290 Prakt. Met. Sonderband 38 (2006) 
The laser treatment is a part of the new generation techniques applied in metal surface ; 
technology and represents the especially promising tool for solving the contemporary 
surface engineering problems thanks to the physical properties of the laser beam, making The 
it possible to focus precisely the delivered energy in the form of heat on the surface layer. X4 
There is an opinion that laser manufacturing techniques belong to the most promising and bar 
efficient ones, for ensuring the development in many industry branches, and especially Sal 
those in which materials processing dominates. Forecasts pertaining to the global din 
economic development factors regard laser manufacturing techniques as the most pre 
promising and efficient ones for ensuring the development in many industry branches in 
which materials processing dominates. It is considered that in future only these economies Tat 
will be competitive in the global market in which laser technologies will be widely used [3]. Ch 
Moreover, methods, which are not based on partial melting of the surface alone, but on - 
partial melting with the simultaneous introduction of the alloying elements with high 
hardness, like carbides, are being employed more and more widely for modification of the 
surface layer. High cooling rates are obtained in this process and its end result is the fine - 
grained material with the super — cooled phases. Material transport in the liquid metal, 
caused by the surface tension forces, features the main factor deciding the development of 
the alloyed layers. The non — uniform material heating resulting from the laser beam 
impact causes development of a big surface tension gradient on the surface of the liquid. 
The force is directed outside from the beam centre, where is the highest temperature value 
to its edge and causes movement of the molten material [4-6]. - 
Diode lasers have been known for many years and used mainly in electronic devices and 
metrology. The dynamical development of materials engineering allowed for the The 
introduction of industrial HPDL lasers. Diode lasers produced nowadays achieve power up of | 
to 6 kW on the surface of the laser beam focusing. Diode lasers of ROFIN DL type are ihe 
characterized by a rectangular or linear shape of beam focus having multi — mode energy ol 
distribution. A HPDL laser is suitable for modification of a material surface layer. It is ten 
confirmed by an empirically proved high energy absorption coefficient for steels, high ane 
efficiency and the possibility of the precious control of the amount of energy delivered to a to! 
material surface layer. The condition of the surface layer of the processed material and Va 
especially its roughness and absorption coefficient are the most important factors in the dur 
process of laser treatment of materials. Currently the HPDL high power diode lasers the 
feature the up-to-date energy source. They are used in the industry scale in materials hot 
engineering only from 1998. They have the controlled energy distribution in the focus SPE 
area with power density of up to 10° W/cm? they have the high coefficient of radiation whi 
absorption, do not require guiding the laser beam by any complex optical systems was 
causing energy loss in the range of 10-30%, they hale the high energetic efficiency the 
reaching 50%. Robotisation of the technological processes is easy, they are reliable mr 
and all-purpose, which makes them very attractive tools in materials engineering [7,8]. Tat 
The main method of improving the abrasive wear resistance of tools made from alloy steel las 
is usually their heat treatment consisting in quenching and tempering, which causes the wit! 
significant hardness increase and deterioration of the plasticity of these steels connected ma 
with it. Laser alloying is used to prevent it and to improve simultaneously the technological car 
properties of the surface layer of the tool steel, and to extend thus the service life of tools. kW 
Laser surface alloying is the state-of-the-art thermo-chemical treatment process, 
consisting in enrichment of the surface layers of materials with the alloying elements and Tal 
change of their structure. Because of the laser alloying, the hot work alloy tool steels, P 
attain the surface layer of a small thickness and specific properties, i.e.: high abrasion 
wear-, erosion-, and corrosion resistance, resistant to the aggressive chemical agents 
attack, with the high hardness and simultaneously high fatigue strength and high heat 
resistance [9,10].