Physico-Chemical nanomaterials science
Structural transformations and surface hardening of       Cu-Cr alloys in the result of impulse laser alloying
Filatov O.V., Pogorelov A.E., Pavliuk Y.O., Pavliuk D.V.
Department of physics for atomic transport processes, G. V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine. 
36 Academician Vernadsky Boulevard, Kyiv-03142, Ukraine. 
E-mail: pavliuk.kpi@gmail.com

Use of the Cu-Cr alloys has attracted extensive attention in Consumer, Industrial and Electrical Industry owing to their high electrical conductivity, hardness, and ductility. The performance characteristics of products made from Cu-Cr alloys can be significantly improved by additional alloying of their working surfaces without changing the composition of the total volume. The possibility of forcibly alloying metals with elements that do not have mutual solubility with the base material has been demonstrated previously by the example of solid-state laser alloying of Al with Cr [1].
Cr was deposited on the sample surfaces (which are supplied after machining) by vacuum electron-beam method. The surfaces of samples with Cr coating with thickness about 1 µm were irradiated by impulse solid-state laser TruePulse 124 with a wavelength 1064 nm. The same laser processing parameters were provided for both experiments (without and with additional cooling) with the aim of correct comparison of the results. The power density of laser irradiation                   Qi = 108-109 W/m2 was chosen to obtain a surface melting without significant evaporation taking into account the reflectivity of the chromium coating, the thermal characteristics of the matrix and the duration of the laser impulse. 
In the result of microstructural study such types of structural were observed (beginning from the surface): a fine-grained layer with thickness up to 6 μm; a layer with elongated columnar crystals with 130 μm thickness formed from the melt; a fine-grained layer with a grain size of about 10 μm with increased hardness (up to 300 HV). It was found that using of additional cooling increases the thickness of the quenched fine-grained layer up to 1,5 times. A local saturation of the alloy surface layer (2 ÷ 2.5 µm) by Cr in higher concentration compared to the equilibrium diagram accompanies the described structural transformations. The X-ray diffraction studies of these surface areas and their increased microhardness have allowed to assume the formation of a supersaturated Cr solution in the alloy.

1.	Kashkarov M., Filatov O. and Pogorelov O. Laser Solid - Phase Alloyage of Aluminium with Chromium // Metallofiz. Noveishie Tekhnol.-2017.- 39. No. 1: P. 83-91. DOI: 10.15407/mfint.39.01.0083.