Microstructural, Electrical, and Tribomechanical Properties of Mo-W-C Nanocomposite Films.

This study investigates the phase composition, microstructure, and their influence on the properties of Mo-W-C nanocomposite films deposited by dual-source magnetron sputtering. The synthesised films consist of metal carbide nanograins embedded in an amorphous carbon matrix. It has been found that nanograins are composed of the hexagonal ß-(Mo2 + W2)C phase at a low carbon source power. An increase in the power results in the change in the structure of the carbide nanoparticles from a single-phase to a mixture of the ß-(Mo2 + W2)C and NaCl-type α-(Mo + W)C(0.65≤k≤1) solid-solution phases. The analysis of electrical properties demonstrates that the nanograin structure of the films favours the occurrence of hopping conductivity. The double-phase structure leads to a twofold increase in the relaxation time compared to the single-phase one. Films with both types of nanograin structures exhibit tunnelling conductance without the need for thermal activation. The average distance between the potential wells produced by the carbide nanograins in nanocomposite films is approximately 3.4 ± 0.2 nm. A study of tribomechanical properties showed that Mo-W-C films composed of a mixture of the ß-(Mo2 + W2)C and α-(Mo + W)C(0.65≤k≤1) phases have the highest hardness (19-22 GPa) and the lowest friction coefficient (0.15-0.24) and wear volume (0.00302-0.00381 mm2). Such a combination of electrical and tribomechanical properties demonstrates the suitability of Mo-W-C nanocomposite films for various micromechanical devices and power electronics.

Effect of 160 MeV Xenon Ion Irradiation on the Tribological Properties and Crystal Structure of 100Cr6 Bearing Steel.

This is the first study ever to show the impact of high-energy 160 MeV xenon ion irradiation on the properties of 100Cr6 bearing steel. The projected range (Rp) of xenon ions is 8.2 µm. Fluence-dependent variations in the coefficient of friction and wear of the 100Cr6 steel material have been observed. These changes correlate with shifts in the crystal lattice constant and variations in the oxygen, carbon, and iron content in the wear track. Fluence-dependent changes in these parameters have been observed for the first time. Irradiation reduces stresses in the crystal lattice, leading to crystallite size increase. The modifications in the properties of 100Cr6 steel result from radiation-induced defects caused by electronic ion stopping. The degree of these modifications depends on the applied irradiation fluence. Furthermore, the use of a higher irradiation fluence value appears to mitigate the effects produced by a lower fluence.

Effect of Nitrogen Ion Implantation on the Cavitation Erosion Resistance and Cobalt-Based Solid Solution Phase Transformations of HIPed Stellite 6.

From the wide range of engineering materials traditional Stellite 6 (cobalt alloy) exhibits excellent resistance to cavitation erosion (CE). Nonetheless, the influence of ion implantation of cobalt alloys on the CE behaviour has not been completely clarified by the literature. Thus, this work investigates the effect of nitrogen ion implantation (NII) of HIPed Stellite 6 on the improvement of resistance to CE. Finally, the cobalt-rich matrix phase transformations due to both NII and cavitation load were studied. The CE resistance of stellites ion-implanted by 120 keV N+ ions two fluences: 5 × 1016 cm-2 and 1 × 1017 cm-2 were comparatively analysed with the unimplanted stellite and AISI 304 stainless steel. CE tests were conducted according to ASTM G32 with stationary specimen method. Erosion rate curves and mean depth of erosion confirm that the nitrogen-implanted HIPed Stellite 6 two times exceeds the resistance to CE than unimplanted stellite, and has almost ten times higher CE reference than stainless steel. The X-ray diffraction (XRD) confirms that NII of HIPed Stellite 6 favours transformation of the ε(hcp) to γ(fcc) structure. Unimplanted stellite ε-rich matrix is less prone to plastic deformation than γ and consequently, increase of γ phase effectively holds carbides in cobalt matrix and prevents Cr7C3 debonding. This phenomenon elongates three times the CE incubation stage, slows erosion rate and mitigates the material loss. Metastable γ structure formed by ion implantation consumes the cavitation load for work-hardening and γ → ε martensitic transformation. In further CE stages, phases transform as for unimplanted alloy namely, the cavitation-inducted recovery process, removal of strain, dislocations resulting in increase of γ phase. The CE mechanism was investigated using a surface profilometer, atomic force microscopy, SEM-EDS and XRD. HIPed Stellite 6 wear behaviour relies on the plastic deformation of cobalt matrix, starting at Cr7C3/matrix interfaces. Once the Cr7C3 particles lose from the matrix restrain, they debond from matrix and are removed from the material. Carbides detachment creates cavitation pits which initiate cracks propagation through cobalt matrix, that leads to loss of matrix phase and as a result the CE proceeds with a detachment of massive chunk of materials.

Application of the TDR Soil Moisture Sensor for Terramechanical Research.

This paper presents examples of the application of the TDR (Time-Domain Reflectometry) sensor in terramechanical research. Examples include the determination of soil moisture content during off-road vehicle mobility tests, the determination of snow density before and after the wheeling of a snow grooming machine and an airplane, as well as the monitoring of turf moisture on a grassy airfield for the analysis and prediction of safe and efficient flight operations (takeoff and landing). A handheld TDR meter was used in these experiments. Soil moisture data were correlated with the vehicle mobility index and a simple model for this correlation was derived. Using grassy airfield research, soil moisture data were related to meteorological impacts (precipitation, sunlight, etc.). Generally, it was concluded that the TDR meter, in its handheld version, was a useful tool in the performed research, but a field sensor that operates autonomically would be an optimal solution for the subject applications.