Mn and Fe‐25% Cr was studied at 700°C in H2‐H2S and the oxidation and sulfidation in H2‐H2O‐H2S after preoxidation in H2‐H2O.The sulfidation rate is strongly increased for the Mn‐containing alloys, layers of (Mn,Cr)S and (Mn,Fe)Cr2S4 are formed. Also the oxidation rate is enhanced compared to Fe‐25% Cr by formation of MnCr2O4 instead of Cr2O3.The sulfidation after preoxidation leads to internal and external sulfidation of the Mn‐containing alloys. With increasing oxygen pressure p(O2) = 10−26…10−22 atm. of the H2‐H2O‐H2S mixtures the sulfidation is suppressed, for the higher oxygen pressure 10−23 and 10−22 atm. fast oxidation prevails under formation of MnCr2O4.Manganese cannot increase the sulfidation resistance of alloys, in spite of the stability and low degree of disorder of its sulfide, since the mixed sulfide (Mn,Cr)S is formed which has a high degree of disorder, high diffusivities and high growth rate according to the doping effect of trivalent Cr3+.

Atmospheric Sulfidation of Copper Alloys: I . Brasses and Bronzes

Although it is widely recognized that copper alloys are subject to sulfidation upon exposure to the atmosphere, the information available on the sulfidation rates of these alloys has come largely from field exposures under uncontrolled conditions. To gain more definitive information on the rates and processes involved in atmospheric sulfidation of copper alloys, we exposed nine copper alloys (brasses, nickel‐substituted brasses, and other common compositions) to low concentrations of hydrogen sulfide in humidified air. Among the specific results are the following. (i) The resistance to sulfidation of the brasses was 50–100 times better than that of pure copper. (ii) The substitution of nickel for part or all of the zinc produces alloys even more resistant to sulfidation for low to moderate exposures; at longer exposures their behavior is mixed. (iii) Beryllium copper and phosphor bronze are somewhat more resistant to sulfidation than copper except for long exposures, when all three behave similarly. (iv) A silicon bronze sulfidized more rapidly than copper for most exposure periods. (v) Alloying copper with 10% aluminum yields an alloy with a sulfidation resistance nearly as good as the brasses. These results are discussed in conjunction with the information available on oxide growth on these alloys, and it is demonstrated that the sulfidation resistance of the alloys is quite similar to their resistance to oxidation, once an initial oxide film has formed. The degree to which the surface oxide film inhibits copper diffusion is thus reflected in the oxidation and sulfidation behavior of a given alloy. The results indicate that the performance in sulfidizing environments of equipment containing copper alloy components or parts can thus be markedly influenced by the particular alloys selected by the physical designer.

The Role of Silicon Additions in the Corrosion Resistance of Chromia‐Forming Alloys in Coal Gasification Atmospheres

The use of silicon in Fe‐18% Cr alloys was investigated to determine whether the poor sulfidation resistance of 18% Cr iron‐base alloys for use in reducing coal gasification system atmospheres could be improved. It was determined that up to 2% Si did not produce an layer, but rather occurred in isolated areas in the corrosion scale and internally in the base metal. The 18% Cr also did not produce a continuous protective scale, permitting rapid corrosion to occur within 100 hr of exposure to , gases at 982°C.

Sulfidation-oxidation of advanced metallic materials in simulated low-Btu coal-gasifier environments

The corrosion behavior of structural alloys in complex multicomponent gas environments is of considerable interest for their effective utilization in coal conversion schemes. Little understanding of the degradation mechanisms of advanced high-temperature alloys in conditions typical of low-Btu coal gasifiers presently exists. Analysis of scale and subscale characteristics of several alloy types after exposure to the aggressive simulated low-Btu gasifier environments yielded a reaction model for these sulfidation-oxidation conditions. Initial competition between reactive metal oxide and base metal sulfide nuclei is followed by base metal sulfide overgrowth, chromium sulfide formation at the scale-metal interface, dissociation near voids in the subscale, and internal chromium sulfide precipitation. Additions of aluminum, titanium, and an oxide dispersion improve the sulfidation resistance by increasing the number of oxide nucleation sites and their growth kinetics on the surface in the crucial competition stage. Thermogravimetric tests carried out in three mechanistic regimes agreed with these hypotheses.

Alloy selection for sulfidation-oxidation resistance in coal gasification environments

A series of iron-nickel-chromium and nickel-chromium alloys were studied for their combined sulfidation-oxidation resistance in simulated coal gasification environments. All alloys contained a minimum of 20 wt pct chromium, and titanium and aluminum in the range 0 to 4 wt pct. Corrosion resistance was evaluated at 1255 K (1800 °F) in both high BTU and low BTU coal gasification atmospheres with 1 vol pct H2S. Titanium at levels greater than 1 wt pct imparted significant sulfidation resistance due to an adherent, solid solution chromium-titanium oxide layer which prevented sulfur penetration. A luminum was less effective in preventing sulfidation since surface scales were not adherent. Of the commercial alloys tested, Nimonic 81, Pyromet 31, IN801, and IN825 exhibited the best overall corrosion resistance. However, further alloy development, tailored to produce solid solution chromiumtitanium oxide scales, may lead to alloys with greater sulfidation-oxidation resistance than those investigated here.

Comparison of fatigue deformation and fracture in a dispersion-strengthened and a conventional nickel-base superalloy

INCONEL alloy MA 753 is a dispersion strengthened nickel-base superalloy made by mechanical alloying which combines γ’ precipitation hardening and yttria dispersion strengthening with good oxidation and sulfidation resistance. At temperatures up to 1227 K (1750°F), the fatigue strength of MA 753 is greater than that of a conventional wrought superalloy which has a composition close to that of the MA 753 matrix. Fatigue strength at elevated temperatures is strongly dependent on testing frequency. This behavior is correlated with the strain rate dependence of tensile strength. Fatigue crack initiation sites and propagation modes in MA 753 are discussed as a function of temperature and microstructure and compared to those in the conventional superalloy. The transition from transgranular to intergranular fracture mode in MA 753 occurs at a higher temperature than found in conventional nickel-base superalloys. While the γ’ precipitate controls the fatigue strength at low and intermediate temperatures, the oxide dispersoid and carbides also affect deformation in this temperature range. At elevated temperatures, fatigue deformation is controlled by the dispersoid and carbides.

Effect of the possible fcc stabilizers Mn, Fe, and Ni on the high-temperature oxidation of Co-Cr alloys

Earlier studies have suggested that manganese might be attractive as an alternative fcc stabilizer to nickel in cobalt base alloys because of its beneficial effect on the sulfidation resistance. Because it has relatively high oxygen affinity, it seemed possible that it might modify the ability of the alloys to form a protective Cr2O3scale. Thus, a range of alloys having compositions close to the critical Co-20 Cr value have been investigated in the temperature range 900–1150° C for times up to 240 hr in air and oxygen. Similar, but less extensive studies, have been conducted on alloys containing iron or nickel. None of these elements has a significant effect on the oxidation behavior, or on the ability of the alloys to develop a protective Cr2O3layer. However, manganese has a significant adverse effect on the scale spallation, apparently because of its increasing the brittleness of the oxide, particularly the CoO.

The relationship between relative oxide ion content of Na2SO4, the presence of liquid metal oxides and sulfidation attack

According to the “oxide ion” theory, sulfidation attack does not occur until oxide ions present in the fused Na2SO4 melt react with the normally protective oxide scale. It has already been shown that chromia reacts with and decreases the oxide ion content of sodium sulfate and inhibits sulfidation attack. Based upon the results reported herein, the reduction of the oxide ion content of sodium sulfate is a necessary but not sufficient condition for sulfidation inhibition. It is shown that the oxides of molybdenum as well as vanadium react with and decrease the oxide ion content of Na2SO4. It is shown that the addition of either Mo or V to nickel imparts sulfidation resistance. However, it is also shown that whereas the addition of Cr2O3 to Na2SO4-coated nickel-base superalloys prevents or inhibits sulfidation attack, no beneficial effects are noted when either MoO3 or V2O5 are codeposited with Na2SO4 onto nickel-base superalloy substrates. The reactions between V2O5 with metal oxides were also studied. V2O5 readily fluxes Al2O3 and slowly reacts with Na2SO4. The relationship between accelerated oxidation, oxide ion content of a fused melt and the fluxing of the normally protective oxide scale by liquid metal oxides is discussed.

The effects of aluminum alloying additions on the sulfidation behavior of iron

As part of an overall research program to examine the possible development of sulfidation-resistant alloys, the corrosion behavior of binary iron-based alloys containing 5, 10, and 20 wt. % of aluminum has been studied in a hydrogenhydrogen sulfide atmosphere for the temperature range 800–1000°C. Details of the observed overall reaction kinetics, the scaling kinetics, and the scales' morphology and composition are given. By considering these results in relation to those reported in an earlier paper concerning the sulfidation of an iron- 5 wt. % aluminum alloy at a lower temperature range, 500–700°C, it has been possible to ascertain the usefulness of aluminum as an alloying addition whereby the sulfidation resistance of iron might be improved. It is concluded that although aluminum can be quite effective in this context at relatively low reaction temperatures at only the 5 % concentration level, at the elevated temperatures likely to be of more industrial importance its usefulness is not maintained, even at the 20% level. The possible reason(s) for the inferior high-temperature performance of these alloys are discussed.

Dispersion strengthened superalloys by mechanical alloying

A new process called “mechanical alloying” has been developed which produces homogeneous composite particles with an intimately dispersed, uniform internal structure. Materials formed by hot consolidation of this powder achieve the long-sought combination of dispersion strengthening and age-hardening in a high temperature alloy. While the process is amenable to making a variety of alloys, its first use has been to combine yttrium oxide and gamma prime hardening hr at 1400°F and 15,000 psi for 100 hr at 1900°F together with excellent sulfidation and cyclic oxidation resistance. From a fundamental standpoint, results show that the age-hardening dominates the low-temperature strength, dispersion strengthening dominates at high temperature, and the two are augmentative in the intermediate temperature range 1300° to 1500°F.

MAR-M Alloy 421

Abstract MAR-M Alloy 421 is a precipitation hardened nickel-base superalloy developed to provide a good combination of high strength, ductility, sulfidation resistance, and stability. It is recommended for gas turbine applications. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as creep. It also includes information on corrosion resistance as well as casting, forming, heat treating, machining, joining, and surface treatment. Filing Code: Ni-141. Producer or source: Martin Metals Division.

アルミニウムを含む鋼の耐硫化性

アルミニウムを含む鋼の耐硫化性

Sulfidcttion Resistance of Aluminum - Containing Steels

Abstract It has been known for some time that alloying of steels with aluminum improves sulfidation and oxidation resistance. The behavior of a number of such alloys in high-temperature H2S-H2 envi...