Papers by Keyword: Laser Surface Alloying

Abstract: Rapidly solidified thin micro-alloyed surface layers are generated by laser melting of plasma thermal sprayed steel surfaces. Samples of carbon steel are plasma sprayed with fine nickel and aluminum powders. Laser surface melting generated a thin localized molten pool of metal with steep horizontal thermal gradient. The latter triggered intense vortex formation in the molten pool which thoroughly mixed the nickel and aluminum powders within the molten pool in a fraction of a second. As the sample is moved away with a predefined velocity, the cold substrate quenched the melt pool, generating rapidly solidified micro-alloyed surfaces. A 2.5 kilowatts continuous carbon dioxide laser was used for surface melting; laser power was maintained at 800 watts while the samples were moved with respect to the laser beam at linear velocities in the range of 100-200 mm/min. The technique generated metallurgical bonded novel surfaces. Depth of the laser modified layer was achieved in the range of 0.2-0.4 mm. Refined microstructures of pre-austenite grain size in the range of 4±2 µm were generated. Micro-hardness measurements of the modified layer indicate an almost three times enhancement in the hardness values; the latter are, in general indicative of mechanical strength of the material. The shape of the solid/liquid interface of the advancing molten pool determines the orientation of the growing dendrites; at higher velocities of sample translation with respect to the laser beam, these are almost parallel to the sample surface. The orientation of the dendrites, the uniformity in surface alloying (within fraction of a second) and the resulting hardness values are explained with the help of the modeled shape of the liquid metal pool. The laser processed material proved to be a flexible technique to synthesize novel surfaces for surface sensitive applications.

Abstract: In this paper, the influence of laser surface alloying on the structure and mechanical properties of aluminium alloy was analysed. As a parent material aluminium EN AC-51300 alloy was applied. The laser surface alloying was executed by direct introduction of metallic powder Fe/Cu into the remelted area (molten pool). As a heat flux, the Hight Power Fiber Laser (HPFL) has been used. Metallic powder before the treatment was mixed in a ball mill and dried on the hot plate (90°C temperature). The mechanical and tribological properties of alloyed surface were analysed including hardness (HRF), microhardness (HV_0.1) and ball-on-plate wear test. The structure of the laser alloyed surface was evaluated by light and scanning electron microscopy.

Abstract: This chapter presents a novel method for analysis and optimization of the in-situ formation of TiC-reinforced composite surface layers (TRL) on a ductile cast iron substrate during the laser surface alloying process, combining the experimental approach with the computational thermodynamics. The microstructure of the TRLs has been assessed by light optical microscopy, scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. The results of thermodynamic calculations with the Scheil-Gulliver model showed a good agreement with the experimental results, indicating that the actual solidification path for the analyzed Fe-C-Si-Ti alloy systems under the investigated range of laser processing conditions is close to the Scheil-Gulliver assumption.

Abstract: Metal matrix composite layers were fabricated on AISI 304L substrate by diode laser surface alloying with direct injection of chromium carbide Cr₃C₂ powder into the molten-pool. The influence of laser alloying parameters on the quality of the alloyed layers were investigated. The alloyed layers were examined by optical metallography and scanning electron microscopy. Comparative erosion tests between the AISI 304L substrate and the alloyed layers have been performed following the ASTM G 76 standard test method. The uniform laser beam intensity profile of the laser used ensures to produce fully dense alloying layers with homogenous distribution of Cr₃C₂ particle throughout the matrix alloy. Distribution and dissolution of Cr₃C₂ particles are strongly dependent on the laser power level. The alloyed layers exhited noticeable increased erosion resistance in comparison to AISI 304L substrate for both 30° and 90° impact angles.

Abstract: Local surface alloying of metallic materials by laser is an issue of interest in the scientific world and materials engineering. Laser surface alloying technology allows diffusion of alloying elements which add special features into the surface of a base material with modest properties but a low price. This paper presents the results of experimental research regarding the process of alloying on steel ST37-2 and the effects obtained after laser surface alloying.

Abstract: The spherical casting WC powder is a kind of new potential wear-resistance ceramic material. In this paper, its chemical composition, surface morphology, microstructure, phase, microhardness and some powder characteristics were investigated, and then the powders were applied in laser surface alloying treatment on medium carbon steel. The results indicate that the spherical WC powder consists of (wt.%) 94.06 W, 4.03 C and 1.91 other elements including Fe, V, Cr and Nb. Most of powder particles have regular spherical shape and smooth surface, and the microstructure is acicular eutectic of WC and W₂C, which leads to high microhardness of 2812 HV. The fluidity of powders is 5.97 s/50g, and the apparent density of powders is 10.1 g/cm³. The laser alloyed layer is characterized by dendritic primary phase, ledeburite microstructure and some residual WC particles. The laser surface alloying treatment with adding material of spherical casting WC powder can enhanc the abrasive wear resistance of medium carbon steel by over 200%.

Abstract: The laser surface alloying for metallic materials has been applied widely to improve the wear resistance, corrosion resistance and other required properties. The studies of laser surface alloying on copper-base materials are becoming more and more important. This work using two methods of pretreated coatings, i.e., chemical bonded 50%Cr-50%Cu and pure Cr powders and electroplating chromium coating respectively, on pure copper substrate surface to prepare laser alloyed Cu-Cr alloy coatings was investigated. The samples were treated with different laser scanning speed. Using scanning electron microscopy (SEM), micro-hardness indentor and wear tester, the effects of different coating processing parameters on the microstructure and properties of Cu-Cr coatings were determined and analyzed respectively.

Abstract: Using laser cladding technique, TiC reinforced Ti matrix composite coatings were fabricated by preplacing TiC, (Ti+C), (Ti+TiC) powders respectively on the TA2 pure titanium surface.By means of XRD, SEM and Hv-Test, microstructures and microhardness were investigated. The results show that phases of the coatings are all composed of TiC and α-Ti. Delamination phenomenon appears when laser clad pure TiC coating, which has deleterious effect on properties. TiC phase is in-situ synthesized during laser clad (Ti+C) coating, but microstructure is coarse. Microstructure of (Ti+TiC) coating is the most uniform and dense of the three coatings. The microhardness sequence of the three coatings is (Ti+TiC)>TiC>(Ti+C), and the maximum value is Hv1246, Hv1213 and Hv1135 respectively. The main reason leads to the highest micro-hardness of (Ti+TiC) coating is the Ti powder is beneficial to laser cladding and large amount of TiC reinforcement formed which is compact and uniform.

Abstract: A permanent mould cast creep resistant MRI 230D Mg alloy was laser surface alloyed (LSA) with Al and Al₂O₃ in order to improve its wear and corrosion resistance. However, this treatment was successful only in improving wear resistance but not corrosion resistance due to the presence of micro−cracks in the coated layer, which has been discussed in an earlier paper. The LSA coated Mg alloy has been further subjected to plasma electrolytic oxidation (PEO) treatment in alkaline silicate electrolyte in order to cover those micro−cracks and improve corrosion resistance, which is discussed in the present manuscript. For comparison, the PEO coating has also been applied on the as−cast MRI 230D Mg alloy. The microstructural characterization of coatings and corroded surfaces was carried out by scanning electron microscope and X−ray diffraction. Electrochemical corrosion tests were conducted in 3.5 wt% NaCl solution having neutral pH to investigate the corrosion behavior. The LSA coatings consisted mainly of β (Mg₁₇Al₁₂) phase, the coatings produced by PEO treatment on MRI 230D Mg alloy consisted mainly of Mg₂SiO₄ phase, and hybrid coatings of PEO on LSA consisted of Mg₂SiO₄ and MgAl₂O₄ phases in the PEO layer. Scanning electron micrographs of the cross−section revealed that the PEO treatment covered the micro−cracks present in the LSA and corrosion tests revealed that it improved the corrosion resistance, though not to the extent of the corrosion resistance of the PEO coated MRI 230D Mg alloy. All the samples exhibited localized form of corrosion.

Abstract: To increase the mechanical properties of the metal rollers, Mo and Mo+Y₂O₃ alloy powders were designed. And a kind of coating fabricated by a continuous wave CO₂ laser surface alloying(LSA) on 40Cr steel roller was obtained. The effect of Mo and Mo+Y₂O₃ on microstructure, hardness and wearing resistance of alloying coating were studied by OM, SEM, XRD, microhardness tester and wearing tester. The experimental results indicate that the grain size in alloying coating is obviously fined, and the grain boundary is strengthened. The uniformity and density of microstructure are improved. The microhardness and wear resistance of alloying coating are significantly increased.