Mo Addition Research Articles

Synthesis and mechanical properties of TiC-Fe interpenetrating phase composites fabricated by infiltration process

TiC-Fe interpenetrating phase composites were fabricated by infiltrating molten iron into porous TiC preforms prepared by the organic template dipping method. The TiC-Fe interpenetrating phase composites exhibited a three-dimensional network structure, in which Fe and TiC phases interconnected with each other. The microstructures of porous TiC preforms and TiC-Fe interpenetrating phase composites were respectively characterized by SEM, and the phase compositions of preforms and composites were analyzed by XRD. No other amorphous phases were detected on the interface between TiC and Fe matrix, indicating that no reaction occurred between them. The Vickers hardness of a 4 vol% TiC (with Fe addition)-Fe interpenetrating phase composite increased gradually from 1.13 GPa for the pure Fe zone to 3.42 GPa for the TiC ceramic zone. The tensile strength of a 4 vol% TiC (with Mo addition)-Fe composite reached 343 MPa. The tensile fracture surfaces showed a strong interfacial bond between TiC and iron matrix. The TiC-Fe interpenetrating phase composites are more suitable for wear resistance applications as compared with Fe-matrix composites reinforced with discontinuous TiC particles.

Microstructure and creep properties of Ni-based single-crystal superalloys with Mo/Al addition at 760 °C/850 MPa

The effect of Mo and Al addition on the microstructure as well as creep rupture properties at 760 °C/850 MPa was investigated by transmission electron microscopy (TEM) in a Ni-based single-crystal (SC) alloy with the composition of Ni–6.5Al–8.0Mo–2.4Cr–6.2Ta–4.9Co–1.5Re–(0.01–0.05)Y (wt%). The microstructure analysis shows that 0.5 wt% Al addition induces rapid decrease in creep rupture life, and this can be attributed to the formation of dense stacking faults cutting into γ′ precipitates, which can be explained by the increase in Orowan stress caused by the narrower γ channel width and the decrease in stacking faults energy. Besides, 1.5 wt% Mo addition increases the anti-phase boundary energy and decreases the stacking faults energy, resulting in fewer stacking faults and thus a slight decrease in the creep rupture life.

Improvement of Creep Resistance at 950 °C and 400 MPa in Ru-Containing Single-Crystal Superalloys with a High Level of Co Addition

Microstructural features, including γ′ volume fraction and size, γ-γ′ lattice misfit, γ channel width, and dislocation substructure, are known to significantly influence the creep performance in Ni-base single-crystal superalloys. In this study, the microstructural characteristics of Ru-containing single-crystal superalloys with different levels of Co, Mo, and Ru additions were quantitatively investigated after ruptured and interrupted creep tests conducted at 1223 K (950 °C) and 400 MPa. The creep lifetime was slightly increased with the high level of Co addition and significantly increased with the coadditions of Mo and Ru. A minor effect of Co content on the γ channel width and γ′ volume fraction was found in experimental alloys. The alloy with high levels of Mo and Ru additions was determined to possess a more negative γ-γ′ lattice misfit, and a high density of stacking faults (SFs) was formed in the γ channels during creep. The combined effects of the SFs in the γ matrix serving as the barriers to dislocation movement, as well as the dense interfacial dislocation networks preventing dislocation to shear the γ′ phase, were considered as the main mechanism responsible for the improvement of creep resistance. Results from this study are helpful to understand the effect of microstructural features on creep performance and contribute to the knowledge of physical metallurgy in Ru-containing single-crystal superalloys.

Enhanced wear resistance of Stellite 12 by Mo addition and LSM

ABSTRACTAiming at additional improvements in the properties of Stellite 12 PTA hardfacing alloy deposited on 4140 steel substrate, the authors have adopted a dual approach. During PTA deposition Stellite 12 hardfacing powder was alloyed with 10 wt-% Mo, followed by laser surface melting (LSM). Addition of 10 wt-% Mo, led to an increase in the volume fraction of Co and W-rich complex carbides. Later on LSM executed on the PTA led to the development of unique microstructure near the surface, characterised by the segregation of hard Cr-rich carbides. The resultant layers were subjected to mechanical characterisation, at room temperature, e.g. hardness and wear resistance. It was concluded that combining both approaches i.e. addition of Mo during the hardfacing process followed by LSM of deposited layer gave additional improvements in mechanical properties owing to evolution of a unique carbide structure.

16%Cr鋳鉄の連続冷却変態挙動に及ぼすMo, V及びNbの影響

16%Cr鋳鉄の連続冷却変態挙動に及ぼすMo, V及びNbの影響

Effect of Molybdenum on Pit Initiation at Manganese Sulfide Inclusions in Stainless Steel

Stainless steels sometimes suffer from pitting corrosion in chloride environments. The pit initiation sites for commercial stainless steels have been attributed to sulfide inclusions such as MnS. It is well known that addition of Mo enhances the pitting corrosion resistance of stainless steels, and the role of Mo has been studied extensively. However, it is still debated how Mo inhibits pitting corrosion of stainless steels. In this study, a microelectrochemical technique was applied to clarify the role of Mo addition in the inhibition of pit initiation at MnS inclusions in stainless steels. Two re-sulfurized stainless steels were prepared by vacuum induction melting (50 kg ingot): one was Mo-free (18Cr-10Ni-0.8Mn-0.03S), and the other was Mo-added (18Cr-10Ni-2.3Mo-0.8Mn-0.03S). The ingots were hot-rolled. In these steels, S was added to form MnS inclusions. To reduce the delta-ferrite phase in the steels, they were heat-treated at 1273 K for 96 h, followed by hot-rolling at 1473 K from 20 mm down to about 12 mm in thickness. Additional heat-treatment was conducted at 1273 K for 96 h and at 1323 K at 0.5 h, and the steels were finally water-quenched. After heat-treatment, the steels were cut into specimens with dimensions of 15 mm × 25 mm × 5 mm. The specimens were abraded with a series of SiC papers up to 1500 grit and then were polished by a diamond paste down to 1 µm. Potentiodynamic polarization curves were measured in naturally aerated 0.1 M NaCl (pH 5.5) at 298 K. The electrode area was ca. 100 µm × 100 µm. All the potentials reported in this study refer to the Ag/AgCl (3.33 M KCl) electrode (0.206 V vs. standard hydrogen electrode at 298 K). The potential scan rate was 3.8 × 10–4 V/s (23 mV/min). To analyze the effect of Mo on the pit initiation at the MnS inclusion, the anodic polarization curves were measured in 0.1 M NaCl. Figure 1a shows the polarization curves of a small area with the MnS inclusions in Mo-free and Mo-added specimens. Figures 1b and 1c show the SEM images of the inclusions in Mo-free and Mo-added specimens after polarization. The experiments were started at –0.2 V. The gradual increases in the current densities of both specimens above ca. 0.1 V are due to the anodic dissolution of the MnS inclusions. The large increase in the current density of the Mo-free specimen at 0.4 V was attributed to the stable pit initiation at the inclusion. As shown in Fig. 1b, a pit was initiated at the MnS/steel matrix boundary. On the other hand, the current density of the Mo-added specimen decreased to the level of the passive state of stainless steel above ca. 0.45 V. In Fig. 1c, no pit was observed in the Mo-added specimen even though the bare steel surface was exposed by the dissolution of the MnS inclusion. Mo species were estimated to be released from the exposed bare steel surface. This suggests that Mo species inhibited pit initiation at the MnS/steel boundary. Figure 1

Effects of Cr and Mo additions on formation and mechanical properties of Arc-sprayed FeBSiNb-based glassy coatings

In this work, a series of dense arc-sprayed Fe-B-Si-Nb-Cr-Mo glassy coatings were developed. The effects of Cr and Mo on glass formation and mechanical properties were explored in details. The coatings have a full glassy state. Thermal stability of the coatings increases remarkably with addition Cr and Mo. The onset crystallization temperature (Tx) increases from 797 K to 912 K. The hardness increases from 16.4 GPa to 18.7 GPa. The relatively wear resistance of the FeBSiNbCrMo glassy coating is about 7.8 times and 1.5 times that of Q235 steel and the FeBSiNb coating, respectively. The corrosion resistance in 3.5 wt% NaCl solution reveals that the FeBSiNbCrMo glassy coating has the lowest Icorr and the highest fitted Rt. An attempt has been established to discuss correlations between structural characteristics and mechanical properties of the coatings with different elements.

Effect of composition, heat treatment and deformation on mechanical properties of tungsten heavy alloys

Five different compositions of tungsten heavy alloy with Ni, Fe, Co and Mo were prepared through powder metallurgy route using liquid phase sintering. Three alloys were based on quaternary W-Ni-Fe-Co (with varying Ni to Fe ratio and Co content) and the other two quinary systems with Mo addition. The sintered alloy blanks (cylindrical cross section) were subjected to a thermo-mechanical treatment, which comprised three vacuum heat treatments (at 1100 °C for 1.5 h followed by oil quenching) before and in between multiple swaging operations (at 500 °C) with a total deformation of 53%. This was followed by a detailed evaluation of different microstructural parameters in all compositions. Mechanical properties such as tensile strength, % elongation and impact were evaluated at the final stage (26 mm dia and 600 mm length). Increase in Co content resulted in better strength and elongation with marginal loss in impact values. The alloy containing 0.25 wt% Mo showed the best combination of tensile and impact properties. Further increase in Mo concentration to 0.5 wt% resulted in marginal increase in strength value but rapid deterioration in elongation and impact values. Scanning electron microscopy, electron probe micro analysis, quantitative metallography and fractography were carried out to establish an inter-relationship between microstructure, properties and fracture behaviour of the alloys investigated.

Tribological behaviour of sinter-forged Fe-2Cu-0.7C-xMo alloys

The paper presents dry sliding wear behaviour of sinter-forged Fe-2Cu-0.7C-xMo alloys wherein effect of Mo addition and heat treatments have been investigated. Three alloy (1, 2 and 3) compositions; 0 wt% Mo (Fe-2Cu-0.7C), 1.5 wt% Mo (Fe-2Cu-0.7C-1.5Mo) and 3 wt% Mo (Fe-2Cu-0.7C-3Mo) have been fabricated by sinter-forging route to full density using elemental powders. All three compositions under normalised condition have been tested to study the influence of Mo addition on wear behaviour of base alloy Fe-2Cu-0.7C whereas the influence of different heat treatments on wear behaviour has been determined on the intermediate alloy composition (Alloy 2) i.e. Fe-2Cu-0.7C-1.5Mo under four heat treatment conditions i.e. annealed, normalised, quenched and quenched plus tempered condition. Wear tests have been performed using a ball-on-disk type tribometer at a fixed load of 10 N and constant speed of 500 rpm for 20 min with track diameter of 6 mm. High Cr bearing grade steel balls of 10 mm diameter and Rockwell hardness of 58–60 HRC were used as the counter material. The wear behaviour was observed as a complex function of strength, ductility and microstructure which was influenced by both Mo addition and heat treatment conditions. Wear mechanism was found to change with Mo addition. Addition of Mo in Fe-2Cu-0.7C alloy promotes oxidative wear as dominating wear mechanism in place of adhesion and consequently showed lower wear loss. The 3 wt% Mo alloy in normalised condition exhibited highest wear resistance while 1.5 wt% Mo alloy in quenched condition showed highest wear volume. The microstructural features also affected wear behaviour; bainitic structure showed high wear resistance compared to martensitic structure.

Influence of Cobalt and Molybdenum Additives on the Structure and Shape Memory Parameters of Reaction-Sintered Porous Nickel Titanium Alloys

We have studied the structure and properties of porous nickel titanium (TiNi) alloys obtained upon reaction sintering of Ti and Ni powders with Co and Mo additives. It is established that Co and Mo doping additives retain the compaction of Ni powder achieved at the initial stage of sintering. The maximum deformation of porous samples loaded in the austenite state was observed upon adding Co, while the addition of Mo resulted in minimum deformation. The addition of Co leads to single-stage martensitic transformation in TiNi phase, while the addition of Mo leads to the two-stage transformation that is more homogeneous over the volume. Both Co and Mo additives lead to increase in the maximum accumulated strain due to the formation of favorably oriented stress-induced martensite and reoriented quench-induced martensite.

Structural Transformation of Mo-Doped In2O3 Nanotubes by Electron-Beam Irradiation

Structural transformation of Mo-doped In2O3 nanotubes (Mo-In2O3 NTs), induced by electron-beam (e-beam) irradiation, was characterized by a high-resolution transmission electron microscope. Results showed that uniform Mo-In2O3 NTs were prepared by electrospinning, where a small amount of Mo additives (5 mol%) could incorporate into the In2O3 NTs to form Mo-In-O solid solution. However, a large number of ultrafine nanoparticles would gradually generate on the surface of Mo-In2O3 NTs after exposure to e-beam irradiation, which were further confirmed to be the nonstoichiometric MoOx. The effects of e-beam irradiation (exposure time and dose rate) and calcination temperature of products were also discussed. This new strategy can be adopted to design some novel nanostructures, which may have great potential applications in nanofabrication and emerging nanodevices.

Influence of Mo on the high temperature wear performance of NiCrBSi hardfacings

Abstract This study investigates the effect of 10 wt% Mo alloying of NiCrBSi hardfacing on the microstructure and dry sliding wear performance at room temperature and elevated temperatures up to 700 °C. Mo additions refined the boride and carbide phases in the microstructure and formed a Mo-rich boro-carbide along with a 20% drop in its hardness. It further improved the wear resistance at all tested temperatures due to the formation of Mo oxides on the worn surfaces.

Development of High Performance Cast Iron with Combination of Improved Mechanical and Thermal Properties Through Mo Addition

High performance cast iron with a combination of improved mechanical properties and thermal conductivity is developed through Mo addition in gray cast iron. The primary austenite dendrite as well as the eutectic cell can be refined by Mo addition. Decrease of the amount and length of graphite flakes as well as Mo solid-solution strengthening leads to high ultimate tensile strength, while the uniform distribution of graphite flakes is responsible for the improved thermal conductivity.

Effect of Mo and Mn Addition on the Oxidation Behavior of Binary Ti-Al Alloys

Effect of Mo and Mn Addition on the Oxidation Behavior of Binary Ti-Al Alloys

Mo Addition to the A354 (Al–Si–Cu–Mg) Casting Alloy: Effects on Microstructure and Mechanical Properties at Room and High Temperature

Cast aluminum alloys are widely used in the automotive field for the production of complex engine parts. However, the mechanical properties of heat-treatable alloys (e.g., Al–Si–Mg or Al–Si–Cu–Mg) are negatively affected by prolonged exposure to temperatures higher than about 200 °C. To date, several researchers have proposed the addition of alloying elements, such as Sc or Hf, for enhancing the high temperature behavior of cast Al alloys, while Mo has not been widely investigated. The present study aimed to assess the effects of Mo addition on microstructure, mechanical properties, and thermal stability of the A354 alloy. Samples of A354 alloy with different amount of Mo (in the range 0.1 to 0.8 wt %) were produced. The casting conditions and heat treatment parameters were optimized by means of optical and scanning electron microscopy, thermal analysis and hardness tests. Tensile tests highlighted that Mo induces a moderate increase of yield strength at room temperature (about 10%), but no appreciable improvement in the performance of the alloy at 250 °C was observed.

Improvement of room and high temperature tensile properties of NiAl-strengthened ferritic heat-resistant steels through Mo addition

In order to improve the room and high temperature strength–ductility balance of ferritic Fe-Al-Ni based alloys strengthened by the B2-type NiAl precipitates, Fe-Al-Ni-Cr-Mo alloys was developed. The microstructures and tensile properties of the alloys were examined focusing on Mo content. We found that the 2 at% or 4 at% Mo addition is effective in the improvement of the elongation of the Fe-Al-Ni based alloys at room temperature (RT) while maintaining high strength, which reflects the suppression of intergranular fracture by the strengthening of the bcc matrix by Mo addition. We also found that the RT tensile properties and deformation behavior of the alloys depend strongly on the volume fraction and the size of the NiAl precipitates. For instance, the yield stress decreases by the change in the primary slip direction from <111> to <001> and the formation of the Orowan loops with increasing the volume fraction and the mean diameter of the NiAl precipitates. In addition, the alloy with the appropriate Mo content exhibits a high yield stress above 660 MPa up to 923 K, owing to the solid-solution hardening by Mo addition and the low growth rate of the NiAl precipitates even at high temperatures. These findings indicate that the alloys have a great potential for steam turbines of advanced ultra‐supercritical thermal power plants.

Failure of super 13Cr stainless steel due to excessive hardness in the welded joint

Supermartensitic stainless steels (SMSS) with 11–13%Cr were developed to show higher corrosion resistance, toughness and weldability than conventional martensitic stainless steels (MSS). The main compositional characteristics of SMSS's, in a comparison to common MSS's, are the extra low C content, Ni and Mo addition. This new sub-family of stainless steels has been used in the oil and gas offshore production, as tubulars and casings in the wheel. Despite of the extra low C (<0.03%), the mechanical resistance of SMSS's is maintained high due to the addition of Mo (up to 2.0%wt.), and other elements, such as N, W, Nb and or Ti. As a consequence of the extra low C, the martensite of SMSS's is relatively soft and tough, which makes these steels, in theory, much more resistant to cold cracking in the heat affected zone (HAZ) of welds. Nevertheless, for applications in saline environments with CO2 and/or H2S a post weld heat treatment (PWHT) is necessary to reduce the peak of hardness in the HAZ. In the present work, the failure of a mandril for chemical products injection in the wheel made of SMSS is reported. The failure occurred in a welded joint between two heavy forged pieces. The hardness of the HAZ was higher than the minimum allowable to sour service conditions, indicating that the PWHT was not performed or it was done uncorrectly.

Influence of Mo and Ru additions on the creep behavior of Ni-based single crystal superalloys at 1100 °C

In order to obtain more knowledge to replace or lower the content of expensive and heavy elements Re and Ru in advanced Ni-based single crystal superalloys, the role of Ru playing in the microstructure and creep performance at 1100 °C and 140 MPa was evaluated in this study by considering its individual effect and also synergizing it with Mo to maximize the beneficial effect from each element. A series of single crystal superalloys with varying alloying elements were investigated and their initial microstructure and microstructural evolution during the creep deformation were characterized. It was shown that both Mo and Ru could increase the γ/γ' lattice misfit and density of interfacial dislocations, that contributed to improve the creep resistance at high temperature and low stress condition. The inferior microstructural stability regarding to the TCP phase formation in alloys with more Mo addition lowered creep performance to some extent, however, that could be restrained by the addition of Ru. The high temperature and low stress creep performance could be enhanced by the co-addition of Mo and Ru since their synergistic effect could be able to enhance the γ/γ' interfacial strengthening and retain the microstructural stability.

Promotional effect of Mo addition on CoOX/Ti-Ce catalyst for oxidation removal of elemental mercury in flue gas

To enhance the catalytic activity for elemental mercury (Hg0) oxidation and SO2 resistance of catalyst, Mo was applied to modify the CoOX/Ti-Ce (Co/TiCe) catalyst for better performance. The results showed that CoMo5/TiCe had the highest activity for Hg0 oxidation in the wide temperature window of 100–400 °C in the presence of 10 ppm HCl and 6% O2. NO exhibited insignificant effect on Hg0 oxidation. SO2 and H2O were found to inhibit Hg0 oxidation. Hg0 oxidation by HCl over CoMo5/TiCe catalyst mainly occurred through the Eley-Rideal mechanism, where gas-phase or weakly-bonded Hg0 reacted with surface chlorine species originated from adsorbed HCl to form Hg2+. SO2 could obstruct the generation of surface active chlorine species, thus inhibiting Hg0 oxidation. Compared with Co/TiCe, CoMo5/TiCe showed better resistance to SO2 and H2O for Hg0 oxidation. In the presence of 200 ppm SO2, CoMo5/TiCe achieved Hg0 oxidation efficiency of 96.1% and a simultaneous NO conversion efficiency of 42.9% at 300 °C, showing better performance than Co/TiCe. The physicochemical properties of the catalysts were examined by BET, XRD, Ranman spectroscopy, H2-TPR, XPS and EDS techniques to reveal the effect of Mo addition on the catalytic performances. It was found that an interaction of Mo with Co promoted the dispersion of Co3O4, increased the Co2+ and Oα concentration and enhanced the reducibility of catalyst, which contributed to the improvement of Hg0 oxidation activity. Moreover, the SO2 resistance of catalyst was enhanced by suppressing the reaction between the catalyst and SO2 due to Mo addition.

Effect of Carbon Content on the Microstructure and Mechanical Properties of NbC-Ni Based Cermets

The aim of this work was to correlate the overall carbon content in NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo starting powders with the resulting microstructure, hardness, and fracture toughness of Ni-bonded NbC cermets. A series of NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo cermets with different carbon content were prepared by conventional liquid phase sintering for 1 h at 1420 °C in vacuum. Microstructural analysis of the fully densified cermets was performed by electron probe microanalysis (EPMA) to assess the effect of carbon and VC or Mo additions on the NbC grain growth and morphology. A decreased carbon content in the starting powder mixtures resulted in increased dissolution of Nb, V, and Mo in the Ni binder and a decreased C/Nb ratio in the NbC based carbide phase. The Vickers hardness (HV30) and Palmqvist indentation toughness were found to decrease significantly with an increasing carbon content in the Mo-free cermets, whereas an antagonistic correlation between hardness and toughness was obtained as a function of the Mo-content in Mo-modified NbC cermets. To obtain optimized mechanical properties, methods to control the total carbon content of NbC-Ni mixtures were proposed and the prepared cermets were investigated in detail.