Nanostructured surfaces

Formation of ultrafine structure of the surface layer of Fe-Si alloy as a result of pulsed laser treatment
V. Danilchenko1, I. Dzevin1
G.V. Kurdyumov Institute for Metal Physics NAS of Ukraine
Vernadsky blvd., 36, Kyiv-03680, Ukraine
E-mail: dzevin@i.ua

	X-ray and microstructure methods showed that pulsed laser heating of a Fe-Si alloy (2.8 wt.% Si, 0.05 wt.% Mn, 0.05 wt.% C) in a melting mode resulted in recrystallization of the α-phase with the formation of ultrafine (0.1 – 2.5 μm) and nanoscale (0.1 – 0.08 μm) grain structure with a crystalline b.c.c. lattice parameter corresponding to the initial value.
	Based on experimental data of the structural state of the surface layer it was estimated by calculation the yield strength (0.2). For a single-phase system 0.2 of a melted layer, it can be represented as the sum of the yield strength 10,2, which depends on the microstructure refinement, and the yield strength σ20,2, which depends on the dislocation density. It was turned out the value 10.2 increased by 1.5 times, compared with the initial state due to the microstructure refinement.
	Taking into account the calculated dislocation density, the value of 20,2 exceeds the initial value in 1,5 – 2,0 times. As a result of laser melting, the value of the yield strength 0,2 varied within 480 – 660 MPa over the depth of the layer. Contribution of the factor of increasing of the dislocation density was stronger than the microstructure refinement one. Thus, after the laser melting, the total value of the yield strength of melted layer more than three times exceeds the initial value. At the depth of the melted layer, the yield strength and microhardness changed in a not monotonous curve in accordance with the change of the dislocation density.