Laser Additive Manufacturing Research Articles

Effect of multi-element synergistic addition on the microstructure evolution and performance enhancement of laser hot-wire cladded Fe-based alloy

To satisfy the requirements of hardness and corrosion resistance for laser additive manufacturing of hydraulic supports, this study applied the synergistic addition of C, B, Cr, Ni, Nb and Mo elements in Fe-based alloys. The multi-phases, martensite + austenite + ferrite were designed. The microstructure, hardness and corrosion resistance of the coatings were analyzed. Increasing the C and B contents could significantly increase the hardness of the coatings, while the corrosion resistance was decreased. The corrosion resistance of the coatings was determined by the Cr contents. However, increasing the Cr contents to 20.0 wt % resulted in the ferrite structure with lower hardness (21 HRC). The coatings with 0.25 wt % C, 1.2 wt % B and 19.0 wt % Cr showed the optimal matching of hardness (56 HRC) and corrosion resistance (survived in neutral salt spray test≥300h). The resulted coatings were mainly consisted of dendritic structure. Fine lath martensite phase was dominant in the dendrite regions. The interdendritic regions were consisted of nano-sized intermetallics with a mixture of σ+Nb + FeNb + Cr2Nb+(Fe,Cr)2B + NbC compounds. These interdendritic regions (14.2 GPa) showed higher hardness than that of the dendritic regions (7.1 GPa). The high Cr contents with finer dendritic structures were the major mechanisms for the excellent combination of hardness and corrosion resistance. The precipitation and growth mechanisms of the interdendritic phases were elaborated. This work provides a valuable reference for laser hot-wire cladding to prepare Fe-based alloys with high hardness and excellent corrosion resistance.

Minimizing Defects in Additive Manufacturing and Laser Welding Through Energy Coupling Experiments and Dynamic Modelling

Additive manufacturing is a revolutionary technology that produces complex components as a single piece, replacing traditional assemblies and reducing waste. Laser powder bed fusion, a type of additive manufacturing, allows for limitless design freedom by building intricate parts layer-by-layer through melting and fusing metal powder. However, build quality remains inconsistent, with deformations like pores and spattering occurring. To improve modelling of the behaviour of melted metal, thus minimizing defects, an experiment which determined the metal’s absorptance of laser energy through integrating sphere radiometry was conducted. The integrating sphere, which spatially integrated a fraction of measured light to calculate full radiance, had to sit above the build plate and not interfere with powder spreading. I designed two parts which attached the integrating sphere to the motorized powder spreading blade. Utilizing small ridges in the enclosure as weight-bearing tracks, the blade’s torque was reduced while allowing precise movement of the sphere. Through implementing these parts, the experiment was conducted, whose results will aid in our understanding of laser-metal interactions. Defects like spattering also occur during laser welding, due to the vaporization of unstable liquid metal. To combat this, novel beam shapes have been seen to increase the stability of the keyhole. To model this effect, I created a phenomenological, dynamic model of the keyhole depth during a copper weld. Two differential equations were created to model the keyhole depth’s rate of change using a dual mode and single mode laser, depending on absorptance and incident laser intensity. The dynamic depth of the keyhole for both modes was numerical solved in Python and iterated using existing copper weld data. Through better quantitative understanding of energy coupling and numerical modelling of the resulting dynamics, defects in laser welding and additive manufacturing can be minimized.

Research status on the effect of energy density on the forming microstructure and properties of nickel-based superalloys for laser additive manufacturing

Abstract Nickel-based superalloys have excellent high-temperature mechanical properties, corrosion resistance and oxidation resistance, and strong machinability. It is widely used in aerospace, submarine and shipbuilding, petrochemical, electronic industry and other industries. However, there are still challenges in the popularization and application of nickel-based superalloys for alloy components with complex structures and extremely harsh working conditions. In this paper, the research status of the influence of energy density on the microstructure and properties of laser additive fabrication of nickel-based superalloys at home and abroad is reviewed. The influence of energy density on the microstructure evolution behavior and mechanical properties improvement effect of laser additive manufacturing nickel-based superalloys is summarized. The mechanism of energy density was discussed from the perspectives of microstructure evolution and macroscopic performance change. Based on the individual effects and synergistic effects of each process parameter, the influence of laser energy density on dendrite growth, phase precipitation characteristics, element distribution and porosity defect control effect of nickel-based superalloy was expounded, as well as the influence mechanism on microhardness, wear resistance and residual stress. Finally, the energy density optimization and development prospect of laser additive fabrication of nickel-based superalloys are prospected.

Sub-surface thermal measurement in additive manufacturing via machine learning-enabled high-resolution fiber optic sensing

Microstructures of additively manufactured metal parts are crucial since they determine the mechanical properties. The evolution of the microstructures during layer-wise printing is complex due to continuous re-melting and reheating effects. The current approach to studying this phenomenon relies on time-consuming numerical models such as finite element analysis due to the lack of effective sub-surface temperature measurement techniques. Attributed to the miniature footprint, chirped-fiber Bragg grating, a unique type of fiber optical sensor, has great potential to achieve this goal. However, using the traditional demodulation methods, its spatial resolution is limited to the millimeter level. In addition, embedding it during laser additive manufacturing is challenging since the sensor is fragile. This paper implements a machine learning-assisted approach to demodulate the optical signal to thermal distribution and significantly improve spatial resolution to 28.8 µm from the original millimeter level. A sensor embedding technique is also developed to minimize damage to the sensor and part while ensuring close contact. The case study demonstrates the excellent performance of the proposed sensor in measuring sharp thermal gradients and fast cooling rates during the laser powder bed fusion. The developed sensor has a promising potential to study the fundamental physics of metal additive manufacturing processes.

Composition design and mechanical properties of B4C/Al-Zn-Mg-Cu functionally graded materials prepared by laser additive manufacturing

In this study, three types of three-layer functionally graded materials (FGMs) were designed by mainting the average content of the reinforcement constant and changing the span of the composition. The B4C particle-reinforced Al-matrix FGMs and a homogeneous composite (HC) with the same average composition were prepared using the laser additive manufacturing technique. The FGMs had a higher average secondary-phase content and grain size than the HC. Large (black) and reticulated (white) secondary phases corresponding to B4C phase, T phase, and MgZn2 were observed in the as-deposited FGM samples. The content of the secondary phase in the middle layer was generally low. The bottom layer, which was in direct contact with the substrate, exhibited the smallest grain size. The hardness and wear resistance significantly improved owing to the high B4C content in the top layer. The flexural behaviors of each layer of the FGM in different directions were systematically studied. The plasticity of the single-layer material decreased with increase in the B4C content. When the bottom layer had a high B4C content, the flexural ability significantly reduced. Among all the samples, G2 with 8% B4C particle content in the top layer exhibited the best comprehensive mechanical properties. The hardness value, wear rate of the top layer, maximum bending stress, and maximum bending strain of the FGM were 177.5 HV, 0.367 × 10−3mm3/(N·m), 585.6 MPa, and 7.36%, respectively. This study can provide a reference value for the future design and development of wear-resistant gradient materials for aerospace applications.

Lossless compression for laser additive manufacturing using continuous rows compressed storage

PurposeThe layer section of laser additive manufacturing (AM) can be rasterized. Subsequently, the rasterized layer section can be converted into sparse matrix. However, large storage space is occupied due to the high manufacturing resolution. In order to reduce the storage space, the purpose of this research is to propose a lossless compression method to compress the sparse matrix.Design/methodology/approachA lossless compression method for additive manufacturing is proposed. According to manifold and irregularity feature of the object of laser AM, a lossless compression method called continuous rows compressed storage (CRCS) based on continuous rows is innovatively proposed. In particular, the better direction strategy of compression method is selected based on the side-projected area per layer.FindingsTake human teeth as an example, compared with compressed sparse row (CSR), the CRCS has advantage up to 98.88% in storage space. Compared with block compressed sparse row (BCSR), the CRCS has advantage up to 60.04% in storage space.Originality/valueThe proposed CRCS could be employed to compress the sparse matrixes of rasterized layer sections of laser AM. Compared with common lossless compression method of sparse matrix, the compression ratio of CRCS is greater. CRCS is propitious to reduce the storage space usage, thereby improving transmission efficiency.

A Study of the Corrosion Resistance of 316L Stainless Steel Manufactured by Powder Bed Laser Additive Manufacturing

Commercially available 316L (1.4404) stainless steel is commonly used for industrial filtration due to its combination of good material properties, particularly its corrosion resistance, which is a critical factor for filters in corrosive (e.g., saltwater) environments. Recently, laser powder bed fusion (LPBF) has enabled new more complex and efficient filtration pieces to be manufactured from this material. However, it is critical to know how the corrosion resistance is affected by this manufacturing strategy. Here, the corrosion resistance of LPBF manufactured 316L stainless steel is compared with wrought 316L sheet. The corrosion of the samples in saltwater was assessed with asymmetric electrochemical noise, potentiodynamic polarisation curve, and electrochemical impedance spectroscopy. The samples before and after corrosion were examined with scanning electron microscopy and energy-dispersive spectroscopy. The LPBF samples had higher corrosion resistance than the sheet samples and were more noble. The corrosion resistance of the LPBF sample increased with time, while the wrought sample corrosion resistance reduced over time. The corrosion mechanism of both samples was stable with time, formed of a passive film process and a bared material process. This paper presents the first study about the temporal evolution of the LPBF 316L stainless steel corrosion mechanism.

Alloying effects on the microstructure and properties of laser additively manufactured tungsten materials

A large body of literature within the additive manufacturing (AM) community has focused on successfully creating stable tungsten (W) microstructures due to significant interest in their application for extreme environments. However, cracking and additional embrittling features at grain boundaries have resulted in poorly performing materials, stymying the application of AM as a manufacturing technique for W. Several alloying strategies, such as ceramic particles and ductile elements, have emerged with the promise to eliminate cracking while simultaneously enhancing stability against recrystallization. In this work, we provide new insights regarding the defects and microstructural features that result from the introduction of ZrC for grain refinement and NiFe as a ductile reinforcement phase – in addition to the resulting thermophysical and mechanical properties. ZrC is shown to promote microstructural stability with increased hardness due to the formation of ZrO2 dispersoids. Conversely, NiFe forms into micron-scale FCC phase regions within a BCC W matrix, producing enhanced toughness relative to pure AM W. A combination of these effects is realized in the WNiFe + ZrC system and demonstrates that complex chemical environments coupled with the tuning of AM microstructures provides an effective pathway for enabling laser AM W materials with enhanced stability and performance.

Enhancing reliability in laser powder bed fusion through substrate modification: microstructure, mechanical properties and residual stress

Laser additive manufacturing (LAM) is prone to excessive tensile residual stresses, leading to cracking or even failure, seriously hindering its wide application. Therefore, controlling residual stress to avoid crack formation and improve forming quality is crucial for reliable LAM. Most of the past research controls the residual stresses by modifying the process during the forming process, which is a very complicated method. In this study, through alterations in the form of a substrate to modify its restraint effect on the resulting structure and heat dissipation channels, the impact of them on the microstructure, defects, residual stress, and fracture characteristics to mitigate the likelihood of cracking in laser powder bed fusion (LPBF) was systematically studied. The results showed that the microstructure of all the specimens consists of fine dendritic, cytosolic, and columnar. Specimens with un-grooved substrates exhibited more holes and cracks, and solidification cracks were predominant. The crack density in specimens with grooved substrates was reduced by 71 %, reaching a relative density of 98.94 %. Tensile test results showed that the mechanical properties of the grooved specimens were excellent, with the tensile strength and yield strength higher than the un-grooved samples by 29 MPa and 11.7 MPa, respectively. And the results of the residual stresses indicated significantly lower tensile residual stresses in specimens with grooves, due to reduced restraint stresses and increased heat dissipation, mitigating the extent of crack propagation. These findings provided a simpler new approach to LPBF of crack-free components with excellent mechanical properties.

Development of Composite Intelligent Services Operating in a Heterogeneous Environment

The paper discusses methods, approaches, tools and technologies for composite service development. The expediency of applying the considered principles to create software application of so-called composite artificial intelligence (AI) is noted in order to implement the latter within the "distributed artificial intelligence as a service" (DAIaaS) paradigm. With the participation of the authors, the IACPaaS (Intelligent Applications, Control and Platform as a Service) cloud platform has been created and continues to be actively developed. It is intended for the creation, use and maintenance of multi-agent intelligent services that process ontological knowledge graphs. Currently, the platform provides such cloud service delivery models as PaaS (platform as a service), SaaS (software as a service), DaaS (data as a service) and Desktop as a Service. One of development directions is to provide support for the DAIaaS paradigm. It consists in the designing and implementation of tools that make it possible to use the platform and its services as components of composite applications (including AI ones) operating in a heterogeneous distributed computing environment. As a result, language and software tools were created that allow the development of distributed intelligent systems, some of the components of which are located on the IACPaaS platform, and the rest are located elsewhere. Depending on where the leading component is placed, certain tools and technologies implemented on the platform are used. The article also contains examples of created services for several domains (medicine, transport modeling, laser additive manufacturing) and options for using the platform.

Optical properties of transparent TiO2 films by sintering anatase nanoparticles with a CO2 laser

A novel CO2 laser additive manufacturing technique is reported in this paper for depositing transparent TiO2 films on quartz substrates using anatase TiO2 nanoparticles (NPs). Single- and double-layers of TiO2 films were prepared in two stages: (i) wet deposition using the spin-coating technique, and (ii) laser-assisted both drying of the wet layer and then sintering of the dried NPs to form a film. A theoretical model is presented to select and optimize the laser processing parameters. Scanning electron microscopy (SEM) revealed that the laser heating induces necking and coalescence of TiO2 NPs without cracking the sintered films or damaging the quartz substrate. An anti-reflection coating (ARC) model is utilized to select the film material and film thickness, aiming to reduce the reflectance and enhance the transmittance at certain wavelengths. UV/Vis spectrophotometry showed transmittance above ∼90% in the visible (Vis) range. The effect of laser power on the enhancement of transmittance is presented in this paper. Different concentrations of TiO2 NPs were used to optimize the film thickness. Single layer (∼110nm thick) and double layer films of the same total thickness as the single layer were analyzed to infer the effects of interface on the transmittance of TiO2 films. The transmittance of the single layer is higher, same as that of the double layer. Therefore, the difference in the transmittance of the single- and double-layer may be due to the effect of interface. The optical properties of the anti-reflection TiO2 coating in the UV–Vis ranges were investigated. X-ray diffraction (XRD) analysis showed that the thickness affects the crystallinity of the sintered TiO2 films.

Effects of post heat treatment on key T-phase evolution and the matching mechanism of enhanced strength-toughness, wear resistance and corrosion resistance in Al-Mg-Zn-(Cu-Er-Zr) alloy by laser powder bed fusion

Al-Mg-Zn-(Cu-Er-Zr) system alloy is a novel alloy designed by materials genetic method for laser additive manufacturing of lightweight brake discs and the T-phase (T-AlMgZnCuZrEr) in this alloy is the most important microstructure for enhancing performance matching of the alloy. Scientifically regulating the T-phase evolution through innovative preparation processes to improve the matching of strength-toughness, wear resistance, and corrosion resistance in this novel alloy is the fundamental work for preparing high-performance lightweight high-speed train brake disc parts using laser additive manufacturing. In this work, laser powder bed fusion and post heat treatments were employed to prepare Al-Mg-Zn-(Cu-Er-Zr) alloy samples with the superior matching of strength-toughness, wear resistance and corrosion resistance, and the key T-phase evolution and performance enhancement mechanisms of the samples were studied. The results indicate that post heat treatments significantly influenced the quantity, size, and structure of the T-phase in the cladded sample, which significantly enhanced the strength-toughness, wear resistance and corrosion resistance matching of the alloy. It is found that under the optimized aging treatment at 200 °C/6 h, due to the evolution of T-phase area fraction and cell-like structure inside the T-phase, the strength-toughness, wear resistance and corrosion resistance were improved by 30 %, 28 %, 1.4 %, respectively. The precipitation and concave dissolution mechanisms of the T-phase during post heat treatment have been finely revealed, and a three-performance matching relationship model has been successfully constructed based on the strength-toughness matching equation. A new laser powder bed fusion followed by the aging process to manufacture an Al-Mg-Zn-(Cu-Er-Zr) alloy sample with the superior matching of strength-toughness, corrosion resistance, and wear resistance has been obtained, which provides a valuable reference for laser additive manufacturing high-performance lightweight aluminum alloy brake disc parts.

Energy-efficient microwelding of copper by continuous-wave green laser: Insights into nanoparticle-assisted absorptivity enhancement

As a highly reflective material, copper has been difficult to weld with IR lasers. Short-wavelength (400–600 nm) lasers offer promising solutions to copper welding due to significant increases in absorptivity (to > 50 %). In this work, we present an experimental study on copper welding by CW green laser. We unveil that nanoparticles redeposited on the copper surface from the vaporized plume can strongly modify the surface condition and result in significant enhancement of the surface absorptivity. The absorptivity can be theoretically enhanced by nanoparticles up to 82 % compared to the polished copper surface. Assisted by this absorptivity enhancement, the threshold power density (critical laser intensity) for copper melting is reduced by more than 50 %, so that continuous and smooth conductive welding tracks can be generated in energy-efficient manner. In situ deposition of nanoparticles generated upon cooling and oxidation of the vapor plume in the vicinity of the melt zone has been identified as the key mechanism of absorptivity enhancement. XPS measurements of the nanoparticles indicated that Cu2O is the dominant species in the redeposited nanoparticles. This study provides novel insights into the fundamental mechanisms in highly-reflective material welding by short-wavelength lasers and offers an opportunity for energy-efficient high-quality welding of highly-reflective material thin films, which can find numerous applications in consumer electronics and electric vehicles, as well as battery industries. Moreover, it enables a new process-material-environment design route for laser additive manufacturing of nanoparticle-reinforced metal matrix composites.

Research on Microstructure and High-Temperature Performance of Novel Ti65 Titanium Alloy with V-Groove Connection in Laser Additive Manufacturing

Research on Microstructure and High-Temperature Performance of Novel Ti65 Titanium Alloy with V-Groove Connection in Laser Additive Manufacturing

Three-dimensional quantitative characterization of defects in inconel 625 superalloy based on deep learning image identification

Three-dimensional (3D) quantitative characterization of defects in superalloys is an important way to promote the ability of material design and service life prediction. In this work, 3D spatial distribution of defects for Inconel 625 superalloy manufactured by laser additive manufacturing (LAM) is carried out deep learning (DL) image identification technology and 3D image reconstruction. Firstly, computer tomography (CT) technology was used to obtain continuous slice images of sample. The U-net DL algorithm was applied to intelligently identify material defects in the continuous slices. On this basis, quantitative identification and analysis of spatial defect positions and typical sizes is achieved by using 3D reconstruction software. Compared with traditional threshold segmentation (TS) techniques, the defect recognition rate has significantly improved from 61.90 ​% to 95.00 ​%. This work provides a promising characterization method for efficient characterizing alloy defects and damage especially during material performance evaluation.

Multi-elemental Control of Non-equilibrium Microstructures and Metastable Phases of Aluminum Alloys Produced by Laser Additive Manufacturing

Multi-elemental Control of Non-equilibrium Microstructures and Metastable Phases of Aluminum Alloys Produced by Laser Additive Manufacturing

Enhancing plasticity in laser additive manufactured high-entropy alloys: The combined effect of thermal cycle induced dissolution and twinning

Breaking the trade-off between strength and ductility and pursuing stronger and more ductile metal materials has been a long-standing dream for scientists. Interestingly, even for the same material, different manufacturing methods can lead to significantly different performance. In this study, we utilized different laser additive manufacturing techniques (laser direct energy deposition (LDED), and laser powder bed fusion (LPBF)) to fabricate FeCoCrNiMo0.5 high-entropy alloy (HEA). Through microstructural analysis, we discovered a novel thermal cycling-induced dissolution (TCID) mechanism. By controlling the cooling rate post thermal cycling, we achieved the dissolution of precipitate phases and increased the Mo content within the matrix. Based on this phenomenon and supported by theoretical calculations, we revealed a reduction in stacking fault energy (SFE), which gave rise to a twinning-induced plasticity (TWIP) mechanism. This led to a dramatical increase in plasticity (LDED: 1.6 %, LPBF: 17.7 %) in the LPBF alloy, while maintaining similar strength (LDED: 784.9 MPa, LPBF: 840.89 MPa). This study provides guidance for designing metals structures with balanced strength and plasticity.

Synergistic Strength-Ductility Improvement in an Additively Manufactured Body-Centered Cubic HfNbTaTiZr High-Entropy Alloy via Deep Cryogenic Treatment.

HfNbTaTiZr high-entropy alloy has wide application prospects as a biomedical material, and the use of laser additive manufacturing can solve the forming problems faced by the alloy. In view of the characteristics of the one-time forming of additive manufacturing methods, it is necessary to develop non-mechanical processing modification methods. In this paper, deep cryogenic treatment (DCT) is first applied to the modification of a HEA with BCC structure, then the post-processing method of DCT is combined with laser melting deposition (LMD) technology to successfully realize the coordinated improvement of forming and strength-ductility synergistic improvement in lightweight Hf0.25NbTa0.25TiZr alloy. The final tensile strength of the alloy after DCT treatment is 25% higher than that of the as-cast alloy and 11% higher than that of the as-deposited alloy, and the elongation is increased by 48% and 10%, respectively. In addition, DCT also achieves induced phase transition without additional deformation.

Sintering parameter optimization by inverse analysis in direct metal deposition of Inconel 718

PurposeThe net power delivered to the surface of parts (i.e. the actual heat flux) is a key parameter in the laser melting process and its exact control has a great impact on the numerical solutions. In this paper, the impact of laser additive manufacturing parameters including laser power, scanning speed and powder injection rate on thermal efficiency, net power delivered to the part and power loss due to powder flow has been investigated.Design/methodology/approachThe response surface method was applied to measure the net laser power in laser deposited Inconel 718 using k-type thermocouples. The temperature history obtained by thermocouples was used to calculate the net power delivered by inverse analysis method. The applied model is Rosenthal's optimized model, in which all the thermal properties of the material are considered to vary with temperature.FindingsThe results indicated that the thermal efficiency, power delivered to the part and power loss can be optimized simultaneously at laser power of 400 W, scanning speed of 2 mm/s and powder injection rate of 200 mg/s. The microstructure analysis indicated that a high-quality sample without microstructural defects was formed under optimal condition of parameters. Moreover, the primary dendrite arm spacing for the optimal sample was higher than that obtained for other samples.Originality/valueThe novelty of this research summarized as follows: Prediction of the thermal efficiency and power loss during the laser metal deposition of Inconel 718 superalloy using the inverse analysis. Finding the optimal values of thermal efficiency, power delivered to the surface and power loss in the laser metal deposition of Inconel 718 superalloy. Investigating the effect of laser power, powder injection rate and scanning speed on the thermal efficiency and power loss of Inconel 718 superalloy during the laser metal deposition.

Laser additive manufacturing of titanium alloys: process, materials and post-processing

Laser additive manufacturing of titanium alloys: process, materials and post-processing