High Temperature Corrosion Performance Research Articles

High temperature corrosion performance of ceria doped Cr3C2-NiCr coated superalloys under actual medical waste atmosphere

Incineration technique is well known process which has been adopted to burn medical or municipal waste. Burning of medical waste generates contaminated environment which can be harmful for the components of incinerator. As the temperature is very high in incinerator, austentic steel and superalloys are generally used in construction of the components. However these alloys also suffered corrosion which can be delayed for some time by providing a coating protection on the surface of the alloys before installation. Hence, in this study, ceria incorporated Cr3C2-NiCr coating powder was deposited on Superni 600 and Superco 605 superalloys. For deposition, one of the thermal spray techniques know as detonation gun was used. The coated samples were drilled to hang using wire in the secondary chamber of incinerator operating at 1050 °C for 1000 h in a hospital. It was observed that coated Superco 605 suffered more corrosion as compared to coated Superni 600.

Influence of Heat Treatment and Sealing on Hot Corrosion Behavior of 80Ni-20Cr Coatings

The present work aims to examine the influence of heat treatment and sealing on high-temperature hot corrosion performance of HVOF-deposited 80Ni-20Cr coating on T347H austenite steel. The high-temperature corrosion performance of T347H, 80Ni-20Cr, 80Ni-20Cr heat-treated and 80Ni-20Cr sealed coatings has been investigated in Na2SO4-60V2O5 atmosphere at 750 °C for 50 cycles. Corrosion kinetics were measured by weight change calculations after each cycle. Bare T347H steel experienced severe spallation of the oxide scale indicating weak resistance toward high-temperature hot corrosion. 80Ni-20Cr coatings have given a significant protection to austenite steel due to the development of oxides and spinels of Ni and Cr. Further, the post-treated by way of heat treatment and sealing improved the corrosion resistance of 80Ni-20Cr coating. Both the post-treatments lead to choking the interconnected porosity of the 80Ni-20Cr coating, which resulted in better performance of post-treated coatings.

Experimental Evaluation of High Temperature Corrosion Performance of 75Ni25Cr Coated and Bare 347H SS in Air and Simulated Husk Fired Boiler Environment

Corrosion occurring at elevated temperatures is a serious problem in areas such as gas turbine applications and power plants that use high temperature boilers. In this paper, we carry out experimental investigation for reducing corrosion rate so as to enhance the corrosion and wear characteristics of 347HSS and quantify the effect of 75Ni25Cr on 347HSS in terms of improved corrosion resistance. A coating of 75Ni25Cr was deposited on 347HSS boiler tube by the process of Detonation Gun. Corrosion studies were conducted on bare as well as D-Gun coated 347H stainless steel specimens in air and simulated husk fired boiler atmosphere at 800°C under cyclic conditions. Each cycle consisted one hour of heating in the tubular furnace and 20 min of cooling at room temperature. Fifty such cycles were completed to observe performance of these specimens. The weight change measurements were performed after each cycle to establish the kinetics of corrosion using weighing balance. Scanning Electron Microscopy, X-ray diffraction and X-ray mapping analysis techniques were used to analyse the corrosion products formed on the surface of these substrates.

High-temperature corrosion performance of HVAF-sprayed NiCr, NiAl, and NiCrAlY coatings with alkali sulfate/chloride exposed to ambient air

The high-temperature corrosion of high velocity air-fuel (HVAF) thermal spray Ni21Cr, Ni5Al, and Ni21Cr7AlY coatings was investigated at 600 °C for 168 h in ambient air under KCl and 50-50 mol% KCl–K2SO4 salts. Chlorination-oxidation cycle and breakdown of the corrosion products layer were the dominant corrosion mechanism in the chromia-forming Ni21Cr and Ni21Cr7AlY coatings exposed to KCl. KCl–K2SO4 was less corrosive to the chromia-forming coatings as K2SO4 was less reactive to the protective Cr-rich oxide. The alumina-forming NiAl exhibited a better corrosion performance under KCl, though it partially suffered from selective sulfidation when exposed to the mixed salt.

The Effect of La on the Oxidation and Corrosion Resistance of $$\hbox {Cu}_{52}\hbox {Ni}_{30}\hbox {Fe}_{18}$$ Cu 52 Ni 30 Fe 18 Alloy Inert Anode for Aluminum Electrolysis

The effect of La on the high-temperature oxidation and corrosion performance of ternary $$\hbox {Cu}_{52}\hbox {Ni}_{30}\hbox {Fe}_{18}$$ alloy inert anode for aluminum electrolysis in low-temperature KF–NaF– $$\hbox {AlF}_{3}$$ electrolyte was studied. The results indicate that the oxidation kinetics of ( $$\hbox {Cu}_{52}\hbox {Ni}_{30}\hbox {Fe}_{18})_{1{-}x}\hbox {La}_{x}$$ (x = 0, 0.5, 1, 2 wt%) alloys at $$850\,^{\circ }\hbox {C}$$ under 1 atm oxygen atmosphere follow the parabolic law. The oxidation scales are stratified state, which contains the Cu oxide as the external layer. While the internal layer of the oxidation products are the mixture of Fe oxide, Ni oxide and nickel ferrite. The Cu outward diffusion oxidation is the dominant factor for the $$\hbox {Cu}_{52}\hbox {Ni}_{30}\hbox {Fe}_{18}$$ alloy during high temperature oxidation. After adding La to the $$\hbox {Cu}_{52}\hbox {Ni}_{30}\hbox {Fe}_{18}$$ alloy, the oxidation mechanism has become the combined action with outward diffusion of Cu and internal diffusion of O to form the Ni/Fe oxide underneath the outmost CuO layer. The corrosion resistance of $$\hbox {Cu}_{52}\hbox {Ni}_{30}\hbox {Fe}_{18}$$ alloy anode during the aluminum electrolysis is further improved by adding 0.5 wt% La. Compared with $$\hbox {Cu}_{52}\hbox {Ni}_{30}\hbox {Fe}_{18 }$$ alloy, the corrosion rate of the $$\hbox {Cu}_{52}\hbox {Ni}_{30}\hbox {Fe}_{18 }$$ alloy with 0.5 wt% addition of La has reduced from 1.9 to 1.8 cm/a.

Accelerated Hot Corrosion Studies of D-Gun-Sprayed Cr2O3–50% Al2O3 Coating on Boiler Steel and Fe-Based Superalloy

In the current investigation, Cr2O3–50% Al2O3 coating was deposited on ASTM-SA213-T-22 boiler steel and Fe-based superalloy Superfer 800H by D-gun spray process. The high-temperature corrosion performance of the coated as well as bare alloys was evaluated in Na2SO4–60%V2O5 molten salt, an aggressive environment at 900 °C under cyclic conditions. The kinetics of the corrosion were analyzed by the change in weight measurements which were taken after each cycle (i.e., 1-h heating in a tube furnace followed by 20-min cooling in ambient air) for a total period of 50 cycles. The X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray analysis techniques were used for the analysis of corrosion products. During investigations, it was found that both the selected bare alloys have suffered intensive spallation in the form of removal of their oxide scales, which may be attributed to the formation of non-protective Fe2O3-dominated oxide scales, whereas the coated alloys have shown lesser weight gains along with better adhesiveness of the oxide scales with the substrate till the end of the experiment. The oxides of chromium and aluminum were the main phases revealed in the oxide scales of the coated specimens, which are reported to be protective against the hot corrosion.

High temperature corrosion performance of Q235 steel in sulfur-bearing solution

The high temperature corrosion performance of Q235 steel in sulfur-bearing solutions as a function of temperature, test time, and sulfur content was investigated by weight loss measurements in this study. The results indicate that the corrosion behavior of Q235 steel in sulfur-bearing solution is directly related to the experimental temperature, immersion time and sulfur content. Higher temperature leads to a higher corrosion rate of the steel. The corrosion rate increases during the initial test time and then decreases with increasing the test time. As the sulfur content increases in the solution, the corrosion rate increases, and further increasing the sulfur content leads to a decreased corrosion rate.

Tailoring a High Temperature Corrosion Resistant FeNiCrAl for Oxy-Combustion Application by Thermal Spray Coating and HIP

Oxy-fuel combustion combined with CCS (carbon capture and storage) aims to decrease CO2 emissions in energy production using fossil fuels. Oxygen firing changes power plant boiler conditions compared to conventional firing. Higher material temperatures and harsher and more variable environmental conditions cause new degradation processes that are inadequately understood at the moment. In this study, an Fe-Ni-Cr-Al alloy was developed based on thermodynamic simulations. The chosen composition was manufactured as powder by gas atomization. The powder was sieved into two fractions: The finer was used to produce thermal spray coatings by high velocity oxy-fuel (HVOF) and the coarser to manufacture bulk specimens by hot isostatic pressing (HIP). The high temperature corrosion properties of the manufactured FeNiCrAl coating and bulk material were tested in laboratory conditions simulating oxy-combustion. The manufacturing methods and the results of high temperature corrosion performance are presented. The corrosion performance of the coating was on average between the bulk steel references Sanicro 25 and TP347HFG.

Effect of additions of TiC and Re on high temperature corrosion performance of cold sprayed Ni–20Cr coatings

Thermal spray coatings have been widely used to combat corrosion and erosion–corrosion problems in power plant boilers. In the present work, commercially available Ni–20Cr powder, Ni–20Cr blended with TiC powder and Ni–20Cr blended with TiC and Re powder were successfully deposited on a boiler steel (SAE 213-T22) by the cold spraying technique. The uncoated and coated specimens were subjected to a molten salt environment of Na2SO4–60wt.%V2O5 at 900°C under cyclic conditions. Mass change was used to establish the kinetics of corrosion. X-ray diffraction, surface and cross-sectional FE-SEM/EDS techniques were used to analyze the corrosion products. All the cold spray coatings performed better than the uncoated steel; the better hot corrosion resistance of the coatings in comparison to the uncoated steel may be attributed to the formation of oxides and spinels of nickel and chromium. The hot corrosion resistance of cold sprayed Ni–20Cr–TiC–Re coating was found to be the best amongst all the studied coatings.

Corrosion Performance of High Strength 15Cr Martensitic Stainless Steel in Severe Environments

High pressure and high temperature corrosion performance of high strength 15Cr martensitic stainless steel was studied in different severe environments—live acid (10% HCl + 1. 5% HF + 3% HAc + 5.1% corrosion inhibitor), spent acid and formation water containing CO2. The results show that the corrosion of high strength 15Cr martensitic stainless steel in live acid is most serious, and the uniform corrosion rate is far greater than those in spent acid and formation water containing CO2 corrosion environments, but all of them can be acceptable for oilfield. Acidizing corrosion inhibitor displays a good matching ability with the high strength 15Cr martensitic stainless steel in terms of decreasing the uniform corrosion rate, which changes mainly the anodic process of high strength 15Cr martensitic stainless steel. The corrosion potential moves to the positive direction, thus the corrosion current density decreases significantly. There arc some different degrees of pitting of high strength 15Cr martensitic stainless steel after corrosion tests in live acid, spent acid and formation water containing CO2, and the pitting density aggravates significantly and the maximum pit depth decreases in the corrosion sequence.

The structure and high temperature corrosion performance of medium-thickness aluminide coatings on nickel-based superalloy GTD-111

Simple and Si-modified aluminide coatings having medium-thickness (40–60 μm) have been applied on the superalloy GTD-111 by a slurry technique. Hot corrosion and cyclic oxidation performance of the uncoated and the coated superalloy were investigated by exposing samples to a molten film of Na 2SO 4-40 %wt NaVO 3-10%wt NaCl at 780 °C and 1 h cyclic oxidation at 1100 °C in air, respectively. The presence of silicon in the aluminide structure increased the oxidation resistance by a factor of 1.7 times. In addition, a SiO 2-containing scale, which formed on the Si-containing coating surface, was stable during of the hot corrosion testing.

Ultrafine Particulate Dispersed High-Temperature Coatings by Hybrid Spray Process

Oxide dispersion strengthened alloys (ODS), although not commonly used in coating applications, have long been used for high-temperature structural applications due to their superior creep properties. In this paper, we present the design, synthesis, and characterization of a new class of functionally engineered high-temperature coatings in which ultrafine oxide particulates are dispersed in the matrix alloy to achieve superior creep resistance along with improved high-temperature corrosion and erosion resistance. These coatings were fabricated using a novel technique called “hybrid spray process”. Hybrid spray technique combines arc spray and high-velocity oxy fuel (HVOF) spray processes; the metallic matrix alloys are fused by the wire arcing component of the process, whereas the ultrafine particles are synthesized in-flight by the HVOF component from liquid precursors. These particulate dispersed high-temperature composite coatings were fabricated using liquid precursors for SiO2, Cr2O3, Al2O3, and wire feed stock of 55/45 NiCr, in one step. The coatings were then characterized using electron microscopy (SEM/TEM) and thermogravimetric analysis (TGA). High-temperature erosion, oxidation, and corrosion performance of these coatings were also evaluated and compared with 304 stainless steel, arc sprayed NiCr coatings as well as Alloy 625 overlay cladding. The hybrid spray process produced dense coatings with uniform dispersion of the ultrafine oxide particles. Further, these coatings also demonstrated superior corrosion, erosion, and oxidation resistance; SiO2 particulate dispersion being most effective in terms of high-temperature corrosion resistance.

Effect of superficially applied ZrO 2 inhibitor on the high temperature corrosion performance of some Fe-, Co- and Ni-base superalloys

High temperature corrosion is an acute form of corrosion occurring at elevated temperature in the presence of an oxidizing gas and is associated with a thin electrolytic deposit (salt or ash) on alloy. Inhibitors and fuel additives have been used with varying success to combat oil ash corrosion. In this paper, the effect of an oxide additive namely ZrO 2 on the hot corrosion behaviour of some superalloys, viz. Superfer 800H (alloy A), Superco 605 (alloy B) and Superni 75 (alloy C) has been investigated in an Na 2SO 4–60%V 2O 5 environment at 900 °C for 50 cycles. Each cycle consisted of 1 h heating in a Silicon Carbide Tube furnace followed by 20 min cooling in ambient air. Weight change measurements after each cycle were taken by an electronic balance having an accuracy of 0.01 mg. XRD, SEM and EPMA analyses of the exposed specimens were carried out to characterize the oxide scales. In the Na 2SO 4–60%V 2O 5 environment, the corrosion rate for the Co-base alloy was found to be highest, whereas that for the Ni-base Superni 75 a lowest. Whereas, with ZrO 2 superficial coating, the overall weight gains got reduced for the alloys B and C, however the inhibitor was marginally effective in the alloy A. A thick scale was observed in the latter case, which was rich in Cr, Ni, Fe and V. Absence of protective continuous chromia layer and presence of less protective NiO was probably the main reason for more corrosion rate in this case.

High-Temperature Corrosion of Y-Doped Fe<SUB>3</SUB> Al in Environments Containing Chlorine and Oxygen

The high-temperature corrosion performance of Y-doped Fe3Al was studied in various environments containing chlorine, oxygen, and argon. Results were compared with Y-free Fe3Al in terms of corrosion rate and microstructure of corrosion products. The kinetic pattern shown in the two types of alloy features two consecutive stages: initial slow mass loss followed by fast linear mass loss. However, addition of Y decreased the rate but increased the duration of the first stage of the corrosion. Microstructure examination indicates that the beneficial effect of Y may be due to the formation of pegs and the development of dense oxide layers.

The corrosion behavior of hafnium in high-temperature water environments

The high-temperature water corrosion performance of hafnium is evaluated. Corrosion kinetic data are used to develop correlations that are a function of time and temperature. The evaluation is based on corrosion tests conducted in out-of-pile autoclaves and in out-of-flux locations of the Advanced Test Reactor at temperatures ranging from 288 to 360 °C. Similar to the corrosion behavior of unalloyed zirconium, the high-temperature water corrosion response of hafnium exhibits three corrosion regimes: pretransition, post-transition, and spalling. In the pretransition regime, cubic corrosion kinetics are exhibited, whereas in the post-transition regime, linear corrosion kinetics are exhibited. Because of the scatter in the spalling regime data, it is not reasonable to use a best fit of the data to describe spalling regime corrosion. Data are presented to show that in the pretransition regime, neutron irradiation does not alter the corrosion performance of hafnium.

High temperature corrosion performance of FeAl intermetallic alloys in molten salts

The corrosion performance of FeAl base intermetallic alloys fabricated by spray-atomization and deposition during their immersion in molten sodium metavanadate (NaVO3), 80% (wt.%) sodium pentoxide (V2O5) +20% sodium sulfate (Na2SO4) and pure Na2SO4 in the temperature range of 600–1000°C during 200 h was investigated. The experiments were realized by the weight loss method in the intermetallic alloys of composition FeAl40(at.%), FeAl40+0.1B and FeAl40+0.1B+10Al2O3. In all cases, the FeAl40+0.1B+10Al2O3 alloy showed the best corrosion resistance in the temperatures interval studied here. This behavior was discussed in terms of the formation of a protective Al2O3 layer and its dissolution by vanadate phases and internal sulfidation in the case of experiments carried out in pure Na2SO4. The morphology of the external layers and the corrosion products formed during the tests revealed that the corrosion rate of this type alloy depends on the corrosion compounds that are formed and the development of protective alumina scales.

Computer Simulations of Heterogeneous Reactions Controlled by Diffusion in Modified Aluminide Coatings on a Nickel-Based Superalloy

Materials used in high temperature applications must possess both strength and corrosion resistance. The increase in operating temperatures of industrial energy systems and gas turbines, often coupled with the decrease in fuel quality being employed, has led to the extensive use of coatings capable of providing improved service life. The application of diffusion aluminide coatings on nickel based superalloys has beneficial influence on the high temperature performance of gas turbines operating at elevated temperatures. Platinum addition to basic aluminide coatings significantly improves the oxidation resistance of these coatings [1]. Evidence has now emerged from the oxidation and hot corrosion studies [2] that the high temperature corrosion (HTHC) performance of nickel based superalloys can be improved by the combined addition of platinum and rhodium to nickel aluminide coatings. In the Figure 1, a comparison of the SEM backscattered electron image of the corrosion products of the uncoated MAR M002, Pt-Aluminide, PtRh-Aluminide coatings after 100 h hot corrosion tests at 1173 K is presented. The protective capability of the aluminide coatings is conferred by the ability of the $-NiAl layer to provide aluminum to maintain an Al2O3 based scale at the surface. It is believed that the incorporation of Rh with Pt increases the stability of $-NiAl [3]. This type of coating is very resistant to oxidation owing to its ability to form a slow-growing and adherent oxide, Al2O3 [4,5]. However prolonged oxidation eventually process leads to the depletion of aluminium in the vicinity of the coating/scale interface decreasing the ability $-NiAl to reform the protective -Al2O3. In this work we will show the possibility of adopting a theoretical approach for describing the complex processes occurring in alloy/coating systems induced by reactions at coating/gas interface, e.g., oxidation, sulphidation or other complex processes like hot corrosion. The mathematical model for interdiffusion in multi-component open systems which allows for the description of a wide range of processes (e.g., processes stimulated by reactions at interfaces) is presented. The inverse problem of interdiffusion and the method which permits calculation of the intrinsic diffusivities, for an arbitrary number of components in a system, is also presented. This approach has been used to calculate the effective intrinsic diffusivities of the elements in Pt modified $-NiAl on MAR M002 superalloy. Subsequently, the evolution of the components’ concentration in oxidized Pt modified $-NiAl/MAR M002 system is presented and compared with the experimental results. Figure 1. Comparison of the SEM backscattered electron image of the corrosion products of the uncoated MAR M002, Pt-Aluminide and Pt-Rh-Aluminide coatings after 100 h hot corrosion test at 1173 K. Generalized Model of Interdiffusion This model follows Darken’s postulate [6] that the total mass flow is a sum of the diffusional and drift flows only. The equations of mass conservation (continuity equations), the appropriate expressions describing the fluxes, the postulate of constant molar volume of the system allow for a complete quantitative description of the diffusional transport process. Some aspects of this model for the closed system has been already published [7]. The formulation of the interdiffusion problem for the multicomponent open system and constant intrinsic diffusivities are presented bellow. Data: 1) molecular masses of the elements: M1, . . . , Mr (g mol ), where r denotes the number of components; 2) constant intrinsic diffusivities: D1, . . . , Dr (cm 2 s), which in general, may depend on composition, 3) initial position of the right end of the system (its right border): 7, 4) time of the process duration: t, 5) initial distribution of the elements:

Critical factors affecting the high-temperature corrosion performance of iron aluminides

Iron aluminides are known to exhibit good-to-excellent corrosion resistance in a number of high-temperature environments. Under most conditions, this resistance derives from the establishment and maintenance of a sound and adherent alumina layer. Consequently the performance of iron aluminides under different aggressive high-temperature can be related to fundamental factors that affect the development, adhesion, and durability (lifetime) of protective alumina. Overall corrosion resistance depends not only on thermodynamic stability of the reaction product in a particular environment and its growth kinetics, but also on scale integrity and morphology, the chemical and physical nature of the oxide–metal interface, alloy strength, and the specific composition of the iron aluminide. Despite the multiplicity of factors, a relatively simple lifetime prediction model based on aluminum consumption can be used to evaluate the influences of changes in material parameters and to determine approaches to improving high-temperature corrosion resistance of iron aluminides.

High-temperature corrosion performance of plasma-sprayed CrNiMoSiB coatings

This study examined the effects of application parameters for plasma spraying and CCh- laser glazing of two types of chromium-base coatings. Coatings were deposited by low-pressure and atmospheric plasma spraying. The high-temperature corrosion resistance of Cr-Ni-2.5Mo-lSi-0.5B (55 and 58% Cr) coatings was evaluated with respect to structural and compositional changes both in the as- sprayed condition and after CCb- laser glazing. Coatings that were deposited by atmospheric plasma spraying and subsequently laser glazed showed excellent resistance to oxidation and sulfate- vanadate attack at 900 °C due to the formation of a protective chromia film and a high silica concentration on the top layers of the oxide.

Alloy corrosion in a coal gasification system

The corrosion performance of alloys in coal gasification systems is of increasing industrial interest as more advanced coal-fired power generating systems are developed. It is necessary to consider the performance of candidate materials under likely exposure conditions to ensure that components have adequate lifetimes. Materials performance can influence the economic feasibility of these systems. This paper reports the high temperature corrosion performance of a range of materials exposed in British Coal's air-blown, spouted fluidised bed coal gasification pilot plant. The exposures were carried out in the hot gas path of this plant for periods of up to 660 hours, in three distinct temperature ranges between 330 and 920 ° C (i.e. ranges representative of possible evaporator, superheater and ductwork conditions). By characterising the gasifier product gas using carefully selected elements and compounds, activity windows have been defined for sulphur and oxygen for this environment in the required temperature ranges. Standard metallurgical analyses were carried out on exposed alloys to determine their performance in the required temperature ranges. It was found that MA956 performed best in the higher temperature ranges, whilst alloys containing 22-28% chromium performed better in the lower temperature ranges.