Laser Additive Manufacturing Technology Research Articles

Laser directed energy deposition remanufacturing of LPBF-processed TA15 parts: Hybrid process interface induced microstructure inheritance and mechanical performance

The laser additive hybrid manufacturing technology, which combines the precision of Laser Powder Bed Fusion (LPBF) and the flexibility of Laser Directed Energy Deposition (LDED), provides an effective solution for efficient forming and remanufacturing of large, complex components. The bonding zone (BZ) between LPBF and LDED forming regions is crucial for the final component performance. This study utilized LDED to remanufacture annealed LPBF substrates and investigated the microstructure and mechanical properties of TA15 alloy remanufactured parts. Results shows that a gradient microstructure forms at the bonding zone (BZ), where the bottom region exhibits a mixed structure including transitional β phase (βt), lamellar α and secondary α phase (αs). The top region shows a "ghost structure" of fine needle-like α phases. The mechanical property matched the microstructure well, as the hardness in the upper BZ reaches up to 463 MPa, whereas the LFZ exhibits the lowest hardness at 401 MPa. As the angle between the LDED region edge and tensile direction increases, the tensile strength first increases and then stabilizes, while elongation increases initially and then decreases. At a tilt angle of 60°, the strength peaks at 1098 MPa; at a 30° angle, the elongation reaches a maximum of 10.336%. All samples fracture at the LPBF zone, indicating that the formation of fine lamellar α phases in the BZ contributes to its higher strength compared to LPBF substrate and LDED deposition zones.

High-power fiber laser incident beam absorptivity variation of molten pool surfaces during their solid-liquid-gas state evolution

The thermal and ablation effects of lasers are widely used in laser additive manufacturing, laser welding, laser cleaning, and laser cladding technologies. Absorptivity is the core index of laser beam-thermal energy conversion efficiency. This paper analyzed the irradiated material's absorption behavior during the solid-liquid-gas evolution of laser-ablated metal surfaces by comparing the temperature fields and the corresponding weld cross-sections for different laser action periods, considering the fusion and vaporization latent heats. The solid-liquid-gas state evolution of high-power fiber laser-irradiated metal surfaces occurs during several milliseconds, with a short solid-phase existence period, since fusion or melting time is much shorter than the vaporization time. As the solid-liquid-gas state evolves, the average absorptivity and the share of thermal conduction energy loss decrease with the laser action time, while the fusion energy loss gradually increases. The solid-phase surface of the metal in laser processing absorbs significantly more incident laser energy than the liquid-phase one. The longer the solid-phase occurrence period of the metal surface during the laser action, the greater its average absorptivity of the incident laser. By increasing the laser spot area and scanning rate, the solid-phase period of the laser-irradiated metal surface can be increased, improving its incident laser absorptivity.

Microstructure and properties of underwater in-situ wire-based laser additive manufactured duplex stainless steel

ABSTRACT A novel underwater in-situ wire-based laser additive manufacturing (ULAM) technology is proposed for the in-service repair of underwater components in nuclear power plant. Duplex stainless steel (DSS) obtained in air and underwater environments were analysed using material characterisation and testing methods. The effects of underwater additive environments on the microstructure evolution, mechanical properties and corrosion resistance of the specimens were investigated. The results show that the laser heat input is consumed to balance the heat loss of the water-cooled base material during the underwater laser additive manufacturing process, leading to a reduction in the heat input to the molten pool. Underwater specimen exhibit a two-phase balance, with small ferrite grain boundary angles, resulting in better tensile strength and corrosion resistance. Laser reheat treatment leads to a phase change in microstructure, which can enhance the microhardness and the tensile strength. The ULAM system can meet the requirements of actual engineering for cladding layer.

A comparative study on the corrosion, wear, and tribocorrosion performances of Ti-6.5Al–2Zr–1Mo–1V (TA15) alloy fabricated by selective laser melting and laser metal deposition

Corrosion-erosion performances of Ti-6.5Al–2Zr–1Mo–1V (TA15) alloy fabricated by two laser additive manufacturing technologies, namely selective laser melting (SLM) and laser metal deposition (LMD) were investigated, and compared with those of traditional forged counterpart. Results show that SLM-ed TA15 possesses better corrosion, wear, and tribocorrosion resistances than LMD-ed and forged TA15. This is mainly attributed to the ultrafine-grain αʹ phase in the microstructure of SLM-ed sample, which improves the hardness and thereby enhances the wear and tribocorrosion resistance. Additionally, the complete αʹ phase formed in SLM-ed sample also avoids the galvanic corrosion that occurs at the α+β-type LMD-ed and forged samples.

Research progress in laser additive manufacturing of aluminum alloys: Microstructure, defect, and properties

Laser additive manufacturing (LAM) has attracted significant interest in developing Al alloys due to its potential to fabricate structural components at low cost and high efficiency. Nevertheless, LAM Al alloys still suffer many issues, including heterogeneous microstructure, various defects, and poor mechanical properties, significantly hindering the advancement of LAM Al alloys. This article seeks to provide a comprehensive overview of the current advancements made in the field of LAM Al alloys and attempts to establish an in-depth relationship between microstructural characteristics, defects, and performances. Development status and limitations of LAM technologies are described, microstructural characteristics of Al alloys in LAM are introduced, mechanisms of formed defects and corresponding mitigation measures are discussed, and current quality improvement strategies are summarized. Following the research of previous work, this review will provide an outlook on overcoming the existing challenges and provide a helpful resource and reference for the development of LAM Al alloys.

Microstructure and mechanical properties of Cu-Cr-Zr alloy prepared by electron beam additive manufacturing and laser-MIG hybrid welding

Cu-Cr-Zr alloys are widely used as medium-strength and high-conductivity copper alloys in aerospace, transportation and electronic information fields. The application of additive manufacturing technology is expected to realize the preparation of Cu-Cr-Zr alloy parts with complex structure and superior property. However, the commonly used laser additive manufacturing technology is not applicable to the preparation of copper alloys due to its intrinsic high reflection to laser. In this study, we adopted two technologies, i.e., electron beam additive manufacturing (EBAM) and laser-metal inert gas hybrid welding (laser-MIG), for the preparation of Cu-Cr-Zr alloys. Finite element simulation was employed to simulate the temperature field and residual stress field of the material during solidification. The microstructure, relative density, microhardness, tensile properties and electrical conductivity of the as-fabricated samples were characterized. The results showed that samples with better moldability were obtained by both methods at a line energy density of 600 J/mm. In the top area, both methods exhibit medium-sized equiaxed grains with more precipitated phases, showing the best comprehensive properties. The EBAM method demonstrates superior formability, better relative density and electrical conductivity due to more stable temperature field changes. On the other hand, the laser-MIG method obtains finer grains and higher mechanical properties because of a faster cooling rate, but leads to a decrease in relative density and electrical conductivity. This study presents new experimental data for Cu-Cr-Zr alloys prepared by EBAM and laser-MIG methods, contributing to extend the application of additive manufacturing in the preparation of Cu alloys.

Hybrid Laser Additive Manufacturing of Metals: A Review

Due to the unparalleled benefits of traditional processing techniques, additive manufacturing technology has experienced rapid development and continues to expand its applications. However, as industrial standards advance, the pressing needs for high precision, high performance, and high efficiency in the manufacturing sector have emerged as critical bottlenecks hindering the technology’s progress. Single-laser additive manufacturing methods are insufficient to meet these demands. This review presents a comprehensive exploration of metal hybrid laser additive manufacturing technology, encompassing various aspects, such as multi-process hybrid laser additive manufacturing, additive–subtractive hybrid manufacturing, multi-energy hybrid additive manufacturing, and multi-material hybrid additive manufacturing. Through a thorough examination of the principles of laser additive manufacturing technology and the concept of hybrid manufacturing, this paper investigates in depth the notable advantages of hybrid laser additive manufacturing technology. It provides valuable insights and recommendations to guide the development and research of innovative machining technologies.

Exceptionally strong and ductile bulk metallic glass composite with bioinspired architecture mimicking porcupine fish spine

Introducing soft crystalline phases into the glassy matrix to produce bulk metallic glass composites (BMGCs) is an effective way to enhance the ductility of bulk metallic glasses (BMGs). However, the introduction of soft crystalline phases severely sacrifices the strength, resulting in the strength-ductility trade-off. To defeat this dilemma, here, we successfully fabricate a bioinspired BMGC with architecture mimicking a porcupine fish spine. The bioinspired BMGC shows a pronounced yield strength of ∼800 MPa with an excellent fracture strain of ∼35 %. The fabrication of the bioinspired BMGC is achieved through infiltration and vitrification of molten Zr50Ti5Cu27Ni10Al8(Zr50) melt into the crystalline Nb skeleton fabricated by laser additive manufacturing (LAM). Such enhanced strength-ductility synergy is attributed to the asynchronous deformation associated with the delicate bioinspired heterogeneous architecture. The bioinspired structural design motif, enabled by the combination of LAM and infiltration casting technologies, opens a new window to develop high-performance BMGCs on a large scale for structural applications.

Enhancing tensile properties of laser additive manufactured FeCoNiCrMn high entropy alloy via adding Fe-based metallic glass

It has always been difficult to significantly improve the tensile strength of FeCoNiCrMn high entropy alloy (HEA) by traditional technical methods. Here, high-strength Fe-based metallic glass (MG) was precisely selected as the strengthening phase to reinforce the mechanical properties of FeCoNiCrMn HEA fabricated by laser additive manufacturing (LAM) technology. The results showed that although the addition of Fe-based MG with 5 wt% did not change the original phase composition of HEA, it facilitated grain refinement to a great extent. Of special significance was that the strength and ductility of HEA-MG exhibited a synergistic enhancement (σy, σUTS and εf were increased by 23.8 %, 28.4 % and 31.0 %, respectively) after Fe-based MG addition, deriving from the grain refinement, increased the dislocation density and formation of deformation twins.

Effect of laser beam energy density distribution on the main properties of laser additive forming of metal parts

Compared to traditional processing techniques, laser additive manufacturing technology has advantages such as short processing cycles, no molds, and is not limited by complex structures. However, the forming quality of GH3625 nickel-base alloy metal parts is affected by various process parameters, in which the distribution characteristics of laser beam energy density, microstructure and mechanical properties play a key role. In order to investigate the influence of beam energy density distribution on the main properties of GH3625 nickel-based alloy metal parts, the beam energy density distribution was changed by controlling the defocusing amount. Then it sets 5 different defocusing parameters to obtain the corresponding energy density distribution characteristics. Observing and analyzing the various properties of alloy powder from the perspectives of different scanning speeds, laser power, and energy density distribution characteristics. The results show that when the laser power is 600 W, the scanning speed is 700 mm/min, and the energy density distribution is characteristic 4, the metal parts have the best performance. Its density is 99.90%, microhardness is 350.44 HV, tensile strength is 1328 Mpa, friction coefficient is about 0.51, and wear rate is 0.55%. This indicates that the laser additive forming method proposed in this study can effectively improve the hardness, density and other properties of GH3625 nickel-based alloy metal parts to achieve the best state, which provides an important reference for the further optimization of the material preparation process.

Simultaneous improvement of strength and ductility of laser additively produced Ti6Al4V by adding tantalum

Laser additive manufacturing (LAM) technique can efficiently fabricate Ti6Al4V components of complex shapes, but often show poor mechanical properties. In this study, tantalum (Ta) was added into Ti6Al4V as an alloying element to improve the overall mechanical performance using a laser cladding system. It was found that Ti6Al4V–4Ta (corresponding to 4 wt% Ta) exhibited excellent mechanical performance with the yield stress of 956 MPa, ultimate tensile strength of 1042 MPa and the elongation of 10.8 %, meeting the ISO 7209 requirements for titanium and titanium alloys. The synergistic improvement of strength-ductility of Ti6Al4V–4Ta was attributed to the microstructure refinement, weakened α-variants selection, Ta solid solution, modified dislocation density and β phase content. Further quantitative analysis demonstrated that the strength increase was mainly contributed from the additional grain boundary, solid solution and dislocation induced by Ta elemental alloying. This study established Ta elemental alloying as an effective method to simultaneously enhance the strength and ductility of Ti6Al4V alloy using LAM technology.

Melt-grown behaviour of heat treated high-purity alumina ceramics prepared by laser directed energy deposition

Laser additive manufacturing technologies have attracted attention for the rapid preparation of melt-grown oxide ceramics, which are promising for high-temperature applications. However, the limitation of the mechanical properties and lack of understanding of high-temperature stability limit the applications of this type of material. In this study, the effect of heat treatment on melt-grown high-purity alumina ceramics prepared by laser-directed energy deposition (LDED) was investigated. The results show that melt-grown alumina ceramics have excellent high-temperature stability, as evidenced by the negligible changes in weight, geometric size, roughness, and phase composition after heat treatment. Compared with the same deposited material without heat treatment, the flexural strength of the heat-treated material is significantly increased, and the maximum strength can reach 547.85 ± 78.81 MPa, an increase of 102.96%. This increase in strength is attributed to crack healing during the heat treatment process. The heat treatment had less influence on the microhardness and fracture toughness. The results presented here can provide technical guidance for the fabrication of high-performance melt-grown high-purity oxide ceramics using LDED technology.

Microstructure and mechanical properties of Inconel 718 thin walls prepared by laser direct energy deposition and selective laser melting

This paper systematically investigates the microstructure, crystal structure and related mechanical properties of Inconel 718 thin walls prepared by two different methods, laser direct energy deposition (LDED) and selective laser melting (SLM), which are representative technologies for laser additive manufacturing of high-performance metal parts, and compares with conventional forged parts. The microstructure of SLM-part consists of columnar and equiaxed crystals with disordered growth directions, while LDED-part is mainly composed of coarse columnar crystals that grow perpendicular to the plane of the molten pool free surface. Unlike a strong 〈001〉 texture in the LDED-part, the SLM-part has a {110} texture in the XY plane, achieving stronger tensile strength due to different grain boundary strengthening and dislocation strengthening effects, which is found by comparing with LDED and forged Inconel 718 alloy. In addition, the difference in crystallographic texture between SLM and LDED-parts results in the different mechanical property anisotropy. The comparative study of two laser additive manufacturing technologies provides guidance for an in-depth understanding about the mechanism of laser additive manufacturing high-performance metal parts.

Enhancement of Microstructure and Mechanical Properties of High Nb-TiAl Alloys Prepared Using Laser Additive Manufacturing by Annealing Treatment

The microstructure, phase composition, hardness, and tensile properties of the Ti-48Al-2Cr-5Nb alloy have been systematically investigated using laser additive manufacturing technology. Results indicate that both the as-deposited and annealed microstructures contain both the α2 (Ti3Al) and γ (TiAl) phases. As the annealing temperature increased, the structure changed significantly from a large block structure to a fine equiaxed structure and finally to a large lamellar structure. Nevertheless, the amount and distribution of precipitation of α2 phase are obviously different, especially during the annealing at 1260 °C, where the fine α2 phases are evenly distributed on the γ phase matrix. The hardness value of the as-deposited sample is the highest, with a HV value of 484 at the room temperature, while the hardness value of the annealed sample at 1260 °C is the smallest, with a HV value of 344. An annealed sample at 1260 °C exhibits the highest tensile strength and elongation at room temperature, with values of 598 MPa and 2.1%, respectively. These values are increased by 1.15 times and 1.4 times compared to the as-deposited sample (519 MPa, 1.5%).

Assessment of self-lubricating coated cutting tools fabricated by laser additive manufacturing technology for friction-reduction

Dry cutting acting as a green machining technology is a promising manufacturing process in industrial applications; however, severe friction under dry cutting conditions aggravates tool wear and reduces tool life. Self-lubricating cutting tools exhibit excellent benefits in improving cutting properties and that can be used in sustainable machining. The complex process, low efficiency and thin coating thickness limit the production and use of present self-lubricating cutting tools with traditional methods. To enhance the lubricating effect and motivate the development of fabrication methods for self-lubricating cutting tools, Ni-based powders dispersed with MoS2 and Al2O3 particles were preset on the tool substrate; afterward, the self-lubricating coatings were deposited by laser powder-bed fusion additive manufacturing (AM) with a nanosecond fiber laser for cutting application. The self-lubricating coatings were characterized, and the friction and cutting performances of the AM self-lubricating coated tools (SLCs) were evaluated by sliding friction and dry machining tests. The results show that the developed SLC tools reduced the friction coefficient by 8.8–11.7%, cutting forces by 17.6–29.6%, and cutting power by 17.3–22.0% compared to conventional high-speed steel cutting tools (HSS). Built-up edge formation and tool wear were also significantly reduced. The observed mechanisms were attributed to the release of MoS2 particles from the coatings forming a lubricating film at the tool-chip interface, while the Al2O3 particles enhanced surface hardness. The results revealed the practicability of self-lubricating coated cutting tools fabricated by laser-based AM for friction-reduction, and that provide a cleaner process for dry cutting applications.

Influence of laser energy density on the microstructure and corrosion resistance of LPBF‐fabricated titanium‐based nanocomposites

AbstractAs a high‐efficiency laser additive manufacturing technology, laser powder bed fusion (LPBF) has unparalleled advantages in the manufacture of titanium matrix composites. In this work, the effect of laser energy density (LED) on the forming quality, microstructure evolution, and corrosion resistance of LPBF‐fabricated nanographene oxide reinforced titanium matrix nanocomposites (GO/TC4) was investigated. The results show that the optimal surface roughness and relative density of GO/TC4 nanocomposites fabricated by LPBF are 11.8 μm and 99.40%, respectively. The microstructure is mainly acicular α/α′‐Ti, accompanied by a small amount of β‐phase grain boundaries. When the LED is increased to 58.33 J/mm3, the self‐corrosion potential of GO/TC4 sample reaches 0.345 V in 3.5 wt% NaCl solution, and the GO/TC458.33 nanocomposite exhibits the highest corrosion resistance. The results revealed that the corrosion products on the surface of the samples were mainly composed of a passivation film of TiO2 and a small amount of Al2O3.

Microstructure and mechanical performance of laser additive manufacturing Ni50Ti40Cu10 and Ni45Ti40Cu15 alloy

Ni-Ti-Cu alloy can not only prevent scale and biological adhesion, but also has applications in aerospace, automotive engineering, and nanotechnology. In this study, Ni50Ti40Cu10 and Ni45Ti40Cu15 alloy large-size thin-walled parts are prepared on the surface of Ti plates using laser additive manufacturing technology. The optimum operational parameters are explored through a two-factor controlled variable method, based on which the effects of TiC and TiB2 addition on the forming quality of Ni50Ti40Cu10 and Ni45Ti40Cu15 alloys are further investigated. SEM, EDS, and other testing methods are used to determine the microstructure composition and distribution, and the composition of the physical phases of the alloy. Finally, tensile and hardness tests are carried out to study the mechanical properties of the alloy. The results show that the better operational parameters for laser additive manufacturing of large-size thin-walled Ni50Ti40Cu10 and Ni45Ti40Cu15 alloys are 1250w laser power and 300 mm min−1 scanning speed. 0.6 wt% TiC addition can achieve better forming quality of the large-size thin-walled parts. The large-size thin-walled Ni50Ti40Cu10 alloy precipitates significantly more Ti2Ni strengthening phases than the large-size thin-walled Ni45Ti40Cu15 alloy. Ni50Ti40Cu10 alloy large-size thin-walled parts have 20% higher tensile strength and 45.4% higher elongation compared to Ni45Ti40Cu15 alloy. The average hardness of Ni45Ti40Cu15 large-size thin-walled parts is 3.4% lower than that of Ni50Ti40Cu10 alloy.

Experimental study of mechanical properties of laser additively manufactured 316L stainless steels

Laser additive manufacturing (LAM), as an advanced additive manufacturing technology, has high efficiency and excellent precision in producing large size 3D printing elements. It has proven potential for application in buildings and civil infrastructure. However, in order to apply LAM technology to the production of components in civil engineering, it is necessary to understand comprehensively the mechanical properties of LAM products. In a previous study, the mechanical properties in the layer plane of LAM 316L stainless steels have been studied, but the mechanical properties in the building elevation plane are still unknown. To this end, an experimental study into the mechanical properties and microstructure of LAM 316L stainless steels has been undertaken and is reported in this paper. A total of 18 tensile coupons with two nominal thicknesses were extracted in various orientation angles relative to the print layer from the LAM prims for the uniaxial tensile tests. The influences of the orientation angle and thickness on the mechanical properties of LAM 316L stainless steels were investigated through the tensile tests. The test results show high anisotropy of the LAM 316L stainless steels in the building elevation plane, for which the anisotropy indexes of all mechanical properties exceed 10%, and the anisotropy indexes of the elastic modulus, Poisson's ratio and the proof stresses even exceed 25%. In addition, a very small Poisson's ratio value and an extreme short softening stage of stress–strain curves after peak values were identified for the coupons with the orientation angle θ = 45°. Microstructural characterisation of the LAM 316L stainless steels was also examined by means of optical microscopy and scanning electron microscope (SEM). The microstructure analyses observe an obvious layered structure perpendicular to the building direction and some columnar crystals perpendicular to the layer plane crossing the boundary, which might explain the reasons causing the high anisotropy of the macroscopic mechanical properties of LAM steels.

Semisolid-Liquid Fabrication of Cu–Cr Pseudobinary Alloy by Laser-Directed Energy Deposition

Copper–Chromium (Cu–Cr) pseudobinary alloys are promising materials for electrical application. Nevertheless, their fabrication remains limited by traditional techniques, which are not suitable for manufacturing homogeneous Cu–Cr alloys with uniformly distributed elements. Recently, semisolid-liquid manufacturing method has emerged as a promising technique route to fabricate Cu–Cr alloys. In this work, the laser-directed energy deposition (L-DED) as one of the laser additive manufacturing (LAM) technology, was successfully introduced for semisolid-liquid fabricating the homogeneous Cu–30 mass%Cr alloys. The obtained Cu–Cr alloys are constituted by fully melted Cu metallurgically combined with semisolid-liquid Cr. The close combination of Cu and Cr is benefit to improve the electrical conductivity of the alloy.

Microstructural evolution and performance improvement mechanism of Ti–6Al–4V fabricated by oscillating-wire laser additive manufacturing

This work proposes an oscillating wire laser additive manufacturing (O-WLAM), which is based on the wire laser additive manufacturing technology (WLAM) and combined with the laser oscillating welding technology. For different laser oscillation patterns, it shows a trend that metallurgical defects such as porosity, microstructural and columnar grain size decrease with the increase of oscillation frequency and oscillation amplitude. In solidified grains formed under laser oscillation, a complex oscillation of melt pool agitation could lead to a refining effect on the β grains size. The corresponding tendency of epitaxial growth of the prior β grains is weakened as well. The process experiments in this work provide a new idea of laser oscillation for wire laser additive manufacturing. The use of laser oscillation to achieve improvement of metallurgical defects and optimization of microstructure has some guiding significance for wire laser additive manufacturing.