Influence of Molybdenum on the Microstructure, Mechanical Properties and Corrosion Resistance of Ti20Ta20Nb20(ZrHf)20−xMox (Where: x = 0, 5, 10, 15, 20) High Entropy Alloys

The presented work was focused on investigating the influence of the (hafnium and zirconium)/molybdenum ratio on the microstructure and properties of Ti20Ta20Nb20(ZrHf)20−xMox (where: x = 0, 5, 10, 15, 20 at.%) high entropy alloys in an as-cast state. The designed chemical composition was chosen due to possible future biomedical applications. Materials were obtained from elemental powders by vacuum arc melting technique. Phase analysis revealed the presence of dual body-centered cubic phases. X-ray diffraction showed the decrease of lattice parameters of both phases with increasing molybdenum concentration up to 10% of molybdenum and further increase of lattice parameters. The presence of two-phase matrix microstructure and hafnium and zirconium precipitates was proved by scanning and transmission electron microscopy observation. Mechanical property measurements revealed decreased micro- and nanohardness and reduced Young’s modulus up to 10% of Mo content, and further increased up to 20% of molybdenum addition. Additionally, corrosion resistance measurements in Ringers’ solution confirmed the high biomedical ability of studied alloys due to the presence of stable oxide layers.

Powder Metallurgical Processing and Characterization of Molybdenum Addition to Tungsten Heavy Alloys by Spark Plasma Sintering

The effect of adding molybdenum to the heavy tungsten alloy of W-Ni-Fe on its material characteristics was examined in the current study. The elemental powders of tungsten, iron, nickel, and molybdenum, with a composition analogous to W-3Fe-7Ni-xMo (x = 0, 22.5, 45, 67.5 wt.%), were fabricated using the spark plasma sintering (SPS) technique at a sintering temperature of 1400 °C and under pressure of 50 MPa. The sintered samples were subjected to microstructural characterization and tested for mechanical strength. The smallest grain size of 9.99 microns was observed for the 45W-45Mo alloy. This alloy also gave the highest tensile and yield strengths of 1140 MPa and 763 MPa, respectively. The hardness increased with the increased addition of molybdenum. The high level of hardness was observed for 67.5Mo with a 10.8% increase in the base alloy’s hardness. The investigation resulted in the alloy of 45W-7Ni-3Fe-45Mo, observed to provide optimum mechanical properties among all the analyzed samples.

Influence of molybdenum content on the microstructure of spark plasma sintered titanium alloys

Five titanium-based alloys containing 4, 8, 12, 16, and 20 wt% molybdenum additive were fabricated by spark plasma sintering process at 1200 ˚C. The samples were scrutinized in terms of relative density, phase evolution, and microstructural development. The relative density reached 99.9% with the molybdenum addition up to 16 wt% but slightly dropped in the sample with 20 wt% additive. In the specimens with 4 wt% Mo, molybdenum solved completely in the matrix and three different phase morphologies were observed, namely continuous α-Ti, laminar α-Ti, and very thin laminar β-Ti. With increasing Mo content to 20 wt%, widespread single β-Ti appeared alongside remained Mo and α-Ti. Ductile fracture mode was dominant in the samples with low Mo contents whilst it changed to brittle in the specimens with higher content of molybdenum.

Investigation of microstructure and selected properties of Al2O3-Cu and Al2O3-Cu-Mo composites

The scope of work included the fabrication of ceramic-metal composites from the Al2O3-Cu and Al2O3-Cu-Mo and examining their microstructure and selected properties. The composites were fabricated by the slip casting method. The rheological behavior, microstructures, X-ray analysis, and mechanical properties were investigated. The rheological study demonstrated that all of the obtained slurries were non-Newtonian shear diluted fluids and stability on time. In both slurries, the flow limit is close to 0 Pa, which is very beneficial when casting the suspensions into molds. The X-ray analysis reveals Al2O3, Cu, and Mo phases in all specimens. No new phases were found in both types of composites after the sintering process. The results provided that the hardness for Al2O3-Cu-Mo composites was equal to 10.06 ± 0.49 GPa, while for Al2O3-Cu, it was equal to 6.81 ± 2.08 GPa. The K1C values measured, with the use of Niihara equation, for composites with and without the addition of Mo were equal to 6.13 ± 0.62 MPa m0.5 and 6.04 ± 0.55 MPa m0.5, respectively. It has been established that the mean specific wear rates of Al2O3-Cu and Al2O3-Cu-Mo samples were 0.35 × 10–5 ± 0.02 mm3 N−1 m−1 and 0.22 × 10–5 ± 0.04 mm3 N−1 m−1, respectively. It was found that molybdenum addition improved wear resistance properties of the composites.

The Effect of Heat-Treatment on the Phase Stability of Fe-28Al-15Si-2Mo Alloy

The structures of Fe-28Al-15Si-2Mo iron aluminide in as cast state and in three states after heat-treatments were investigated for the verification of secondary phases stability. Short-term (at 1000 °C for 24 h and at 1200 °C for 2 h) as well as long-term (at 800 °C for 100 h) annealing were performed. Molybdenum addition enhances the high-temperature mechanical properties due to solid solution strengthening, however the mechanism of hardening could be modified (to solid solution strengthening + strengthening by incoherent precipitates) by another alloying element (f. e. Si or C). The phase compositions of alloys were described by means of scanning electron microscopy equipped with energy dispersive analysis. The complex Fe-Si-Mo carbides were found in the structure. The bulk hardness measurement and image analysis were performed for the verification of secondary phase stability. Particles became coarse with increasing temperature of annealing.

Effects of Molybdenum Addition on Rolling Contact Fatigue of Locomotive Wheels under Rolling-Sliding Condition

Rolling contact fatigue (RCF) damages often occur, sometimes even leading to shelling on locomotive wheel treads. In this work, the RCF damage behaviors of two locomotive wheel materials with different molybdenum (Mo) contents were studied, and the influence of depth of wheel material was explored as well. The result indicates that with the increase in the Mo content from 0.01 wt.% (wheel 1, i.e., a standard wheel) to 0.04 wt.% (wheel 2, i.e., an improved wheel), the proeutectoid ferrite content and the interlamellar spacing of pearlite decreased, the depth and length of the RCF cracks increased and the average RCF live of locomotive wheel steel improved by 34.06%. With the increase in the depth of material, the proeutectoid ferrite content and the interlamellar spacing of pearlite increased, the depth of RCF cracks increased, the length of RCF cracks of wheel 1 increased and then decreased whereas that of wheel 2 decreased, the RCF live showed a decrease trend for wheel 1, while the RCF life increased and then decreased for wheel 2. The processes of shelling can be divided into three patterns: cracks propagating back to the surface, crack connection and fragments of surface materials.

Impact of Zinc, Boron and Molybdenum Addition in Soil on Mungbean Productivity, Nutrient Uptake and Economics

Zinc (Zn), boron (B) and molybdenum (Mo) are essential to increase the productivity of mungbean (Vigna radiata L.) and help to maintain the soil fertility but mostly ignored. Hence, an experiment was conducted during the years of 2016 and 2017 to know the impact of Zn, B and Mo on mungbean yield, nutrient uptake, economics and soil fertility improvement. The experiments were planned in randomized complete block design including of eight treatments with three replications. The treatments were T1 = Control, T2 = Zn 2 kg ha-1, T3 = B 1.5 kg ha-1, T4 = Mo 1 kg ha-1, T5 = Zn2B1.5, T6 = Zn2Mo1, T7 = B1.5Mo1 and T8 = Zn2B1.5Mo1. The other fertilizers, N, P, K and S at 20, 20, 30 and 10 kg ha-1, respectively were used in all treatments. The results indicate that the highest seed yield (1522 kg ha-1) was obtained from T8 treatment followed by T7. The highest percent seed yield increment (51.6%) over control was achieved in T8 treatment. Most of the growth and yield contributing characters of mungbean were recorded highest in T8 treatment. The maximum nodulation (37.6) and highest amount of protein (24.3%) was also obtained from T8 treatment. The T8 treatment contributed positively to attain higher total uptake of N, P, K, S, Zn and B by mungbean. The combination of Zn, B and Mo is showed more productive compare to sole or couple use of these micronutrients. The T8 (Zn2B1.5Mo1 kg ha-1) treatment exhibited helpful effects on soil organic matter, total N, available P, Zn and B. This treatment also showed economically better on the basis of net return. Results of the present study suggest that the combination of Zn, B and Mo applied at 2, 1.5 and 1 kg ha-1, respectively could be recommended for mungbean cultivation.