Enhanced Oxidation Resistance Research Articles

Effect of Al on oxidation behavior of AlxCrCuFeNi2 (x = 0.2, 0.4, 0.6) high entropy alloys

The effect of Al on the oxidation behavior of AlxCrCuFeNi2 (x = 0.2, 0.4, 0.6) high entropy alloys was investigated at 700 °C in water vapor. The oxidation kinetics of all the alloys followed parabolic behavior, with their oxidation rates decreasing with increasing Al concentration. Thick triplex oxide scales with discontinuous Al2O3 formed on the Al0.2CrCuFeNi2 alloy, while a continuous Al2O3 layer and thinner spinel oxide scale grew on Al0.4CrCuFeNi2 and Al0.6CrCuFeNi2 alloys. The early formation of continuous Al2O3 scale in the initial stage of oxidation contributes to the enhanced oxidation resistance of high Al content alloys.

Au-coated Ag alloy bonding wires with enhanced oxidation resistance for electronic packaging applications

PurposeThe purpose of this paper is to develop high-performance Au-coated Ag alloy wires (ACAA wires) and demonstrate the effect of Au coating layers on the bonding performance and oxidation resistance for stable and reliable electronic packaging applications.Design/methodology/approachACAA wire with a diameter of approximately 25 µm and Au layer thickness of approximately 100 nm were prepared by the continuous casting, plating and wire drawing method. The bonding performance of the ACAA wires were studied through bonding on 3,535 chips. The oxidation resistance of ACAA wires and Ag alloy wires (AA wires) were comparatively studied by means of chemical oxidation tests, accelerated life tests and electrochemical tests systematically.FindingsACAA wires could form axi-symmetrical spherical free air balls with controllable diameter of 1.5∼2.5 times of the wire diameter after electric flame-off process. The ball shear strength of ACAA wire was higher than that of AA wires. Most importantly, because of the surface Au coating layer, the oxidation resistance of ACAA wires was much enhanced.Research limitations/implicationsACAA wires with different lengths of heat affected zone were not developed in this study, which limited their application with different loop height requirements.Practical implicationsWith higher bonding strength and oxidation resistance, ACAA wires would be a better choice than previous reported AA wire in chip packaging which require high stability and reliability.Originality/valueThis paper provides a kind of novel ACAA wire, which possess the merits of high bonding strength and reliability, and show great potential in electronic packaging applications.

Enhanced oxidation resistance of an AlSi alloy coating via Cr barrier layer insertion

A novel Cr barrier layer was designed for suppressing the interdiffusion of an AlSi alloy coating on stainless steel. Without a Cr barrier layer, the same coating experienced a severe element interdiffusion upon exposure to high-temperature air. The rapid upward movement of the Fe atoms induced the formation of the (FeAl + Fe2Al5) alloy compounds and eventually led to severe volume shrinkage and the ultimate fracture of coating. The significant downward diffusion of the (Al + Si) atoms not only triggered numerous pores but also induced the accumulation of the FeAl alloy compound in the substrate resulting in extreme interfacial cracking. In contrast, a diffusion barrier layer comprising (Cr2O3 + SiO2) and Al2O3 was formed in the coating with a Cr layer during high-temperature exposure, effectively preventing the rapid elemental interdiffusion. Moreover, it inhibited the formation of the (FeAl + Fe2Al5) alloy compounds in the coating as well as prevented the accumulation of the FeAl in the substrate. The obvious upward diffusion of Cr atoms further healed these pores induced by the downward diffusion of (Al + Si) atoms. The strong barrier capability of this composite oxide layer and the healing effect of Cr diffusion eventually led to an improved oxidation resistance of the Cr-coated layer.

Effects of boron and carbon on the oxidation behavior of a NbMoTaW refractory high entropy alloy

Refractory high entropy alloys (RHEAs) are typically sensitive to oxygen, suffering from their poor oxidation resistance at elevated temperatures. Here we dope a NbMoTaW alloy with boron (B) and carbon (C) by 0.5 at% and 2 at% and then compare their oxidation behavior with that of pure tungsten (W) at 800 ℃ in air. We show that the NbMoTaW alloy exhibits a higher oxidation resistance than pure W; doping 0.5 at% B or C may sacrifice the oxidation resistance of the NbMoTaW alloy; doping 2 at% B and C enhances the oxidation resistance of the NbMoTaW alloy. We discuss the mechanisms of such doping effects and demonstrate substantially enhanced oxidation resistance for RHEAs.

Single-source-precursor derived SiHfBCN enhancing oxidation resistance of SiC/SiC composites in wet oxygen

Semi-dense SiC fiber reinforced SiC (SiC/SiC) composites were modified by single-source-precursor derived SiHfBCN ceramics to obtain SiC/SiC-SiHfBCN composites with enhanced wet oxidation resistance. Wet oxidation behavior of SiC/SiC-SiHfBCN composites at 1200–1400 ℃ in different atmospheres were investigated. It was found that the SiC-SiHfBCN ceramic matrix can provide at least 100 h of damage-free protection for SiC fibers up to 1300 ℃ in wet oxygen. HfSiO4 with low oxygen diffusivity is found on the surface of SiC/SiC-SiHfBCN composites after oxidation, which is discussed in terms of diffusion of HfO2 from the bulk to the surface via liquids.

Reduction and stabilization of Cr(VI) in groundwater by using polysulfide-modified nanoscale zero-valent iron

Hexavalent Chromium Cr(VI) is highly toxic in groundwater as a result of natural and anthropogenic sources. As a widely reported material for Cr(VI) remediation, sulfide-modified nZVI (S-nZVI) can enhance the nanoparticle selectivity and reaction rate, but has deficiencies of instability and low removal efficiency. In this study, the optimal S-nZVI used for Cr(VI) removal from groundwater was selected, and the mechanism and influence of environmental factors had been discussed. Among the selected sulfur sources including Na2S, Na2S2O3, Na2S2O4, and CaSx, the CaSx-nZVI had the highest removal efficiency. A 1.5-fold removal rate than traditional S-nZVI was observed for CaSx-nZVI during the treatment of a highly chromium-containing groundwater (200 mg/L), because of its significant inhibition on Fe0 oxidation due to the stable shell-core structure. With the sulfur-iron ratio increased from 1/20 to 1/2, the removal efficiency displayed a trend of first increase followed by a decrease. This was ascribed to the enhanced oxidation resistance with the increased ratio of S/Fe since FeSn (n > 2) were generated inside the materials. However, the excessive sulfidation of nZVI likely led to redundant FeS deposition on its surface to reduce the removal efficiency. The reaction process of Cr(VI) removal by CaSx-nZVI was composed with chemical reduction and physical adsorption. Combined with XPS and SEM-EDS analysis, the reaction mechanism was first the Cr(VI) reduction by CaSx-nZVI via a surface-covered layer of FeSn and then the Cr(III) adsorption. Hence, Sn2− was critical to promote the reduction of Fe3+ and the generation of FeS and FeS2. According to the Gibbs free energy results, the reaction occurred spontaneously with increasing temperature. The initial pH affected the removal efficiency by influencing the phase state of chromium. Cations promoted the reactivity to Cr(VI) in solution, while the influence of the anions was quite different. Our research demonstrated that CaSx-nZVI was a promising technique for the in-situ remediation of Cr(VI)-contaminated groundwater.

A chromium carbide coating in-situ formed on C/C composites by the novel reactive wetting strategy to enhance oxidation resistance

A chromium carbide (Cr-C) coating in-situ formed on the C/C substrate is successfully prepared by a novel reactive wetting strategy. The interfacial microstructure and oxidation resistance of coated C/C composites are investigated in detail. The as-prepared coating mainly consists of Cr23C6 and Cr7C3, forming a tight joining with the C/C substrate. Compared to uncoated samples, the oxidation weight loss of coated C/C composites is substantially reduced at high temperatures. Furthermore, the hardness of coated C/C composites is significantly increased, enhancing their ability to resist external damage. This reactive wetting strategy can also be used to prepare uniform coatings on C/C composites with complex grooved structure or large size. Surprisingly, coated C/C composites possess a low weight gain of 3.7% due to thin coating (< 10 µm), which can maintain their advantage of low density.

Stabilizing Oxide Nanolayer via Interface Confinement and Surface Hydroxylation.

Surface hydroxylation over oxide catalysts often occurs in many catalytic processes involving H2 and H2O, which is considered to play an important role in elementary steps of the reactions. Here, monolayer CoO and CoOHx nanoislands on Pt(111) are used as inverse model catalysts to study the effect of surface hydroxylation on the stability of Co oxide overlayers in O2. Surface science experiments indicate that hydroxyl groups formed on CoO nanoislands produced by deuterium-spillover can enhance oxidation resistance of the Co oxide nanostructures. Theoretical calculation shows that the interfacial adhesion between CoO and Pt is linearly strengthened with the increasing hydroxylation degree of CoO surface. Thus, the interface confinement effect between CoO and Pt can be enhanced by the surface hydroxylation due to the more reduced Co ions and stronger Co-Pt bonding at the CoOHx/Pt interface.

Enhanced oxidation resistance and failure mechanism of carbon/carbon composites with ZrO2/ZrSiO4-glass composite coating

A new coating of ZrO2/ZrSiO4-composited borosilicate glass (ZO-glass) was developed to protect the carbon/carbon composites (C/C) from oxidation in the air. It was found that the oxidation resistance first increased and then decreased with the increase of ZO content, and the ZO content of 20% corresponded to the best anti-oxidation properties (the weight loss was only 0.6% at 1573 K after 650 h). The significant enhancement of oxidation resistance was probably attributed to the stabilization effect of ZO filler and self-healing effect of glass. Excessive ZO may decrease the viscosity, self-healing ability of glass, and shorten the coating’s protection time (crack failure model). On the other hand, inadequate ZO can hardly restrain the bubble growth during oxidation, resulting in premature failure of the coating (bubble control model). The growth of bubbles was due to the active reaction between SiC and oxygen from crack diffusion, and the oxygen increases the gas concentration in the coating, and then diffuses into bubbles to its expansion. Different thermal expansion coefficient (CTE) of substrate and coating results in the formation of high thermal stress at the interface, which may induce through-cracks in coating during cooling. This paper gives insight into the oxidation resistance of composite coating, and offers an effective way for durable oxidant protection of C/C.

Dependence of the lubrication enhancement of alkyl-functionalized graphene oxide and boric acid nanoparticles on the anti-oxidation property

The influence of anti-oxidation property of nanoparticles on the tribological properties is rarely reported. In this study, the alkyl-functionalized graphene oxide (FGO) and alkyl-functionalized boric acid (FBA) were fabricated as oil additives to explore their lubrication effectiveness. FBA exhibited remarkable lubricating properties which reduced friction coefficient by approximately 24 % and the wear depth by about 94 %. However, the friction coefficient and wear depth of FGO were reduced by only 9.5 % and 44 %, respectively. Worn surface analysis shows a bunch of deep-plowing on rubbing surface in the case of FGO, while the wear scar was smooth and almost wear-free for FBA. Lubrication mechanism analysis by X-ray Photoelectron Spectroscopy revealed the formation of carbon-based tribofilm for FGO and boron-based tribofilm for FBA during rubbing. In the thermal behavior analysis, graphene oxide (GO) nanoparticles were completely decomposed at 650 °C, whereas, B2O3 nanoparticles remained stable. It indicated that the excellent thermal stability and anti-oxidation property of boron-based tribofilm benefited to the lubrication enhancement. This study highlights the importance of oxidation resistance in designing novel nanoparticle additives, and the enhancement of oxidation resistance of GO will be a promising way to further application as oil additives.

Enhanced oxidation resistance of low-carbon MgO–C refractories with ternary carbides: a review

Enhanced oxidation resistance of low-carbon MgO–C refractories with ternary carbides: a review

TiN-SiO2 double layer composite coating with enhanced oxidation resistance and reusability in anti-coking applications

The passivation coating has been the main solution to the coking problem in the field of active cooling technology and ethylene cracking furnace. The need for repeated use and essential decoking process poses a great challenge to the single-layer coating. Herein, a new TiN/SiO2 double-layer coating suitable for internal channels has been prepared and characterized, whose results are compared with single-layer TiN coating. The oxidation resistance was revealed by HT-XRD and TGA. The reusability was analyzed from surface roughness, bonding force and coking inhibition performance in the repeated use of the coking-decoking cycle (RP-3 supercritical pyrolysis, on-line decoking technology). Results reveal the synergistic effect of the inner and outer layers of TiN/SiO2 coatings. The outer amorphous SiO2 with high crystallization temperature plays the role of isolating O and C atoms from penetrating, and the inner TiN acts to reduce the mismatch of thermal expansion coefficient between substrate and SiO2. Therefore, excellent oxidation resistance, with a bearable temperature of 1000 °C, can be obtained for the TiN/SiO2 coatings. In addition, during the coking-decoking cycles, the roughness of TiN/SiO2 coatings has been maintained at a low level; the coating has been tightly adhered to the substrate throughout the process; and the coking resistance has not been weakened with an average anti-coking ratio of 93%, higher than that of TiN (31–67%).

Simultaneously enhanced oxidation resistance and mechanical properties in a novel lightweight Ti2VZrNb0.5Al0.5 high-entropy alloy

Enhanced oxidation resistance is a primary demand for the application of refractory high-entropy alloys (RHEAs) at elevated temperatures. In this study, Al was added to a Ti2VZrNb RHEA to partially substitute Nb to improve its oxidation resistance and mechanical properties. The alloy was found to have an increased oxidation resistance by forming a continuous Al2O3 + ZrO2 oxide protective surface. At the same time, the room-temperature yield strength was also increased by 66% to 1273 MPa via solid solution strengthening. The low atomic mass of Al also helped to reduce the density of the alloy by 8.2% to 5.44 g cm−3. This resulted in a high specific yield strength of 234 MPa cm3 g−1 for the alloy. Meanwhile, the Ti2VZrNb0.5Al0.5 alloy also exhibited a high compressive plasticity of >50%. These values are among the best reported so far for RHEAs.

Flexible Full-Surface Conformal Encapsulation for Each Fiber in Graphene Glass Fiber Fabric against Thermal Oxidation.

Encapsulation for carbon-based electronic devices against oxidation can enhance their long-term working stability. Graphene glass fiber fabric (GGFF), as an advanced flexible electrothermal material, also struggles with graphene oxidation. The flexible, full-surface, conformal encapsulation for each fiber in the large-area fabric puts forward high requirements for encapsulating materials and techniques. Herein, the nanometer-thick h-BN layer was in situ grown on cambered surfaces of each fiber in GGFF with the chemical vapor deposition method. Stable heating duration (500 °C) of h-BN-encapsulated GGFF (h-BN/GGFF) was increased by 1 order of magnitude without compromising the electrothermal performances and flexibility. Theoretical simulations revealed that the enhanced oxidation resistance of h-BN/GGFF was attributed to the decreased interaction and adsorption life of oxygen. The proposed flexible, full-surface, conformal encapsulation technique targeting the fiber-shaped graphene electrothermal device is scalable and can be extended to the other carbon materials, even devices with intricate shapes, which will promote the development of flexible electronics.

Enhanced Oxidation Resistance of Ultrafine-Grain Microstructure AlCoCrFeNi High Entropy Alloy.

This work investigates the effect of ultrafine-grain microstructure on the oxidation behavior of AlCoCrFeNi high entropy alloy (HEA). The ultrafine-grain microstructure is obtained using stationary friction processing performed at two different rotational speeds, 400 and 1800 rpm, for 5 min duration. Processed samples demonstrate high depth of refinement (DOR) and ultrafine grain size (0.43–1 μm) at high rotational speeds along with significant phase transformations from BCC/B2 to FCC microstructure. Further, surface free energy of the ultrafine-grain microstructure is enhanced up to 35%. Oxidation kinetics of the ultrafine-grained sample is decelerated up to 12–48% in a temperature range of 850–1050 °C for a duration of 100 h. Chromia and alumina were the predominant oxides formed in almost all the samples oxidized at elevated temperature. In addition, spinel Co(Cr,Fe)2O4/Fe(Co,Cr)2O4 formation is also detected in the unprocessed oxidized samples. Processed samples rich in grain boundaries (GBs) promote internal oxidation to form Al-rich inner oxides. The enhanced oxidation resistance of the processed samples is attributed to the microstructural refinement and homogenization resulting in the formation of protective chromia followed by Al-rich inner oxides.

Radiation-Induced Sharpening in Cr-Coated Zirconium Alloy.

To improve the safety of nuclear power plants, a Cr protective layer is deposited on zirconium alloys to enhance oxidation resistance of the nuclear fuel cladding during both in-service and hypothetical accidental transients at High Temperature (HT) in Light Water Reactors. The formation of the Cr2O3 film on the coating surface considerably helps in reducing the oxidation kinetics of the zirconium alloy, especially during hypothetic Loss of Coolant Accident (LOCA). However, if the Cr coating is successful to increase the oxidation resistance at HT of the zirconium substrate, for in-service conditions, under neutron irradiation, Cr desquamation has to be avoided to guarantee a safe use of the Cr-coated zirconium alloys. Therefore, the adhesion properties have to be maintained despite the structural defects created by sustained neutron irradiation in the reactor environment. This paper proposes to study the behavior of the Zircaloy-Cr interface of a first generation Cr-coated material during a specific in situ ion irradiation. As deposited, the Cr-coated sample presents a f.c.c. C15 Laves-type intermetallic phase at the interface with off-stoichiometric composition. After irradiation and for the specific conditions applied, this interfacial phase has significantly dissolved. Energy Dispersion Spectroscopy revealed that the dissolution was accompanied by a counterintuitive “sharpening” effect.

Polyphenylene sulfide fabric with enhanced oxidation resistance and hydrophobicity through polybenzoxazine surface coating for emission control in harsh environment

Emissions from power generation and municipal waste incineration sources are primarily at high temperatures and contain corrosive gases, particulate pollutants and are enormously challenging on the performance of the filtration systems in use. Here, polyphenylene sulfide (PPS) nonwoven fabric, a primary material used commercially in such settings, is modified with a polybenzoxazine precursor as a coating to deliver improved thermal and oxidation resistance to the fibrous substrate. The polybenzoxazine precursor undergoes chain propagation and crosslinking upon the treatment process to provide a protective layer over the PPS fibers such that enhanced structural stability in a harsh environment was demonstrated. We have shown the improved overall tensile strength (+15%), Young’s modulus (+26%), and more hydrophobic nature of the modified PPS fabric, while the superior environmental stability and better filtration performance could be achieved. Such methodology may lead to higher service temperature and extended service time of the PPS filtration bags in harsh fire exhaustion airstreams encountered in power plants or municipal garbage incineration facilities. The crosslinkable benzoxazine could also be the most cost-effective high temperature coating layer on fibers, enabling future high-performance air filtration materials.

Effects of vanadium content on the high temperature oxidation behavior of NbTiZrAlV refractory complex concentrated alloys

Oxidation behavior and microstructural evolution of NbTiZrAlV refractory complex concentrated alloys (RCCAs) with vanadium (V) concentration of 3 and 11 at% were investigated at 500 and 800 °C in the air atmosphere. When NbTiZrAlV RCCAs were exposed at 500 °C, the oxidation behavior was controlled by internal oxygen (O) diffusion, and single oxide layer predominating by Ti2ZrO6 and Nb2Zr6O17 were produced after oxidation for 200 h. The mass gains of alloys with 3 and 11 at% V were 0.042 and 0.018 mg/mm2, and corresponding average thickness of oxide layer was 70 and 30 µm. As oxidation temperature was increased to 800 °C, volatilization of V2O5 brought out the aggravation of oxidation degree for NbTiZrAlV RCCA, and complex oxide layers consisting of Nb9VO25, Nb2Zr6O17 and TiO2 were obtained after thermal exposure for 24 h. The mass gains of alloys with the V content of 3 and 11 at% were 1.135 and 0.514 mg/mm2, and the average thickness of oxide layer was 500 and 300 µm, respectively. In both cases, the antioxidant performance of NbTiZrAlV RCCA was significantly improved by the increased content of V. And the enhanced oxidation resistance could be ascribed to the fact that the increase of V addition enhanced the atom diffusion resistance via minimizing mixing enthalpy and maximizing configurational entropy.

Oxidation resistance and mechanical properties of sputter-deposited Ti0.9Al0.1B2-y thin films

Direct-current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) were used to deposit understoichiometric Ti1-xAlxB2-y diboride coatings by sputtering from a segmented TiB2-AlB2 target using Ar and Kr as sputtering gas. For films with a fixed Al/(Ti + Al) ratio of x = 0.1 (Ti0.9Al0.1B2-y), the B content was varied with y ∈ (0.1, 0.6 and 0.7). For films with a fixed y = 0.7 (Ti1-xAlxB1.3), the Al content was varied with x ∈ (0.1, 0.4 and 0.7). Evaluation of the mechanical properties of the Ti1-xAlxB1.3 samples showed a reduction in both hardness and elastic modulus with increasing Al concentration, while the Ti0.9Al0.1B2-y samples showed a hardness increase with decreasing B content. Thus, Ti0.9Al0.1B1.3 films exhibited a superior hardness of 46.2 ± 1.1 GPa and an elastic modulus of 523 ± 7 GPa, compared to the values for Ti0.9Al0.1B1.4 and Ti0.9Al0.1B1.9, showing a hardness of 44 ± 1 GPa and 36 ± 1 GPa, and an elastic modulus of 569 ± 7 GPa and 493 ± 6 GPa, respectively. The oxidation behavior of the mechanically most promising Ti0.9Al0.1B2-y sample series was investigated through air-annealing at 600 °C for durations from 1 h to 10 h. All films formed a mixed non-conformal Al2O3-TiO2 oxide scale which acts as an inward and outward diffusion barrier, significantly reducing the oxidation rate compared to TiBz films, which form an oxide scale consisting of porous TiO2. The thinnest oxide scale after 10 h was found in the B-deficient samples, Ti0.9Al0.1B1.3 and Ti0.9Al0.1B1.4, at ~200 nm, which is significantly below that for Ti0.9Al0.1B1.9 at 320 nm. The enhanced oxidation resistance of highly understoichiometric films is due to the elimination of the B-rich tissue phase that is present at the grain boundaries for higher B content, where the latter has been shown to enhance the rate of oxidation in borides.

Formation and oxidation behavior of TiO2 modified Al2O3-Nb2O5/NbAl3 composite coating prepared by two-step methods

To improve the high-temperature oxidation resistance, Al2O3-Nb2O5/NbAl3 composite coating with or without TiO2 particles was prepared on Nb-based alloy through a two-step method of halide activated pack cementation (HAPC) and micro arc oxidation (MAO). NbAl3 layer was firstly formed on the substrate by HAPC treatment. Then, TiO2 was introduced into the Al2O3-Nb2O5 coating on NbAl3 by hydrolysis reaction of K2TiF6 during MAO process. In this paper, the effect of TiO2 on the morphology and formation of the MAO coating was studied. Furthermore, the oxidation resistances of the TiO2-Al2O3-Nb2O5/NbAl3 and Al2O3-Nb2O5/NbAl3 composite coated Nb alloy were investigated. The results showed that the addition of K2TiF6 could promote the growth of MAO coating and increase the density. After oxidation at 1200 °C for 100 h, a dense protective oxides scale was found on the TiO2-Al2O3-Nb2O5/NbAl3 coating sample, and the weight gain was only 4.75 mg/cm2, which was significantly lower than the coated sample without TiO2. The mechanism of oxidation resistance enhancement of coating with TiO2 should be ascribed to the formation of a dense TiO2 + Al2O3 scale, which could effectually prevent the diffusion of O and suppress the formation of Nb2O5.