[SY-C7] Symposium C-7

[SY-C7] Understanding the grain refinement mechanism in surface mechanical attrition treatment of Fe14Ni18Cr by molecular dynamics simulations

^○Ali Rida¹, Matthieu Micoulaut², Emmanuelle Rouhaud¹, Ali Makke^1,3 (1.University of Technology of Troyes , France, 2.Sorbonne Université, France, 3.EPF, Engineering school, France)

In surface mechanical attrition treatment the surface of a treated material is submitted to a severe local plastic deformation. This deformation results from the random impacts of spherical shots with high velocity on the surface of the specimen. Therefore, a nanocrystalline layer is generated on the surface. The thickness of this layer can reach a depth of 50 micrometers. The grain refinement mechanisms that lead to the formation of the nanocrystalline layer are still not well understood. In this work, molecular dynamics simulation has been employed to simulate the compression of a single crystal Fe14Ni18Cr at strain rate of 5.10⁹ s^-1 in order to analyze its main plastic deformation mechanisms. Therefore, the relationship between the impacts of the shots and the refinement mechanisms in a grain has been investigated. A combination of dislocation slips and mechanical twinning have been found to be the main refinement mechanisms. High density of dislocations and twins nucleation are observed on the surface. Moreover, the large density of generated twin boundaries modify the monocrystal into lamellar twin-matrix blocks with a nanometer sized thickness. Finally, twin-twin and twin-dislocation interactions lead to the transformation of the twin-matrix blocks to small grains.