Cr2O3 Oxide Research Articles

Amphoteric SnO2 nanoparticles via pH-controlled continuous flow solvothermal synthesis

Amphoteric oxides can be challenging to produce in phase pure form due to their sensitivity to the pH of the reaction mixture. The high-pressure, high-temperature reaction conditions of hydrothermal processes make the pH difficult to control. Here we report a simple approach to obtain nanoparticles of amphoteric oxides, where cheap metal nitrate precursors are reacted in alcohol (2-propanol) water mixtures (25 vol%:75 vol%) to maintain a neutral pH under solvothermal conditions. Phase pure SnO2 nanoparticles were synthesized in a continuous flow solvothermal reactor at 250 °C, 300 °C, 350 °C and 400 °C with sizes ranging from 3 nm to 7 nm. The nanoparticles were characterized using powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, 119Sn MAS NMR spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption, UV–VIS, and as anode material in CR2032 Li-ion battery cells. To demonstrate generality, amphoteric oxides ZnO, Bi2O3, Cr2O3 and γ-AlOOH were also synthesized.

Effect of Heat Treatment Temperature on Isothermal Oxidation of Ni-based Fe-33Ni-19Cr Alloy

This project studies the influence of different grain sizes of Ni-based Fe-33Ni-19Cr alloy obtained from heat treatment procedure on high temperature isothermal oxidation. Heat treatment procedure was carried out at two different temperatures, namely 1000℃ and 1200℃ for 3 hours of soaking time, followed by quenching in the water. These samples are denoted as T1000 and T1200. The heat-treated Ni-based Fe-33Ni-19Cr alloy was subjected to an isothermal oxidation test at 950℃ for 150 hours exposure. Oxidized heat-treated alloys were tested in terms of oxidation kinetics, phase analysis and surface morphology of oxidized samples. Oxidation kinetics were determine based on weight change per surface area as a function of exposure time. Phase analysis was determined using the x-ray diffraction (XRD) technique and surface morphology of oxidized samples was characterized using a scanning electron microscope (SEM). As a result, the heat treatment procedure shows varying grain sizes. The higher the heat treatment temperature, shows an increase in grain size with a decrease in hardness value. The oxidation kinetics for both heat-treated samples showed an increment pattern of weight change and followed a parabolic rate law. The oxidized T1000 sample recorded the lowest parabolic rate constant of 3.12×10–8 mg2cm–4s–1, indicating a low oxidation rate, thus having good oxidation resistance. Phase analysis from the XRD technique recorded several oxide phases consisting of Cr2O3, MnCr2O4, and (Ti0.97Cr0.03)O2 oxide phases. In addition, a uniform oxide layer is formed on the oxidized T1000 sample, indicating good oxide scale adhesion, thereby improving the protective oxide behavior.

Structure and mechanical properties of multi-principal AlCrNbSiTiON oxynitride coatings

The multi-principal AlCrNbSiTiON oxynitride coatings were deposited by pulsed arc ion plating under different oxygen flow. The structure and mechanical properties of the coatings were systematically investigated. The surface of all coatings is smooth and flat. The cross section is compact and smooth. The coatings transform from FCC solid solution crystal structure with (200) preferred orientation to amorphous/nanocrystalline nanocomposite structure with increasing oxygen flow. Upon increasing oxygen flow from 0 to 150 SCCM, their hardness decreases from 43.4 to 15.6 GPa. The hardness of the coatings increases to 26.4 GPa with increasing oxygen flow again. The Cr2O3 oxides are formed on the surface of the coatings during the friction process.

Effect of Yttrium Additions on the High-Temperature Oxidation Behavior of GH4169 Ni-Based Superalloy.

The effect of the active element yttrium and its content on the oxidation behavior of GH4169 Ni-based superalloy at extreme temperature was studied by isothermal oxidation experiments. The results show that the oxide scale of GH4169 alloy presents a multi-layer structure, in which the continuous and dense Cr2O3 oxide layer is located in the subouter layer (II layer) and the continuous Nb-rich layer is in the subinner layer (III layer). These layers can inhibit the diffusion of oxygen and alloying elements, preventing the further oxidation of the alloy. The appropriate addition of yttrium can promote the selective oxidation of Cr element, reduce the thickness of the oxide scale and the oxidation rate of the alloy, inhibit the formation of voids at the interface of the oxide scale/alloy matrix, improve the resistance of the alloy to spalling as well as the adhesion of the oxide scale, and improve the high-temperature oxidation resistance of the alloy. Of those tested, the alloy containing 0.04 wt.%Y has the lowest oxidation weight gain, the slowest oxidation rate, and less oxide scale spalling. Based on this, the effect of yttrium on the high-temperature oxidation behavior of GH4169 Ni-based superalloy and its mechanism were revealed.

Corrosion behavior of YSZ and YSZ/NiCo coatings on inconel 625 exposed alkali chlorides

Alkali chloride attack on boiler pipe walls is considered the main problem of corrosion in the waste-to-energy (WTE) industry, even though uses superalloy. Electrophoretic deposited (EPD) yttria-stabilized zirconia (YSZ) coating is carried out to protect the Inconel 625 substrate. YSZ is deposited directly both on the Inconel 625 substrate and NiCo-Inconel 625. Corrosion resistance was conducted using the 3.5% NaCl electrochemical test and the hot salt corrosion test at 600°C in alkaline salt media such as NaCl, KCl, and CaCl2. The potentiodynamic polarization curve shows that the YSZ coating deposited on the substrate (single-layer) has a corrosion rate of 0.065 mm∙y‒1, lower than that deposited on NiCo coating (double-layer). The double-layer, NiO2 is formed in the NiCo layer due to the NaCl solution being trapped. Meanwhile, in hot salt corrosion at 600°C, CaCrO4 is formed as a protective oxide layer. Furthermore, in the double-layer, an imperfect oxide layer is formed causing spallation and coating failure. The corrosion rate for single-layer hot salt corrosion for 40 h is 0.310 mm∙y‒1. As a result, the corrosion resistance of the single-layer is increased by the presence of the Cr2O3 oxide layer formed during sintering.

The Microstructure, Surface Topography and Wear Resistance of Cold-Sprayed (Cr3C2-25(Ni20Cr))-(Ni-graphite) Composite Coatings Modified by Diode Laser Treatment

Cold-sprayed composite coatings have several advantages; however, some properties, such as hardness and abrasion resistance, are lower than those in plasma- or HVOF-sprayed deposits. This work showed that the use of surface diode laser processing allowed the development of (Cr3C2-25(Ni20Cr))-(Ni-graphite) cermet coatings with good adhesion to the steel substrate, and increased properties in the near-surface zone, below which the properties of cold-sprayed coatings were retained. Studies of the microstructure in the micro/nanoscale of the laser-treated coatings showed strong grain refinement after surface treatment. Cr7C3 carbide of various shapes and sizes was formed in the structure; while, a several hundred nanometre layer of Cr2O3 oxide appeared on the coating surface. The changes occurring in the microstructure have resulted in increased mechanical and tribological properties of the laser-treated zone of deposits.

Production of iron triad-based colored spinels by the self-propagating high-temperature synthesis

Blue, green, and khaki spinels were produced by self-propagating high-temperature synthesis (SHS) using Co3O4–ZnO–Mg(NO3)2·6H2O–Al(OH)3–Al, Ni2O3–ZnO–Cr2O3–Al(OH)3–Al, and Co2O3–Fe2O3–Al(OH)3–Al mixtures. The composition of the synthesis products was characterized by X-ray diffraction and IR spectroscopy. The oxides Co3O4, Co2O3, ZnO, Ni2O3, Cr2O3, Fe2O3, and aluminum hydroxide Al(OH)3 were used for the synthesis. Fuel was provided by aluminum powder (ASD-4). The spinel-type ceramic pigments were synthesized using layer-by-layer combustion, which involves two parallel exothermic reactions: aluminum oxidation and aluminothermic reactions. The fast self-propagating reactions and high synthesis temperatures rapidly destroy the structure of Al(OH)3 hydroxide in the starting mixture, producing gaseous reaction products that prevent the sintering of the spinels. The surface morphology of pigment powders and their composition was studied using a Quanta 3D 200i, FEI Co. scanning electron microscope and a Philips SEM 515 scanning electron microscope equipped with a local energy dispersive X-ray analysis (EDAX). The particle size of the synthesized spinels was approximately 1–5 μm. Colored spinels powders obtained by the SHS process can be used as ceramic pigments.

Microstructure, high temperature mechanical properties and sliding wear behavior of (NiCrW)1-x(Al2O3)x

(NiCrW)1-x(Al2O3)x composites with different nano-Al2O3 ratios (x = 0, 1, 2.5, 5 wt %) were prepared using powder metallurgy techniques. The influence of the Al2O3 content on the microstructure, phase composition, high-temperature mechanical properties, and wide-temperature-range friction and wear performance of the composites was investigated. The corresponding high-temperature strengthening and wear-resistance mechanisms were also investigated. The results indicated that as the alumina content increased, the tensile and compressive strengths of the composites decreased at room temperature (RT). However, at high temperatures (800 °C), the opposite trend was observed. Notably, the composite with 5 wt % Al2O3 exhibits the highest tensile strength (189.20 MPa) and compressive strength (446.61 MPa) at 800 °C. The addition of alumina had a relatively minor impact on the friction coefficient of the composites but significantly affected the wear rate. Specifically, the composite with 5 wt % Al2O3 demonstrates optimal friction and wear performance at high temperatures. This enhancement was primarily attributed to the reinforcement of the mechanical properties of the matrix material owing to the addition of alumina. Additionally, the formation of a friction glaze layer rich in Cr2O3 and NiO oxides on the worn surface contributed to improved wear resistance. This study is important for understanding the performance and applications of metallic materials.

Enhancing the corrosion resistance of high Mo S31254 super austenitic stainless steel using grain boundary engineering

Super austenitic stainless steel (SASSs) with a high Mo content exhibit excellent resistance to intergranular corrosion (IGC), Its mechanical properties mainly depend on solid solution strengthening. Meanwhile, grain boundary engineering (GBE) can simultaneously improve the corrosion resistance and mechanical properties of Mo-rich austenitic stainless steel using the resistance to IGC of Mo. However, recrystallization annealing is extremely difficult due to the sensitive precipitation of Cr-rich and Mo-rich precipitations in SASSs. Therefore, this study explores the effect of large deformation, high temperature, and short-time annealing on the corrosion resistance of SASSs. The results show that a recrystallized organization with an average grain size of 13.3 μm was prepared by 50% cold rolling deformation and 2 min high-temperature short-time annealing at 1150 °C. The highest percentage of Σ3 GBs is about 34%, the percentage of other low-energy GBs is relatively low (only about 6%), and the rest are random high-angle grain boundaries (RHAGBs), which account for about 60%. It can be seen the corrosion resistance of random GBs after GBE treatment is superior to that of solution treatment. Meanwhile, medium-temperature aging improved the resistance to IGC of SASSs, especially after aging at 450 ℃, a small amount of Mo is enriched along the GBs, which promotes the formation of Cr2O3 and Mo-rich oxides in the passivation film and improves the corrosion resistance. The above results provide guidance for improving the corrosion resistance of Mo-rich austenitic stainless steels.

The negative effect of V content on high temperature oxidation resistance of austenitic stainless steels at 850 °C

The effect of V on the high-temperature oxidation performance of austenitic stainless steel has been investigated by the constant-temperature oxidation weight gain approach, while the morphology, composition and elemental distribution of the oxide film are further analyzed by scanning electron microscopy and energy dispersive spectrum, transmission electron microscope and X-ray powder diffractometer as well as X-ray photoelectron spectroscopy, revealing the mechanism of the effect of V on the high-temperature oxidation performance of austenitic stainless steel. As a result, the addition of V has a significant adverse effect on the oxidation resistance of steel. Noteworthy, vanadium pentoxide generated during the oxidation process increases the internal stress of the surface oxide layer, reduces the integrity of the oxide layer and promotes oxygen penetration into the matrix. Simultaneously, the Z-phase formed at the grain boundaries of the matrix inhibits the diffusion of Cr ions, resulting in the inability to form an effective protective layer of Cr2O3 oxidation on the surface.

Effects of Zr content on microstructure and properties of 9Cr ferritic/martensitic steel

The effect of the Zr content range in 0.03–0.63 wt% on the microstructure, mechanical properties and high-temperature oxidation behaviors of 9Cr ferritic/martensitic (FM) steels was investigated. The microstructural evolution of steels was studied using Thermo-Calc software, SEM, EBSD and TEM technologies. A full martensite structure was obtained in steels with various Zr contents. The small-sized M23C6 decrease and the larger-sized Zr(C, N) increase with the increasing Zr content, which leads to the increase of martensitic lath width and martensitic block size. The proper Zr content can enhance the oxidation resistance of steel, but Zr addition will reduce the mechanical properties. The decrease in strength and hardness can be ascribed to the reduction of precipitation strengthening and gain size strengthening. The increase in Zr content promotes the formation of Zr oxides, which reduces the formation of MnCr2O4 oxides and Cr2O3 oxides, and finally improves the oxidation resistance of steels.

Corrosion behavior of δ-ferrite in AISI 316 austenitic stainless steel exposed to oxygen-saturated lead‑bismuth eutectic at 550 °C

δ-ferrite is usually found in the 300 series austenitic stainless steels (ASS), but the role of δ-ferrite on corrosion behaviors exposed to oxygen-controlled lead–bismuth eutectic (LBE) has not yet been elucidated. The corrosion behaviors of AISI 316 ASS containing δ-ferrite in the oxygen-saturated static LBE at 550 °C were studied in terms of their solution-treated and accelerated-aging treated conditions. The δ-ferrite and decomposed δ-ferrite exhibit the superior resistance to oxidation attack compared to the austenite, and the δ-ferrite possesses a better corrosion resistance than the decomposed δ-ferrite. Compared with the austenite, the higher diffusivities of Cr and Si in δ-ferrite cause a reduction in the critical concentration required for the formation of chromium oxide and Si-rich oxide. A mixture of Cr2O3 oxide and Fe-Cr-Si spinel oxide developed on the surface of δ-ferrite can effectively impede the metal transfer, leading to the superior resistance to oxidation attack. The retained δ-ferrite and M23C6 carbides in the decomposed δ-ferrite oxidizes independently into FeCr2O4 and Cr2O3 oxides, respectively. The presence of Cr2O3 scale around the retained δ-ferrite decreases its oxidation rate, resulting in the non-uniform oxide phenomenon.

Temperature-time dependence and mechanisms of redox reaction in Cr-coated Zr alloy cladding during steam oxidation at 900–1250 ℃

The structural integrity of the Cr coating can be significantly affected with increasing temperature during steam oxidation. Herein, the elemental diffusion, layered structure, and kinetics evolution of Cr coating in steam environment of 900–1250 ℃ for 0.5 to 3 h were studied. The oxidation behavior of Cr-coated Zr claddings associated with redox reaction between Cr2O3 and Zr were investigated in detail. Cr2O3 layer forms on Cr coating for steam oxidation at 900 ℃ and Cr-Zr diffusion layer appears at interface between Cr coating and Zr substrate when the samples are subjected to steam oxidation at 1000–1150 ℃ for 3 h. The starting time for redox reaction decreases dramatically when the temperature is higher than 1150 ℃. A prediction modal based on Fick's Law was put forward to predict the starting time of redox reaction for 1100 to 1250 ℃. The prediction is consistent with the experimental results. Furthermore, the initial process of redox reaction was investigated and analyzed in detail. Predominated by ion transportation within residual Cr layer, O2- from Cr2O3 could diffuse along the ZrO2 particles at Cr coating boundaries to the Cr-Zr layer, resulting in the reduction of Cr2O3 and partial oxidation of diffusion layer.

High temperature oxidation behaviors of TaCrTiW and TaCrTiZrW alloy coatings

The high-temperature oxidation behaviors of a series of refractory high entropy alloys TaCrTiW and TaCrTiZrW alloy coatings at 1073 K in air were studied. A complex protective oxide layer consisting of Cr2O3, TiO2, and CrTaO4 oxides was generated on the alloys surface. Among the TaCrTiW alloy coatings, the presence of TiO2 inhibited the generation of unfavorable oxides and promoted the generation of CrTaO4. The Ta41.7Cr50.3Ti4.5Zr1.6W1.9 exhibits excellent oxidation resistance. The addition of Zr not only accelerated the initial oxide formation but also promoted the rapid formation of Cr2O3.

Thermal fatigue performance enhancement of new high-Cr martensitic die steels based on overall microstructure manipulation by trace TiC–TiB2 nanoparticles

Thermal fatigue failure is one of the main factors affecting the service life of hot work die steel. Achieving excellent thermal fatigue resistance for hot working die steels can benefit the industry economically. In this work, (TiC + TiB2)/Al master alloys were used to add TiC–TiB2 nanoparticles into high-Cr die steels, which achieves microstructure manipulation and obtains excellent thermal fatigue resistance and strength-plastic combination. The results showed that after being manipulated by 0.02 wt% TiC–TiB2 nanoparticles, the surface oxidation zone of the high-Cr die steel after different thermal fatigue cycles is reduced than high-Cr die steel without manipulation. TiC–TiB2 nanoparticles effectively refined the heat-treated microstructure of high-Cr die steel, promoting the Cr element and alloy carbides being more uniformly distributed in the matrix, which prevents the occurrence of oxidative pitting and conducive to the formation of a dense and uniform Cr2O3 oxide layer, and further preventing the initiation of thermal fatigue cracks. Moreover, these finer and more uniformly distributed precipitates in TiC–TiB2 nanoparticles manipulated high-Cr die steels will promote stress dispersion and hinder thermal fatigue crack propagation. This work provides a promising avenue for the design of low-cost, high-performance, and long-life die steels for industrial applications.

Microstructural evolution and high-temperature oxidation behavior of oxide dispersion strengthened Inconel 625 superalloy fabricated by directed energy deposition

In the present study, wire arc-directed energy deposition (DED) technology was developed to fabricate the Oxide dispersion strengthened (ODS) Ni-based superalloy employing an Inconel 625 flux-cored wire including nano-La2O3 oxides. The microstructural evolution, mechanical properties and high-temperature oxidation behavior were systematically investigated. The results indicate that the melting and decomposition of La2O3 are thought to take place within the melt pool, followed by rapidly combining with Ti to re-precipitate as La2Ti2O7 oxides during DED. These oxides can serve as a highly effective nucleation site according to edge-to-edge matching calculation, resulting in the columnar-to-equiaxed transition and the refinement of grains. However, it is found that plenty of La elements are absorbed by the molten flux in the filler wire, resulting in the formation of slag and the loss of La. Consequently, the strength increases slightly due to the combined effects of precipitation strengthening and grain boundary strengthening. Furthermore, The ODS Inconel 625 sample can achieve a higher oxidation resistance after high-temperature oxidation at 900 °C for 150 h. The fine microstructure promotes the rapid formation of dense Cr2O3 oxide scales. On the other hand, the precipitation of La-rich oxides retards the outward transport of cation such as Ni, Fe and Nb, leading to the formation of a protective δ-Ni3Nb layer beneath the Cr2O3 layer to prevent the oxidation of matrix.

Corrosion behavior of magnetron sputtering Fe31Cr20Al17Ti16Nb16 high entropy coating in liquid lead-bismuth eutectic with different oxygen concentration at 500 °C

The major concern of the structure integrity of lead cooled reactor is the corrosion behavior of fuel cladding and other core internal materials. Magnetron sputtering technology is adopted as an surface coating method to improve the corrosion resistance of nuclear fuel cladding exposed to liquid lead-bismuth eutectic (LBE). Fe31Cr20Al17Ti16Nb16 high entropy alloy (HEA) coatings were prepared on tubular ferritic/martensitic (F/M) steel which is the candidate fuel cladding material, and the corrosion behaviors of Fe31Cr20Al17Ti16Nb16 coatings in LBE are investigated in this work. F/M steel specimens with Fe31Cr20Al17Ti16Nb16 coatings were exposed to 500 °C stagnant liquid LBE with oxygen concentration of Co ≈ 1 × 10−4 wt% and Co ≈ 1 × 10−7 wt% for 1000 h respectively. The primary findings suggest that the oxygen content of LBE mainly affects the morphology of duplex oxide layers generated during corrosion process, which resulting from the different inward diffusion flux of oxygen. In oxygen-saturated (Co ≈ 1 × 10−4 wt%) LBE, the overall oxide layer exhibits bulging and incompact morphology and infiltration of Pb is probed at inner Cr2O3 oxide layer, larger-sized cavities (the observed maximum dimension reaches 233.5 nm) distribute close to the outer Fe3O4/FeCr2O4 layer; In oxygen-depleted (Co ≈ 1 × 10−7 wt%) LBE, duplex oxide layer presents relatively dense and uniform state, tiny cavities (observed maximum dimension is 38.3 nm) dispersing at the internal of oxide areas. Corrosion rates of the Fe31Cr20Al17Ti16Nb16 coatings under two oxygen situations are 2 orders of magnitude lower than uncoated F/M steel under same exposure condition, the oxide layers with better uniformity and density produced in Co ≈ 1 × 10−7 wt% LBE indicating the better application advantage of Fe31Cr20Al17Ti16Nb16 coatings in oxygen-depleted LBE.

Synergistic effects of Cr addition on surface characteristics and its implications on wear and in vitro biocompatibility of TiMoNbTaW alloys

Refractory metal based high entropy alloys (RHEAs) presents promising anti-wear and cytocompatibility to meet the articulating demands in artificial hip/knee prosthesis. In this study, TiMoNbTaW RHEAs were fabricated through arc melting, and modified with Cr to enhance their bulk, and surface characteristics. The Cr addition resulted in a gradual increase in bulk hardness from ⁓4.9 GPa to ⁓7.1 GPa, and yield strength from ⁓1.3 GPa to ⁓1.9 GPa, attributed to lattice distortion induced misfit strain. X-ray photoelectron spectroscopy (XPS) confirmed the formation of a native passive film on alloys surface, consisting of oxides TiO2, MoO2, MoO3, WO3, Nb2O5, Cr2O3 and Ta2O5. The wear resistance improved in accordance with Archard's law, while friction responses were influenced by Cr2O3 content. Higher Cr2O3 content imparted lubricating effect, reducing friction coefficient ⁓0.18–0.23, and wear rate in the order 10−5 mm3/Nm. Moreover, higher Cr2O3 in the native film contributed to the excellent cytocompatibility against MC3T3-E1 cells. Cell proliferation increased with increase in Cr content in the RHEA and showed higher alkaline phosphatase activity (ALP) activity when Cr content was 10% or more. This study evaluates the effect of Cr increment on the microstructural and mechanical properties in TiMoNbTaW RHEAs, and highlights the synergistic effects of the passivation-mediated native film, influencing tribological, and in-vitro cellular response.

The effect of temperature on the transfer layer of an aluminium alloy on tool steel and the effect of CrN coating

It is essential to explore temperature's crucial role while unveiling the intricacies of tribological interplay in CrN-coated steel-alloy systems. In the present study, tribological potential of CrN-coated hot-work tool steel was investigated under unidirectional single-pass sliding wear conditions. The sliding wear tests were performed at different temperatures (i.e., 20 °C, 100 °C, 200 °C, 300 °C, 400 °C and 500 °C) for the different sliding distances between 2 mm and 68 mm to explore the effect of temperature on the initiation and evolution of the transfer of an aluminium alloy (EN AW-6060). The effect was studied in terms of the contact area of the aluminium alloy and the volume transferred to the surface of the CrN. In addition, the structure of the wear trace and the equivalent friction coefficient were monitored with respect to the sliding distance and the temperature. The results show the strong dependency of the tribological potential of the CrN coating and the aluminium alloy on the temperature but show insignificant dependency on the sliding distance. When sliding up to 200 °C, the transfer was found to be dependent on the surface roughness of the coating, while strong adhesion led to the aluminium alloy's transfer during sliding at higher temperatures, that is, above 300 °C. At 500 °C, the CrN coating formed a self-protective Cr2O3 oxide that reduced the adhesive transfer of the alloy to the CrN compared to that at 200 °C–300 °C.

Temperature-adaptive lubrication of Ag doped Cr2AlC nanocomposite coatings

Self-lubricating nanocomposite carbides and nitrides coatings that enable to exhibit both low friction coefficient (CoF) and high wear resistance over a wide temperature range, are in high demand for mechanical components used in aerospace and marine systems. In this work, we developed high-purity Ag-doped Cr2AlC (Ag–Cr2AlC) nanocomposite coatings using a facile arc/sputter deposition technique followed by annealing. Compared to typical nanocrystalline Cr2AlC MAX phase coatings, the incorporation of Ag resulted in a unique nanocomposite structure, where Ag encapsulates elongated Cr2AlC nanograins. The dry sliding wear of this material was evaluated using the ball-on-disc method, with an Al2O3 ball as the counter body, at temperature ranging from 25 °C to 700 °C. Interestingly, Ag dopants contributed to a significant reduction in COF and wear rate at temperatures below 500 °C, while the synergistic effect of the Ag distributed at grain boundaries and the outermost oxides of Cr2O3 and Al2O3 generated during friction dominated the excellent self-lubrication at 500–700 °C. Notably, the Ag–Cr2AlC coatings promoted the in-situ formation of gradient bilayer oxides, consisting of a loosely coarse-grained inner layer and a densely refine-grained outmost layer. The combination of unique gradient oxides and a combined nanocomposite matrix allows the coating to accommodate plastic strains without extended cracks or localized brittle fracture.