Laser cladding technology enables the regeneration or manufacturing of machine parts with the improved surface layer properties. The materials applied during the laser cladding processes very often ...contain hard and wear-resistant tungsten carbide (WC) particles. However, the parts obtained after the laser cladding have usually unsatisfactory surface quality and thus require post-process finishing. In addition, the content of WC particles causes that clad layers are difficult to cut. Therefore, in order to improve their machinability, the laser-assisted machining (LAM) technology can be applied. Nevertheless, the material removal mechanisms during LAM of WC/NiCr clad layers are not recognized. Thus, this study is focused on the estimation of minimum uncut chip thickness and analysis of cutting forces which are important factors describing the chip decohesion process. The proposed method is based on the novel approach dedicated directly to the oblique cutting, considering the zeroth tangential force increment located onto rounded cutting edge. The experimental procedure involves cutting force component (
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) measurements in the range of variable cutting conditions, as well as the cutting tool’s micro-geometry inspection. On the basis of the measurements carried out, the force regression equations are formulated and subsequently applied to the determination of tangential force expression. Subsequently, the minimum uncut chip thickness is calculated on the basis of the equation derived from the zero tangential force increment condition and presented in function of cutting speed. The obtained results enable the effective selection of the cutting parameters during LAM of WC/NiCr clad layers.
This paper presents the study on the formation of surface layer in A359/20SiCP metal matrix composite (MMC) during laser assisted turning, with the consideration of SiC particles’ sedimentation in a ...liquid matrix. The developed model includes the effect of gravity, buoyancy, resistive force of liquid matrix and centrifugal force of the rotating work material. On the basis of the proposed approach the instantaneous sedimentation speed, as well as the depth of sedimented SiC particles are calculated. Consequently, the applied model enables the selection of the effective depth of cut and tool’s angular distance from the laser beam, which can improve the machined surface quality and composite’s exploitation properties. The experiments confirm that sedimentation phenomenon plays an important role during the surface layer formation in laser heating conditions. Furthermore, the laser assisted turning with the selection of the recommended cutting conditions affects the improvement of surface quality, and composite’s wear resistance.
Nitriding, as one of the most widely used surface treatment, was often applied in order to improve the hardness, fatigue strength as well as wear and corrosion resistance of steels. The controlled ...gas nitriding resulted in a formation of a compound zone ε+(ε+γ′) of limited thickness close to the surface and the diffusion zone below it. It was easy to identify the two separate zones in the microstructure: more porous zone with only ε-Fe3N iron nitrides and zone with ε+γ′ iron nitrides' mixture (Fe3N + Fe4N). In this study, the laser modification without re-melting was carried out after the controlled gas nitriding in order to change microstructure. The nanomechanical properties of the zones with iron nitrides, observed in the compound zone, were examined using the nanoindenter with a Berkovich diamond tip. Young's modulus and hardness were measured and compared to the literature data. The load-displacement curves and the indentation images were shown for the selected measurements. The advantageous influence of laser heat treatment on the Young's modulus and hardness was confirmed for the outer ε zone as well as for the laser quenched diffusion zone. The higher average values of indentation modulus and hardness characterized ε iron nitrides (EIT = 165.72 ± 18.67 GPa and HIT = 9.90 ± 0.47 GPa) and laser quenched diffusion zone (EIT = 199.06 ± 28.80 GPa and HIT = 7.11 ± 0.61 GPa) after laser heat treatment. The diminished porosity of ε zone and the presence of martensite in the diffusion zone were the reason for such a situation. The laser heat treatment almost didn't influence the indentation modulus of zone with ε+γ′ iron nitrides' mixture (EIT = 175.27 ± 4.81 GPa), whereas its hardness was slightly increased (HIT = 11.87 ± 0.43 GPa). The conclusion regarding the percentage of the separate phases (ε and γ′) in this zone was ambiguous.
•Controlled gas nitriding provided the surface layer with iron nitrides close to the surface.•The two zones of iron nitrides were easy to identify: ε-Fe3N and ε+γ' (Fe3N + Fe4N).•After laser heat treatment, ε zone was characterized by a diminished porosity.•Nanoindenter was used for determining the Young's moduli and hardness of nitrides.•Laser heat treatment improved the nanomechanical properties of ε iron nitrides.
Laser surface alloying with boron and carbon was applied to produce the composite layers, reinforced by the hard ceramic phases (titanium borides and titanium carbides), on commercially pure ...titanium. The external cylindrical surface of substrate material was coated by paste containing boron, boron and graphite, or graphite. Then, the laser re-melting was carried out with using the continuous-wave CO2 laser. This enabled the formation of laser-borided, laser-borocarburized, and laser-carburized layers. The microstructure or the re-melted zone consisted of the hard ceramic phases (TiB+TiB2, TiB+TiB2+TiC, or TiC) located in the eutectic mixture of Tiα'-phase with borides, borides and carbides, or carbides, respectively. All the composite layers were characterized by the sufficient cohesion. The significant increase in microhardness and in wear resistance of all the laser-alloyed layers was observed in comparison with commercially pure titanium. The percentage of hard ceramic phases in more plastic eutectic mixture influenced the measured microhardness values. The dominant wear mechanism (abrasive or adhesive) depended on the method of laser alloying, and the type of test used. The wear tests for longer duration, without the change in the counter specimen, created the favourable conditions for adhesive wear, while during the shorter tests the abrasive wear dominated, as a rule.
•Laser surface alloying with boron and carbon was proposed to formation of composite layers on pure titanium.•The microstructure of laser-alloyed layer consisted of hard ceramic phases and eutectic mixture.•The increased hardness and wear resistance of composite layers were obtained.•The wear tests of the layers showed the catastrophic wear of the counter-samples.•The dominant wear mechanism (abrasive or adhesive) depended on the method of laser alloying and on test duration.
Metal matrix composites and Si3N4 ceramics are very attractive materials for various industry applications due to extremely high hardness and abrasive wear resistance. However because of these ...features they are problematic for the conventional turning process. The machining on a classic lathe still requires special polycrystalline diamond (PCD) or cubic boron nitride (CBN) cutting inserts which are very expensive. In the paper an experimental surface roughness analysis of laser assisted machining (LAM) for two tapes of hard-to-cut materials was presented. In LAM, the surface of work piece is heated directly by a laser beam in order to facilitate, the decohesion of material. Surface analysis concentrates on the influence of laser assisted machining on the surface quality of the silicon nitride ceramic Si3N4 and metal matrix composite (MMC). The effect of the laser assisted machining was compared to the conventional machining. The machining parameters influence on surface roughness parameters was also investigated. The 3D surface topographies were measured using optical surface profiler. The analysis of power spectrum density (PSD) roughness profile were analyzed.
Laser boriding, instead of diffusion boriding, was proposed to formation of gradient borocarburized layers. The microstructure and properties of these layers were compared to those-obtained after ...typical diffusion borocarburizing. First method of treatment consists in diffusion carburizing and laser boriding only. In microstructure three zones are present: laser borided zone, hardened carburized zone and carburized layer without heat treatment. However, the violent decrease in the microhardness was observed below the laser borided zone. Additionally, these layers were characterized by a changeable value of mass wear intensity factor thus by a changeable abrasive wear resistance. Although at the beginning of friction the very low values of mass wear intensity factor Imw were obtained, these values increased during the next stages of friction. It can be caused by the fluctuations in the microhardness of the hardened carburized zone (HAZ). The use of through hardening after carburizing and laser boriding eliminated these fluctuations. Two zones characterized the microstructure of this layer: laser borided zone and hardened carburized zone. Mass wear intensity factor obtained a constant value for this layer and was comparable to that-obtained in case of diffusion borocarburizing and through hardening. Therefore, the diffusion boriding could be replaced by the laser boriding, when the high abrasive wear resistance is required. However, the possibilities of application of laser boriding instead of diffusion process were limited. In case of elements, which needed high fatigue strength, the substitution of diffusion boriding by laser boriding was not advisable. The surface cracks formed during laser re-melting were the reason for relatively quickly first fatigue crack. The preheating of the laser treated surface before laser beam action would prevent the surface cracks and cause the improved fatigue strength. Although the cohesion of laser borided carburized layer was sufficient, the diffusion borocarburized layer showed a better cohesion.
•Laser boriding, instead of diffusion boriding, was proposed to produce the gradient borocarburized layers.•Microstructure consisted of: laser-borided zone, hardened carburized zone and carburized layer without heat treatment.•Eutectic mixture of iron borides and martensite was identified in the laser-borided zone.•Abrasive wear resistance was comparable to that-obtained in case of diffusion borocarburizing.•The surface cracks formed during laser re-melting were the reason for relatively quickly first fatigue crack.
The paper presents the study results of laser modification of Vanadis-6 steel after diffusion boronized. The influence of laser beam fluence on selected properties was investigated. Diffusion ...boronizing lead to formation the FeB and Fe2B iron borides. After laser modification the layers were consisted of: remelted zone, heat affected zone and substrate. It was found that increase of laser beam fluence have influence on increase in dimensions of laser tracks. In the thicker remelting zone, the primary dendrites and boron eutectics were detected. In the thinner remelting zone the primary carbo-borides and eutectics were observed. In obtained layers the FeB, Fe2B, Fe3B0.7C0.3 and Cr2B phases were detected. Laser remelting process caused obtained the mild microhardness gradient from the surface to the substrate. In the remelted zone was in the range from 1800 HV0.1 to 1000 HV0.1. It was found that the laser beam fluence equal to 12.7 J/mm2 was most favorable. Using this value, microhardness was relatively high and homogeneous.
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