Effect Of Mo Addition Research Articles

Effect of Mo Addition on Nanostructured Ni50Al50 Intermetallic Compound Synthesized by Mechanical Alloying

The mechanical alloying process was used to synthesize the Ni50Al50−xMox nanocrystalline intermetallic compound using pure Ni and Al elemental powder. This process was carried out in the presence of various Mo contents as a micro-alloying element for various milling times. Structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Results showed that mechanical alloying in various combinations was completed after 48 h of milling time. Minimum crystallite size of the as-milled powders (∼10 nm) was achieved after introducing Mo and milling for 128 h. Also, lattice strain decreased with increasing milling time up to 48 h and again increased after 48 h of milling time. On the other hand, the presence of Mo significantly affected variation intensity of the lattice parameter and morphology of the powder particles.

Effect of Mo addition on the microstructure and properties of WC–Ni–Fe hard alloys

In the research, an investigation has been carried out on the influence of Mo content and sintering temperature on the microstructure and mechanical properties of WC–Ni–Fe hard alloys. The WC–Ni–Fe hard alloys with various Mo contents were processed by powder metallurgy. The samples were prepared by vacuum sintering at various temperatures. The research results indicate that the addition of Mo was beneficial for increasing transverse rupture strength and inhibiting grain growth without an appreciable influence on hardness at room temperature. The highest mechanical properties were obtained by the specimen including 0.25 wt.% of Mo sintered at 1300 °C.

Effects of Mo addition on precipitation in Zr–1.2Nb alloys

Mo-modified Zr–1.2Nb alloys were prepared and the effects of Mo addition on precipitation in Zr–Nb alloys were elucidated. It was found that an increase of Mo content decreased α→(α+β) phase transformation temperature in Zr–Nb alloys. A new kind of precipitate, β-(Nb, Mo, Zr), was identified in the Mo-containing alloys. These particles are formed because Mo atoms replace Nb atoms in the β-(Nb, Zr) phase. Further, it was found that Mo retarded the growth of the precipitates but increased their number density.

Corrosion Resistance of Powder Metallurgy Processed TiC/316L Composites with Mo Additions

To find out the effects of Mo addition on corrosion resistance of TiC/316L stainless steel composites, TiC/316L composites with addition of different contents of Mo were prepared by powder metallurgy. The corrosion resistance of these composites was evaluated by the immersion tests and polarization curves experiments. Results indicated that Mo addition decreased the corrosion rates of TiC/316L composites in H2SO4 solution in the case of Mo content below 2% whereas it displayed an opposite effect when Mo content was above that value. It was found that with an increase in the Mo content, the pitting corrosion resistance increased monotonically for TiC/316L composites in NaCl solution.

Effect of Mo Addition on the Grain Growth of IN718 Alloy

The effect of Mo addition on the grain growth of Inconel 718 alloy has been investigated. It was revealed that δ phase was precipitated at the grain boundaries when the Mo addition is in the range of 2.80% - 4.00%, while the Mo-bearing phase was precipitated at the grain boundaries when the Mo addition is in the range of 5.50% - 7.50%. By pinning the grain boundary, the grain boundary precipitate can effectively prevent the grain growths. So the grains grow rapidly with increase the solution temperature when the grain boundary precipitate is absent. The activation energy value for grain growth of IN718 alloys with different Mo addition is 210 - 255 kJ/mol and the grain growth mechanism is controlled by the self-diffusion. The grain growth exponent reduces with increasing Mo addition.

Magnetic Force Microscopy Study of Zr2Co11‐Based Nanocrystalline Materials: Effect of Mo Addition

The addition of Molybdenum was used to modify the nanostructure and enhance coercivity of rare‐earth‐free Zr2Co11‐based nanocrystalline permanent magnets. The effect of Mo addition on magnetic domain structures of melt spun nanocrystalline Zr16Co84-xMox (x = 0, 0.5, 1, 1.5, and 2.0) ribbons has been investigated. It was found that magnetic properties and local domain structures are strongly influenced by Mo doping. The coercivity of the samples increases with the increase in Mo content (x ≤ 1.5). The maximum energy product (BH) max increases with increasing x from 0.5 MGOe for x = 0 to a maximum value of 4.2 MGOe for x = 1.5. The smallest domain size with a relatively short magnetic correlation length of 128 nm and largest root‐mean‐square phase shift Φrms value of 0.66° are observed for the x = 1.5. The optimal Mo addition promotes magnetic domain structure refinement and thus leads to a significant increase in coercivity and energy product in this sample.

Secondary hardened bainite

The effect of Mo additions on the development of bainitic ferrite in hot rolled low carbon (0·05 wt-%C) Nb containing steel strips has been studied. The steel strips were fabricated by a combined process of controlled rolling and accelerated cooling. Microstructural characterisation and mechanical testing for the corresponding strips were investigated. The results indicated that a small amount of Mo addition (0·1–0·3 wt-%) causes the production of a high volume fraction of bainite, which undergoes significant secondary hardening after tempering treatment at 600°C for 1 h. It is noticeable that the secondary hardening effect provides an additional way to significantly increase the strength of low carbon Nb–Mo containing bainitic steels.

Effect of Mo Addition on Strength of Fire-Resistant Steel at Elevated Temperature

A series of Fe-Mo-C steels with Mo addition from 0.1 to 0.8 wt.% has been prepared for studying the effect of Mo on the elevated-temperature strength of fire-resistant steel. Two heat treatments were performed for obtaining either ferrite microstructure or ferrite-bainite microstructure to study the contributions from two strengthening mechanisms with Mo addition, namely solid-solution strengthening and bainite strengthening. The results show that solid-solution strengthening is the predominant elevated-temperature strengthening mechanism of Mo in fire-resistant steel. This strengthening effect has a huge contribution in improving elevated-temperature strength when Mo content is below 0.5 wt.%, and the yield strength at 600 °C goes up by a significant 13.7 MPa per 0.1 wt.% Mo addition. However, it becomes relatively weak when Mo content is more than or equal to 0.5 wt.%. Moreover, results indicate that the elevated-temperature strength remarkably increases when the volume fraction of bainite is above 15%. Furthermore, it is found that the ferrite grain size has minor effect on elevated-temperature strength of fire-resistant steel. Results also provide fundamentals of designing low-cost fire-resistant steels with excellent strength.

Effect of Mo Addition on Microstructural Characteristics in a Re-containing Single Crystal Superalloy

The effect of Mo addition on microstructural characteristics of a nickel-base single crystal superalloy containing 4 wt% Re was investigated. The γ/γ′ partitioning ratios determined by energy dispersive spectrometer attached to a transmission electron microscope showed that the addition of Mo enhanced the partitioning of Re, W and Cr in the γ matrix while decreased the concentration of Ta in the matrix. Synchrotron radiation diffraction was adopted to measure the γ/γ′ lattice misfit at room temperature. The results indicated that Mo addition changed the γ/γ′ lattice misfit towards larger negative as well as increased the tetragonal distortion of the γ lattice. Additionally, Mo addition led to microstructural instability and altered the precipitation behavior of topologically close-packed phases during 1100 °C exposure. Instead of precipitating directly from the matrix, the μ phase was observed to be converted from the σ phase which precipitated preferentially as a metastable intermediate in the alloy with high Mo content.

Effects of Mo addition on the metallic glass formation of (ZrNi)100−xMox alloys

The formation of (ZrNi)100−xMox metallic glasses was predicated by thermodynamic calculation. It is found that the (ZrNi)100−xMox metallic glasses could be formed in the composition range of 0–64at.% Mo, and the minor addition of Mo could facilitate the formation of the (ZrNi)100−xMox metallic glasses. To verify thermodynamic prediction, ion beam mixing experiments were carried out. The results showed that no unique amorphous phase would be formed when the addition of Mo was higher than 60at.%, indicating that the thermodynamic prediction is reasonable. Besides, the possible formation mechanisms of these metastable phases were discussed in terms of phase competition and the atomic collision theory.

Effects of Mo addition on thermal stability and magnetic properties of a ferromagnetic Fe75P10C10B5 metallic glass

The effects of Mo content on the thermal stability, glass-forming ability (GFA), magnetic and mechanical properties of Fe75−xMoxP10C10B5 (x = 0–10) metallic glasses were investigated. The stabilization of supercooled liquid and GFA were significantly enhanced by addition of Mo. Although the saturation magnetization (Is) of the alloys reduced with increasing Mo content, the coercive force (Hc) decreased. The metallic glasses with x = 2.5–7.5 exhibit low glass transition temperature of 733–749 K, large supercooled liquid region of 61–96 K, and high GFA with critical fully glassy sample diameters of 1.5–3.0 mm. They also possess rather high Is of 0.81–1.11 T, low Hc of 2.07–4.87 A/m, high Vicker's hardness of 860–992, high compressive yield strength of over 3000 MPa with a distinct plastic strain.

Effect of Mo Addition on the Microstructure and Properties of TiNiNb Alloy

The influence of Mo addition on the microstructure and properties of TiNiNb alloy with 4.5 at.% Nb has been investigated systemically. The experimental results indicated that the uniform distribution of Mo depresses the appearance of coarse β-Nb particles at the grain boundaries and short stripped texture consisting of abundant fine disperse Nb-rich particles appears around the grain boundaries. The yield strength of the alloy was enhanced from 450 to 600 MPa due to the solution strengthening of Nb and Mo and the elongation reached 18% when the Mo content is 0.5 at.%. At the same time, the shape memory effect of the alloy also is improved significantly by the Mo addition. The maximum recoverable strain of the alloy with 0.5 at.% Mo is near 8% and has reached the high level of Ni–Ti binary alloys. This novel high-strength alloy is promising to be used for high pressure tube and the macro-scale coupling with higher-quality requirements.

Phase composition and nanostructure of Zr2Co11-based alloys

The effect of Mo addition on phase composition and nanostructure of nanocrystalline Zr16Co84−xMox (x = 0–2.0) melt spun at 55 m/s has been investigated. All the ribbons consist mainly of a hard magnetic Zr2Co11 phase with rhombohedral crystal structure but also contain minor amounts of soft-magnetic phases. The increase in cell volume on alloying suggests that Mo mainly enters the rhombohedral Zr2Co11 structure and occupies the Co site. Mo addition promotes the formation of the hard magnetic phase and increases its volume fraction. The mean grain size of the hard magnetic phase remains almost unchanged with the increase of Mo content. But the average grain size of the soft magnetic phase decreases from about 200 nm to 50 nm. This promotes the exchange coupling of the hard and soft magnetic phases and thus leads to a significant increase in coercivity and isotropic energy product, from 0.6 kOe and 0.5 MGOe for x = 0 to 2.9 kOe and 4.2 MGOe for x = 1.5.

Effect of Mo addition on microstructure and mechanical properties of (Ti,W)C solid solution based cermets

(Ti,W)C solid solution was synthesized by milling a mixture of C and oxides and then reducing it at 1350°C for 2h. The microstructure and mechanical properties of (Ti,W)C solid solution based cermets with various Mo additions were systemically studied. The dark core–gray rim carbide grains and/or gray carbide grains embedded in black Ni based binder phase were observed. The grain size of the cermets decreased with increasing Mo addition, while excessive Mo addition would result in agglomeration and inhomogeneity of the grains. The dark core was transformed from (Ti,W)C into (Ti,W,Mo)C and Mo concentration in the dark core increased with increasing Mo content. The fracture toughness of the cermets decreased with the increase of Mo content, while the hardness and TRS reached a peak value at 10wt.% and 15wt.% Mo additions respectively, and declined with the further increase of Mo content.

Effect of Mo Addition on Structure and Magnetocaloric Effect in γ-FeNi Nanocrystals

Nanocrystalline powders of (Fe70Ni30)100−xMox (x = 1 to 4) were produced by high-energy (SPEX) mechanical alloying. Increasing the Mo content was found to stabilize the face-centered cubic phase in mechanically alloyed nanopowders. To obtain a single γ-phase, a powdered sample was solution annealed in the γ-phase field and water quenched. The Curie temperature, TC, of the alloys was lowered with Mo addition, without decreasing the refrigeration capacity (RC), due to the additional temperature broadening of the magnetic entropy change. Based on previous study on the role of disorder, the additional temperature broadening was attributed to increased positional disorder and changes in the distribution of ferromagnetic exchange bonds introduced by Mo addition into the γ-FeNi system. (Fe70Ni30)97Mo3 and (Fe70Ni30)96Mo4 alloys have RCFWHM values of ∼440 J/kg and ∼432 J/kg at 5 T, comparable to other prominent magnetic refrigerants operating near room temperature. The economic viability of these alloys, along with their competitive magnetocaloric properties and potential for scalable production, make them good candidate magnetic refrigerants without critical rare-earth materials.

Influence of molybdenum on the microstructure and properties of a FeCrBSi alloy coating deposited by plasma transferred arc hardfacing

FeCrBSi alloy powders without and with 2–6wt.% Mo (Mo-free and Mo-added, respectively) were deposited on a plain steel using plasma transferred arc (PTA) hardfacing. The effects of Mo addition on the microstructure and properties of the FeCrBSi alloy coating were investigated by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) attachment, transmission electron microscopy (TEM), Vickers hardness tester, hydraulic universal testing machine, dry sand abrasion test (DSAT) and water quenching method. The results show that the Mo-free coating consists of γ (Fe, Ni), M7(C, B)3, and (Fe, Cr)2B phases. Adding Mo leads to the formation of M23(C, B)6, Mo2(B, C) and Fe3Mo3(C, B) phases, except for those phases existed in the Mo-free coating. The twinning with 101¯ twinning plane is observed in the orthorhombic M7(C, B)3 (M=Fe, Cr, Mo) phase. A hypoeutectic microstructure can be seen in the Mo-free and 2wt.% Mo-added coatings. Increasing Mo addition to 4wt.% and 6wt.%, a hypereutectic microstructure can be obtained. The microstructure of the Mo-free coating can be refined after adding 2–6wt.% Mo. The finest microstructure can be obtained in the 4wt.% Mo-added coating. Adding Mo in the FeCrBSi alloy coating can increase its abrasive wear resistance that has no direct relation with H/E or H3/E2 because brittle fracture occurred occasionally in the abrasive wear test. The thermal shock resistance of the Mo-free coating can be improved after adding 2–6wt.% Mo. The best abrasive wear resistance and thermal shock resistance can be received in the 4wt.% Mo-added coating.

Effect of Mo on the High Temperature Oxidation Behavior of Co-Al-W Based Alloys

2 at.% and 4 at.% Mo were added to Co-9Al-9W-2Ta-0.02B alloy to replace W (hereafter referred to as the alloys of 2Mo and 4Mo, respectively; Mo-free alloy was referred to as the 0Mo alloy). The effects of Mo additions on the high temperature oxidation behavior of the alloys at 800 °C in air have been studied. The results indicated that, after oxidation in air at 800 °C for 100 h, the oxide film of the 0Mo alloy remained intact, but the cracking and spallation of the oxide film took place in the alloys of 2Mo and 4Mo. Oxidation kinetic curves revealed weight gain per unit area of the 0Mo alloy was 36.86 mg·cm-2, which was lower than that of the alloys of 2Mo (65.16 mg·cm-2) and 4Mo (48.54mg·cm-2). These suggested that the 0Mo alloy displayed superior oxidation resistance compared to the alloys of 2Mo and 4Mo caused by the formation of volatile MoO3 oxide, and sharp compressive stress formed in the outer layer during the oxidation. The oxide layer was composed of three layers of the Co3O4 + CoO outer layer, middle complex oxide layer containing Co, Al and W (Mo), inner Al2O3 layer and γ/Co3W zone adhere to the γ/γ' substrate.

Effects of Mo additions on the corrosion behavior of WC–TiC–Ni hardmetals in acidic solutions

The corrosion behavior of WC–TiC–Ni cemented carbides with the additions of molybdenum was investigated in 1M H2SO4 and 1M HCl solutions utilizing potentiodynamic polarization, long-term immersion tests and surface analytical techniques. The results show that the Mo additions can enhance the corrosion resistance of WC–TiC–Ni hardmetals owing to the formation of new (Ti, W, Mo)C phase based on TiC. Pseudopassivity was observed in the polarization curves of WC–Ni and WC–TiC–Ni hardmetals in HCl. However, the additions of molybdenum can make WC–TiC–Ni hardmetals passivated visibly in curves at 600mV–1000mV and enhance the pitting corrosion resistance due to the formation of MoO3 film. In addition, all nickel based alloys show the typical passivation behavior in H2SO4 caused by the formation of NiSO4, NiWO4 and continuous metal oxide films.

Crystallization behaviors of FeSiBPMo bulk metallic glasses

The effect of Mo addition on the crystallization behaviors of FeSiBPMo glassy alloys was investigated and the phase transformation behaviors were summarized. Three primary phases identified as Fe23B6, (Fe, Mo)23B6 and α-Mn type phases were found by using X-ray diffraction transmission electron microscopy. The relationship between the glass-forming ability and the precipitated primary phase was discussed and the results demonstrate that the tendency of both the atom structured complexity and the difficulty of geometrical rearrangement for the precipitation of the primary phase coincides with the changing trend of the glass-forming ability for the FeSiBPMo bulk metallic glasses.

The Effects of Mo Addition on the Structure of Scales Formed in High Si Steel at 1150°C

High Si steels (base steel and with addition of 0.1, 0.3, 0.5mass% Mo) were oxidized in a N2-3%O2-20%H2O atmosphere at 1150oC for 0.3-10.8ks. The oxidation kinetics showed that base steel has the highest weight gain. In contrast, 0.5Mo has the lowest weight gain. From SEM results, the scale thickness decreased as Mo content increased. Distribution of alloying elements showed that Mo is enriched in internal oxidation zone (IOZ) and played a role in slowing the outward diffusion of Fe, thus, producing a thinner Fe oxide scale and lower weight gain.