Formation of superdense hadronic matter in high energy heavy-ion collisions

We present the detail of a newly developed relativistic transport model (ART 1.0) for high energy heavy-ion collisions. Using this model, we first study the general collision dynamics between heavy ions at the AGS energies. We then show that in central collisions there exists a large volume of sufficiently long-lived superdense hadronic matter whose local baryon and energy densities exceed the critical densities for the hadronic matter to quark-gluon plasma transition. The size and lifetime of this matter are found to depend strongly on the equation of state. We also investigate the degree and time scale of thermalization as well as the radial flow during the expansion of the superdense hadronic matter. The flow velocity profile and the temperature of the hadronic matter at freeze-out are extracted. The transverse momentum and rapidity distributions of protons, pions and kaons calculated with and without the mean field are compared with each other and also with the preliminary data from the E866/E802 collaboration to search for experimental observables that are sensitive to the equation of state. It is found that these inclusive, single particle observables depend weakly on the equation of state. The difference between results obtained with and without the nuclear mean field is only about 20\%. The baryon transverse collective flow in the reaction plane is also analyzed. It is shown that both the flow parameter and the strength of the ``bounce-off'' effect are very sensitive to the equation of state. In particular, a soft equation of state with a compressibility of 200 MeV results in an increase of the flow parameter by a factor of 2.5 compared to the cascade case without the mean field. This large effect makes it possible to distinguish the predictions from different theoretical models and to detect the signaturesComment: 55 pages, latex, + 39 figures available upon reques

Rapid solidification induced low lattice misfit and associated enhancement of mechanical property in the NiCoCr medium entropy alloy

Medium entropy alloys (MEAs) have a high potential in industrial applications due to their excellent mechanical properties. Here we report a strategy to improve the ductility of the Ni40Co30Cr20Al5Ti5 MEAs by rapid solidification (RS). The as-cast alloy is composed of dendritic structure and L12 nano-precipitates. After RS, the lattice misfit of precipitate and matrix is reduced from 0.251 % to 0.167 %, and the size of the precipitate decreases from 85 nm to 28 nm. Meanwhile, RS also reduces the grain size of matrix. Gliding dislocation can cut through precipitates with low lattice misfit and smaller size, which can avoid strain accumulation and prevent crack initiation at the precipitate-matrix interfaces. Compared with the as-cast alloy, the ductility of the RS alloy is increased by 17 %–42 % without a decrease in strength. Our results can provide a guidance for other experiments using the RS technology (laser cladding, magnetron sputtering, etc.) to achieve the strength-ductility balance in the MEAs