Internal Zone Research Articles

Formation mechanism and evolution model of buried hill reservoir in BZ19‐6 structural belt, Bozhong Sag, Bohai Bay, East China

The BZ19‐6 structural belt is the largest buried hill oil‐gas‐bearing area recently discovered in Bohai Bay Basin. The formation and evolution of the buried hill reservoirs are complex. Presently, the development law and controlling factors of this reservoir is unclear. Based on 3D seismic, drilling data, thin section, and regional tectonic background, we explored the controlling factors and development law of the high‐quality buried hill reservoir. The results show that the buried hill reservoir can be vertically divided into a weathered glutenite zone, weathered fracture zone, internal fracture zone, and tight zone. The development of reservoir is mainly controlled by lithotypes, tectonic movement, and weathering. The rocks in the study area with low compressive strength, provided the material basis for the formation of fractures. The strongly reformed multi‐stage tectonic movements provides the external dynamics for the formation of fractures. Weathering further improved the physical properties of the reservoir. The buried hill reservoir is mainly distributed in the weathered fracture zone and internal fracture zone. Currently, natural gas mainly found in nearly E‐W‐trending and N‐S‐trending fractures. The nearly E‐W‐trending fractures are developed in the thrust nappe structure formed by N‐S‐trending extrusion in the Indosinian. The hinge zone of the structure is the main development area of fractures. The nearly N‐S‐trending fractures are associated with strike‐slip faults formed by sinistral strike‐slip stress in the Yanshanian. Under the background of NNE–SSW direction extensional stress during the Himalayan, early fractures were reactivated, opened and expanded, forming the reservoir space for later natural gas charging.

Oxidation behaviour of Ni-base superalloy 617 in simulated Advanced Ultra Supercritical (AUSC) steam

Alloy 617 was exposed in a simulated Advanced Ultra Supercritical (AUSC) steam oxidation test loop at 650–710 ℃, 31 MPa for 600 h. Detailed characterization of the oxide scales was carried out using Transmission Electron Microscopy coupled with Precession Electron Diffraction. The alloy 617 showed insignificant weight gains with super-parabolic kinetics. The oxide scale formed on the alloy consisted of a thin inner Cr2O3 layer and outer islands of (Mn,Ni,Fe)Cr2O4 spinel with negligible internal oxidation zone comprising Al2O3. The mechanistic aspect of AUSC steam oxidation is discussed.

The Adrenal Gland of Squamata (Reptilia): A Comparative Overview.

The adrenal gland is a complex endocrine organ composed of two components: a steroidogenic tissue, which produces steroid hormones, and a chromaffin tissue, which mainly produces norepinephrine and epinephrine. Through evolution, their relationships with each other changed. They begin as isolated chromaffin and steroidogenic cell aggregates, typical of fish, and end with the advanced compact gland, typical of mammals, which consists of an external steroidogenic cortical zone and an internal chromaffin medullary zone. The adrenal gland of reptiles is unique because, with few exceptions, it is near the gonads and genital ducts, and the chromaffin and steroidogenic tissues are closely associated. However, the degree of mixing is variable. For example, in Squamata, the mixing degree of chromaffin and steroidogenic tissues, their reciprocal position in the gland, and the relative quantities of norepinephrine and epinephrine secreted by the chromaffin cells are extremely variable. This variability could be related to the phylogenetic history of the species. After a brief discussion of the adrenal gland and its main functions in vertebrates, this overview will examine the general characteristics of the adrenal gland of squamates, the differences in morphology of the gland, and the possible relationships with the phylogeny of the different species.

Ascent rate of the Udachnaya-East kimberlite melts from olivine diffusion chronometry

Kimberlite melts are low volume, volatile-rich melts formed in the asthenosphere at depth >150-250 km. Due to their low viscosity and the exsolution of CO2 triggered by their interaction with the sub-cratonic mantle, these melts are highly buoyant and rise rapidly through the lithosphere, ultimately reaching the surface and erupting at sonic to super-sonic speed. Studies based on fluid/melt dynamics, fracturing and disaggregation of the transported mantle-derived cargo, as well as on H diffusion in olivine and Ar diffusion in magmatic phlogopite showed that the ascent rate of kimberlite melts can vary between 0.1 and 30 m/s. However, these rates are extrapolated from processes starting at different depths, and thus may not be representative for the whole ascent path of kimberlite melts through the sub-cratonic lithosphere. To shed light on this issue, we applied diffusion chronometry to the deepest feature ascribable to the liquid line of descent of the melts, i.e. early liquidus olivine formed around mantle-derived xenocrystic cores from the Udachnaya-East pipe (Siberian craton). Our results showed that the time elapsed between the formation of the Internal Zone II (early olivine on the liquidus) or rims (typical magmatic olivine) around xenocrystic cores and final cooling is between 5 and 74 days. Considering travelled distances of 80-110 km in accordance with thermobarometric calculations, this implies overall average ascent rates of kimberlite melts of 0.02 to 0.23 m/s, which are comparable to those of typical alkali basalts, albeit starting at much greater depth. This indicates that kimberlite melts start with moderate ascent rates and only later increase their speed, likely due to massive CO2 exsolution triggered by decarbonation reactions during melt/fluid-rock interactions in the lithospheric mantle. The overall timescales of 5 to 74 days obtained in our study overlap with the lowest values reported in the literature from chemical zoning of mantle-derived minerals (25 days to >100 years), confirming that the time elapsed between kimberlite-related mantle metasomatism and the ascent of kimberlite melts was short. Importantly, our data show that Fe-Mg interdiffusion in olivine can be used as a trustable chronometer in kimberlite systems, opening new perspectives on the study of ascent dynamics in kimberlites worldwide.

Study of main factors influencing unsteady-state temperature drop in oil tank storage under dynamic thermal environment coupling

With the increasing oil demand, the construction of oil energy reserves in China needs to be further strengthened. However, given that there has been no research on the main influencing factors of crude oil temperature drop in storage tanks under actual dynamically changing environments, this paper considers the influence of dynamic thermal environment and internal crude oil physical properties on the fluctuating changes in crude oil temperature. A theoretical model of the unsteady-state temperature drop heat transfer process is developed from a three-dimensional perspective. According to the temperature drop variation law of crude oil storage tank under the coupling effect of various heat transfer modes such as external forced convection, thermal radiation, and internal natural convection, the external dynamic thermal environment influence zone, the internal crude oil physical property influence zone, and the intermediate transition zone of the tank are proposed. And the multiple non-linear regression method is used to quantitatively characterize the influence of external ambient temperature, solar radiation, wind speed, internal crude oil density, viscosity, and specific heat capacity on the temperature drop of crude oil in each influencing zone. The results of this paper not only quantitatively explain the main influencing factors of the oil temperature drop in the top, wall, and bottom regions of the tank, but also provide a theoretical reference for oil security reserves under a dynamic thermal environment.

Модифицирование поверхности быстрорежущего инструмента совместным насыщением вольфрамом и азотом

Research significance is contingent on the requirement strengthening for high-speed cutting tools performance and wide-spread introduction of automatic lines and NC-machines. An increase of the tool service life is also necessary for the reduc-tion of putting expensive alloying elements to use, primarily, tungsten. The solution of these problems requires the use of technologies for hardening cutting surfaces. Combined processes of thermochemical treatment processes, uniting diffusive surface alloying with nitrogen saturation have shown their effectiveness in the surface hardening of various steels. Now the aim is to study the process of combined surface tungsten and nitrogen saturation of high-speed steel for increasing small-sized tool durability. Experimental studies were carried out on samples and small-diameter drills made of P6M5 steel. For laboratory experiments connected with combined process of thermochemical treatment an installation for nitriding in multi-component media was used. Metallization with tungsten was carried out by the slip method with parallel nitriding of the tool in a glow discharge. To determine the regime that provides the necessary temperatures for oxygen and nitrogen saturation, the temperatures of the control steel samples were measured on the surface and in the core at different durations of the cur-rent pulse in the heating phase. Metallographic analysis proved that thermochemical treatment resulted in a modified sur-face layer with a thickness of 10…15 microns, formed in P6M5 steel. The structure of the layer is an internal nitriding zone, which consists of a solid tungsten and nitrogen solution in iron and dispersed inclusions of tungsten nitrides. Dispersion and solid solution hardening provide a two-fold increase in the microhardness of the modified W-N layer compared to the alloy base. A transitional diffusion zone of nitrogenous martensite has been revealed under the hardened layer, creating a smooth microhardness gradient from the layer to the core, protecting it from embrittlement, peeling and staining. Using a metallophysical simulated test in predeveloped methodology, the calculation of the hardening index of the modified layer (yield point increase) was made. It showed that with increase in the concentration of tungsten in the layer, the proportion of the component of the dispersion hardening by W2N particles also increases. Full-scale tests in production conditions showed that the tool with a hardened layer had increased resistance. The durability of drills, determined by the number of drilled holes made before its dropping-out, increases by 2,2 times when drilling on 30XGSA steel and by more than 7,0 times when drilling a titanium alloy VT-23.

The Dynamics and Driving Mechanisms of Rural Revitalization in Western China

By constructing a rural revitalization index evaluation system and using measurement models and software such as AHP, the entropy method, the BCG matrix, and GeoDetector, this paper quantitatively analyzed the evolution mode and driving mechanism of rural revitalization performance based on the research of 131 cities and autonomous prefectures in western China to further put forward relevant policy suggestions and establish a new framework that integrates “performance evaluation, evolution model, driving mechanism, and management strategy”. Findings: firstly, rural revitalization in western China showed slow development and significant regional heterogeneity, with a coefficient of variation of 0.46 or even higher; secondly, the different dimensions of rural revitalization and development varied greatly, with the order being: thriving businesses (about 0.04) < effective governance (about 0.06) < pleasant living environment (about 0.09) < social etiquette and civility (about 1.0) < prosperity (about 0.23); thirdly, the growth and decline of rural revitalization performance coexisted in the context of rapid development in western China, and the evolution was in diversified patterns; fourthly, there were many factors affecting the change of rural revitalization performance, and different factors exhibited significant synergistic effects with each other, with super-interacting factor pairs having a force of over 0. 7 (maximum 1), including permanent population, urbanization rate, added value of primary industry, and per capita GDP as key factors; fifthly, based on the superposition analysis of the evolution pattern and driving forces of rural revitalization, western cities are classified into 8 types (including external assistance zone, general development zone, general retention zone, general demonstration zone, internal governance zone, important development zone, important retention zone, important demonstration zone) for establishment of a zoning planning and management system and design of differentiated development policies, providing a basis for “evidence-based decision-making” for the government.

A Python Application for Visualizing an Imbricate Thrust System: Palomeque Duplex (SE, Spain)

This paper introduces a Python application for visualizing an imbricate thrust system. The application uses the traditional geologic information to create an HTML geological map with real topography and a set of geological cross-sections with the essential structural and stratigraphic elements. On the basis of the high geological knowledge gained during the last three decades, the Palomeque sheets affecting the Cenozoic Malaguide succession in the Internal Betic Zone (SE Spain) were selected to show the application. In this area, a Malaguide Cretaceous to Lower Miocene succession is deformed as an imbricate thrust system, with two thrusts forming a duplex, affected later by a set of faults with a main strike-slip kinematic. The modeled elements match well with the design of the stratigraphic intervals and the structures reported in recent scientific publications. This proves the good performance of this Python application for visualizing the structural and stratigraphic architecture. This kind of application could be a crucial stage for future groundwater, mining, and civil engineering management.

Barrovian metamorphism in nominally lowermost Alpujarride Complex units: tectonic implications for the development of the orogenic wedge in the Western Mediterranean

ABSTRACT The sedimentary successions of the Permian-Triassic rifting related to the Alpine Tethys in the easternmost Lower Alpujarride units (Internal Betic Zone, south Spain) host shallow-intrusive basic bodies of Mesozoic age. These gabbroic bodies experienced low-grade Alpine metamorphic overprint, singularly recorded in three outcrops nearby Alicante city in southeast Spain: Callosa and Orihuela Ranges and Nueva Tabarca Island. Overall, the metabasic bodies still preserve magmatic ophitic/subophitic texture and relicts of magmatic augite and ferropargasite-ferroedenite-edenite and kaersutite. In contrast, metamorphic minerals include magnesioriebeckite, actinolite, albite, stilpnomelane, phengite, and chlorite. Major and trace element geochemical data suggest crystallization of the igneous protoliths from subalkaline (tholeiitic) to alkaline within-plate (continental) basaltic magmas slightly enriched in incompatible elements. These magmas with E-MORB geochemical affinity very likely intruded at shallow crustal levels in an extensional-synrift-geodynamic setting related to the breakoff of Pangea in the region. Pressure-Temperature (P-T) conditions estimated by average P-T method and pseudosection calculations suggest metamorphic peak at ca. 6 kbar at 340°C consistent with burial metamorphism down to ca. 18 km depth with intermediate thermal gradients of ca. 18°C/km. These conditions are different to the typical subduction-related blueschist facies conditions of the Lower Alpujarride units and suggest, instead, a collisional (Barrovian) event. This can be explained by a late-stage accretion of the studied units after the main subduction-related event, pointing to the dispersion of the corresponding Lower Alpujarride sections along the margin in different palaeogeographic positions before deformation and movement to their actual structural position. The metamorphic correlation of the studied units with the accreted passive margin of South Iberia (Subbetic zone) is also discussed.

A Visualized Method of Airflow between Adjacent Zones inside a Multizone Building Based on Pressure Difference Frequency: Airflow Mapping

The airflow movement inside a multizone building has a significant impact on pollutant transfer, thermal comfort, and indoor air quality. However, there are difficulties in visualizing the airflow movement with existing methods. This study proposes a visualization method for evaluating airflows between adjacent internal zones inside a multizone building based on the analysis of pressure difference frequency. After the distribution of absolute pressure is measured and the wind pressures on the surfaces of the building are calculated, the variation of pressure differences between each couple of adjacent zones is analyzed for three levels: greater than 0 Pa, equal to 0 Pa, and less than 0 Pa (for any given zones selected as target zones). Finally, an airflow mapping is created for each floor using the visNetwork tool based on the R language. A target building was selected for applying the proposed method. The airflow mappings were derived from a detailed analysis of the pressure difference frequency between each couple of adjacent zones, presenting the variations of airflow direction and the dominant airflow during the measurement period in a visualized form. For example, the airflow direction from 1F_Z2 to 1F_Z3 is 92.0%. The spatial similarity in the variations of the airflow directions can also be observed on certain floors. The results of this experimental study show that the airflows between multiple zones can be easily identified without a complex building zone analysis. The variation in internal airflow direction between adjacent zones can be intuitively visualized, providing insight to the airtightness levels of building components. It is also observed that the airflow rates computed based on the airflow mappings can provide more guidance for the control of HVAC systems.

Alpine structural evolution of the Internal Piedmont Zone in the Upper Viù Valley (Lanzo Valleys Ophiolite, Western Alps)

New structural data have been collected in the high-pressure meta-ophiolites exposed in the Lanzo Valleys (i.e., the Lanzo Valleys Ophiolite, LVO) and tectonically overlying the continental crust of the Dora-Maira and Gran Paradiso massifs in the Western Alps. Detailed geological mapping and structural analysis carried out in the south-western sector of the LVO (i.e., the Upper Viù Valley) allow to distinguish four ductile deformation phases, corresponding to the subduction-related D1 phase, the early exhumation-related D2-phase and the late exhumation-related D3 and D4 phases. The geometry of structures and kinematics have been reconstructed, and their regional tectonic meaning is discussed in the frame of the Alpine tectonic evolution of the Internal Piedmont Zone (i.e., the remnants of the Alpine Tethyan oceanic lithosphere) in the Western Alps.

The effect of the dielectric barrier discharge plasma actuator in the control of non-reactive flow in a non-premixed bluff body burner

Active flow control methods based on dielectric barrier discharge plasma actuators can be used to increase the efficiency of combustion systems. In this study, the influence of the location of plasma actuators on the bluff body in a non-premixed burner on the non-reactive flow field of fuel and oxidizer is investigated numerically. Flow field properties and spatial mixing deficiency (SMD) are calculated to evaluate the plasma actuator's influence on the reactants' mixing inside the burner. The results show that the plasma actuator can influence the recirculation areas and are effective in mixing fuel and oxidizer. The presence of the plasma actuator results in the formation of a vortex, which slows down the movement of the flow and improves the mixing between the fuel and airflow streams resulting in more favorable combustion. The results show that at a higher air velocity (4 m/s), the formation of a plasma zone near the air duct strengthens the external circulation zone (ERZ) in such a way that it surrounds the internal recirculation zone and reduces the value of SMD by an average of 7.89%. While activating the actuator also strengthens the ERZ for a lower air velocity (0.3 m/s), this affects the air inflow, and the flow field becomes dominated by the fuel jet flow. When the diameter of the bluff body is increased, both when the plasma actuator is active or inactive, the ERZ is greatly strengthened, and the flow field is more dominated by the airflow.

The influence of flow pattern and hopper angle on static and dynamic pressures in slender silos

This paper focuses on the influence of flow pattern and hopper angle (β) on static and dynamic pressures in slender silos. The results were obtained using a test station developed by the authors, consisting of a silo (6 m high and 0.7 m internal diameter). Maize was used to generate the pressures. Five different hopper angles were tested by filling, static phase followed by complete silo discharge. Results are reported for pressure and flow analyses, and show that hopper angle influences normal pressures on the silo wall; Silos with transition flow do not have a concrete pattern of distribution of thrusts; pressure values are proportional to the variation of the hopper angle; and internal shear zones vary according to hopper angle, completely modifying the behaviour of static and dynamic pressures. Friction pressure and lateral pressure ratio values exceeded those calculated by the Eurocode 1, part 4.

When do rebels sign agreements with the United Nations? An investigation into the politics of international humanitarian engagement

International actors engage rebel groups in conflict zones for better humanitarian outcomes. What are the political conditions under which such external engagement occurs in internal conflict zones? We argue that “insecure governments” and politically “modulated rebels” are the key factors that explain the international humanitarian engagement with rebels in civil conflicts. With the history of instability marred by coups and frequently changing hands of governments, insecure governments resort to international help and allow international actors to interact with their internal enemies. In contrast, with strong political control and military capacity, secure governments play a gatekeeper role, dealing with internal enemies autonomously. On the rebel side, politically “modulated rebels” are the prime candidates for international humanitarian engagement. Such modulation is likely to occur after civilian-connecting experiences over time by holding territory or after peace talks. We test these arguments using the case of the United Nations (UN) action plans between 2000 and 2015, in which some rebel groups committed to reducing the practice of child soldiering. We find that the combination of “insecure governments” and “modulated rebels” can systematically account for the UN action plans occurrence. Our analysis has implications for the role of external actors in internal conflict zones around the world.

Influence of seawater concentration on alkali-silica reaction of seawater sea-sand concrete: Mimicking through NaCl solution and recycled glass aggregate

Seawater sea-sand concrete (SSC) is one environment-friendly and promising construction material. Nevertheless, limited research shed favorable light on alkali-silica reaction (ASR) of SSC. This work provided a novel insight regarding the fast test method that (i) the recycled glass aggregate (RGA) was used for fast assessing the effect of seawater concentration on ASR, reusing its characteristic resource; (ii) the NaCl solutions with different concentrations were used to mimic different salinities of sea waters; and (iii) a modified curing method was adopted. The results showed that the NaCl solution could be used for assessing ASR risk of SSC instead of seawater. The specimens mixed with twice and above the sodium concentration of seawater would exhibit ASR expansion, strength reduction, coarsening of nanopore distribution, and the cracks on the macro and micro levels. However, the change of NaCl concentration scarcely affected the composition and content of hydration products. Additionally, with increasing the mixing Na+ concentration, the ASR crack would firstly appear in the interface between the cement paste layer and the glass layer, and then developed in the internal zone of RGA matrix with different hardness, elastic modulus, and Si contents based on the destroyed degree.

Behavior of new hybrid connection between steel beam and concrete-encased composite column

A new bending connection between a steel beam and concrete-encased composite column (CECS) with a bolted flange plate is proposed which maintains the integrity of the column and allows for the interchangeability of the beam for improvement of the connection. The confinement of the steel plates and the central steel core (H-section column) is provided by reinforced concrete and cover plates, thus lateral torsional and local buckling of the through plate (TP) and the central core is prevented. Three full-scale samples of the proposed exterior connection with variable TP thickness and different bending capacities under lateral cyclic and constant axial loads in the column were tested. The moment contribution in the components and seismic behavior of the connection were studied. The load transfer to the panel zone occurred through four components in the bending plane; TP, concrete performance, tensile studs, and side plates. The average share of the resistant elements which is immediately behind the front plate were determined as 56%, 26%, 12.50%, and 5.5%, respectively. The internal panel zone remained undamaged and the stresses were below the yield limit, so that the plastic hinge could occur outside the connecting members in the beam. In general, the specimens with sufficient pre-tensioning in the connection bolts had stable hysteresis curves and less pinching. In addition, these specimens showed acceptable energy dissipation that provided a high ductility index.

Effect of laser shock peening and surface mechanical attrition treatment on the oxidation resistance of a 20Cr-25Ni-Nb stainless steel

In this study, the effects of laser shock peening (LSP) and surface mechanical attrition treatment (SMAT) were comparatively investigated on the oxidation behaviors of 20Cr-25Ni-Nb stainless steel in a high-temperature (650 °C) CO2 environment up to 1000 h. The results show that the oxidation resistance of stainless steel can be improved by LSP but deteriorated by SMAT. LSP promoted the formation of a thin and uniform Cr-rich oxide layer on the 20Cr-25Ni-Nb stainless steel instead of a thick duplex oxide layer with Fe-rich outer layer and Cr-rich inner layer which appeared on the untreated sample. For the SMAT-treated sample, besides the oxide scale, a thick internal oxidation zone (IOZ) and oxides spallation were also observed. The formation of a Cr-rich oxide layer was facilitated by the enhancement of the Cr diffusion within the LSP-induced hardened layer. The unsatisfying oxidation performance of the SMAT-treated sample is due to the surface micro-cracks and significant grain refinement which synergistically contributed to the visible carburization and oxidation in a high-temperature CO2 environment.

Hierarchical FeCoNiCr high entropy alloy thin films with combined high strength and excellent corrosion resistance

A two-step temperature-controlled magnetron sputtering procedure was adopted to obtain a bilayer hierarchical Fe25.2Co25.2Ni27.4Cr22.2 high entropy alloy (HEA) thin film consisting of the external nano-lamellar layer and internal equiaxed zone, which displayed combined advantages of high hardness, good modulus and excellent corrosion resistance. The roles of heterogeneous nanostructure on the mechanical and corrosion behavior were revealed by nano-indentation and Scanning Kelvin probe (SKP) methods. Compared to the substrate 304 ASS, the hierarchical HEA film not only shows much higher nano-hardness and modulus values, but also possesses a higher electron transfer resistance (12158 vs 4567 Ω.cm2) and lower overall corrosion rate (6.28*10−4 vs 6.84*10−3 mm·year−1). Moreover, the outer nano-lamellar layer shows higher nano-hardness (∼8.1 GPa) but lower surface potential values (∼-261 mV) than those of the inter equiaxed zone (∼5.9 GPa and ∼−150 mV). The former arises from the significant grain refinement strengthening effect, while the latter is attributed to an obvious increase in the high energy and chemically active areas such as grain boundaries and triple junctions. This work demonstrates the capability of hierarchy to adjust the comprehensive performance of multi-functional films, which possess superior mechanical property and comparable corrosion performance than those of the as-cast bulk HEA alloys.

Effects of salt and ash deposits on corrosion behaviour of Ni-25Cr in Ar-60CO2-20H2O gas at 650 oC

ABSTRACT A Ni-25Cr (wt.%) alloy coated with the salts and mixtures of these salts with an industrial coal ash was exposed to Ar-60CO2-20 H2O at 650 °C for 300 h. The alloy without any deposit developed a uniform internal oxidation zone (IOZ) and an external metallic nickel layer surmounted by a thin NiO scale. Salt deposits changed the scale constituents and morphology. Predominantly, a duplex scale of NiO over a Cr2O3 layer grew with an underlying IOZ containing large Cr-rich oxide precipitates. Under a deposit of ash plus salts, the basic reaction morphology was the same as in the gas-only case, but the oxide layer was non-uniform. Local voids were formed within the alloy beneath chloride plus ash deposits. Under ash with sulphates, the alloy formed both partially protected areas and non-protective multi-layered scales. Spherical ash particles were enveloped by NiO in both salt-ash deposits.

Corrosion Behavior of Alumina-Forming Austenitic Steel in Supercritical Carbon Dioxide Conditions: Effects of Nb Content and Temperature.

The corrosion behavior of alumina-forming austenitic (AFA) stainless steels with different Nb additions in a supercritical carbon dioxide environment at 500 °C, 600 °C, and 20 MPa was investigated. The steels with low Nb content were found to have a novel structure with a double oxide as an outer Cr2O3 oxide film and an inner Al2O3 oxide layer with discontinuous Fe-rich spinels on the outer surface and a transition layer consisting of Cr spinels and γ'-Ni3Al phases randomly distributed under the oxide layer. Oxidation resistance was improved by accelerating diffusion through refined grain boundaries after the addition of 0.6 wt.% Nb. However, the corrosion resistance decreased significantly at higher Nb content due to the formation of continuous thick outer Fe-rich nodules on the surface and an internal oxide zone, and Fe2(Mo, Nb) laves phases were also detected, which prevented the outward diffusion of Al ions and promoted the formation of cracks within the oxide layer, resulting in unfavorable effects on oxidation. After exposure at 500 °C, fewer spinels and thinner oxide scales were found. The specific mechanism was discussed.