High Temperature Oxidation Resistant Coatings Research Articles

Review on plasma sprayed oxidation resistant coatings for C/C composites

Oxidation sensitivity is a critical obstacle to the rapid development of carbon/carbon(C/C) composites as the thermal structural materials in aerospace applications. Currently, surface coating technology is the most effective method to achieve the long-term stable service of C/C composites in high temperature oxygen-containing environments. Among them, plasma spraying technology, which has been widely used in the preparation of thermal barrier coatings for aero-engines, has attracted much attention. In this paper, starting from the plasma sprayed high-temperature oxidation resistant coatings for C/C composites, domestic and international research progress of boride, silicide and oxide based oxidation resistant coatings have been reviewed, the protective properties based on different spraying technologies, composition/structure designs and service conditions have been compared and summarized, and the prospect future for subsequent research in this field has been proposed.

High-temperature oxidation resistance of chromium-based coatings deposited by DLI-MOCVD for enhanced protection of the inner surface of long tubes

For nuclear safety issues, there is an international effort to develop innovative “Enhanced Accident Tolerant Fuels” (EATF) materials. EATF cladding tubes are of particular interest because they constitute the first barrier against radioactive fission species dispersal in case of accidental scenario such as LOCA (LOss of Coolant Accident). Actual nuclear fuel claddings are made from Zr-based alloys and to increase safety margins, both mechanical strength and resistance to high-temperature oxidation have to be improved. Several alternatives using high-temperature oxidation resistant coatings for outer-wall protection have been proposed worldwide but there is currently no solution for the inner-wall protection. In order to resist to high temperature steam environment upon LOCA transients, internal Cr-based coatings deposited by DLI-MOCVD (Direct Liquid Injection of MetalOrganic precursors) were investigated. These hard metallurgical coatings could also be used in high-temperature corrosive environments as those encountered in aeronautics and other industries to protect 3D complex components. Thanks to a suitable chemistry of the liquid Cr precursor, bis(ethylbenzene)chromium, different coatings were deposited including: metal Cr, chromium carbides CrxCy and mixed carbides CrxSizCy. The high-temperature behavior of these Cr-based coatings under oxidizing atmospheres has been studied using several techniques and various oxidation tests including pure steam environment followed by water quenching down to room temperature to be representative of LOCA situations. Amorphous CrxCy coatings showed the most promising properties. For instance compared to uncoated substrate, they shift the catastrophic oxidation towards higher temperatures and delay the complete oxidation of the substrate at 1473K of >2h. The results are discussed in terms of oxidation mechanisms and protection of the fuel claddings inner surface deduced from fine characterizations of the samples before and after oxidation tests.

Microstructure and oxidation resistance of Mo–Si–B coating on Nb based in situ composites

The development of robust high temperature oxidation resistant coatings for Nb–Si based alloy was evaluated for a Mo–Si–B coating system that was applied by a two step process. It is observed that the coating is composed of an outer layer of MoSi2 containing boride dispersoids and an inner layer of unreacted Mo. The mass gain of substrate and Mo–Si–B coating is 190.08 and 1.28mgcm−2 after oxidation at 1250°C in dry air for 100h, respectively. The good oxidation resistance of the coating is attributed to the formation of a continuous borosilicate glass coverage.

Research on the Si-Ti High Temperature Oxidation-Resistant Coatings for Tantalum Alloys

Si-Ti coatings were prepared on the surface of T-222 alloy by fused slurry method at different temperatures (1425-1500°C). Microstructure and composition of the coatings were characterized and analysed through scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), energy dispersive X-ray spectrometry (EDS) respectively. The coating fabricated at 1450°C exhibited excellent structure compatible with high temperature oxidation resistance. Its surface is relatively smooth with few holes and cracks and the main phase on the surface is (Ti, Ta)Si that possesses outstanding corrosion resistance. Moreover, the cross-sectional structure of the coating is smooth and compact which can effectively prevent O2 from permeation. The isothermal oxidation behaviors in pure O2 atmosphere at 1500°C for 2h finally demonstrate that the optimum coating temperature is 1450°C.

Multicomponent coating for enhanced oxidation resistance of tungsten

The development of robust high temperature oxidation resistant coatings for tungsten was evaluated for a Mo–Si–B coating system that was applied by a two step process. The synthesized coating shows a graded structure composed of various amounts of molybdenum and tungsten disilicide as well as an aluminoborosilica top layer. Oxidation tests conducted at 1100–1400°C demonstrate that the coating provides effective oxidation protection for tungsten. Furthermore, the Mo–Si–B coatings provide an enhanced oxidation resistance compared to that for W–Si–B-coatings or WSi2 coatings.

Influence of processing parameters on deposition rate and crystal structure of reactively sputtered HfC

Hafnium carbide is one of the materials with the most potential that can be used for high temperature oxidation resistant coatings. So far, HfC coatings are mainly being produced by chemical vapour deposition technique. In this work, HfC coatings were produced using a reactive magnetron sputtering method. The reactive gas used in these experiments was mixture of CH4 and H2. The study is focused mainly on the effect of process parameters, applied radio frequency (RF) power, process pressure and reactive gas flow, on the deposition rate and crystal structure of the deposited HfC coatings.

High Temperature Oxidation and Corrosion Resistant Nanocrystalline Coatings

Traditional high temperature oxidation resistant coatings are divided into three types: aluminide or modified aluminide coatings such as Cr-Al, Si-Al and Pt-Al; MCrAlY(M = Fe,Co and/or Ni) overlayer coatings and MCrAlY + Y2O3/ZrO2 thermal barrier coatings. Characteristic of these coatings is that their compositions are very different from their substrate alloys. Protection comes from the higher aluminium content in the coating to form Al2O3 at high temperature. However, these coatings may be harmful to the mechanical properties of the alloys as a result of the interdiffusion or thermal mismatch between the coating and substrate. Recently, a new kind of coating has been developed: high temperature oxidation resistant and hot corrosion resistant nanocrystalline coating, the composition of which is the same as the substrate. The only difference is that the grain size of the coating is several orders of magnitude smaller than that of the substrate. The formation of protective Al2O3 scale is not from the high aluminium content, but from the grain boundary diffusion. The main advantages of this kind of coating are that neither interdiffusion nor thermal mismatch exist between coating and substrate. The present paper reviews the high temperature oxidation and hot corrosion resistant nanocrystalline coating with particular reference to the authors' own results.

High Temperature Oxidation of HFPD Thermal-Sprayed MCrAlY Coatings in Simulated Gas Turbine Environments

NiCrAlY and CoNiCrAlY powders were thermal-sprayed using the high frequency pulse detonation method (HFPD) onto AISI 310 austenitic stainless steel samples to obtain dense, adherent, high temperature oxidation resistant coatings. The oxidation behavior of both types of coatings in a 1000°C simulated gas turbine environment was experimentally determined. The porosity, hardness, coating thickness, and microstructure were not significantly modified by the high temperature oxidation cycles, but the internal oxidation increases significantly after a very low oxidation time. Surface phase composition was evaluated using x-ray diffraction (XRD) and scanning electron microscope (SEM) techniques, revealing the formation of a continuous and highly protective alumina layer. The oxidation kinetics of both coatings can be characterized by parabolic rate constants, which are very close to those for the formation of aluminum oxide on nickel or cobalt based alloys at similar conditions.

Synthesis of nanocrystalline ceria particles for high temperature oxidation resistant coating

Cerium oxide has been investigated to be an effective coating material for high temperature applications for various alumina- and chromia-forming alloys. The present study investigates the use of microemulsion method to obtain monodispersed, non-agglomerated nanocrystalline ceria particles in the range of 5 nm using sodium bis(2-ethylhexyl) sulphosuccinate (AOT) as a surfactant. Furthermore, the use of non-agglomerated nanocrystalline ceria particles to develop improved high temperature oxidation resistant coatings on AISI 304-grade stainless steel was investigated. It was found that non-agglomerated nanocrystalline ceria particles were more effective in improving the oxidation resistance than the agglomerated nanocrystalline particles.

High Temperature Oxidation Resistant Coatings Produced by Electro-Spark Deposition

A simple but efficient technique has been developed to produce surface coatings on metals and alloys. The technique uses direct high frequency electrical sparks to melt and deposit metal or alloy coatings onto the substrate surface. This paper reports on Al and FeCrAl coatings on AISI 304 stainless steel. Cyclic oxidation tests at 1000°C in air showed that the oxidation rates of the coated specimens were much lower than that of the un-coated 304. The scale spallation resistance was also dramatically improved. The phases and microstructures of the coatings and oxide scales were characterised using XRD and HRSEM. The effects of the processing parameters are discussed based on the experimental results. Further improvements in an effort to obtain more uniform coatings are also proposed.

Evolution of metastable microstructures in laser ablation deposited Ni75Al25 thin films

Intermetallic thin films find application as protective high-temperature oxidation resistant coatings on gas turbine and aerospace components. The Intermetallic compound $Ni_3Al$ has potential towards application as protective coating and as well as bond coat between thermal barrier coating and superalloy engine components. Laser ablation is a powerful technique of depositing thin films of refractory materials. Due to the fast nature of the deposition process, the deposited matter experiences conditions far away from equilibrium. It is therefore important to study the phase evolution in laser ablation deposited $Ni_3Al$ film. In the present paper the phase formation in vapour deposited film and phase evolution during heating will be discussed.

High temperature oxidation of HFPD thermal-sprayed MCrAlY coatings

NiCrAlY and CoNiCrAlY powders were thermal-sprayed using the high frequency pulse detonation method (HFPD) onto AISI 310 austenitic stainless steel samples in order to obtain dense, adherent high temperature oxidation resistant coatings. The cyclic oxidation behaviour in air of both types of coatings was determined at a maximum temperature of 1273 K. The porosity, internal oxidation (after the first 8-h oxidation cycle), hardness, coating thickness and substrate-coating adherence were not significantly modified by the high temperature oxidation cycles. The surface phase composition was evaluated throughout the tests using X-ray diffraction and scanning electron microscope techniques revealing the formation of a continuous and highly protective alumina layer. The oxidation kinetics of both coatings can be characterized by parabolic rate constants, which are very similar to those of pure alumina.

Protective Coatings For Tungsten

S>Analysis was made of the reactions with the environment, vaporization processes, and coating-substrate reactions important in high-temperature oxidation-resistant coatings for tungsten. Evaluation of Pt-group metal and silicide coatings were given. (Rev. Metal Lit., 21: No. 1, Jan.