Influence Of Mo Addition Research Articles

The influence of Mo addition on static recrystallization and grain growth behaviour in CoNiFeMn system subjected to prior deformation

The influence of Mo addition on static recrystallization and grain growth behaviour in CoNiFeMn system subjected to prior deformation

High-temperature oxidation resistance of ternary and quaternary Cr-(Mo)-Si-B2-z coatings — Influence of Mo addition

The Si-based alloying of transition metal diborides is a promising strategy to improve their limited oxidation resistance in high-temperature environments. In this study, we investigate the oxidation resistance of ternary and quaternary Cr-(Mo)-Si-B2-z coatings sputter-deposited from alloyed CrB2/TMSi2 targets (TM = Cr or Mo). The as-deposited Cr-(Mo)-Si-B2-z coatings are stabilized in the single-phased hexagonal AlB2-structure, except the high-Si containing Cr0.26Mo0.11Si0.24B0.39 presenting amorphous character. The Mo-containing Cr-Mo-Si-B2-z films exhibit relatively high hardness compared to their ternary Cr-Si-B2-z counterparts, obtaining up to 26 GPa due to the formation of (Cr,Mo)B2 solid solutions. The Si-alloying in ternary and quaternary coatings provides oxidation resistance up to 1200 °C, owing to the formation of highly protective double-layered scales consisting of SiO2 with a Cr2O3 layer on top, inhibiting oxygen inward diffusion. The quaternary Cr0.31Mo0.07Si0.15B0.47 coating is distinguished by superior oxidation resistance with lower porosity and void formation compared to the ternary Cr0.37Si0.16B0.47. Mo proved to be the key element for the higher stability and enhanced oxidation resistance due to the evolution of the MoSi2 phase at ~600 °C. This phase formation controls the Si diffusion and mobility within the microstructure, thus reducing the porosity and governing the Si supply to form SiO2 scale. The quaternary Cr0.31Mo0.07Si0.15B0.47 coating maintained an oxidation resistance up to 30 h at 1200 °C by forming a 2.5 μm dense amorphous Si-based oxide scale with a thin Cr2O3 on top.

Influence of Mo addition on microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in-situ carbothermal reduction of TiO2

Series of Ti(C,N)-based cermets, with various amounts of Mo, are fabricated by in-situ carbothermal reduction of TiO2. SEM, TEM, XRD and EDS analysis are utilized to analyze the phase composition and microstructure of as-prepared cermets. The results reveal that the volume percentage of white-core grains in as-prepared cermets significantly larger than that in cermets fabricated by traditional methods. In addition, there are two types of white core/gray rim grains. One is the grains with bright white cores and the other is grains with offwhite cores. Mo plays an important role in the formation of rims and white cores. With increasing Mo addition, the rims of grains with white core tend to be complete and the rims of grains with black core become thinner. The volume percentage of grains with white core significantly increases due to the diffusion of Mo during solid-state sintering. Moreover, the dislocation formed in rim phase adjusts the misfit of rim/binder interface. As a result, the semi-coherent interface is observed in rim/binder interface of grains with black core. Overall, the cermet, with Mo content of 14 wt %, renders optimal mechanical properties, with fracture toughness (KIC) of 11.2 MPa m1/2, transverse rupture strength (TRS) of 2403 MPa and a hardness of 90.8 HRA.

The Influence of Mo Additions on the Microstructure and Mechanical Properties of AlCrFe2Ni2 Medium Entropy Alloys

The alloy system Al-Cr-Fe-Ni provides means for developing novel duplex materials composed of face-centered cubic (FCC) and body-centered cubic (BCC) phases with nearly equal volume fraction. We performed an alloy development study starting from the medium entropy alloy AlCrFe2Ni2 and adding small amounts of molybdenum in the following series (at.%): Al17Cr17Fe33Ni33, Al17Cr17Fe33Ni33Mo1, Al16Cr16Fe33Ni33Mo2, Al16Cr16Fe33Ni33Mo3. We focused the research on samples with an ultrafine vermicular duplex microstructure, a unique structure requiring sufficiently high cooling rates to suppress the conventional Widmanstatten colony formation. The samples were produced by arc melting in buttons of 300 g each. We characterized the microstructure of the samples using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD). The EBSD results revealed significant strain in the FCC phase, which is characteristic for the ultrafine vermicular duplex microstructure and its specific formation pathway. We investigated mechanical properties of the samples by micro-indentation and 3-point bending in a miniature testing device. The test specimens were in the as-cast condition, as well as in distinct annealed conditions. Annealing treatments were carried out at 950 °C and 1100 °C under argon. The annealing lasted from 10 minutes to 6 hours, followed by water quenching. Prolonged annealing at 950 °C of Mo-containing samples resulted in the formation of sigma-phase. Annealing at 1100 °C safely avoided sigma-phase formation, while leading to a good balance between the flexural strength and ductility of these samples. Mechanical testing also included the well-established superduplex steel 1.4517 (DIN EN 10283 / ASTM A890) as reference material.

Stabilizing fluorite structure in ceria-based high-entropy oxides: Influence of Mo addition on crystal structure and transport properties

(Ce,Gd,Nd,Sm,Pr)O2-δ and (Ce,Gd,La,Nd,Pr)O2-δ rare-earth high-entropy oxides (HEOx) with the oxygen vacancy-ordered Ia-3 structure are doped with a small amount of molybdenum, to prepare two series of materials, (Ce,Gd,Nd,Sm,Pr,Mox)O2-δ and (Ce,Gd,Nd,Sm,Pr,Mox)O2-δ with x = (0, 0.1, 0.2, 0.3 and 0.5). The first-ever stabilization of the fluorite-type Fm-3m structure (i.e. with disordered vacancies) in the ceria-based HEOx is achieved. Structural, microstructural and transport properties of the compounds are systematically studied. The substitution level of x ≥ 0.3 allows to fully stabilize Fm-3m symmetry, with samples exhibiting good homogeneity. Influence of Mo on the oxygen vacancy concentration and charge state of the elements is studied with the use of Raman spectroscopy and XPS methods, showing decrease of the vacancy content and dominating presence of Mo6+, Ce4+ and mixed Pr3+/4+ states. Measured for the first time in this group of materials, the electrical conductivity of the Mo-doped oxides indicates the mixed ionic-electronic behavior.

Influence of Mo addition on the structural and electrochemical performance of Ni-rich cathode material for lithium-ion batteries

Molybdenum modified LiNi0.84Co0.11Mn0.05O2 cathode with different doping concentrations (0–5 wt.%) is successfully prepared and its electrochemical performances are investigated. It is demonstrated that molybdenum in LiNi0.84Co0.11Mn0.05O2 has a positive effect on structural stability and extraordinary electrochemical performances, including improved long-term cycling and high-rate capability. Among all samples, the 1 wt. % molybdenum LiNi0.84Co0.11Mn0.05O2 delivers superior initial discharge capacity of 205 mAh g−1 (0.1 C), cycling stability of 89.5% (0.5 C) and rate capability of 165 mAh g−1 (2 C) compared to those of others. Therefore, we can conclude that the 1 wt. % molybdenum is an effective strategy for Ni-rich LiNi0.84Co0.11Mn0.05O2 cathode used in lithium ion batteries.

Micropillar Compression Study on the Deformation Behavior of Electrodeposited Ni–Mo Films

The influence of Mo addition on the compression behavior of Ni films was studied by micropillar deformation tests. Thus, films with low (0.4 at.%) and high (5.3 at.%) Mo contents were processed by electrodeposition and tested by micropillar compression up to the plastic strain of about 0.26. The microstructures of the films before and after compression were studied by transmission electron microscopy. It was found that the as-deposited sample with high Mo concentration has a much lower grain size (~26 nm) than that for the layer with low Mo content (~240 nm). In addition, the density of lattice defects such as dislocations and twin faults was considerably higher for the specimen containing a larger amount of Mo. These differences resulted in a four-times higher yield strength for the latter sample. The Ni film with low Mo concentration showed a normal strain hardening while the sample having high Mo content exhibited a continuous softening after a short hardening period. The strain softening was attributed to detwinning during deformation.

Influence of Mo Additions on the Mechanical Properties of Cast Duplex Stainless Steels before and after Thermal Aging

The influence of Mo additions on the mechanical properties of cast duplex stainless steel (CDSS) before and after thermal aging was investigated using a series of model alloys with different Mo contents ranging from 0 to 1.75 wt%. By increasing Mo content, the content, morphology, and distribution of ferrite in CDSS change significantly. After thermal aging at 400 °C for 3000 h, the impact properties of all CDSS specimens obviously decline, and their hardness values in ferrite significantly increase. The impact energies of the aged CDSS decline, and the proportion of cleavage features significantly increases with Mo content increasing. The spinodal decomposition kinetics in ferrite is not significantly affected by the Mo contents. High content and interconnected ferrite will lead to the severe embrittlement in CDSS after thermal aging.

The influence of Mo addition on the microstructure and its thermal stability for electrodeposited Ni films

An investigation was conducted to study the effect of molybdenum (Mo) alloying on the grain size and lattice defect structure in nanocrystalline nickel (Ni) films processed by electrodeposition. Moreover, the influence of saccharin addition to the electrolyte bath on the microstructure of Ni-Mo layers with low and high Mo contents was studied. It was found that the higher Mo content resulted in a larger dislocation density and twin fault probability as well as a smaller grain size. The addition of saccharin to the bath resulted in a further increase in the density of both dislocations and twin faults. It was also revealed that Mo alloying improved the thermal stability of the nanostructure in Ni films while saccharin addition yielded a reduction of stability. The reasons for these opposite behaviors were discussed in detail. In addition, the defect structure and its stability in Ni-Mo layers were compared with that for fine-grained bulk samples with the same composition but processed by severe plastic deformation.

Influence of Mo addition on the microstructure and mechanical properties of TiC-NiTi cermets

TiC0.7 cermets with 20 vol% NiTi binder, containing up to 1.8 vol% Mo, were prepared by pressureless liquid-phase sintering at 1380 °C for 60 min. The pore size, apparent porosity, TiC grain size and binder mean free path length decreased with increasing Mo content up to 1.2 vol%. Further increasing the Mo content to 1.8 vol% resulted in a MoTi phase formation. Upon Mo addition, the carbides obtained a core-rim structure with dissolved Mo in the rim. The Mo distribution in the carbide and binder phases of the TiC0.7-NiTi and TiC-Ni cermets was correlated with the calculated Ti-Mo-C and Ti-Mo-Ni phase diagrams. The hardness significantly increased with increasing Mo addition up to 1.2 vol% and saturated upon further increasing the Mo content, while the bending strength remained almost the same. The E-modulus increased with increasing Mo addition up to 1.8 vol%, whereas the fracture toughness decreased.

Structural and low temperature electrical transport properties of Mo-doped vanadium oxide NTC ceramic thin films

Mo doped V2O3 [V1−xMoxO2−x/2 (x = 0, 0.5–1)] ceramic thin films were prepared on metal substrates by sol-gel dip coating and the influence of Mo addition on their microstructure, negative temperature coefficient (NTC) electrical transport properties and metal to insulator phase transition behavior were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and resistance-temperature measurements. Resistivity-temperature curves (over a temperature range of 273.15–253.15 K) indicated that all of the prepared thin films have NTC effects, after annealing with 20 sccm N2 at 673.15 K. It was demonstrated through microstructure analysis at Mo high concentration, (i.e., x > 0.07) it segregates at the V2O3 grain boundaries, causing scattering and distortion of the crystal lattice. Compared with the other V2O3 films, the films prepared at Mo x > 0.07 offered the high resistivity and moderate thermal constant (B) values. In particular, V2O3 doped with 10 mol % Mo showed excellent NTC properties and high resistivity (0.072 Ω cm). At sub-zero temperatures, the variation of electrical transport properties of the V2O3 films is correlated with Mo concentration, micro-structure and Joule effect.

Influence of Mo on High-Temperature Oxidation Behavior of La- and Zr-added 20 mass%Cr–6 mass%Al Ferritic Stainless Steels

The influence of Mo addition on the high-temperature oxidation behavior of La or La + Zr-added 20 mass%Cr–6 mass%Al steel at 1100 °C was investigated. The oxidation rates of the La-added steel and La + Zr-added steel were found to be increased by the addition of Mo. In both steels, the increase in the growth rate of columnar layers was more noticeable than that of equiaxed layers in the Al2O3 scales. The segregation of La to the Al2O3 grain boundaries of 5Mo steel was lower than that observed in 0Mo steel. It is suspected that the increase in oxidation rate caused by Mo addition arose from the suppression of La segregation, which controls the diffusivity of O and Al ions at Al2O3 grain boundaries. These results suggested that the addition of Mo reduced the activity of La in the steel.

Influence of Mo Addition on High Temperature Deformation Behavior of L12 Type Ni3Al Intermetallics

The high temperature deformation behavior of Ni3Al and Ni3(Al,Mo) single crystals that were oriented near was investigated at low strain rates in the temperature range above the flow stress peak temperature. Three types of behavior were found under the present experimental conditions. In the relatively high strain rate region, the strain rate dependence of the flow stress is small, and the deformation may be controlled by the dislocation glide mainly on the {001} slip plane in both crystals. At low strain rates, the octahedral glide is still active in Ni3Al above the peak temperature, but the active slip system in Ni3(Al,Mo) changes from octahedral glide to cube glide at the peak temperature. These results suggest that the deformation rate controlling mechanism of Ni3Al is viscous glide of dislocations by the {111} slip, whereas that of Ni3(Al,Mo) is a recovery process of dislocation climb in the substructures formed by the {001} slip. The results of TEM observation show that the characteristics of dislocation structures are uniform distribution in Ni3Al and subboundary formation in Ni3(Al,Mo). Activation energies for deformation in Ni3Al and Ni3(Al,Mo) were obtained in the low strain rate region. The values of the activation energy are 360 kJ/mol for Ni3Al and 300 kJ/mol for Ni3(Al,Mo).

Hardenability of sinter-forged Fe–2Cu-0.7C-xMo alloys

The paper reports the hardenability response of Mo (0.25–3.0 wt%) addition in Fe–2Cu-0.7C alloy under sinter-forged conditions evaluated by Jominy end quench test. Powder alloy compositions were processed by mixing of elemental powders followed by sintering at 1150 °C in N2–10%H2 atmosphere in a mild steel capsule. The sintered capsules were immediately forged at the sintering temperature to obtain a forged slab which was further homogenized at 1250 °C. Hardenability test specimen of 12.7 × 101.6 mm sub standard size as prescribed by ASTM standard A 255–02 were prepared from the homogenized slabs. Jominy end quench test was carried out on all specimens using the standard practice after which the hardenability plot was obtained. In depth discussion was carried out on the influence of Mo addition on hardenability plots with microstructural analysis which has been correlated with the hardness profile.

Dispersoid strengthening of a high temperature Al–Si–Cu–Mg alloy via Mo addition

Abstract The influence of Mo addition on the microstructure and mechanical properties of an Al–7Si–0.5Cu–0.3Mg alloy (wt%) was investigated. The Mo-containing alloy exhibited significant improvement in creep resistance over the base alloy. At 300 °C and 30 MPa, the minimum creep rate decreased by 95% while creep time-to-fracture was increased by 2 orders of magnitude, from 50 min to 1500 min. The tensile yield strength at 300 °C was also increased by 25%. These effects were attributed to the formation of novel Al–(Fe,Mo)–Si dispersoids during solution treatment in the grain interiors (intradendritic regions). Unlike the age-hardening precipitates, which coarsened resulting in loss of strength, these dispersoids were thermally stable and retained their strengthening effect at 300 °C. TEM investigations showed that the dislocation motions were effectively hindered by these fine dispersoids, leading to the reduction in the minimum creep rate. The onset of the tertiary creep stage was delayed by postponing the dislocation pile-up at the interdendritic Si particles. It was found that Mo addition suppressed the formation of the brittle plate-like β-Al5FeSi intermetallics and formed a blocky phase in the cast microstructure, which resulted in 34% increase in elongation at 300 °C.

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.

Effect of Molybdenum on the Microstructure and Mechanical Properties of TiC-Fe Cermets

The influence of Mo addition on the microstructure and mechanical properties of the TiC-Fe cermets has been studied. The specimens with different contents of Mo (4-8 wt.%) added into the TiC-Fe cermets were fabricated by conventional powder metallurgy and vacuum sintered at temperatures of 1440 °C. The microstructure and mechanical properties such as bending strength, impact toughness, hardness, wear resistance were investigated. The micrographs with different Mo content show that the final grain size of carbide phase became smaller and the specimens became more homogeneous and compact with increasing Mo content from 4 wt.% to 8 wt.% in raw powders. The mechanical properties measured show that the bending strength, impact toughness and wear resistance are the best when the Mo content is 6 wt.%.

Lean duplex stainless steels—The role of molybdenum in pitting corrosion of concrete reinforcement studied with industrial and laboratory castings

The influence of Mo addition on pitting corrosion resistance of lean duplex stainless steels is not clearly understood in alkaline chloride conditions even if this element is widely recognized to increase corrosion resistance in acidic and neutral environments. This work aims to study the effect of Mo on pitting corrosion of lean duplex stainless steels in synthetic concrete pore solutions simulating degraded concrete. Results are discussed with respect to the influence of Mo on pitting potential for two industrial alloys in chloride rich and carbonated solution simulating concrete pore environments. To establish the real effect of Mo addition on lean duplex corrosion and passivation properties, two specific laboratory lean duplex alloys, for which the only difference is strictly the Mo content, are also studied. Mo presented a strong positive influence on the pitting corrosion resistance of industrial and laboratory lean duplex stainless steels in all studied chloride-rich solutions, but its effect is as less pronounced as the pH increases. In presence of Mo, pitting initiates and propagates preferentially in the austenitic phase at high temperature.

Lean duplex stainless steels – The role of molybdenum addition on pitting corrosion of concrete reinforcements

The use of stainless steels as concrete reinforcement is becoming increasingly popular in coastal and marine constructions in order to prevent corrosion induced by chloride ions penetrating into the concrete. In these highly aggressive situations, the lean duplex stainless steels have been extensively employed due to their high mechanical and corrosion resistances. However, the influence of Mo addition on pitting corrosion resistance of these steels is not clearly understood in alkaline chloride conditions even if this element is widely associated to an increasing corrosion resistance in acidic and neutral environments. Therefore, understanding Mo mechanism on corrosion resistance in alkaline media is hence of major importance to the setting of optimized alloy composition. The present work aims to study the effect of Mo addition on pitting corrosion properties of lean duplex stainless steels in alkaline environments (concrete). The results are discussed with respect to the influence of Mo addition on pitting potential for two industrial duplex alloys (1.4362 and 1.4462) in several aggressive media mainly in synthetic, chlorinated and carbonated solution simulating concrete pore environments (pH10 solution with carbonates and chlorides ions). In order to establish the real role of Mo addition on lean duplex corrosion and passivation properties, the corrosion behaviors of two specific laboratory lean duplex alloys, which the only difference between then is the amount of Mo (0 and 3% wt. Mo), are also studied. Furthermore, scanning electronic microscopy (SEM) was used to verify which phase of duplex microstructure (ferritic or austenitic) is mostly susceptible to the pit nucleation in these corrosion conditions as the role of Mo is probably different to each simple phase.

Influence of Mo addition on the solvus temperature of Ni2(Cr,Mo) phase in Ni2(Cr,Mo) alloys

Abstract The present paper reports the results of a detailed investigation carried out to determine the solvus temperature of Ni 2 (Cr,Mo) phase in Ni 0.66 Cr 1− x ,Mo x alloys, with x varying from 0 to 0.5, using differential scanning calorimetry and transmission electron microscopy. It was noticed that the precipitation of this phase is very sluggish. The solvus temperature was determined from specimens aged for long periods of time to precipitate Ni 2 (Cr,Mo) phase. The solvus temperature was found to vary from 627 °C (for a Mo/Cr ratio = 0) to 773 °C (for a Mo/Cr ratio = 1) for a heating rate of 2 °C/min and the data could be fitted with second-order polynomial relation. The isothermal solvus temperature for two alloy compositions was determined from the results of influence of heating rate on solvus temperature. The experimentally observed results on solvus temperature were confirmed by the microstructural examination of aged specimens in electron microscope.