Increasing Laser Scanning Speed Research Articles

Electrochemical behaviour of laser-clad Ti6Al4V with CP Ti in 0.1 M oxalic acid solution

The relationship between the microstructure and corrosion behaviour of Ti6Al4V alloy and laser-clad commercially pure (CP) Ti coating was investigated. The microstructure, phases and properties of the clad layers were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Electrochemical measurement techniques including open circuit potential (OCP) and potentiodynamic polarisation were used to evaluate the corrosion behaviour of Ti6Al4V alloy in 0.1 M oxalic acid solution and the results compared to the behaviour of laser-clad CP Ti at varying laser scan speed. Results showed that laser-clad CP Ti at scan speed of 0.4 m/min formed a good cladding layer without defects such as cracks and pores. The phase present in the cladding layer was mostly α′-Ti. The microstructures of the clad layer were needle like acicular/widmanstätten α. An improvement in the microhardness values was also recorded. Although the corrosion potentials of the laser-clad samples were less noble than Ti6Al4V alloy, the polarisation measurement showed that the anodic current density was lower and also increases with increasing laser scanning speed.

S0440101 酸化銅ナノ粒子のレーザ直接還元を利用した銅細線パターニング([S044]次世代3Dプリンティング,機械材料・材料加工部門)

CuO nanoparticles were directly reduced to form fine Cu micropatterns using femtosecond laser pulses. CuO nanoparticles were dispersed into reductant agent and base-polymers. When the focused laser pulses were irradiated into the CuO nanoparticle based films on glass substrates, the Cu micropatterns were formed by reducing and sintering of CuO nanoparticles. XRD spectrum of the laser irradiated areas shows Cu peaks although the Cu peaks were not observed in XRD spectra of the non-irradiated area. The width of the Cu micropatterns were increased by decreasing laser pulse energy and increasing laser scanning speed. The minimum line width was 7 μm under the condition that the laser pulse energy and scanning speed were 0.36 nJ and 100 μm/s, respectively. When the pulse energy was low and the scanning speed was high, the line width of the Cu micropatterns only depended on the pulse energy, not the scanning speed. This result indicates that the threshold fluence could exist to form Cu micropatterns.

Synthesizing, microstructure and microhardness distribution of Ti–Si–C–N/TiCN composite coating on Ti–6Al–4V by laser cladding

A micro-textured Ti–Si–C–N/TiCN composite coating was obtained using laser direct cladding method. A mixture of 20wt.% SiO2 and 80wt.% TiC0.3N0.7 was used as the precursor. A metallurgical bonding at the interface was achieved. Variation in the laser scan speed appeared to have no detectable influence on the evolution of phase type in the modified surface region. All samples demonstrated the presence of the same phases such as Ti3SiC2, TiC0.3N0.7, and Ti2O. The average crystallite size and the average surface roughness Ra of the coatings presented a decreasing trend with increasing laser scan speed. Laser scan speed has an obvious influence on the thickness and the microstructure of the coating. The microhardness in the coating depends on laser scan speed. It increased first, followed by a decreasing trend with increasing laser scan speed, and got a maximum value of about 1400HV at laser scan speed of 3mm/s, which is more than 4 times of that of titanium substrate. Ti–Si–C–N coating distributes in a distance of about 100μm.

Laser nitriding of steel surface: efficiency analysis

Laser gas assisted nitriding improves the properties of steel surfaces through grain refinement and nitride compounds formation in the surface region. In the present study, laser gas assisted nitriding of tool steel (H13) is carried out. The microstructural and morphological changes in the laser nitrided region are examined using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The first and second law efficiencies of the laser nitriding process are formulated using the lump parameter analysis. It is found that the depth of nitride layer extends 60 μm below the surface. The nitrided layer is free from cracks and voids. The first and second law efficiencies reduce with increasing laser power; however, they increase significantly with increasing laser scanning speed.

3D Finite Element Modelling of Contour Laser Transmission Welding of Polycarbonate

A three-dimensional finite element model was developed for the simulation of heat transfer in contour laser transmission welding of amorphous polymer — polycarbonate. By introducing mass flow in the model, a time-dependent, contour welding process was solved as a time-independent heat transfer problem (Quasi-static model). The short solution convergence times (under three minutes for a set of process and material conditions) and model output agreement with the experimental data indicate that the Quasi-static approach is convenient for use in solving heat transfer problems in laser contour welding. Combined with experimental data, the simulation results indicate that, in contour welding of PC, welding initiates when temperature at the weld interface reaches the maximum of 200 °C. The simulation results also provide further insight into the effect of proportionally increasing laser scan speed and power (i.e., while maintaining constant line energy).

Wettability and kinetics of hydroxyapatite precipitation on a laser-textured Ca–P bioceramic coating

Surface-textured calcium phosphate coatings at four different length scales were synthesized on titanium-based alloys using a pulsed Nd:YAG laser system by a direct melting technique. The textures were obtained by varying the laser spot overlap with a change in laser traverse speed. Surface roughness measurements of the textured coatings carried out using a white light interferometer indicated a decrease in roughness with increasing laser scan speed. Wettability of the coated samples measured using a static sessile drop technique demonstrated an increased hydrophilicity with increasing laser scan speed. The influence of such textures and the associated surface roughness on the precipitation kinetics of hydroxyapatite (HA) during immersion in simulated body fluid (SBF) was the prime focus of the present paper. The mineralized samples obtained after immersion in SBF were characterized using X-ray diffraction, energy-dispersive spectroscopy and scanning electron microscopy to understand the kinetics of HA precipitation. The results thereafter confirmed that the precipitation kinetics of HA was strongly modulated by the varying surface roughness.

Fabrication and evaluation of a pulse laser-induced Ca–P coating on a Ti alloy for bioapplication

In the present paper, we demonstrate the feasibility of depositing a tailored calcium phosphate (Ca–P) coating on a Ti–6Al–4V substrate by using a pulsed Nd:YAG laser system. Different textures were obtained by varying the laser spot overlap with change in laser traverse speed. Surface roughness measurements using laser confocal microscopy indicated a decrease in roughness with increasing laser scan speed. X-ray diffraction studies revealed the formation of α-TCP, TiO2, Ti and Al as the major phases. An instrumented nanoindenation technique used to study the mechanical properties of the coatings, revealed a very high hardness and Young's modulus of the coating surface as compared to the substrate. This further proved the retainment of the ceramic phase on the surface. Wear studies in a simulated biofluid (SBF) environment demonstrated an increased wear resistance of the coated samples as compared to the bare Ti–6Al–4V. Formation of an apatite-like layer after immersion in SBF for different time periods further demonstrated the bioactivity of the coated samples.

Laser processing of bioactive tricalcium phosphate coating on titanium for load-bearing implants

Laser-engineered net shaping (LENS™), a commercial rapid prototyping (RP) process, was used to coat titanium with tricalcium phosphate (TCP) ceramics to improve bone cell–materials interactions. During LENS™ coating process, the Nd:YAG laser melts the top surface of Ti substrate in which calcium phosphate powder is fed to create a TCP–Ti composite layer. It was found that an increase in laser power and/or powder feed rate increases the thickness of the coating. However, coating thickness decreased with increasing laser scan speed. TCP coating showed columnar titanium grains at the substrate side of the coating and transitioned to equiaxed titanium grains at the outside. When the scan speed was reduced from 15 to 10 mm s −1, coating hardness increased from 882 ± 67 to 1049 ± 112 Hv due to an increase in the volume fraction of TCP in the coating. Coated surfaces showed uniformly distributed TCP particles and X-ray diffraction data confirmed the absence of any undesirable phases, while maintaining a high level of crystallinity. The effect of TCP coating on cell–material interaction was examined by culturing osteoprecursor cells (OPC1) on coated surfaces. The results indicated that TCP coating had good biocompatibility where OPC1 cells attached and proliferated on the coating surface. The coating also initiated cell differentiation, ECM formation and biomineralization.

Thermal fatigue characteristics of gray cast iron with non-smooth surface treated by laser alloying of Cr powder

In order to enhance thermal fatigue resistance of gray cast iron with non-smooth surface further, researches on laser alloying of Cr powder with different scanning speed were performed to change both the composition and microstructure of non-smooth unit. The results indicated that there was an optimal scanning speed (2 mm/s) which can contribute maximal Cr element in alloyed zone, and increasing laser scanning speed resulted in smaller non-smooth unit and more pores in it. The microstructure in alloyed layer was composed of pre-eutectic phases, ledeburite eutectic and chromium carbides of Cr 23C 6. Thermal fatigue resistance of non-smooth sample is better than that of smooth sample, and among non-smooth samples, sample treated by laser Cr alloying has superior resistance to thermal fatigue compared with laser melting treated sample, in addition, the resistance of laser alloying non-smooth samples increases with scanning speed slowing.

Microstructure characteristics of Ni-based WC composite coatings by laser induction hybrid rapid cladding

To avoid low cladding rate and cracks of cladding layer, laser induction hybrid rapid cladding (LIHRC) has been put forward in the paper. The microstructure characteristics of Ni-based WC composite coatings at the different laser scanning speed were investigated. For low laser scanning speed, the growth of γ-nickel was characterized by coarse columnar dendrites and eutectics, blocky W 2C + Fe 3W 3C carbides, and bar-like (W, Cr, Ni) 23C 6 carbides were formed. With increasing laser scanning speed, the growth of γ-nickel presented the fine dendrites and eutectics, the only blocky mixed carbides were precipitated and identified as W 2C + FeW 3C + W 6C 2.54 carbides. With further increasing laser scanning speed, the growth of γ-nickel was characterized by cellular crystals and eutectics, the only blocky carbides were identified as W 2C + W 6C 2.54. Moreover, experimental results showed that the efficiency of LIHRC was increased much four times higher than that of laser cladding without preheating, ceramic–metal composite coatings detected were free of cracks and had a good metallurgical bonding with substrate.

レーザー加熱を用いた鉄の局所表面アルミニウム粉末被覆

A local surface coating using Al and Ti powders on Fe substrate is successfully performed by a laser heating method. A high hardness and high oxidation resistance can be achieved by this method. The thickness of aluminum rich layer can be controlled by the amount of the Al and Ti powder mixture paste. Concentration of aluminum at the coating layer increases with increasing laser scanning speed. Pre-heating at 573K for 10.8 ks improves the uniformity of the coating.

Entropy generation analysis of turbulent transport in laser surface alloying process

A numerical formulation involving second law of thermodynamics is examined for analysis of three-dimensional surface tension driven turbulent transport during laser materials processing. A modified k–ϵ model is used to address turbulent melt pool convection in the presence of a continuously evolving phase change interface. Phase change aspects are addressed using a modified enthalpy–porosity technique. It is revealed that both energetic and exergetic efficiencies increase with increasing laser power, and remain insensitive to changes in powder feedrate over the range of parameters chosen. However, the energetic efficiency is found to increase with increasing laser scanning speed whereas the exergetic efficiency shows a reverse trend. Accordingly, a tradeoff in the laser scanning speed can be sought for while designing the process parameters, in order to ensure a maximum utilisation of the thermodynamic potential offered by the intense laser heat source.

Laser heating of sheet metal and thermal stress development

Lasers are widely used in modifying metallic surfaces. During the laser heating process, thermal stresses develop in the region heated by a laser beam. In the present study, laser heating of sheet metal is formulated analytically and thermal stress field is obtained using a finite element method (FEM). It is found that laser scanning speed influences considerably temperature and stress fields. In this case, increasing laser scanning speed reduces temperature in the region away from the centre of the laser heat source. Stress components are compressive in the region close to the source; however, it becomes tensile in the region away from the heat source.

Laser cutting quality assessment and thermal efficiency analysis

Lasers are widely used in industry as cutting tools due to ultra flexibility of the cutting conditions, obtaining high quality end product, quick set up, non-mechanical contact between the workpiece and the tool, and small size of the heat affected zone. In the present study, laser gas assisted cutting process is examined. Statistical method based on factorial analysis is introduced to identify the influence of cutting parameters on the resulting cut quality. International standards for thermal cutting is employed to identify the measurable variables when assessing the cut quality. Kerf width size is presented using scaling laws. Contribution of high temperature oxidation reaction in cutting due to assisting gas is accommodated in the analysis. First and second law efficiencies for laser cutting process are formulated. An experiment is conducted to assess the cutting quality and validate the Kerf width predictions. It is found that increasing laser beam scanning speed reduces the Kerf width while Kerf width increases with increasing laser output power. The main effects of all the parameters employed have significant influence on the resulting cutting quality. First law efficiency increases with increasing laser scanning speed, which substantiates as the workpiece thickness is doubled.

Microstructure of laser clad TiC/NiAl–Ni3(Al,Ti,C) wear-resistant intermetallic matrix composite coatings

TiC-reinforced NiAl–Ni3(Al,Ti,C) intermetallic matrix composite coatings are fabricated by laser cladding with powder blends of Ni–Al–Ti–C on substrate of electrolyzed nickel plate. The microstructure consists of TiC particles, primary NiAl dendrites and the interdendritic Ni3(Al,Ti,C) phase; the composite coatings can be obtained with the features of high-quality metallurgical bonding with the substrate. The volume fraction of Ni3(Al,Ti,C) phase increases with increasing laser scanning speed, but that of dendritic NiAl intermetallic alloy shows a decreasing tendency. Furthermore, the growth morphology of reinforcements changes from octahedron to developed dendrite with laser scanning speed.

Effect of processing parameters on the cohesive strength of laser surface engineered ceramic coatings on aluminum alloys

The mechanical performance of laser surface engineered ceramic composite (TiC/Al) coating on 2024 and 6061 Al alloy substrates has been evaluated using four-point bend test. The performance of the coating is expressed in terms of the cohesive strength of the coating. Load-displacement measurements carried out during the bend test helps to determine the load corresponding to crack initiation. This load required to initiate fracture in the coating provides a measure of the strength of the coating. A simplistic approach based on elementary beam theory and strength of material in conjunction with rule of mixture was adopted to calculate the cohesive strength of the composite coating. This approach is also further extended for attempts to evaluate apparent residual stress within the coating. Since process parameters exert a significant influence in controlling the end properties of the component, the effect of laser power and laser scan speed on the cohesive strength has also been investigated. It is observed that coatings with lower scan speeds have much higher cohesive strengths and they also seem to have good metallurgical bond with the substrate thus showing better mechanical behavior than the other high scan speeds used in this present study. The apparent residual stress in the coating appears to transform from compressive to tensile in nature with increasing laser scan speed eventually contributing to delamination of the coating.