SearcharxivSearch

arXiv subjects

Cameron L. Tracy

Publications and source records attributed to Cameron L. Tracy.

2 recordsLinked to original sources

Hypersonic Weapons-Part 1: Background and Vulnerability to Missile Defenses

Assessing the desirability of hypersonic glide vehicles (HGVs) requires understanding what capabilities they may provide compared to alternative systems that could carry out the same missions, particularly given the technical difficulties and additional costs of developing hypersonic gliders compared to more established technologies. Part 1 of this paper considers the primary motivations given for developing HGVs and summarizes the current development programs of the United States, Russia, and China. It then analyzes the vulnerability of hypersonic boost-glide vehicles (BGVs) to missile defenses and finds that evading the most capable current endo-atmospheric defenses requires that BGVs maintain speeds significantly higher than Mach 5 throughout their glide phase. Achieving these high speeds has important implications for the mass and range of these weapons, which in turn affect what delivery vehicles can carry them and how their performance compares to other means of delivery, as is discussed in Part 2.

physics.soc-ph

High pressure synthesis of a hexagonal close-packed phase of the high-entropy alloy CrMnFeCoNi

High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transition metal high-entropy alloys exhibiting only face- or body-centered cubic structures. Here, we report the high-pressure synthesis of a hexagonal close-packed phase of the prototypical high-entropy alloy CrMnFeCoNi. This martensitic transformation begins at 14 GPa and is attributed to suppression of the local magnetic moments, destabilizing the initial fcc structure. Similar to fcc-to-hcp transformations in Al and the noble gases, the transformation is sluggish, occurring over a range of >40 GPa. However, the behaviour of CrMnFeCoNi is unique in that the hcp phase is retained following decompression to ambient pressure, yielding metastable fcc-hcp mixtures. This demonstrates a means of tuning the structures and properties of high-entropy alloys in a manner not achievable by conventional processing techniques.

cond-mat.mtrl-sci