Alignment Of Basal Planes Research Articles

Tribological behavior of molybdenum disulfide and tungsten disulfide sprayed coatings in low viscosity hydrocarbon environments

The tribological behavior of MoS2 and WS2 transition metal dichalcogenide (TMD) spray coatings in low-viscosity hydrocarbon environments was investigated. Sliding tests were performed in two hydrocarbons – hydrophilic ethanol and hydrophobic dodecane and were compared to tests in humid air and dry nitrogen conditions. Coating steel surfaces decreased friction across all test conditions, with the largest and most sustainable decreases being in dry nitrogen and dodecane environments, where friction coefficients of less than 0.1 were sustained. Analysis was performed using scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. Friction reductions in dodecane were explained by reduced oxidation of the coating, due to protection from the hydrophobic hydrocarbon film, allowing basal plane alignment and uninhibited sliding of TMD sheets.

Effect of Ca and Nd on the microstructural development during dynamic and static recrystallization of indirectly extruded Mg–Zn based alloys

The present study examines the influence of Ca or Nd on the microstructure and texture modification during indirect extrusion and after subsequent annealing of Mg–Zn based alloys. The addition of such elements influence the recrystallization processes, i.e. dynamic (DRX) and static recrystallization (SRX), and leads to distinctive texture changes of samples extruded at different extrusion speeds. In the binary Mg–Zn alloys, the resulting texture after extrusion is the classical basal type texture, where there is an alignment of basal planes along the arc between the <10–10〉> and <11–20> poles. This development is independent of the extrusion speed, as the resulting microstructures are almost completely recrystallized. In the case of the Mg–Zn–Ca, there is a distinctive <10–11> component together with a <11–20> pole, while in the Mg–Zn-Nd alloy the so-called <11–21> rare-earth texture component and the <20–23> pole intensity are observed as DRX dominates the microstructural development. It is found that this distinctive behavior can be changed if partially recrystallized microstructures are subsequently annealed. This leads to an increase of the importance of SRX and a different resulting texture while maintaining a similar grain structure. Both recrystallization processes lead to different mechanical properties, yielding behavior and toughness as a result of the different texture development.

Effect of Ag, In and AgIn Alloying Additions on Microstructure and Texture of Mg-3Al-1Zn Alloy during Multi-Pass Warm Rolling

In the present investigation the rolling response, microstructure and texture evolution of four Mg alloys during multi-pass warm rolling were evaluated. The nominal composition of the base alloy (alloy-1) was Mg-3Al-1Zn. The alloy-2, 3 and 4 were developed by separate additions of non-rare earth elements Ag and In, and a master alloy 85Ag15In (wt.%) to make target compositions Mg-3Al-1Zn-0.5x, (x = Ag ,In, AgIn). Samples from all four alloys were subjected to multi-pass warm rolling at 300 °C to accumulative reductions of 50, 75 and 90% with 8 minutes inter-pass annealing. For all four alloys, crack free sheets of less than 1 mm thickness were produced successfully with true strain corresponding to 90% reduction. The as-cast microstructures revealed second phase particles at grain boundaries and grains interiors for all alloys. A slight scatter in the size of the deformed grains was observed for alloy-1, 2 and 3 after rolling reductions of 50, 75 and 90%. However, a sustained decrease in grain size with increasing the rolling reductions was only observed in alloy-4, despite inter-pass annealing. XRD macro-texture results of alloy-2 and 3 presented very strong basal texture showing almost concentric contours around normal direction (ND). Such strong sheet texture is attributed to a preferential alignment of basal planes parallel to the sheet surface. On the other hand alloy-1 and alloy-4 revealed a weaker texture with basal poles spread more towards transverse direction (TD) as compared to rolling direction (RD) and may be due to the activation of some &lt;c+a&gt; non-basal slip and twinning in addition to basal slip under the same processing parameters.

Shock consolidation of crystallographically aligned Bi2Sr2CaCu2O8 powders

Bulk samples of crystallographically aligned Bi2Sr2CaCu2O8 were fabricated by shock-consolidation of tapped micaceous powders. Basal plane alignment was verified by means of optical microscopy, X-ray diffraction and magnetic measurements. We have explored the dependence of this crystallographic alignment as a function of both shock pressure (from 35 kbar to 135 kbar) and powder particle size (from < 5 μm to 30–37 μm). The degree of crystallographic alignment as determined by SQUID magnetometer measurements and X-ray diffraction measurements was found to be insensitive to the shock consolidation pressure, but sensitive to powder particle size, with a decrease in the powder particle size resulting in a decrease in the amount of crystallographic alignment.