MSc. Prashant Dwivedi, Ph.D.

High-entropy coatings (HECs) are of a great interest for the protection of structural steels and alloys used in the costal and offshore areas. Here, thick, dense, and uniform Fe-Cr-Ni-Co-(Cu) coatings with a crack-free surface have been successfully deposited on AISI 420S steel by vacuum electro-spark deposition using CrNiCo and CrNiCoCu electrodes. The coatings consist of columnar grains (approximately 300 nm in diameter) and subgrains (10–50 nm thick) of an fcc phase and spherical inclusions of mixed SiO2 + (Cr,Ti)2O3 oxide, 30–50 nm in size. Although Cu is an element prone to segregation, the experimental results show that Cu does not form its own phase and is in the metal solid solution. Molecular dynamics simulation shows that Cu has a slight tendency to self-clustering and form Cu-rich clusters in FeCrNiCo-Cu HECs. However, several regions enriched in Cu are observed in the FeCrNiCo-Cu samples. FeCrNiCo coatings tested in artificial seawater and the Black Sea exhibited enhanced corrosion resistance. In tribocorrosion tests, FeCrNiCo-(Cu) coatings performed better than steel substrate due to faster recovery of a passive film. The addition of Cu has a positive effect on the antibacterial activity of FeCrNiCo coatings against Gram-positive B. cereus Arc30 and B. cereus F strains.

The atomistic mechanisms of damage initiation during high velocity (v up to 9 km s(-1), kinetic energies up to 200 keV) impacts of W projectiles on a W surface have been investigated using parallel molecular-dynamics simulations involving large samples (up to 40 million atoms). Various aspects of the high velocity impacts, where the projectile and part of the target material undergo massive plastic deformation, breakup, melting, and vaporization, are analyzed. Different stages of the penetration process have been identified through a detailed examination of implantation, crater size and volume, sputtered atoms, and dislocations created by the impacts. The crater volume increases linearly with the kinetic energy for a given impactor; and the total dislocation length (TDL) increases with the kinetic energy but depends on the size of the impactor. We found that the TDL does not depend on the used interatomic potential. The results are rationalized based on the physical properties of bcc W.

In recent years, computer simulations have played a fundamental role in unveiling some of the most intriguing features of prime numbers. In this paper, we define an algorithm for a deterministic walk through a two-dimensional grid, which we refer to as a prime walk. The walk is constructed from a sequence of steps dictated by and dependent on the sequence of the last digits of the primes. Despite the apparent randomness of this generating sequence, the resulting structure-in both two and three dimensions-created by the algorithm presents remarkable properties and regularities in its pattern, which we proceed to analyze in detail.