Effect Of Laser Energy Density Research Articles

Effects of laser energy density on morphology features and microstructures of the single molten track in selective laser melting

Single molten track (SMT) is the basic unit of the selective laser melting (SLM) process, of which the morphology features and microstructures have great significance on the molding quality. In this study, the effects of laser energy density (LED) on characteristics of SMT were studied with 316 L stainless steel processing by SLM. The results indicate that an optimized range of LED was between 200 and 500 J/mm3, which was the best for SLM process of 316 L leading to beautiful SMT appearance such as continuous uniform water-ridge-like surface, good contour straightness, smooth edges, little adhesive powder, and high densification. The microstructures of the SMT molten pool are mainly composed of equiaxed cellular and columnar dendrites. As the LED decreased, the cellular became smaller and disappeared, while the length and width of columnar crystals even gradually increased. The size of the cellular varies between 0.43 and 1.70 μm with the LEDs increase. The relationship between SMT characteristics and LED found in this work can be readily used to optimize SMT and control the microstructures in situ, and the laser energy density range that the work has identified will simplify most of the guess work in additive manufacturing.

Fabrication of high-performance copper circuits using laser-induced forward transfer with large receiving gaps based on beam modulation technology

Laser-induced forward transfer (LIFT) technology has been widely used to print 2D/3D structural patterns in the micron level of metals due to its contactless and maskless advantages. Still, it cannot meet the practical needs of the industry due to its drawbacks, such as low efficiency and a small receiving gap. This study proposes a new LIFT by modulating a Gaussian beam into an Arc beam using a liquid crystal on silicon spatial light modulator (LCOS-SLM) to achieve stable preparation of high-performance Cu circuits at large receiving gaps. First, the laser-induced monomer transfer modes of Gaussian beams and arc beams are studied. Then the effects of laser energy density, scanning velocity, and reception gap on the microcircuits prepared by Gaussian beam laser-induced forward transfer (GB-LIFT) and Arc beam laser-induced forward transfer (AB-LIFT) are studied systematically, and suitable process parameters are found. The transfer process of action of AB-LIFT is revealed. Under the optimized process parameters, the flight distance of AB-LIFT is up to 120 μm, which is about twice that of GB-LIFT, when the laser energy density is 1.94 μJ, and the scanning velocity is 3 mm/s. And the height of the microcircuit can be controlled by the number of depositions. It is demonstrated that the AB-LIFT can achieve stable transfer with large receiving gaps and efficiently prepare continuous Cu circuits with high bonding strength and low resistance. The minimum resistivity (7.46 μΩ∙cm) obtained by selecting optimized process parameters is about 4 times that of Cu bulk (1.76 μΩ∙cm). The application of the AB-LIFT method based on the beam modulation technique in microcircuit defect repair is verified.

Effect of absorption depth on chemical energy release from laser ablation of ADN-based liquid propellants

Ammonium dinitramide is a new green oxidant, which has been widely used in the field of liquid propulsion. In order to study the influence of doping laser absorber on the propulsion performance of liquid targets, the mixed solution of ammonium dinitramide and ionic liquid 1-allyl-3-methylimidazolium dicyandiamide was used as the ablation target, and the infrared dye was used as the laser absorber to change the doping content of infrared dye and laser energy density. The results show that the light absorption performance of liquid propellant is obviously improved with the increase of infrared dye content. The absorption coefficient and absorption depth of liquid propellant with infrared dye content of 0.6wt% are 425.19 cm−1 and 23.52 μm, respectively. The propellant with lower absorption depth produces high values of impulse bit, specific impulse, impulse coupling coefficient and ablation efficiency under the ablation of high laser energy density. The propellant sample doped with 0.6wt% infrared dye yielded the highest impulse bit of 114.32 μN·s, largest specific impulse of 84.14 s, highest impulse coupling coefficient of 1.07 mN·s·J−1, and the maximal ablation efficiency of 44% at the laser energy density of 21.51 J·cm−2. Furthermore, the effects of laser energy density and absorption depth on the chemical energy release of liquid propellant were studied. It was found that the maximum contribution of chemical energy to kinetic energy of ammonium dinitramide based liquid propellant is 93.93%. In general, improving the absorption performance of propellant can significantly enhance the energy release of energetic propellant. Which has guiding significance for propellant design and selection.

Surface Topography and Biocompatibility of cp–Ti Grade2 Fabricated by Laser‐Based Powder Bed Fusion: Influence of Printing Orientation and Surface Treatments

The selective laser melting process, commonly known as laser‐based powder bed fusion (LB‐PBF), enables the production of structures with unprecedented degrees of freedom that represents an excellent condition for development of metallic implants for biomedical applications. Herein, the effects of laser energy density on relative density and microstructure (presence of internal defects) of cp‐TiGd2 fabricated by LB‐PBF are studied. Additionally, the influence of printing orientation and different surface treatments on surface topography and biocompatibility are investigated. The aim of the research is to develop additive manufacturing process parameters that can achieve full density of cp‐TiGd2 with satisfactory biocompatibility, as a low‐cost alternative to biomedical materials such as Ti–6Al–4 V and Ti–6Al–7Nb. A wide range variation of process parameters leads to an optimized process with high density up to 99.97 ± 0.008%, improved surface roughness, and noncytotoxicity in horizontal and inclined as‐built condition, as well as in Al2O3 (blasting angle 0°) condition.

Improving the microstructure and mechanical properties of laser powder bed fusion-fabricated tantalum by high laser energy density

The effect of laser energy density on the microstructural evolution and the mechanical properties, including tensile property and nanoindentation creep behavior of Ta parts were investigated. A high laser power strategy (600 W) was used to obtain Ta part with high density. The microstructure of Ta fabricated with 200 W comprised columnar grains with strong 〈111〉 texture, while equiaxed grains with random orientation were found in Ta fabricated with 600 W. The elongation to failure of the specimen fabricated at 600 W was higher than that of the specimen fabricated at 200 W, which stemmed from pore elimination and equiaxed grains. Nanoindentation creep results showed that the movement of dislocations was the main creep mechanism and the influence of laser energy density was discussed.

A multiscale composite silicon carbide wick with excellent capillary performance

Wick is the key component of the heat pipe. Composite wick with multiscale porous structure has gained increasing interest for the high permeability and large capillary pressure. In this study, a grooved silicon carbide wick (GSCW) with a multiscale porous structure was fabricated via sintering and laser ablation. The resultant wick is composed of main grooves, the surrounding porous space formed by the stacking silicon carbide (SiC) particles, the microscale netted pores, and nanoscale pores on the groove walls. The effects of laser energy density on the surface morphology, wettability, capillary rise velocity, and overall capillary performance parameter of the GSCW are investigated. The presented wick is hydrophilic. The capillary rise velocity in the initial stage of GSCW was 7 times that of sintered SiC wick. The capillary performance parameter increased with the increasing laser energy density. The laser-ablated grooves improve the capillary performance parameter over 50 times. The rising performances of water, acetone, methanol, and ethanol were tested. The wick thickness has a significant effect on the capillary performance. The comparison of GSCW with other composite wicks in the literature reveals that it has very good capillary performance, making it an excellent wicking structure for heat pipe.

Effect of laser energy density on microstructural evolution of selective laser melted Ti-15Zr alloy

Selective laser melting (SLM) has been widely applied to the design and production of alloys due to the efficiency in processing components with complex structures and large sizes, especially Ti alloys. However, SLMed Ti alloys always exhibit undesirable ductility since the amount and morphology of the acicular α′ martensite phase are difficult to control. In this study, a SLMed Ti-15Zr alloy with an excellent combination of strength (a yield strength of 792 ± 11 MPa, an ultimate strength of 837 ± 13 MPa) and ductility (18.7 ± 0.5 %) was successfully fabricated by adjusting laser energy density (E) during the SLM process and the subsequent heat treatment. The influence of E on densification and microstructural evolution was investigated. When E is in the range of 69–125 J/mm3, Ti-15Zr alloys can achieve a relative density greater than 99 %. With the increase of E, the coarse equiaxed α phase decreases, and the fine lamellar α phase increases in the alloys after the heat treatment, owing to the slow cooling rate in the molten pool at high E. The excellent mechanical properties were attributed to the coordinated effects of the coarse equiaxed α phase and the fine lamellar α phase.

The effect of laser energy density on microstructural evolution and mechanical properties of laser clad 316L stainless steel for repair

Laser energy density can affect the powder forming state in laser metal deposition (LMD), ultimately altering the evolution pattern and mechanical properties of formed structures. This work uses high-speed LMD technology to repair the 316L austenitic stainless steel plate with a trapezoidal groove. By analyzing the microstructural evolution and mechanical properties of repaired specimens under different laser energy densities, we revealed the effects of density on LMD shaping. Results indicated that the microstructure in the repair zone developed alternately in forms of columnar, branch, and isometric crystals in the opposite direction of heat flow. Increased laser energy density could enlarge crystal grains in formed structures. Meanwhile, γ-Fe tended to transform into δ phase that was distributed among crystal grains in γ-Fe. When the density reached its peak, the number of the δ phase plummeted. The average microhardness of specimens first increased and then decreased in the repair zone, with its distribution fluctuating repeatedly, and the values in this zone were 1.5–1.7 times that of the substrate. The mechanical properties of repaired specimens were superior to those of the rolled steel substrate at room temperature, and these specimens' ultimate tensile strength (UTS) and elongation at this temperature were positively correlated with the laser energy density. There were dimples and typical cleavage patterns around the fracture of tensile specimens, indicating that the fracture mechanism at room temperature was of quasi-cleavage type. As the density rose, the UTS first increased and then reduced in a tensile test conducted at 500 °C, during which the strain kept growing. Simultaneously, numerous dimples with congregate micropores but without typical cleavage patterns were observed in the fracture, which revealed that all specimens exhibited ductile fracture at high temperatures.

Effect of Laser Energy Density on the Microstructure and Microhardness of Inconel 718 Alloy Fabricated by Selective Laser Melting

This work focused on the effects of laser energy density on the relative density, microstructure, and microhardness of Inconel 718 alloy manufactured by selective laser melting (SLM). The microstructural architectures, element segregation behavior in the interdendritic region and the evolution of laves phases of the as-SLMed IN718 samples were analyzed by optical metallography (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and electron probe microanalysis (EPMA). The results show that with an increase in the laser volume energy density, the relative density and the microhardness firstly increased and then decreased slightly. It also facilitates the precipitation of Laves phase. The variation of mechanical properties of the alloy can be related to the densification degree, microstructure uniformity, and precipitation phase content of Inconel 718 alloy.

Effect of laser energy density on transformation behavior and mechanical property of NiTi alloys fabricated by laser powder bed fusion

This research investigated the influence of laser energy density on the phase transformation characteristics and structure, together with the mechanical property of NiTi shape memory alloys fabricated by laser powder bed fusion (LPBF). Results showed that randomly oriented needle-shaped martensite was distributed in the B2 austenite matrix in samples with the higher energy density. In contrast, typical columnar grains were observed throughout multiple melt pools, showing obvious epitaxial growth characteristics in the samples with lower energy density. Besides, the martensite transformation temperature varied approximately linearly with the increasing laser energy density, showing a positive correlation. It can be explained that more intense evaporation of Ni element in the melt pool under higher energy density leads to a reduction in the Ni content of the matrix and contributes to a reduction in the lattice distortion of the B2 matrix. Finally, the samples with the energy density of 138.89 J/mm3 showed optimal tensile and compression strength of 648 and 2970 MPa, respectively. This work provides a novel approach to optimize the performance of LPBF NiTi sample by tailoring the phase composition and structure through the laser energy density.

An austenite-rich composite of stainless steels with high strength and favorable ductility via selective laser melting of a powder mixture

Austenitic stainless steels (SSs) with excellent mechanical properties can be fabricated by selective laser melting (SLM). To enrich the variety of SLM-fabricated austenitic SSs and develop some SSs which possess desired properties and cost, an austenite-rich composite of stainless steels was fabricated by SLM of a powder mixture composed of 310 S and 430 SSs. The effect of laser energy density on the defects, microstructure and mechanical properties of materials was investigated. At an appropriate energy density (89.3 J/mm3), samples exhibited the best ultimate tensile strength (∼701 MPa) and elongation to failure (∼46.6%). However, the occurrence of strong keyholing and spattering phenomena severely weakened the tensile properties of samples at the highest energy density (113.6 J/mm3). For all samples, their microstructure was mainly composed of lots of austenite phase and some delta (δ) ferrite phase. The existence of ultra-fine sub-grains surrounded by dislocation networks played an important role in the tensile properties of samples. Particularly, the formation of fine δ-ferrite at grain boundaries of austenite could hamper the growth of austenite grains, and lots of dislocations are formed at the interface between austenite and δ-ferrite. The existence of δ-ferrite with a circular flow feature could inhibit the epitaxial growth of austenite grains.

Effects of laser energy density and path on residual stress of remanufactured key components for shield tunneling machine

Due to the abrasion and high cost of key components for shield tunneling machines, the failed or worn components are remanufactured by laser melting deposition (LMD) with paraxial powder feed. However, the residual stresses distributed in the cladding layer reduce the service life of remanufactured parts. In this paper, an experimental study is presented on residual stresses along the depth direction of cladding with varied laser energy density and deposition path. Residual stress in Fe-based coating and heat-affected zone (HAZ) is characterized by X-rays with the method of layer-removal. The microstructural evolution and the phase structure of laser deposited cladding layers are analyzed. The results indicate that the residual stresses, in the range of −624 to −86 MPa in the cladding layer, are mainly compressive while the tensile stresses (in the range of 200–550 MPa) are primarily in the heat-affected zone (HAZ). With the increase of the thickness of the cladding layer, the depth of the zero stress layer increases. The main phases in the cladding layer are α-Fe and γ-Fe. The microstructure in the top layers of the cladding consists of fine, equiaxed grains while in the lower layers, the grains are distinctly cellular.

Toward tunable microstructure and mechanical properties in additively manufactured CoCrFeMnNi high entropy alloy

Tailoring microstructure and mechanical properties of structural materials to meet application requirements is a long-standing challenge in materials science. Here we have studied the effects of laser energy density (LED) on the microstructure and mechanical properties of single-track CoCrFeMnNi high entropy alloy (HEA) samples fabricated by laser directed energy deposition (LDED). The results indicate that the molten pool size of the single-track HEA samples gradually increases with increasing LED. All of the samples possess a single face-centered cubic (FCC) solid solution structure. The microstructures of the single-track HEA samples are mainly composed of columnar and equiaxed grains, and as the LED increases, their grain size increases while the micro-hardness decreases. Additionally, the relationship among the processing parameters, cooling rate and grain size was investigated via combining the numerical simulation and experimental observations. This work provides mechanistic insights into establishing the processing-structure-property relationships in the additively manufactured HEAs and contributes to achieve LDED of tunable HEA parts with desired microstructure and mechanical performance.

Effect of laser energy density on microstructure, wear resistance, and fracture toughness of laser cladded Mo2FeB2 coating

To expand the applications of Mo2FeB2 ternary borides in industry, laser cladding technology was utilized to prepare Mo2FeB2 coating to improve the properties of the AISI 1045 medium steel substrate. The influence of cladding laser energy density (75–175 J⋅mm−2) on the obtained coating properties was studied, such as geometric characteristics, microstructure, microhardness, wear resistance, and fracture toughness. It can be found from the results that width and dilution rate increased with the increase of laser energy density when the coating had the same scanning speed or laser power, while the wetting angle had an opposite result. The ability of Marangoni convection was increased with the increase of laser energy density, and the hard phase particles became coarse and formed needle-like structures and herringbone structures. An excellent bonding zone was formed between the coating and the substrate. The direction of crystal structures in the bonding zone grew along the direction of heat dissipation. Based on the results of the mechanical properties of the coating, it can be concluded that the coating fabricated with 90 J⋅mm−2 laser energy density had the highest microhardness (1283.7 HV0.5) and excellent wear resistance (0.34 coefficient of friction, 2.9 mg wear mass loss). The wear forms were typical abrasive and adhesive wear, where a smooth worn surface was formed, and only pits or shallow grooves existed. The coating obtained with the highest laser energy density (175 J⋅mm−2) had a high fracture toughness value (16.73 MPa⋅m1/2). Besides, the coatings had typical transgranular fractures with different laser energy densities. Hence, a coating with perfect properties can be fabricated by adjusting laser cladding parameters.

Effect of laser energy density on microstructural evolution and wear resistance of modified aluminum bronze coatings fabricated by laser cladding

Modified aluminum bronze coating was successfully prepared using laser cladding. This research aimed to clarify the relationship between laser energy density and macrostructure, microstructure, microhardness and wear resistance of modified aluminum bronze coating. According to the experimental results it could be concluded that the reduction of laser energy density effectively improved the formability of the cladding layer surface, but low energy density could not fully melt powder. At the optimum laser energy density of 42.4 J/mm2, the cladding layer had the best combination of good flatness and density. There was no change in the composition phase categoryof samples prepared with varied laser energy densities, but the content of each phase varied. The aluminum bronze coating was mainly composed of α phase, κ phase, β’ phase. The content of α phase and κ phase reduced due to the decrease of laser energy density, and Widmanstatten side plate structure appeared in the case of low energy density. As the laser energy density decreased, the crystal grain size first decreased and then increased. An orthogonal scanning strategy leading to a random orientation of the aluminum bronze coating prepared by laser cladding shown as the EBSD pattern. The Schmidt factor and KAM increased with laser energy density decreased. Laser energy density played an important role in controlling the microhardness and wear resistance of coatings. Under the optimized process parameters, the maximum microhardness could reach 341.72 HV, and the minimum wear was only 4.37 × 10−2 mm3/N m.

Effects of laser energy density on microstructure and corrosion resistance of FeCrNiMnAl high entropy alloy coating

In this work, FeCrNiMnAl high entropy alloy (HEA) coating was successfully prepared by laser cladding technology on 17-4PH stainless steel substrate. The aim of the study was to investigate the effects of laser energy density (Led = 50 ∼ 70 J/mm2) on the geometric characteristics, microstructure and corrosion resistance of HEA coatings. The results indicated that Led would significantly affect the Geometrical characteristics of the coatings, and the height, depth and width increased with increasing laser energy density. In electrochemical tests, the corrosion resistance of coatings tended to increase and then decreased with increasing Led. At the Led of 65 J/mm2, the corrosion current density of the coating was only 1.156 × 10-5 A/cm2, indicating that the dense passive film was formed on the surface of HEA coating. The corrosion resistance of the coating was closely related to the passivation film on the surface of the coating. At the Led of 50 J/mm2, microcracks on the coating surface could facilitate ionic intrusion, resulting in poor corrosion resistance. However, at the Led of 65 J/mm2, the corrosion products on the coating surface were less and the corrosion resistance was optimum. Accordingly, the laser cladding process had a significant impact on the quality and performance of HEA coating. Modulation of laser process parameters was an effective method to optimize coating performance.

Correction to: Effect of Laser Energy Density on Surface Morphology, Microstructure, and Magnetic Properties of Selective Laser Melted Fe-3wt.% Si Alloys

Correction to: Effect of Laser Energy Density on Surface Morphology, Microstructure, and Magnetic Properties of Selective Laser Melted Fe-3wt.% Si Alloys

Structure and morphology of graphite nanoparticles treated by fiber laser irradiation

The graphite nanoparticles (GNPs) were prepared on the surface of monocrystalline Si by laser irradiation under different laser energy densities (3.3–8.33 kJ/cm2). The effects of laser energy density on structure and surface morphology were systematically investigated. The results show that the morphology of GNPs remained polycrystalline structure under laser irradiation with an energy density of 2.22 kJ/cm2. When the laser energy density was 2.78 kJ/cm2, the GNPs can induce the preset GNPs to transform into amorphous graphite nanofibers. The GNPs under the laser density of 3.33 kJ/cm2 showed a more amorphous structure. With the further increase of the laser energy density to 5.55 kJ/cm2, the main phase composition turned to SiC and Si.

Mechanism analysis of laser coloring of Ti alloy by optical simulation

The effects of laser energy density on the coloring effect were examined using a nanosecond fiber laser to color the surface of a TC4 Ti alloy. The surface of samples turns yellow, orange, purple, and blue as the single pulse energy density increases. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) results demonstrated that a mixed film containing TiN and TiO was formed on the surface of samples after laser coloring. The TiN content in the mixed film reduced with increase in single pulse energy density, whereas the TiO content increased. Based on the equivalent medium and optics theory, the SCOUT optical simulation software was used to create a three-layer structure model of ambient/mixed film/Ti alloy substrate. The superposition of reflection and interference in the mixed film was simulated to examine the effect of the mixed film’s composition and thickness on the reflective spectrum of sample. The reflective spectrum of different colors obtained by simulations and tests was extremely consistent, and the simulation composition and thickness of the mixed film were consistent with the tested results, indicating that the laser coloring mechanism is influenced by light interference between mixed films of different composition and thickness formed on the sample surface.

Effects of laser energy density on carbide dissolution, element distribution and microstructure evolution of AISI P20 steel after laser surface quenching

Effects of laser energy density on carbide dissolution, element distribution and microstructure evolution of AISI P20 steel after laser surface quenching