Increasing Mo Content Research Articles

Distribution of molybdenum in soft tissues and blood of rats after intratracheal instillation of molybdenum(IV) sulfide nano- and microparticles

There is still little literature data on the toxicity and safety of the commonly used molybdenum (Mo) disulfide which is present in the working as well as living environments. Thus, an experiment was carried out involving rats, with single and repeated intratracheal exposure (in the latter case, 7 administrations at 2-week intervals with the analysis performed after 90 days) to lower (1.5 mg Mo kg−1 b.w.) and higher (5 mg Mo kg−1 b.w.) doses of molybdenum(IV) sulfide nanoparticles (MoS2-NPs) and microparticles (MoS2-MPs). The analysis of Mo concentrations in the tail and heart blood as well as in soft tissues (lung, liver, spleen, brain), after mineralization and bioimaging, was meant to facilitate an assessment of its accumulation and potential effects on the body following short- and long-term exposure. The multi-compartment model with an exponential curve of Mo concentration over time with different half-lives for the distribution and elimination phases of MoS2-MPs and MoS2-NPs was observed. After 24 h of exposure, a slight increase in Mo concentration in blood was observed. Next, Mo concentration indicated a decrease in blood concentration from 24 h to day 14 (the Mo concentration before the second administration), below the pre-exposure concentration. The next phase was linear, less abrupt and practically flat, but with an increasing trend towards the end of the experiment. Significantly higher Mo concentrations in MoS2-NPs and MoS2-MPs was found in the lungs of repeatedly exposed rats compared to those exposed to a single dose. The analysis of Mo content in the liver and the spleen tissue showed a slightly higher concentration for MoS2-NPs compared to MoS2-MPs. The results for the brain were below the calculated detection limit. Results were consistent with results obtained by bioimaging technique.

Physical, mechanical, and corrosion properties of Ti–12Mo and Ti–15Mo alloys fabricated by elemental blend and mechanical alloying techniques

Ti–Mo alloys have received increased attention and concern in several applications, especially in biomedical, because of their appropriate properties, non-toxicity, and reasonable cost. This work investigated the different Mo powder content (12 and 15 wt%) fabricated by elemental blended and mechanical alloying. The microstructure, density, microhardness, compressive, wear, and corrosion properties were characterized. It was found that the volume fraction of β-phase increases with increasing Mo content to around 85%, mainly due to the robust β-phase stabilizer effect. Moreover, the microhardness and compressive properties were enhanced with Mo addition and MA fabrication by 11.5 and 27%, respectively, mainly due to solid solution strengthening, plastic deformation, high dislocations, and lattice defects. However, the strain at failure decreased with decreasing sintered density and increasing porosity. From this study, the corrosion rate decreased with decreasing the porosity, reaching 0.226 × 10−3 mm/year for Ti–12Mo alloy fabricated by elemental blend with a minimum porosity of 3.6%. Ti–Mo alloys can also tolerate properties and impurities, making them suitable for biomedical applications.

Effects of Mo doping on the phase transformation behaviors and the magnetic properties of rare-earth-free MnBi alloy

The high-performance rare-earth-free low-temperature phase Mn–Bi-based permanent magnet alloys (LTP-MnBi) have gained widespread attention, but it still presents a challenge. Here, the LTP-MnBi alloy with Mo element doping was prepared by using arc-melting and subsequent high-vacuum annealing. The crystalline structure, phase transformation behavior, and magnetic properties were systematically investigated. The result showed that Mo element doping significantly improved the stability of the LTP in MnBi alloy. The investigation revealed that the disparity in atomic radius between Mo and Mn, Bi elements played a pivotal role in the formation and stability of the LTP-MnBi. With the increase of Mo content in the LTP-MnBi alloy, the coercivity value remarkably increased from 8.1 kOe to 11.7 kOe with a decrease of saturation magnetization from 71.6 emu/g to 56.5 emu/g, and the maximum energy product gradually reduced from 10.6 MGOe to 7.9 MGOe. The underlying mechanism revealed that magnetic properties were closely related to the fraction and crystal structure of LTP-MnBi. Therefore, magnetic properties of Mo-doped MnBi alloy make them an attractive candidate among the rare-earth-free permanent magnets.

Effect of Mo Content on Friction and Wear Properties of Fe-Mn-Al-C Alloys Under Different Working Conditions

For this study, Fe-25Mn-9Al-8Cr-1C-xMo alloys (x = 0, 0.1, 0.2, 0.3, 0.4 wt%) were prepared by mechanical alloying combined with vacuum hot-pressing sintering. The corresponding microstructure, mechanical properties, and friction and wear properties under different working conditions (dry friction, oil lubrication and sulfur-containing boundary lubrication) of materials were studied. The results show that the Fe-25Mn-9Al-8Cr-1C alloy is mainly composed of the austenite phase, Cr7C3 phase, and a small amount of a-Al2O3 phase. After adding Mo element, the Fe2MoC phase appears. With the increase of Mo content, the tensile strength and elongation of the alloys increase first and then decrease. In particular, when the Mo content is 0.3 wt%, an excellent combination of strength and toughness is obtained. The product of strength and elongation of the Fe-25Mn-9Al-8Cr-1C-0.3Mo alloy reaches a maximum value of 3.69 GPa·%, which is improved by 158.04% compared with the matrix alloys. With the increase of Mo content, the average friction coefficient and volume wear rate of the alloys show a trend of first decreasing and then increasing under different working conditions. Also, the average friction coefficient and volume wear rate of the alloy with 0.3 wt% Mo reach a minimum value, especially under the condition of sulfur-containing boundary lubrication. The average friction coefficient and volume wear rate of Fe-25Mn-9Al-8Cr-1C-0.3Mo alloy are 0.051 and 0.222 × 10−4 mm3·N−1·m−1, respectively, which are 40.69% and 46.38% lower than those of the matrix alloys.

Influence of Si and Mo on the Sigma-Phase Precipitation in S32750 Super Duplex Stainless Steel Slab

In this study, we investigated the effect of Si and Mo on the sigma-phase precipitation in S32750 super duplex stainless steel slab. The activity for Mo with increasing Si and Mo was calculated by the Wagner formula, and the equilibrium solidification phase diagrams of S32750 duplex stainless steels with different Si and Mo contents were calculated using the thermo-calc software. The sigma phase precipitated mainly at ferrite/austenite phase boundaries and grew up towards the interior of ferrite phase in S32750 SDSS slab. The area fraction and size of the sigma phases significantly increased with increasing Mo content and Si content. Also, the increment in Mo and Si content affected the Mo concentration in sigma phase. The sample（Mo:3.4%,Si：0.3%） had a lowest sigma-phase area fraction of 2.84% and had lowest Mo content in σ phase.The calculation results showed that the increase of Mo and Si content increased the initial precipitation temperature and maximum precipitation amount of σ phase in S32750 SDSS equilibrium phase diagram. The activity of Mo also increased with increasing Si content and Mo content. That is, Mo and Si elements promoted the precipitation of σ phase.

Mechanism of Mo content on improving the high-temperature corrosion performance of APS sprayed Ni-clad Al coatings in simulated biomass corrosion condition

The study examined the impact of varying molybdenum content (0 %, 5 %, and 10 % wt) on the high-temperature corrosion resistance of APS-sprayed Ni-clad Al coatings. The coatings were exposed to a simulated biomass-firing environment with pure KCl deposition at 600 °C for 168 h, and a mixed gas containing 15 % water vapor was passed through. The findings revealed that increasing Mo content improved the coating's high-temperature corrosion resistance. The coating with 10 % Mo displayed a continuous layer of Ni and Al oxides on its surface, while KCl was concentrated in the Mo region. Based on the experimental results, a mechanism for how the presence of Mo element contributes to the high-temperature corrosion resistance of NiAl coatings was proposed.

Grain boundary segregation behavior of Mo atoms in nanocrystalline Ni–Mo alloy

In this paper, molecular dynamics method was used to design the grain boundary (GB) segregation structure of solute atom Mo in nanocrystalline nickel, and the effect of the segregation structure on the migration and deformation mechanism of nanocrystalline Ni–Mo alloy boundaries was studied. The results indicate that the addition of solute atom Mo can cause segregation at GBs, and the yield strength and tensile strength of nanocrystalline Ni are significantly increased through solid solution strengthening. Mo atoms segregation result in an increase of the GB thickness and stability of the GB. In addition, by labeling GB atoms and tracking their diffusion trajectories, it was found that after adding Mo atoms, the probability of atomic diffusion at GBs decreased. This indicates that Mo atoms reduce GB energy and improve GB stability. Meanwhile, as the Mo content increases, the degree of atomic disorder increases, and the probability of GB migration decreases. This leads to the inability of grains to merge and inhibit their growth, effectively improving the mechanical properties of the material. As the strain increases, the number and length of dislocations increase, and a large amount of entanglement occurs at GBs. With the increase of Mo content, the number of dislocations decreases sharply, with Shockley dislocations having the highest number. Shockley dislocations interact with other dislocations and hinder their generation and movement, forming a more stable dislocation system structure and increasing the strength of the alloy. Our work focuses on observing the influence of GB segregation structure on the mechanical properties and deformation mechanism of nanocrystalline polycrystalline Ni–Mo alloys, establishing the mechanism of the influence of segregation structure on the stability and coarsening of nanocrystalline metal GBs, examining the influence of segregation structure on dislocation motion and GB migration process during deformation, and proposing positive research and development ideas and theoretical basis for designing nanocrystalline metal materials with excellent performance.

Effect of Mo content on interfacial microstructure and properties of explosive welded Mo–Cu/Cu plates

In this study, Mo–Cu/Cu plates were successfully fabricated by explosive welding and the influence of Mo content on their interfacial microstructure, shear strength, thermal conductivity and electrical conductivity was investigated. The results showed that as the Mo content increased to 70 wt%, the number of serrations at the interface of the Mo70Cu30/Cu plate increased, exhibiting a more complete shape and periodically ordered arrangement. In addition, increasing the Mo content to 70 wt% leads to a significant improvement in the interdiffusion distance at the interface, resulting in significant improvements in shear strength, thermal conductivity and electrical conductivity compared to the corresponding Mo70Cu30 plate. More serrations, more complete serrations and periodically arranged serrations benefit from increased Mo content to 70 wt% while improving the shear strength, thermal conductivity and electrical conductivity compared to raw material of Mo–Cu plate.

Synergistic effects of multi-strengthening mechanisms in exceptionally high-strength W-Ni-Fe composites

Tungsten heavy alloys (WHAs) are typical tungsten-based composites and are considered as important materials in kinetic energy penetrators that currently use depleted uranium munitions. However, the incongruity between strength and plasticity is the “Achilles’ heel”, which restricts further application in national defense and military industries. Herein, a novel fine-grained La2O3 strengthened W-Mo-Ni-Fe composites were fabricated successfully via using nanoscale solid-solution composite powder and the optimized two-stage sintering as well as vacuum heat-treatment techniques. In the model W-xMo-4.9Ni-2.1Fe-1La2O3 composites (x = 2.5, 5, 10 and 20 wt%), the heat-treated alloys had a highly homogeneous microstructure, consisting of equiaxed W grains, matrix phase and dispersed La2O3 reinforced particles. Increasing Mo content promoted microstructure refinement and caused the formation of MoNi3 intermetallic compound (IMC). As a result, benefiting from the multiple strengthening mechanisms containing fine-grained, solid-solution and oxide dispersion strengthening effects, the 88 W-5Mo-4.9Ni-2.1Fe-1La2O3 composite exhibited a superb synergy of tensile strength and ductility (1116 MPa and ∼ 15%). Moreover, the analysis of the lattice strain fluctuations and dislocation behaviors of WHAs were conducted by means of the geometric phase analysis (GPA) approach for the first time. The plastic deformation mechanism was studied to elucidate the fracture characteristics and slip systems with Schmid factor (SF) and Kernel Average Misorientation (KAM) analysis. Our findings not only shed light on the understanding of the deformation mechanisms of WHAs, but also provide a new avenue for the design of WHAs with outstanding mechanical properties.

High thermal stability and optical contrast of Mo-doped Ge8Sb2Te11 films prepared by magnetron co-sputtering

In this work, Ge8Sb2Te11 (GST) films with high melting point element Mo doping were prepared by magnetron co-sputtering, and the influence of Mo content on the phase transformation and optical properties of the films was investigated. The results of GIXRD, XPS, and ellipsometry analysis show that Mo will occupy the lattice vacancy, promoting grain growth and accelerating phase transitions. With an increase in Mo content, the phase transition temperature of the films can reach 360 °C, and the amorphous thermal stability of the films can be enhanced by Mo doping. Meanwhile, the optical properties of the films are improved. The optical band gap of Mo-doped films is reduced, the absorption coefficient rises, and the refractive index contrast of GST films with low Mo-doping in the Vis-NIR band is as high as 2.27. This result will make it possible to apply Ge8Sb2Te11 thin films in structural color fields and broaden their color spectrum.

Thermal, Mechanical, and Electrochemical Characterization of Ti50Ni50−XMox Alloys Obtained by Plasma Arc Melting

This study aims to manufacture and characterize titanium and nickel alloys with different molybdenum (Ti–Ni–Mo) contents, focusing on the influence of these additions on the microstructure, mechanical properties, and corrosion resistance. The relevance of this work stems from the lack of research on this specific alloy and the absence of reports in the literature with molybdenum percentages above 2 at.%. Ti50Ni50−XMox alloys were produced by the plasma arc melting method, with six different compositions (x = 0, 0.5, 1, 2, 3, and 4 at.% Mo), and a comprehensive analysis of microstructure, chemical composition, thermal, mechanical, and electrochemical properties was carried out. The results demonstrated significant alterations in the microstructure of the Ni–Ti alloy with the addition of molybdenum presenting several phases, precipitates (TiNi, Ti2Ni), and oxides (Ti4Ni2O, TiO, and TiO3). The stability of the B2 phase increased with molybdenum content, and the monoclinic martensite (B19′) phase was identified only in the Ni–Ti sample. Introducing molybdenum into the Ni–Ti alloy generated the R-phase and shifted the phase transformation peaks to lower temperatures, as differential scanning calorimetry (DSC) indicated. Microhardness and elastic modulus decreased with increasing Mo content, ranging from 494 HV to 272 HV and 74 GPa to 63 GPa, respectively. Corrosion tests revealed increased corrosion resistance with increasing Mo content, reaching a polarization resistance of 2710 kΩ·cm2 and corrosion current of 11.3 µA. Therefore, this study points to Ti–Ni–Mo alloys as potential candidates to increase the range of Ni–Ti alloy applications, mainly in biomaterials, reinforcing its relevance and need in current alloy research.

High magneto-mechanical hysteresis-type damping in FeGaMo alloys

Optimization of the damping capacity of conventional FeCr-based ferromagnetic high damping alloys (HDAs) usually involves a trade-off in terms of degradation of mechanical properties due to grain coarsening caused by high-temperature annealing. In this work, new ferromagnetic HDAs of FeGaMo alloys with different Mo contents are reported, which can exhibit high damping when treated in a medium temperature range. Among these alloys, the alloy with Mo content of 2 at% exhibits the best damping capacity of 4.20 × 10−2 (Q−1, equivalent to a special damping capacity SDC of 0.26). It is found that the Mo element has a high solid solubility in the FeGa alloy, and when the Mo content is 2 at%, only isolated tiny precipitations are observed in the matrix. These small precipitates have a negligible effect on hindering domain motion, and the corresponding coercivity change is extremely weak compared to the Mo-free FeGa alloy. As the Mo content increases to 4 at% or 6 at%, Mo-rich phases precipitate within the grains and along the grain boundaries, resulting in an increasing coercivity. Interestingly, as the Mo content increases, the domain density in the (001) and (110) surfaces gradually increases and the arrangement of magnetic domains becomes more tortuous due to the decrease in the magnetocrystalline anisotropy constant. For the FeGaMo alloy with 2 at% Mo content, the high damping capacity mainly arises from the energy loss caused by the high density of irreversible motion of domain walls (DWs) under the applied stress, and as the Mo content continues to increase, the significant precipitation of Mo-rich phases severely restricts the movement distance of DWs, leading to a decrease in damping. This work provides valuable insights for the design and research of new ferromagnetic high damping materials in the future.

Bandgap tuning by controlled growth of Mo doped NiO nanoparticles and their functional role as excellent photocatalytic degradation agent

Semiconductor materials are in leading role for elimination of organic pollutants in water with an effective tuning of bandgap and improving their photocatalytic activity. Pristine and Mo-doped (0, 1, 2, 3, 4 and 6 %) NiO nanoparticles have been synthesized by sol–gel method. The synthesized nanoparticles were examined by XRD, SEM, EDS, UV–visible spectroscopy and photoluminescence (PL) analysis. The synthesized nanoparticles exhibit spherical morphology and their crystallite size decreases with an increase in Mo concentration. The average crystallite size decreases from 67 nm to 44 nm and the drastic reduction in band gap occurs from 3.5 eV to 2.9 eV at 3 wt% Mo doping. The photocatalytic activity against Rhodamine-B (RhB) and methylene blue (MB) showed that the Molybdenum doping improves the performance of NiO photocatalyst. The PL analysis revealed that the Molybdenum substitution in NiO host lattice specifically reduces the recombination rate with an improved photo-efficiency. The reaction kinetics examination showed pseudo-first-order kinetics with an improved rate constant. The sample containing 3 wt% Mo doped NiO showed highest efficiency among all the prepared samples. The sample with 3 wt% doping shows 90% degradation after 90 min when using against MB dye, whereas with RhB dye it shows 98% degradation in 120 min. The retention of high performance after five consecutive cycles confirms the reusability of synthesized nanoparticles.

Investigation of the effect of Mo+2 ion concentration on linear and non-linear optical properties of tungsten trioxide thin films for optoelectronic applications

To achieve the goal of creating a single-phase mixture of transition metal oxides with high electrical efficiency, our investigation focused on studying the linear and nonlinear optical properties of a mixture of transitional oxides that is electrophoretically colored. For finding the best ratios, we also investigated the impact of adding molybdenum ion to tungsten trioxide on the linear and non-linear optical properties of the samples made using the spray pyrolysis method on heated glass substrates. The as-deposited films were amorphous, as demonstrated by the X-ray diffraction (XRD). All of the samples were transferred to the polycrystalline and acquire a triclinic structure after the thermal annealing at 500 °C for 2 h. At room temperature, transmission and reflection measurements in the wavelength range of 300–2500 nm were utilized to evaluate the absorption coefficient. MoxW1-xO3 thin films' optical density, optical energy gap, skin depth, and Urbach's parameters were also estimated. Urbach's energy, EU, decreases from 0.355 to 0.154, eV as Mo-content rises, while Tauc's band gap energy, Eg, decreases from 2.76 to 2.56 eV. The films' static refractive indices dropped from 2.832 to 2.081 in the low-energy region and from 3.832 to 2.446 in the high-energy region. The dispersion energies and other variables were investigated using the Wemple–DiDomenico and Sellmeier models. In addition, various dispersion and nonlinear parameters were estimated and thoroughly discussed. It was observed that the improvement in the crystallinity of W1-xMoxO3 thin films led to a decrease in the values of the third-order nonlinear susceptibility (χ(3)), mainly affected by the constant refractive index, which decays with an increase in Mo concentration. Simultaneously, the conductivity of the films rises proportionally with the photon energy and Mo content, which is attributed to the concurrent increase in the dielectric constants. In this work, new approach for fabrication of quality thin film of MoxW1-xO3 was demonstrated. This is the reason for obtaining the best results, which made these films an effective contribution to many important applications. Furthermore, MoxW1-xO3 thin films perovskite has large nonlinear optical proper. These findings highlight the potential utility of these films in diverse critical optical applications, such as commercial lasers, ultra-fast signal processing in optical communication systems, sensors, environmental monitoring, medicine, manufacturing and materials processing, military applications, as well as scientific instrumentation.

Insight into the Role of Mo Content on the Microstructure and Impact Toughness of X80 Thick-Walled Low-Temperature Pipeline Steel

In this manuscript, the effects of Mo content on the microstructure and impact toughness of X80 thick-walled low-temperature pipeline steel were studied. Two test steels with different Mo content (0.25% and 0.40%) were prepared by the thermo-mechanical control process. The impact properties were measured at −45 °C, and the microstructure evolution was observed via an optical microscope (OM), a scanning electron microscope (SEM), electron back-scattered diffraction (EBSD), and a transmission electron microscope (TEM). Each steel showed the formation of a mixed microstructure consisting of polygonal ferrite (PF), granular bainite (GB), and lath bainite (LB). Increasing Mo content resulted in the rise of LB at the expense of PF and GB. At the same time, the morphology of martensite/austenite (M/A) constituents changed from blocky to slender. The dislocation density in the ferrite matrix around the M/A constituents enhanced with an increase in Mo content. This also led to an increase in the microstrains around the M/A constituents. Also, the number fraction of the high angle grain boundary (HAGB) (MTA > 15°) decreased with the addition of more Mo content. Furthermore, with an increase in Mo content from 0.25% to 0.40%, the low-temperature impact toughness decreased from 206 to 57 J. Both an increase in the slender M/A constituents and a decrease in the HAGB number fraction deteriorated the low-temperature impact toughness of the X80 thick-walled low-temperature pipeline steel.

Effect of molybdenum on cyclic oxidation behavior of 4th generation nickel-based single crystal superalloys

The cyclic oxidation behavior of fourth-generation nickel-based single crystal superalloys with 2–4 wt% Mo content were studied at 900 ℃ and 1100 ℃. At 900 ℃, with the increase of Mo content, the oxide layer accumulates more growth stress, resulting in the interface between the outer oxide layer and the inner oxide layer more prone to crack initiation. At 1100 ℃, the oxidation layer accumulates more growth stress and thermal stress, so the oxidation layer occurs large scale spalling, which is more severe in 4Mo alloy. The results show that the increase of Mo content of alloy promotes the oxidation of containing W-Re alloy, which promotes the volatilization of oxides and the spalling of oxide, decreases the protection of oxide layer, and deteriorates the oxidation resistance of the alloy.

High-temperature tribological properties of the novel NiCr(MoNb)x-Ag self-lubricating composite films

The representative FCC structured NiCr(MoNb)x-Ag (x = 0, 0.65 and 1.05) composite films were developed in this work, and the microstructure, mechanical, and tribological properties were studied. It is shown that small amounts of nm-sized Ag particles are dispersed in the thin film matrix. With the increase of Mo and Nb content, the hardness of the films is enhanced while the elastic modulus increases first and then decreases. The NiCr(MoNb)1.05-Ag composite film shows the best tribological performance. The average friction coefficients of the NiCr-Ag, NiCr(MoNb)0.65-Ag and NiCr(MoNb)1.05-Ag films from room temperature to 600 °C are 0.35–0.46, 0.27–0.4 and 0.26–0.32, respectively. NiCr(MoNb)0.65-Ag and NiCr(MoNb)1.05-Ag films show good lubricity at room temperature to 500 °C, and NiCr(MoNb)1.05-Ag film still maintains a low friction coefficient at 600 °C. The wear rate increases with temperature and decreases successively with increasing Mo and Nb content. Moreover, the distribution of elements in the films with higher Mo and Nb content is more stable at high temperatures, which contributes to the improvement of wear resistance.

Corrosion Behavior of SiMo Ductile Cast Iron in Different Corrosive Environments

Standard SiMo ductile cast iron automotive alloys are typically subjected to various hostile environmental conditions. For the current investigation, SiMo with a silicon content of 5% and molybdenum contents ranging from 0 to 1.5% was used. In two corrosive environments of 0.6 M NaCl and 0.5 M H2SO4, the study intends to present the corrosion behavior of high silicon molybdenum ductile cast iron (SiMo). Moreover, the impact of changing Mo on the microstructural characteristics has been investigated. The SEM-EDX examinations revealed that the nodule counts, M6C carbides, and lamellar pearlite increased while the ferritic matrix decreased with increasing Mo contents. It is clear that the addition of Mo reduces cast iron's rate of corrosion and thus increases its corrosion resistance. The results showed that SiMo cast iron alloy with 1.0 wt% Mo had a lower corrosion current (Icorr) in 0.6 M NaCl solution while lower corrosion current (Icorr) with the cast iron containing 1.5 wt% Mo in 0.5 M H2SO4 solution, which resulted in the lowest corrosion rate. The occurrence of a galvanic couple between the alloy matrix and the graphite nodules results in electrochemical corrosion, with the largest corrosion rates taking place at Mo-free alloy in both media.

Effect of molybdenum addition on oxidation behavior and secondary protection mechanism of FeCrAl coatings

FeCrAl alloy coatings are widely used for their excellent oxidation resistance at high temperatures, but they can suffer from rapid material degradation due to breakaway oxidation of the coating. Composition manipulation is an essential way to prompt the oxidation resistance of the coatings. In this study, we prepared Fe-13Cr-7Al (at.%) alloy coatings with varying Mo contents (Mo = 0, 1.5, 3, 6 at.%) by magnetron sputtering and investigated their oxidation behaviors at 550 °C. The surface and cross-sectional morphologies of the coatings before and after oxidation were examined using electron microscopy. The results showed that the crystalline grain and particle size of the coatings decreased significantly with the increase of Mo content, leading to a notable increase of grain boundaries and further enhancing element diffusion during the oxidation tests. As a result, a protective and stable oxide scale rapidly grew on the surface of FeCrAlMo coatings during oxidation. Moreover, FeCrAlMo coatings demonstrated improved secondary protection mechanisms with increasing Mo contents. This was attributed to the formation of an internal oxidation layer of a spinel barrier (M3O4, M = Fe, Cr, Al, Mo) beneath the outer oxidation layer. The spinel barrier impeded inward diffusion of oxygen ions and outward diffusion of metal cations, resulting in enhanced oxidation resistance of the spinel-type oxide. The thermodynamic calculations were used to evaluate the oxidation mechanisms of the coatings. These results provide a deeper understanding of the effect of Mo addition on the oxidation behavior and underlying protection mechanisms of FeCrAl coatings, and can be beneficial for designing and developing materials for use in oxidation environments.

Influence of Al and Mo on microstructure and tribological behaviors of Co-based superalloy

In this study, three Co-based superalloys with different Al and Mo concentrations were prepared by powder metallurgy (PM) method to investigate their influences on the microstructure and tribological properties. Replacing Al with Mo in the alloy has been found to decrease its hardness and yield strength, but increases its compressive ductility at room temperature. With the increase of Mo content, the formation of the HCP phase from the original FCC solid solution phase was promoted, and the microstructure of the alloy became relatively coarse. All superalloys showed decreased friction coefficient during sliding wear at 800 °C. The alloy with the highest content of Mo and lowest content of Al exhibited the greatest wear resistance at both room temperature and 800 °C. Formation of a continuous compact glaze layer rich in Cr2O3 and CoMoO4 oxides results into a significant reduction in both friction coefficient and specific wear resistance, and the synergistic effect of high temperature wear-induced oxides is the dominant contribution rather than the transformation of HCP from the original FCC solid solution phase at high temperature.