Influence Of Mo Content Research Articles

Microstructure, mechanical properties and incipient plasticity of (Ti42.5Zr42.5Nb10Ta5)100-xMox refractory high-entropy alloys

A series of (Ti42.5Zr42.5Nb10Ta5)100-xMox (x = 0, 3, 5 and 7 at.%) refractory high-entropy alloys (RHEAs) were prepared, and the influence of Mo content on microstructure and mechanical properties of the RHEAs were systematically studied. All the RHEAs consist of a single body-centered cubic (BCC) phase. As the Mo content increases from 0 at.% to 7 at.%, the yield strength of RHEAs increases from 670 MPa to 975 MPa at room temperature. The high strength of the BCC RHEAs mainly depends on solid-solution strengthening caused by the Mo addition. The RHEAs with low Mo content (0–5 at.%) can possess high tensile plasticity of ∼20 %, while it reflects brittle after the 7 at.% Mo addition. The high tensile plasticity of the RHEAs was attributed to the combined effects of lattice rotation to promote and refine crystalline strengthening. The RHEAs with 5 at.% Mo addition have high specific yield strength (∼32 MPa g−1cm3) and excellent fracture strains (＞60 %) at 1173 K. Moreover, the incipient plasticity of the RHEAs was analyzed by nanoindentation. It is shown that the maximum shear stress (τmax) of the RHEAs from 1.80–2.34 GPa to 2.67–4.83 GPa. The activation volumes (v∗) of the RHEAs from 0.7 Ω to 1.1 Ω. The nanomechanical properties of the RHEAs are related to the Mo content. The purpose of this work is to design RHEAs with excellent mechanical properties and to offer a theoretical foundation to assist new RHEA design.

The Influence of Mo Content and Annealing on the Oxidation Behavior of Arc‐Melted Cr–xMo–8Si Alloys

The influence of Mo (10–40 at%) additions to Cr–8 at%Si is systematically studied by analyzing arc‐melted alloys in the as‐cast and annealed state. The oxidation resistance is tested by thermogravimetric analysis (TGA) at 1200 °C in air for up to 100 h. Samples are characterized by X‐ray diffraction, scanning electron microscopy, and wavelength‐dispersive X‐ray spectroscopy. The studied Cr–xMo–8Si alloy series shows a beneficial effect of Mo on the corrosion behavior. For all of the investigated Mo contents, no nitridation is observed and the oxide scale adhesion is improved. An increased amount of intermetallic A15 phase leads to the formation of a SiO2 scale beneath the Cr2O3 layer during high‐temperature exposure. The internal SiO2 layer inhibits further internal oxidation of the A15 phase. Uniform size and distribution of A15, benefits the formation of a duplex oxide scale. Cr–25Mo–8 at%Si, shows the most promising oxidation behavior. The TGA data follows the paralinear law, with both the growth rate, kp, and volatilization rate, kv, of Cr2O3 being reduced by adding 10–25 at% Mo. A binary Cr/Mo–Si phase diagram is generated in order to determine accurate annealing conditions and estimate the stability range of the metastable σ phase.

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.

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.

Effect of Mo addition on the mechanical and tribological properties of magnetron sputtered TiN films

Ternary-based titanium nitride (TiN) thin films have drawn attention toward rational applications due to their wear resistance, high hardness, and corrosion resistance. The influence of Mo content on the structural, tribological, and mechanical properties of TiN films is reported in this study. The microstructure and elemental composition of the as-deposited TiMoN films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nanoindentation, and ball-on-disc wear tests. XRD results showed that the as-sputtered TiMoN films consisted of a formation of solid solution of TiN and MoN mixture phases. With 18 at. % of Mo, the mechanical property of TiMoN films was enhanced, and the film exhibited a high hardness of 28 GPa. Moreover, this addition led to a wear rate of 0.40 and 6.34 × 10−6 mm3/Nm and to lower the friction coefficient to values lower than the corresponding binary TiN film. This was attributed to the multi-phase strengthening and higher (H/E, H3/E2) values, which indicate that the mechanical properties and the wear resistance of TiN can be enhanced by alloying with Mo.

Influence of Mo modification on coaromatization coupling methanol with n-hexane over [Zn,Mo]/HZSM-5 catalysts

Zn and Mo modified HZSM-5 catalyst benefits the formation of aromatics and the yield of BTX reached 64%. The influence of Mo content on the catalytic performance and carbon deposit were investigated in detail.

Influence of Mo Content on the Microstructure and Mechanical Properties of Ti6AlxMo Alloy

Now a days, extensive research has been attracted by the α + β based Ti alloys in biomedical applications due to their low elastic modulus and high strength properties. In order to explore the performance of Ti6AlxMo based alloys, Ti6Al with different amount of Mo-based samples were fabricated by powder metallurgy technique. The mechanical properties of the samples such as elastic energy, total energy and elastic recovery were studied through nanoindentation tests. Designed alloys exhibit elastic recovery values in the range of 25.4% - 33.7% which is higher than commonly used biomaterial such as CP Ti therefore it has good impact resistance properties. Ti6Al15Mo alloy with dominant β phase microstructure shows a high elastic energy as well as elastic recovery values which makes it more advantageous than CP Ti for load bearing implant applications.

Influence of Mo content on the properties of multilayer nanostructured coatings based on the (Mo,Cr,Al)N system.

The study is focused on the comparison of two coatings with the identical thickness, structure, and the content of aluminum (Al) (10 at %), but different ratios of chromium (Cr) and molybdenum (Mo) content in the wear-resistant layer of (Mo,Cr,Al)N: Cr/Mo – 70/20 and 45/45 at%. The tribological properties of the coatings within a range of the temperatures of 500–900 °C and the wear resistance of carbide tools with the coatings under study during the turning of 1045 steel were considered. The study was also focused on the wear patterns on the coatings and diffusion and oxidation processes during the cutting. While there is a rather active formation of an aluminum oxide layer on the free surface of the coating, this layer is not able to have any noticeable effect on the cutting conditions, since it is not directly involved in the cutting process. The contact pads of the tool bear no such layer or extremely small amount of this layer (at an adherent boundary). At the same time, the presence of chromium and molybdenum oxides are detected in the contact areas, and therefore, these oxides can affect the cutting process. The coating with the Mo content of 45 at% ensured both the minimum of the adhesion component of the coefficient of friction (COF) during the tribological tests at high temperatures (800 °C and higher) and the maximum wear resistance during the turning of steel.

Evolution in microstructure features and properties of Mo-containing Fe-Cr-Ni-B-Si composite coatings by laser cladding

The nano-crystalline strengthening Fe-based amorphous composite coatings were successfully prepared by optical laser cladding technology. The influence of Mo content on the microstructure, mechanical, corrosion and tribological properties of Fe-Cr-Ni-B-Si composite coatings were studied. Results indicated that the phase composition and the relative content of amorphous changed obviously with the increases of Mo content. The microstructure could transform from coarse columnar into disorder amorphous matrix accompanying nano-precipitates of Fe-based composite coating with the appropriate Mo content, and while the excessive Mo element caused severe segregation of MoSi2 ceramic. The micro-hardness and plastic deformation resistance of the composite coatings dramatically improved due to the increased content of amorphous phases and in-situ nanocrystalline reinforcing, which had a favorable influence on the corrosion resistance and tribological property. The modified composite coating with the component of Fe41.4Cr16.2Mo10Ni5.4B1.5Si1.5 (atm.%) exhibited the most excellent mechanical properties (1102 HV), corrosion resistence (0.2216 μA/cm2) and wear resistance (2.96 × 10−6 mm3/N·m) among the three composite coatings. At this time, the modified coating had excellent resistance to pits corrosion and oxidation abrasive wear. However, the coating without Mo element occurred serious pits corrosion, abrasive and oxidation wear. The uneven distribution of MoSi2 brittle ceramic tended to the formation of microcracks and fatigue shedding for the composite coating with excessive Mo content.

Syngas to ethanol on MoCu(2 1 1) surface: Effect of promoter Mo on C O bond breaking and C C bond formation

The mechanism of syngas to ethanol on MoCu(2 1 1) surface has been researched by density functional theory (DFT) calculation, and the effects of Mo as a promoter on C O bond breaking and C C bond formation have been discussed. Calculations show that Cu-Mo atoms constitute the active sites on MoCu(2 1 1) surface after Mo atom being served as a promoter of Cu catalyst. Compared with Cu(2 1 1), MoCu(2 1 1) has two improvements. Firstly, CH 3 is the most advantageous monomer on the MoCu(2 1 1) surface, which provides abundant CH 3 intermediate for syngas to ethanol. Secondly, the C C bond is formed mainly by inserting CHO into the abundant CH 3 , and the generated CH 3 CHO through multiple steps of hydrogenation to generate C 2 H 5 OH. The key of the promoter Mo on the MoCu(2 1 1) surface also has been verified by the analysis of its electronic properties. Differential charge density shows that the massive electron transfer from Mo to Cu, projected density of states ( p DOS) shows that the electron transfer from Mo to Cu makes the d-band center of MoCu(2 1 1) nearer to the Fermi level, these indicate that the MoCu(2 1 1) catalytic capacity increased. The addition of Mo in the Cu-based catalyst not only can effectively solve the problem of C O bond breaking, but also promote C C bond formation. About the influence of Mo content on C O bond breaking and C C bond formation, compared with MoCu(2 1 1), the DFT results and the d-band center of Mo 2 Cu(2 1 1) show that the increase of Mo content could not promote the synergistic effect of Cu/Mo on the generation of ethanol more effectively.

Mechanical and tribological properties of (FeCoNi)88-x(AlTi)12Mox high-entropy alloys

In this study, we designed and prepared (FeCoNi)88-x(AlTi)12Mox high-entropy alloys (HEAs) with good comprehensive properties by vacuum arc melting technology. The influence of Mo content on the microstructure, mechanical properties, and tribological properties of the HEAs were systematically studied. The results showed that all HEAs in this study are simple fcc solid solution structure, all HEAs are composed of γ + γ' phase, and they are in a coherent relationship. The tensile test results show that all the HEAs exhibit excellent strength-ductility combination, and the final tensile fracture mechanism is a ductile fracture. Mo1.0 HEA has the best comprehensive mechanical properties, with the yield strength, tensile strength, and elongation of 980 MPa, 1260 MPa, and 34.5%, respectively. The reciprocating friction and wear test results show that the HEAs have excellent friction and wear properties. Compared with the four HEAs, the order of friction and wear properties from good to poor is Mo1.0 HEA, Mo1.5 HEA, Mo0.5 HEA, and Al6Ti6 HEA. The wear mechanisms of all HEAs are abrasive wear and oxidation wear, as well as the Al6Ti6 and Mo1.0 HEAs also have delamination wear.

Low-temperature oxidation of methanol to dimethoxymethane over Mo-Sn catalyst

A new Mo-Sn catalyst prepared by hydrothermal method was used for the synthesis of dimethoxymethane (DMM) from methanol oxidation. The catalyst with low Mo content can achieve low-temperature oxidation of methanol to DMM with high selectivity. The influence of Mo content on the structure and the catalytic performance of the catalyst was investigated. It was found that Mo1Sn10 catalyst showed the best catalytic performance under the conditions of 140°C and atmospheric pressure, the methanol conversion was 14.2%, and the selectivity of DMM reached 88.9% without the formation of COx during the reaction process. The catalysts were characterized by XRD, Raman, FT-IR, XPS, NH3-TPD and H2-TPR. The results showed that the catalysts with different Mo content had obvious differences in structure and performance. Lower Mo content was more conducive to the formation of Mo5+ and MoOx, and the resulting changes in acidity and redox properties were the important reasons for the excellent performance of the catalysts.

Electrochemical corrosion and tribological properties of CrMoCN coatings sliding against Al2O3 balls in artificial seawater

Due to low density and high specific strength, titanium alloys have been widely used for marine applications. However, the severe wear and corrosion of titanium alloy components is still a problem. To alleviate this problem, protective coatings are applied. In here, the influence of Mo content on the protective performance of CrMoCN coating for Ti-6Al-4V substrate has been investigated. The short- and long-term corrosion resistances of coating in artificial seawater are studied using an electrochemical workstation with three-electrode configuration. The tribological behaviors of CrMoCN coating sliding against Al2O3 ball are evaluated using a ball-on-disk tribo-meter. The results reveal that the CrMoCN coated samples have higher wear- and corrosion-resistances than the bare substrate. The CrMoCN coating with 8.1 at.% Mo displays the highest values of OCP (0.22 V), Rct ((8.639 ± 0.270) × 107 Ω·cm2) and Rp ((3.04 ± 0.24) × 106 Ω·cm2). However, their protective performances are degraded in the long-term, and then the Rp of CrMoCN-2.5 coating continuously decreases from (5.99 ± 0.47) × 105 Ω·cm2 at 7 days to (0.13 ± 0.01) × 105 Ω·cm2 at 35 days. With an increase in the Mo content, the friction coefficient of CrMoCN coating/Al2O3 tribopair decreases from 0.36 to 0.31 while the coating wear rate increases from 4.65 × 10−7 mm3/Nm to 1.01 × 10−6 mm3/Nm.

Influence of Mo content on properties of Ti–Al–Mo–N films

ABSTRACT Ti–Al–Mo–N composite films with different molybdenum content were deposited by reactive magnetron sputtering. The results showed that the films consisted of fcc-(Ti, Al, Mo) N substitutional solid solution within 8.2 at.-% Mo. The films consisted of two phases which were fcc-(Ti, Al, Mo) N substitutional solid solution and fcc-Mo2N at 27.7–49.4 at.-% Mo. The hardness increased slowly at 0–27.7 at.-% Mo and then increased rapidly at above 27.7 at.-% Mo. A ball-on-disc dry sliding test was conducted on films deposited on stainless-steel substrates. The friction coefficient quickly decreased within 8.2 at.-% Mo and then gently declined at 8.2–49.4 at.-% Mo. The value of wear rate remained quite constant for compositions in the range 0–34.3 at.-% Mo and then dropped quickly at 34.3–49.4 at.-% Mo. The addition of Mo content effectively improved the hardness and tribological properties of the films.

Improvement of High Temperature Wear Behavior of In-Situ Cr3C2-20 wt. % Ni Cermet by Adding Mo

Cr3C2-Ni cermet is a kind of promising material especially for wear applications due to its excellent wear resistance. However, researches were mainly concentrated on the experiment condition of room temperature, besides high-temperature wear mechanism of the cermet would be utilized much potential applications and also lack of consideration. In present paper, the influence of Mo content on the high-temperature wear behavior of in-situ Cr3C2-20 wt. % Ni cermet was investigated systematically. The friction-wear experiment was carried out range from room temperature to 800 °C, while Al2O3 ceramic was set as the counterpart. According to experimental results, it is indicated that the coefficient of friction (COF) of friction pairs risen at the beginning of friction stage and then declined to constant, while the wear rate of Cr3C2-20 wt. % Ni cermet risen continuously along with temperature increased, which attributes to the converted wear mechanism generally from typical abrasive wear to severe oxidation and adhesive wear. Generally, the result of wear resistance was enhanced for 13.4% (at 400 °C) and 31.5% (at 800 °C) by adding 1 wt. % Mo. The in-situ newly formed (Cr, Mo)7C3 ceramic particle and the lubrication phase of MoO3 can effectively improve the wear resistance of Cr3C2-20 wt. % Ni cermet.

Tribological Performance of Molybdenum Stellite Alloys under Dry-Sliding Wear

Elements tungsten and molybdenum are the key constituents of Stellite alloys as solutes to strengthen the solid solution matrix. Meanwhile, they also promote formation of W-rich and Mo-rich carbides when present in large quantities in high-carbon Stellite alloys. Extensive studies on tungsten Stellite alloys, in particular, Stellite® 6, have been reported in the literature; however, molybdenum Stellite alloys, especially, the influence of Mo content on the performance of the alloys, have been rarely investigated. In this research, the tribological performance of three molybdenum Stellite alloys with varying C and Mo contents is studied using pin-on-disk dry-sliding wear test at ambient temperature, focusing on the effect of test duration and interrupted test on the wear behavior of the alloys. The worn surfaces are examined using SEM/EDS, and the analyses of the surface morphologies help explore the wear mechanisms of these alloys in dry-sliding condition. A wear model is developed for molybdenum Stellite alloys, based on the Archard equation in check with the wear test data, using hardness as a controlling factor.

Mechanical and tribological properties of Hf1-xMoxNy thin films as a function of Mo contents

Ternary transition metal nitrides have procured wide attention towards practical application due to their high hardness, wear resistance and thermal stability. In this study, Hf1-xMoxNy thin films are deposited by reactive direct current magnetron sputtering (R-DCMS) system in an effort to improve further the properties of their analogous binary compounds. In addition, the influence of Mo content on the structure, mechanical and tribological properties of the films are also investigated. The composition and microstructure of the as-deposited Hf1-xMoxNy films are characterized by X-ray diffraction, Raman and scanning electron microscopic techniques. Spectroscopic results show that, as-sputtered Hf1-xMoxNy films mainly consist of single solid solution phase with rock-salt structure. Ultra-micro hardness and ball-on-disc wear tests are conducted to evaluate the mechanical and tribological properties of Hf1-xMoxNy films. The toughness Hf1-xMoxNy films are enhanced, and the film with x = 0.589 shows better mechanical properties, meanwhile, the lowest wear rate of 0.57 × 10−6 mm3/Nm, which is two order magnitudes lower than corresponding binary compounds viz., δ-HfN and γ-Mo2N, and lowest friction coefficient of 0.35 are also obtained. This could be attributed to the effect of solution reinforcement and valence electron concentration. The unique wear resistance of Hf1-xMoxNy is ascribed to the outstanding oxidation resistances and higher H/E and H3/E2 values, which indicate the mechanical properties, wear resistance and anti-friction of δ-HfN and γ-Mo2N can be improved by alloying with each other.

Influence of Local Heterojunction on the Thermoelectric Properties of Mo-SnSe Multilayer Films Deposited by Magnetron Sputtering

Mo-SnSe multilayer films were deposited by multi-step magnetron sputtering. The Mo-SnSe multilayer films are then annealed, and the new phases including SnSe2 and MoSe2 are observed by x-ray diffraction and Raman spectroscopy. Scanning electron microscopy reveals that the SnSe exhibits the columnar grain structure with sizes from 50–100 nm. The high-resolution transmission electron microscopy shows the SnSe2 is dispersed at the boundary of the columnar grain and the local MoSe2/SnSe heterojunction is formed in the interior of the columnar grain. The influence of Mo content on the thermoelectric properties of SnSe thin films was investigated. A maximum power factor of 0.44 μW cm−1 K−2 was obtained for a 2.6 at.% Mo-doped SnSe thin film at 576 K, which is higher than that of a SnSe thin film deposited under the same conditions.

Influence of Mo content on microstructure and mechanical properties of β-containing TiAl alloy

The influence of Mo content on the microstructure and mechanical properties of the Ti-45Al-5Nb-xMo-0.3Y (x=0.6, 0.8, 1.0, 1.2) alloys was studied using small ingots produced by non-consumable electrode argon arc melting. The results show that small quantities of β phase are distributed along γ/α2 lamellar colony boundaries as discontinuous network in the TiAl alloys owing to the segregation of Mo element. The γ phase forms in the interdentritic microsegregation area when the Mo addition exceeds 0.8%. The β and γ phases can be eliminated effectively by subsequent homogenization heat treatment at the temperature above Tα. The evolution of the strength, microhardness and ductility at different Mo contents under as-cast and as-homogenization treated conditions was analyzed, indicating that excessive Mo addition is prone to cause the microsegregation, thus decreasing the strength and microhardness obviously, which can be improved effectively by subsequent homogenization heat treatment.

Influence of Mo content on the γ-phase stability and properties of U-Mo alloy

U-Mo alloys have been considered as the potential new advanced nuclear fuel, due to its favourable irradiation stability associated with the presence of the metastable γ-phase in the microstructure. Thus its γ-phase stability and performance are of great importance. In this work, three kinds of U-Mo alloys with the content of 6, 8 and 10wt.% Mo were prepared by non consumable arc melting technology, the homogenization annealing and heat treatment of isothermal decomposition. Through metallographic microscope, scanning electron microscope (SEM), X-ray diffraction, Brinell hardness tester, the microstructure and mechanical properties of U-Mo alloys were investigated. The results indicate that the stability of γ-phase in the U-Mo alloy is directly related to the content of Mo. With the increase of Mo, the stability of γ-phase is enhanced and the decomposition of γ-phase is delayed during the isothermal decomposition at 565°C. In addition, the mechanical properties of this alloy are closely associated with its phase rather than directly related to the content of Mo.