NR 3/2017 INŻYNIERIA MATERIAŁOWA MATERIALS ENGINEERING 137 Microstructure and selected properties of Fe–B coatings reinforced with B 4 C and Si particles produced by laser cladding using Yb:YAG disk laser Dariusz Bartkowski 1* , Aneta Bartkowska 2 , Adam Piasecki 2 , Waldemar Matysiak 1 1 Institute of Materials Technology, Poznan University of Technology, Poznan, Poland, 2 Institute of Materials Science and Engineering, Poznan University of Technology, Poznan, Poland, * dariusz.bartkowski@put.poznan.pl The paper presents the study results of Fe–B coatings produced on C45 steel using laser cladding with powder technology. For this purpose, 5-axis CNC laser machining center equipped with Yb:YAG disk laser with a power rating of 1 kW and three streams powder feeding system. The powder that was used to produce Fe–B coatings was subsequently modified by the particles of boron carbide B 4 C and Si particles. The resulting powder mixture to the particles included 25 wt % respectively 20% B 4 C, 5% Si. During these studies a laser beam power of 600 W and variable scanning speed 600 mm/min, 800 mm/min and 1000 mm/min were used. Thickness and microhardness of coatings were investigated and relationship between these properties and microstructure of the applied production parameters were described. The microstructure of producing coatings was characterized by dendritic shape. It was found that boron carbide particles and silicon particles have significant influence on increase the microhardness of produced coatings. Coatings were produced using the prepared powder mixture allowed to obtain more than twice greater microhardness than in case of coatings produced using only the Fe–B powder. Phase composition was examined by XRD. Phases of Fe 3 B, Fe 5 Si 3 , Fe 2 Si and SiB 6 were identified. The influence of B 4 C and Si particles in the mixture of powder on the corrosion resistance of produced coatings were discussed. It was found gradual reduction of corrosion resistance with decreasing scanning speed of laser beam. Less scanning speed result in less intense interaction of laser beam on the material. As a result of this, the remelting degree of powder material with steel substrate was smaller. The surface condition after corrosion tests were examined using a scanning electron microscope. This paper also shows a calculation related to the power density of the laser beam, interaction time of beam on material and fluence. Key words: laser cladding, Fe–B coatings, boron carbide B 4 C, microstructure, corrosion resistance. Inżynieria Materiałowa 3 (217) (2017) 137÷142 DOI 10.15199/28.2017.3.5 © Copyright SIGMA-NOT MATERIALS ENGINEERING 1. INTRODUCTION There are many methods of surface engineering used to improve the surface layers properties of machine parts [1÷6]. In recent time, there is a great interest of coatings production by the high energy methods [1÷14]. In whole world, the laser cladding with powder is increasingly applied [15÷32]. Laser cladding is a process during which the powder is deposited on substrate material, and this two kind of materials are fused by metallurgical bonding through the action of a laser beam. Laser cladding is widely used as one of the surface modification techniques. The main fields of application is primarily the aircraft industries and automotive. This method re- quires the laser device equipped to remelting powder with substrate and some kind of powder feeding system. The idea of method is to produce coating with good bonding to substrate and obtain mini- mal thickness of heat affected zone. An important advantage of this method is ability to produce coating characterized by individual chemical composition. Laser cladding can be used to produce wear and corrosion resistant coatings. In the paper [16] the authors found that laser cladding of Ni–WC composites with a high weight fraction of WC is disadvantageous because the coating demonstrated cracking susceptibility, non-ho- mogeneity of coating, and WC particle dissolution. Laser cladding of Ni–60% WC using a high-power diode laser was investigated. The effects of synthesizing a nano-WC powder and rare-earth ele- ment (RE) on the quality of Ni–WC coatings were investigated. In the same paper the heating effect by induction heater on the qual- ity of laser cladded coating was analysed. It was observed that la- ser cladding assisted with an induction heater caused smooth and homogeneous composite coatings without cracks or porosity. The authors found that the addition of nano-WC particles and La 2 O 3 en- hanced the coating homogeneity. The average coating microhard- ness was improved to 1400 HV by adding nano-WC particles (5%) and to 1200 HV by adding La 2 O 3 (1%) [16]. In the paper [17] the influence of FeCrBSi alloy powder with higher Cr content by using laser cladding by means of a 3 kW solid- state laser on microstructure and microhardness was analysed. Ni- and Fe-based alloy powders, which were more resistant to cracking, were added into FeCrBSi alloy powder with higher Cr content to in- crease the ductile phases, lower thermal expansion coefficient, and reduce the crack sensitivity of the cladding layer. The hard phases of the cladding layer were composed of carbide phase M 23 C 6 , and the ductile phases which played a lubrication function in the clad- ding layer and were composed of austenite γ-Fe and γ-Ni. The av- erage microhardness of the cladding layers varied from 760 HV0.2 to 950 HV0.2. In paper [18] a Fe-based composite coating reinforced by in situ synthesized TiC particles was produced on Cr12MoV steel by using 6 kW fiber laser cladding. After laser cladding the α-Fe, TiC and Fe 3 C phases in the cladded layer were detected. TiC particles com- monly precipitated in three kinds of morphologies, such as quad- rangle, cluster, and flower-like shape. From the surface of cladding layer to the substrate the microhardness is up to 930 HV0.5, obvi- ously higher than that of the substrate. The high hardness of cladded layer is ascribed to the presence of TiC reinforcements, martensitic transformation and fine grain structure from rapid melting and cool- ing. There is a clear lack of papers about production technology of laser cladding the Fe–B coating reinforced by carbide particles. In this paper the laser cladding using mixture powders with FeB, B 4 C and Si is presented. The microstructure, microhardness and corrosion resistance of surface layer produced on C45 steel using these mixed powders were analysed. 2. RESEARCH METHODS C45 steel of chemical composition presented in Table 1 was inves- tigated. The specimens of about 60 mm length, 12 mm width and height of 4 mm were used.