Increasing Laser Scanning Speed Research Articles

Effect of powder and process parameters on in-situ alloying of nitinol during laser powder bed fusion

Powder characteristics such as flow energy, bulk density, compressibility, morphology, particle size distribution (PSD) and laser energy absorbtivity have a significant impact on the Laser Bed Powder Fusion (L-PBF) process. The impact of powder characteristics on in-situ nickel-titanium alloy formation within the L-PBF process is not well understood. In this work, the characteristics of nickel, titanium and two elemental blends of nickel-titanium powder were compared with those of a pre-alloyed nitinol powder. L-PBF solidification tracks were generated using selected powders and characterised for resulting track dimensions and chemical homogeneity. This study demonstrates that the melt homogenisation time and the size of titanium particles relative to nickel particles are critical factors for successful in-situ alloying of nitinol within the L-PBF process. The variation in elemental composition within solidification track cross sections, as measured by EDX point spectra, was found to increase significantly for laser scanning speeds of 400 mm/s and above. Furthermore, the elemental composition inhomogeneity with increasing laser scan speed was found to be significantly more pronounced for a nickel-titanium powder blend of spherical particles with average titanium particle size of 48 μm compared to an otherwise similar blend with an average titanium particle size of 32 μm. There was no significant difference recorded between solidification track widths of in-situ alloyed blends compared to pre-alloyed blends, indicating that optimal hatch spacing for in-situ alloying is likely to be similar to that required for pre-alloyed powders.

Optimising the manufacturing of a β-Ti alloy produced via direct energy deposition using small dataset machine learning

Successful additive manufacturing involves the optimisation of numerous process parameters that significantly influence product quality and manufacturing success. One commonly used criteria based on a collection of parameters is the global energy distribution (GED). This parameter encapsulates the energy input onto the surface of a build, and is a function of the laser power, laser scanning speed and laser spot size. This study uses machine learning to develop a model for predicting manufacturing layer height and grain size based on GED constituent process parameters. For both layer height and grain size, an artificial neural network (ANN) reduced error over the data set compared with multi linear regression. Layer height predictions using ANN achieved an R2 of 0.97 and a root mean square error (RMSE) of 0.03 mm, while grain size predictions resulted in an R2 of 0.85 and an RMSE of 9.68 μm. Grain refinement was observed when reducing laser power and increasing laser scanning speed. This observation was successfully replicated in another α + β Ti alloy. The findings and developed models show why reproducibility is difficult when solely considering GED, as each of the constituent parameters influence these individual responses to varying magnitudes.

Analysis of mechanical properties of 3D printed metallic specimens of aluminum (CL31) bronze (CL80) material manufactured at varying laser scanning speed

In our research work, we analyzed the mechanical properties of 3D-printed metallic specimens of aluminium bronze material. In our evaluation, we had five groups of specimens, manufactured at different laser scanning speeds. In total, we had 25 specimens for which we examined various parameters like ultimate tensile strength, engineering yield point, relative strain, and hardness. Results showed that specimens prepared with a lower laser scanning speed of 300mm/s showed the lowest tensile strength. The tensile strength increased with increasing laser scan speed and the highest tensile strength was attained by specimens of the fourth group that were produced at a laser scanning speed of 500mm/s. The relative strain of specimens also increased with the increasing scan speed of the laser. The Brinell hardness test also showed an elevation in hardness values with increasing laser scan speeds.

Modeling of epitaxial growth of single crystal superalloys fabricated by directed energy deposition

Single crystal (SX) nickel-based superalloys have been used for turbine blades fabrication in recent years because of their superior mechanical performance at high temperature. The restoration of SX blades is significant considering the high cost to re-manufacture the blade. Directed energy deposition (DED), as a laser additive manufacturing technique, is a promising method for repairing the SX blades. Continuous epitaxial growth from the substrate to deposited layers is vital for successful restoration of SX blades. In this work, a novel single crystal texture cellular automata (SITCA) method is developed to simultaneously predict the columnar to equiaxed transition (CET) and crystal growth direction at the molten pool scale. Based on the grain envelope simplification, the SITCA method introduces a random variable to trace the growth trajectory, and therefore indicates the partition of the growth regions in the molten pool. A continuous nucleation model is introduced for nucleation simulation, and the crystal growth is simulated using the Kurz–Giovanola–Trivedi (KGT) model. The validation of SITCA model is performed by casting solidification cases under uniform temperature and uniform temperature gradient. The SITCA method is then integrated with a thermo-fluid molten pool simulation using finite element method to comprehensively compute the epitaxial growth. SX remelting experiments are carried out with different laser scanning speeds using a flat top laser source, and compared with the numerical results. The experimental and numerical results both indicate that increasing laser scanning speed will increase the ratio of crystals growing in the [001] direction while facilitate the CET on the other hand. This work shows the capacity of the SITCA method to predict epitaxial growth in DED process, and we anticipate to deploy the SITCA method to complex SX additive manufacturing.

Microstructure, mechanical properties and corrosion behavior of additively-manufactured Fe–Mn alloys

In this paper, we describe the effects of different scanning speeds (600–900 mm/s) on the microstructure, mechanical properties and corrosion behavior of biodegradable bone-substitution alloys produced from 80:20 (by wt.) Fe:Mn powders using laser powder bed fusion (LPBF). Both the Mn content (18.9–15.1 wt% Mn) and density (7920–7730 kg/m3) of the LPBFed samples decreased slightly with increasing laser scanning speed, while the oxygen content increased (0.12–0.40 wt%). Increasing scanning speed also led to increased porosity (from 0.27% to 2.5%) and increased cracking. The specimen produced at the lowest scanning speed of 600 mm/s, which consisted of only the HCP ε-martensite phase, showed by far the highest yield strength (YS) at 644 MPa and the highest ultimate tensile strength (UTS) at 857 MPa, but the lowest elongation to failure (El) of only 13.7%. Specimens produced at higher scanning rates consisted of both BCC α′-martensite and ε-martensite phases. The sample fabricated at a scanning speed of 700 mm/s showed the best balance of mechanical properties with a YS of 330 MPa, a UTS of 839 MPa, and an El of 36.1%. Electrochemical testing showed corrosion rates from 0.09 mm/yr (600 mm/s specimen) to 0.22 mm/yr (700 mm/s specimen), which are higher than those of both pure Fe and most Fe–30Mn and Fe–35Mn alloys reported in the literature. The work demonstrates that the meso-/micro-scale structure, and, hence, the mechanical properties and corrosion rates of Fe–Mn alloys can be tailored by varying the scanning speed during LPBF processing. It also demonstrates the potential of LPBFed Fe–Mn alloys with low Mn content for use as biodegradable bone substitutes.

Effect of phase composition on microstructure and wear resistance of (Al16.80Co20.74Cr20.49Fe21.28Ni20.70)99.5Ti0.5 high-entropy alloy coatings

The (Al16.80Co20.74Cr20.49Fe21.28Ni20.70)99.5Ti0.5 high-entropy alloy coating was successfully prepared by laser cladding. The microstructure of the coating was controlled by changing the laser scanning speed, and three kinds of high-entropy alloy coatings with different microstructures were obtained. All coatings had an equiaxed grain structure, but the content of the BCC phase gradually increased with increasing laser scanning speed. In addition, the micro-mechanical properties of each phase in the coating and the creep characteristics of the coating were explored by the nanoindentation method. It was found that the BCC phase had greater hardness and elastic modulus than the FCC phase, so the content of the BCC phase dominated the hardness and wear resistance of the coating. At the same time, as the laser scanning speed increased, the creep resistance of the coating was gradually enhanced. When the laser scanning speed was 17 mm/s, the coating had the best wear resistance at room temperature and 500 ℃ high temperature. The main wear forms of the coating were abrasive wear, surface fatigue wear, and oxidative wear.

High-temperature oxidation performance of laser-cladded amorphous TiNiSiCrCoAl high-entropy alloy coating on Ti-6Al-4V surface

To enhance the high-temperature oxidation performance of Ti-6Al-4V alloy, we successfully prepared a TiNiSiCrCoAl high-entropy alloy coating on its surface via laser cladding technology. X-ray diffraction, scanning electron microscopy, and electron probe microanalysis were used to characterize the microstructure, elemental distribution, and high-temperature oxidation resistance of the coating. The results indicated that the microstructure of the coating was composed of a matrix and a σ phase. Owing to the rapid cooling via laser processing and the matched δ, ∆Hmix, and Ω, the matrix phase was an amorphous structure rich in Ti, Si, Cr, and Co, and the σ phase was an FCC structure rich in Ti, Ni, Co, and Al. The volume fraction of the amorphous-structured matrix in the coating increased with increasing laser scanning speed. The section after the oxidation treatment was composed of an oxide layer, a transition layer, and a coating matrix. The oxide layer was composed of TiO2, Al2O3, and NiAl2O4, and the transition layer was rich in Si, Ni, and Co. The amorphous-structured matrix exhibited a higher oxidation resistance than the FCC-structured σ phase. Compared with the Ti-6Al-4V substrate, the oxidation resistance of the coating increased by 10.7, 28.1, 40.5, and 65.1 times at different laser scanning speeds under oxidation at 800 °C for 48 h, which indicates that the coating has better oxidation resistance than the Ti-6Al-4V alloy at high temperatures.

Microstructural Development in Inconel 718 Nickel-Based Superalloy Additively Manufactured by Laser Powder Bed Fusion

Excellent weldability and high temperature stability make Inconel 718 (IN718) one of the most popular alloys to be produced by additive manufacturing. In this study, we investigated the effects of laser powder bed fusion (LPBF) parameters on the microstructure and relative density of IN718. The samples were fabricated with independently varied laser power (125–350 W), laser scan speed (200–2200 mm/s), and laser scan rotation (0°–90°). Archimedes’ method, optical microscopy, and scanning electron microscopy were employed to assess the influence of LPBF parameters on the relative density and microstructure. Optimal processing windows were identified for a wide range of processing parameters, and relative density greater than 99.5% was achieved using volumetric energy density between 50 and 100 J/mm3. Microstructural features including melt pool geometry, lack of fusion defect, keyhole porosity, and sub-grain cellular microstructure were examined and quantified to correlate to LPBF parameters. A simple empirical model was postulated to relate relative sample density and LPBF volumetric energy density. Melt pool dimensions were quantitatively measured and compared to estimations based on Rosenthal solution, which yielded a good agreement with the width, but underestimated the depth, particularly at high energy input, due to lack of consideration for keyhole mode. In addition, the sub-grain cellular-dendritic microstructure in the as-built samples was observed to decrease with increasing laser scan speed. Quantification of the sub-micron cellular-dendritic microstructure yielded estimated cooling rate in the order of 105–107 K/s.

Nanosecond laser-induced controllable oxidation of TiB2–TiC ceramic composites for subsequent micro milling

Laser-induced controllable oxidation coupled with micro-milling (LOMM) provides a feasible way to machine difficult-to-machine materials such as TiB 2 –TiC ceramic composites. The oxidation mechanism of the material under laser irradiation represents the fundamental issue of LOMM. In this paper, laser-induced controllable oxidation of spark plasma sintered TiB 2 –TiC ceramic composites as the workpiece material was studied. A three-dimensional finite element model was established based on ABAQUS/CAE 6.14 software to simulate the effect of laser parameters on temperature field distribution and was verified by experiments. The influence of laser processing parameters and assisted gas atmospheres on the oxidation behavior of TiB 2 –TiC ceramic composites was investigated. Results revealed that the irradiated temperature which had a significant impact on oxidation behavior, increased with an increment of the laser fluence and decreased with an increment of scanning speed with other laser parameters fixed. In addition, based on experimental analysis, the thickness of the oxide-layer increased with an increase of laser fluence and reduced with increasing laser scanning speed. At a laser fluence of 10.78J/cm 2 and scanning speed of 1 mm/s as well as in an oxygen-rich atmosphere, a loose and porous oxide-layer was produced on the irradiated surface. Cross-section thicknesses of the oxide-layer and sub-layer reached 63 μm and 22 μm, respectively. Moreover, the thickness of the oxide-layer was 22 μm in air surroundings and hardly be found in argon and nitrogen atmospheres under identical laser parameters, which indicated that oxygen content had a significant influence on the oxidation reaction of the material. The products of the oxide-layer were mainly composed of rutile- and anatase-TiO 2 . Furthermore, the hardness of the sub-layer was 9.6 ± 0.7 GPa at a laser fluence of 10.78J/cm 2 and scanning speed of 1 mm/s, which was far lower than that of the substrate with a hardness of 20 ± 0.7 GPa. This study provides a theoretical basis for subsequent micro-milling.

Effects of Laser Scanning Speed on Microstructure, Microhardness, and Corrosion Behavior of Laser Cladding Ni45 Coatings

The effects of laser scanning speed on the microstructure, microhardness, and corrosion behavior of Ni45 coatings were investigated by using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness, and electrochemical measurements. The results showed that increasing laser scanning speed promotes the transformation from planar crystals to dendrites and refines the grains concurrently. The γ-(Ni, Fe), FeNi3, and M23(C,B)6 are identified as the primary phase composition in the Ni45 coatings regardless of the laser scanning speed. Thereinto, the formation and growth of M23(C,B)6 precipitates can be inhibited with increasing laser scanning speed due to the higher cooling rate, which affects the microhardness distribution and corrosion resistance of the coating. On the one hand, the microhardness of the whole coating presents a downtrend with increasing laser scanning speed due to the reduction of M23(C,B)6 phase. On the other hand, the corrosion resistance in 0.5 M NaCl solution is improved to some extent at higher laser scanning speed because the less precipitation of M23(C,B)6 reduces the depletion of Cr around the precipitates. In contrast, all the coatings exhibit undifferentiated but poor corrosion resistance in the highly corrosive 0.5 M NaCl + 0.5 M H2SO4 solution.

Evolution of functional properties realized by increasing laser scanning speed for the selective laser melting fabricated NiTi alloy

The near equiatomic NiTi alloy was fabricated with selective laser melting method at a constant laser power coupled various scanning speeds from 300 mm/s to 480 mm/s. The evolution of functional properties was observed on cyclic tensile curves with emphases on the critical stress for inducing martensitic transformation and the mechanical recoverable strain. Results show that the critical stress for inducing martensitic transformation increases linearly with scanning speed, and the mechanical recoverable strain is indeed enhanced by increase of the scanning speed. Further, the highest mechanical recoverable strain of 2.29% is achieved at the applied strain of 4.5% in the sample fabricated with the highest scanning speed of 480 mm/s. The phase constitution, microstructural features and crystallographic texture were characterized in detail to interpret such evolution. It is found that the different Ms temperature and corresponding different phase constitution obtained with different scanning speed are mainly responsible for the variation of critical stress for inducing martensitic transformation and the mechanical recoverable strain. The co-existence of <111>//BD and <100>//BD crystallographic textures, as well as the variation of dislocation density show limited effect on the evolution amongst different samples.

Temperature Field Numerical Analysis Mode and Verification of Quenching Heat Treatment Using Carbon Steel in Rotating Laser Scanning.

Temperature history and hardening depth are experimentally characterized in the rotational laser hardening process for an AISI 1045 medium carbon steel specimen. A three-dimensional finite element model is proposed to predict the temperature field distribution and hardening zone area. The laser temperature field is set up for an average distribution and scanned along a circular path. Linear motion also takes place alongside rotation. The prediction of hardening area can be increased by increasing the rotational radius, which in turn raises the processing efficiency. A good agreement is found between the experimental characterized hardness value and metallographic composition. The uniformity of the hardening area decreases with increasing laser scanning speed. The increased laser power input could help to expand the hardening depth.

Friction wear property of laser surface processed Ni-based amorphous alloy coatings

A Ni–Fe–B–Si–Nb amorphous alloy was deposited on a steel substrate surface via a laser cladding process, and a laser cladding plus laser remelting process. The wear behavior of the laser processed samples and the bulk metallic glass (BMG) sample with the same nominal composition were tested using a pin-on-disc type testing machine. The nano-mechanical properties of the samples were measured with a nano-characterization system. The friction wear tests showed that deep grooves and wear debris were formed on the worn surface of the laser cladded coating, while only shallow grooves for the laser remelted coatings. The friction coefficients of laser remelted coatings and BMG were lower than the laser cladded coating. The wear mass losses of the laser remelted coating were less than the BMG when the laser remelting scanning speed was higher than 6 mm/min. The nano-hardness and elastic modulus of the remelted coating is higher than that of the laser cladded coating. Also, they increase with the increasing laser scanning speed with 1227.9 HV and 277.4 GPa when the remelting scanning speed is 8 m/min. Based on the nano-indentation and friction wear tests results, it was found that the friction wear properties of the laser cladded coating, laser remelted coatings and BMG related well to the ratio of H3/E2. A higher value of H3/E2 can lead to a better wear resistance property.

Enhancement of bioactivity of glass by deposition of nanofibrous Ti using high intensity laser induced reverse transfer method

The aim of this research is to develop a new method for the enhancement of bioactivity of glass and transparent materials by the deposition of Ti nanofibrous structures generated by a high intensity laser induced reverse transfer method (HILIRT). Titanium nanofibers with different porosity, fiber diameter, and bioactivity are synthesized at various ranges of pulse frequency, power, and scanning speed combined with the HILIRT method. Features and bioactivity of these deposited Ti coatings before and after seven days immersion in simulated body fluid are compared. The results show increasing laser frequency and laser power leads to more Ti nanofiber generation and enhanced biocompatibility, while increasing laser scanning speed results in lower Ti nanofiber growth and lower biocompatibility. Combination of the laser parameters such as frequency, power, and scanning speed can optimize the deposited Ti nanofiber properties for a wide range of biomedical applications using transparent biomaterials such as implanted optoelectronics and light guiding devices, lab on a chip (LoC) and in-vitro and real time analysis of living cells in laboratories.

Enhanced corrosion and wear resistance properties of carbon fiber reinforced Ni-based composite coating by laser cladding

To enhance the wear resistance and corrosion resistance of Ni-based coatings, carbon fibers reinforced nickel-based composite coatings (CFs/Ni) were fabricated on the surface of 1Cr13 stainless steel by laser cladding (LC). The microstructure characteristics, microhardness, wear and corrosion performances of the composite coatings were investigated. The results show that CFs can effectively improve the corrosion and wear resistances of Ni-based coatings. With increasing laser scanning speed, the morphology of CFs in composite coatings is more integral and the corrosion and wear resistances of the composite coatings are improved. Especially, when laser scanning speed is increased to 8mm/s, the average microhardness of the composite coating reaches up to 405HV0.2, which is about 1.3 times higher than that of Ni-based coating. Moreover, the corrosion current density and the wear rate of the composite coating are only 7% and 55% of those of the Ni-based coating, respectively, which is attributed to the good properties and homogeneous distribution of CFs and finer microstructure of composite coating.

Discrete element modeling of powder flow and laser heating in direct metal laser sintering process

A novel particle-based discrete element model (DEM) is developed to simulate the whole Direct Metal Laser Sintering (DMLS) process, which includes simplified powder deposition, recoating, laser heating, and holding stages. This model is first validated through the simulation of particle flow and heat conduction in the powder bed, and the simulated results are in good agreement with either experiment in the literature or finite element method. Then the validated model is employed to the DMLS process. The effects of laser power, laser scan speed, and hatch spacing on the temperature distributions in the powder bed are investigated. The results demonstrate that the powder bed temperature rises as the laser power is increased. Increasing laser scan speed and laser hatch spacing will not affect the average temperature increase in the powder bed since energy input is kept same. However, a large hatch spacing may cause non-uniform temperature distribution and microstructure inhomogeneity. The model developed in this study can be used as a design and optimization tool for DMLS process.

Fabrication of wear-resistant layers with lamellar eutectic structure by laser surface alloying using the in situ reaction between Cr and B4C

To improve the wear resistance of Cr5 steel, wear-resistant layers with lamellar eutectic microstructure were fabricated by laser surface alloying (LSA), which is dependent on the in situ reaction between Cr and B4C. Our results indicated that the hypoeutectic structures of the LSA layers were divided into interdendritic eutectic structures and dendrites. The area fraction of the eutectic structures increased with increasing laser scanning speed, which improved the hardness and wear resistance of the LSA layers. The average hardness of the LSA layer prepared at a scanning speed of 8 mm/s was HV0.2 883.9, which was 1.8 times greater than that of the traditional quenched layer (approximately HV 480). After sliding for 659.4 m, the specimen prepared at a scanning speed of 8 mm/s exhibited a volume loss of 0.0323 mm3, which was only 29.5% of the volume loss of the traditional quenched specimen.

Effect of laser scanning speed on a Ti-45Al-2Cr-5Nb alloy processed by selective laser melting: Microstructure, phase and mechanical properties

This work presents a comprehensive study on the laser scanning speed on the microstructure development, phase evolution and nanohardness of a TiAl alloy, Ti-45Al-2Cr-5Nb (at.%), processed by selective laser melting (SLM). The experimental results show that when increasing the laser scanning speed from 500 to 800 mm/s, the average grains size decreases from 7.11 μm to 5.43 μm, whereas the crystallographic texture showing a combination of (0001), (101¯1) and (112¯1) orientations basically remains unchanged. The SLM-processed TiAl alloy is dominated by high-angle (>15°) grain boundaries (HAGBs) and the contents of HAGBs decrease from 91.6% to 86.1% when the laser scanning speed varies from 500 to 800 mm/s. The α2 phase decreases while the γ and B2 phases increase with increasing the laser scanning speed. Moreover, the phase evolution mechanism in the SLM-processed TiAl alloy can be described as follows: (200) β transforms to (202¯0)α2 and (110) γ, and then the residual B2 and the incompletely transformed γ phase randomly distributed in the α2 phase matrix. The nanohardness of the SLM-process TiAl alloy increases from 7.90 ± 0.32 GPa to 9.49 ± 0.46 GPa with increasing laser scanning speed from 500 to 800 mm/s, which is much higher than those of traditionally manufactured counterparts, such as casting parts (4.98 ± 0.10 GPa) and TiB2 reinforced TiAl alloy fabricated by roll bonding (6.73 GPa). With the increase of laser scanning speed from 500 to 800 mm/s, compression properties of the SLM-process TiAl alloy increases from 829.41 ± 24.88 MPa to 1216.16 ± 36.48 MPa.

Laser sintering of copper nanoparticles on top of silicon substrates

This study examines the sintering of inkjet printed nanoparticle copper ink in a room environment using a laser as a high speed sintering method. Printed patterns were sintered with increasing laser scanning speed up to 400 mm s−1. The resistivities of the sintered structures were measured and plotted against the scanning speeds. Increased resistivity seems to correlate with increased scanning speed. A selections of analytical methods was used to study the differences in microstructure and composition of the sintered structures. Based on the results, no discernable difference in the microstructure was noticed between the structures sintered using 20 mm s−1 to 400 mm s−1 scanning speeds; only the structure scanned using 5 mm s−1 speed showed a vastly different microstructure and no resistivity was measurable on this structure. Compositional studies revealed that, apart from the structure scanned with 5 mm s−1 speed which contained the highest oxygen, the rest of the structures showed a steady oxygen increase with increased scanning speed.

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.