Laser Additive Manufacturing Research Articles

A high-temperature Ti-6.8Al-6.8Zr-2.3V-2.1Mo-0.7Nb alloy suitable for laser-additive manufacturing

A high-temperature Ti-6.8Al-6.8Zr-2.3V-2.1Mo-0.7Nb alloy suitable for laser additive manufacturing is designed on the basis of the cluster formula of Ti–6Al–4V, composed of twelve α-[Al–Ti12](AlTi2) units and five β-[Al–Ti12Zr2](AlV1.2Mo0.6Nb0.2) ones, featuring enhanced β stability via Zr, Mo, Nb, and V co-alloying. Using pre-alloyed powders, this alloy shows a fine surface roughness about 83 μm, which is comparable to that of reported Ti–6Al–4V. The as-deposited alloy exhibits a typical bimodal basket-weave microstructure and superior mechanical properties at room temperature (ultimate tensile strength (UTS) of 1348 MPa, yield strength (YS) of 1253 MPa, and elongation of 4.4%) as well as at 600 °C (UTS of 657 MPa, YS of 578 MPa, and elongation of 44.6%), which are comparable to wrought-state high-temperature Ti alloys. At 650 °C, its UTS of 424 MPa and YS of 337 MPa still maintains a high level.

Study on overlap rate and machinability of selected laser melting of maraging steel

Abstract In order to investigate the material properties of maraging steel laser additive manufacturing, the cladding layers with different overlap rates on the surface of 18Ni300 were prepared by laser cladding technology, and the morphology, microstructure, and hardness of the cladding layer with different overlap rates were analyzed by various means. The results show that the macroscopic morphology of the cladding layer mainly presents three states under different overlap rates, and the change of overlap rate has no effect on the microstructure in the same area of the cladding layer, but does have an effect on the size of the cladding layer. In the end, the optimum overlap rate is 50%, the surface is smooth, the inner is free from defects, the bonding effect is good, and the metallographic structure is even with high hardness. Milling experiments were carried out on the material after laser additive manufacturing, and the surface morphology was observed, confirming a smooth and well-flattened surface with a roughness of 0.342 μm had been obtained. The suitable overlap rate can make the coating surface smoother, reduce the subsequent processing loss, and improve the production efficiency and powder utilization rate while ensuring the coating quality.

Wire arc additive manufacturing of porous metal using welding pore defects

A novel wire arc additive manufacturing process is proposed to produce porous metal (PM). The innovation is to convert harmful welding pore defects into a beneficial structure of PM, and then the PM parts can be additive manufactured layer by layer. Air was transferred to the molten pool as pore promoters to maximize the formation of the welding pore defects. The triple-wire indirect arc process was used for fabricating multi-layer parts to reduce interlayer filling. The primary advantage is that the process can directly produce macro-pore structures rather than depositing pore walls along micro paths in laser additive manufacturing. The uniform diameter of the pore ranges from 500 to 2700 μm, and the typical porosity is 64%, 49%, and 87%. The process could achieve a high deposition rate of 11.5 kg/h. Due to martensite formation, the pore walls can achieve high microhardness of over 200 HV.

Achieving isotropic microstructure in an additively manufactured Ti-6Al-4V alloy enabled by dual laser processing

With the development of science and technology and the popularization of intelligent manufacturing, laser additive manufacturing of titanium alloys is being attractive in industrial adoption due to its advantages of near-net shape and cost-saving features, and especially laser melting deposition is an effective additive manufacturing technique for large-scale and lightweight components such as TC4 alloy. However, inside the as-prepared alloy, large scale columnar crystals are formed along the forming direction, which will lead to anisotropic macroscopic properties of the alloy parts, further affecting their service life. In view of this, we report an innovative strategy of dual laser processing integrating laser melting deposition and laser shock peening, which can be used to achieve isotropic microstructure along three building directions in Ti-6Al-4V alloy. Interestingly, the isotropic microstructure is basket-weave structure of ultrafine α and nanometer β lamellar colonies together with abundant nanometer β fragments/particles distributed dispersedly inside ultrafine α matrix. Especially, the as-fabricated alloy exhibits approximately isotropy of mechanical properties along three building directions, and circumvents the strength–ductility trade-off of Ti-6Al-4V alloy with different microstructures reported so far. This study validates the feasibility of manufacturing high performance complex structural components by coupling technology of laser melting deposition and laser shock peening, for grain refinement and isotropic microstructure of additive manufactured titanium alloys in a low-cost and effective method. Impact statementThe proposed dual laser processing technology integrating additive manufacturing of laser melting deposition and synchronous laser shock peening, can provides insight into fabricating isotropic metal components with higher performance through additive manufacturing of one-step forming.

Pre–Placed Metal Laser–Additive Manufacturing on Grade 5 Titanium Substrate: Layer Formation, Oxidation Resistance, and Wear Resistance

The laser parameters and additive materials were investigated for the laser–additive manufacturing of titanium alloys. A pre–placed metal–strip–based method for 3D printing titanium components was proposed. Before laser processing, the metal strips were fixed to a Grade 5 titanium substrate using resistance spot welding. The effect of the processing conditions (laser power: 1.5–3.0 kW; scanning speed: 3–9 mm·s−1; one or three layers; 1, 6, or 12 passes; Grade 2 and Grade 5 as additives) on the microstructures, oxidation resistance, and wear resistance of the as–printed samples was investigated. The results showed that the microstructure consisted of α′ martensite, oxygen–stabilized α, transformed β that contains coarse and fine acicular α, titanium oxides, and carbides. Cracks were observed, particularly near the upper surface of the three–layer samples. The cracks were suggested to have formed due to cumulative residual stresses and the formation of oxygen–stabilized α and α′ martensite that might cause embrittlement. Both oxidation and wear tests were conducted to verify the improved performance. After 55 h of oxidation, the as–printed samples showed mass gains of 0.029–0.035 g·cm−2, which were smaller than those of the substrate (0.039 g·cm−2).

Microstructure and mechanical properties of ZrC modified Ni60 hard-facing alloy fabricated by laser metal deposition

Crack-free specimens were prepared from ZrC-modified Ni60 alloy by laser metal deposition. The effects of ZrC powder adulteration on the mechanism of microstructure refinement were investigated. The results demonstrated that the adulteration of ZrC powder did not provide nucleation sites for the hardening phase. The ZrC powder was added to Ni60 alloy powder to reduce the content of columnar dendrites and the eutectics of laser metal deposition specimens. The transformation of the dendritic hardening phase into a massive hardening phase was induced. The fine Ni–B–Si eutectic microstructure changed to a massive NiZr eutectic and peritectic microstructure with increasing ZrC powder mass fraction. The microstructure transformation mechanism constrained the initiation and propagation of cracks in the deposited specimens. The present research provides a method for improving the cracking defect of laser additive manufacturing Ni–Cr–B–Si system alloys and a theoretical basis for promoting the application of the alloy in additive manufacturing.

An oxygen self-supplied CuO2@g-C3N4 heterojunction endows photodynamic antibacterial performance of scaffold

Graphite carbon nitride (g-C3N4) was regarded as a promising photodynamic antibacterial material due to its desirable bandgap and favorable visible light absorption. However, its photodynamic antibacterial effect was weakened by too rapid recombination of electron-hole and hypoxic environment of infection site. Herein, an oxygen self-supplied heterojunction was constructed via in-situ growing CuO2 on g-C3N4 (CuO2@g-C3N4). For the heterojunction, on the one hand, it could response to the weak alkaline of infected site to decompose to CuO@g-C3N4, where CuO could form a built-in electric field with g-C3N4 to promote the electron-hole separation. On the other hand, it could produce oxygen in the decomposition process, which achieved oxygen self-supply for photodynamic reaction. Subsequently, the heterojunction was introduced into poly-para-dioxane (PPDO) scaffold fabricated by laser additive manufacturing. The photoluminescence results confirmed that the electron-hole separation efficiency was significantly improved. The release kinetics results indicated that the scaffold could continuously release oxygen. As a consequence, the reactive oxygen species (ROS) generation ability of the scaffold was increased by approximately tenfold. The generated ROS effectively killed bacteria by disrupting membrane structure, triggering protein leakage and depleting glutathione. Eventually, the scaffold exhibited an antibacterial rate of 89.8% and 90.5% against S. aureus and E. coli, respectively.

High-Throughput Synthesis and Characterization Screening of Mg-Cu-Y Metallic Glass

Bulk metallic glasses can exhibit novel material properties for engineering scale components, but the experimental discovery of new alloy compositions is time intensive and thwarts the rate of discovery. This study presents an experimental, high-throughput methodology to increase the speed of discovery for potential bulk metallic glass alloys. A well-documented system, Mg-Cu-Y, was used as a model system. A laser additive manufacturing technique, directed energy deposition, was used for the in situ alloying of elemental powders to synthesize discrete compositions in the ternary system. The laser processing technique can supply the necessary cooling rates of 103–104 Ks−1 for bulk metallic glass formation. The in situ alloying enables the rapid synthesis of compositional libraries with larger sample sizes and discrete compositions than are provided by combinatorial thin films. Approximately 1000 discrete compositions can be synthesized in a day. Surface smoothness, as discerned by optical reflectivity, can suggest glass-forming alloys. X-ray diffraction coupled with energy dispersive X-ray spectroscopy can further refine amorphous alloy signatures and compositions. Transmission electron microscopy confirms amorphous samples. The tiered rate of amorphous alloy synthesis and characterization can survey a large compositional space and permits a glass-forming range to be identified within one week, making the process at least three orders of magnitude faster than other discrete composition techniques such as arc-melting or melt-spinning.

An ultrasound-activated heterojunction as ROS generator given scaffolds sonodynamic antibacterial effect

Potassium niobate (KNbO3) with favorable biocompatibility presented a great potential in the sonodynamic therapy of implant-related infection due to its superior piezoelectric performance. However, the rapid electron-hole pair recombination weakened its sonodynamic therapy effect. In this work, Au@KNbO3 heterojunctions were synthesized by depositing Au nanoparticles on KNbO3, and then mixed with poly-l-lactic acid (PLLA) powder to prepare scaffold by laser additive manufacturing. Herein, Au with lower Fermi level acted as electron trap to capture the ultrasonic-excited electrons from KNbO3. Subsequently, Au formed Schottky barrier with KNbO3 to prevent electrons backflow. As a result, the electron-hole was expected to be separated. EIS curves indicated that Au@KNbO3 presented a smaller arc radius than that of KNbO3, confirming the electron-hole separation efficiency of Au@KNbO3 was enhanced. Following that, ROS generation ability of the scaffold was significantly strengthened. Antibacterial tests revealed that the generated ROS could not only trigger protein leakage by disrupting bacterial cell membranes, but also deplete glutathione to weaken the antioxidant defense of bacteria. As a consequence, the scaffold exhibited excellent antibacterial abilities of 92% and 90% against S. aureus and E. coli, respectively. Collectively, this work provided a promising countermeasure to fight the implant-related infection.

The Use of Boron Fibers and Particles for Creating Functionally Graded Material Based on Ti64 Using the Laser Additive Manufacturing Method

This work presents a study on the additive manufacturing of functionally graded metal-ceramic materials based on Ti64 with boron fibers and particles. For the first time, the phase composition of the obtained composite was investigated using synchrotron radiation. It was shown that during laser exposure and in situ synthesis, boron dissolves in the titanium matrix, forming secondary compounds such as TiB and TiB2. An increase in the microhardness of the formed material compared to the titanium alloy was established. High-speed impact tests on the Ti64-B samples were conducted using an electrodynamic mass accelerator. It was shown that the use of boron fibers in the metallic matrix reduces the depth of the crater created during impact testing by 40% compared to the Ti64 reinforcement-free coating.

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.

Significant transitions of microstructure and mechanical properties in laser additive manufacturing AlCoCrFeNi2.1 eutectic high-entropy alloy under heat treatment

In this work, the AlCoCrFeNi2.1 eutectic high-entropy alloys (EHEAs) were fabricated by laser additive manufacturing and subsequently heat-treated at various temperatures between 800 and 1200 °C to achieve excellent strength-plasticity synergy. The high solidification rate of selective laser melting (SLM) leads to instability of the eutectic growth front, resulting in a typical melt pool morphology of equiaxed and columnar crystals for AlCoCrFeNi2.1. The body-centered cubic (BCC) content of ∼82% in the SLM specimens leads to a higher tensile strength of ∼1175 MPa and poorer plasticity of ∼6.42%. After heat treatment, the BCC transforms to face-centered cubic (FCC) and the microstructure changes to a dendrite containing eutectic lamellar structure. As the temperature increases, Ni–Al aggregates, B2 phase particles precipitate and grow in the BCC matrix. Meanwhile, the uniform heating mode eliminates the orientation of the SLM melt pool structure, reduces the internal stress and dislocation density of the SLM alloy. In addition, high-temperature heating promotes the stable growth of lamellar structure. These combined effects allow the strength-plasticity trade-off to be achieved in the heat-treated specimen. The HT-1200 sample has a strength of 1065 MPa and a ductility of 21.97%.

Designing an Fe-Ni-Ti maraging steel tailor-made for laser additive manufacturing

Designing an Fe-Ni-Ti maraging steel tailor-made for laser additive manufacturing

Temperature gradient induced tough-brittle transition behavior of a high-strength Al-4.2Mg-0.4Sc-0.2Zr alloy fabricated by laser powder bed fusion additive manufacturing

The complex process and thermal behavior of laser additive manufacturing will lead to complex microstructure and property evolution. In order to enhance the processing efficiency of a high-strength Al-4.2Mg-0.4Sc-0.2Zr alloy fabricated by laser powder bed fusion (LPBF) additive manufacturing, a temperature gradient induced ductile-brittle transition behavior caused by changes in laser scanning speed for LPBF processed Al-4.2Mg-0.4Sc-0.2Zr alloy was reported in this study. As the laser scan speed increased from 0.4 ms-1 to 2.4 ms-1, a transition in fracture mode from toughness to brittleness was observed, where the tensile strength was decreased from 547.6 MPa to 472.3 MPa while the elongation decreased from 13.8% to 1.9%. Based on transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) characterizations, it was attributed to the cross-scale different microstructures from mesoscopic to microscopic as laser scan speed increased, including (i) more porosity in microscale (~30 μm), (ii) slenderer coarse grains and narrow equiaxed grain regions within melt pools in sub-microscale (~1 μm) and (iii) suppression of the Mg segregation along grain boundaries and formation of higher dislocation densities and stacking faults in the nanoscale (~200 nm). These changes in the microstructure caused the specimens processed with high scan speeds (above 1.6 ms-1) to be more prone to initiation of cracks during tensile, the ability of synergistic deformation between grains to decrease, and the bonding strength between grains to reduce. By simulating the thermal field of the melt pool, the formation mechanism of the different microstructures was ascribed to the different temperature gradients, which further determined the grain structures and element distributions. This work demonstrated that the structure and properties of LPBF processed high-performance Al alloys can be well tailored by processing parameter control.

Process based modelling of power density for wire laser additive manufacturing using a coaxial head

Process based modelling of power density for wire laser additive manufacturing using a coaxial head

A novel Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy designed using cluster-plus-glue-atom model for laser additive manufacturing

A novel Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy designed using cluster-plus-glue-atom model for laser additive manufacturing

Tribute edition to Professor Jyotirmoy (Jyoti) Mazumder laser additive manufacturing from cladding to complex parts

Tribute edition to Professor Jyotirmoy (Jyoti) Mazumder laser additive manufacturing from cladding to complex parts

Microstructure characteristics of a γ single-phase Ti-55Al-7.5Nb alloy fabricated via additive manufacturing

Developing a new ordered single-phase TiAl alloy, with no solid-state transformation operated at a long-term high temperature, is important in the aerospace industry. Here, the preparation of newly Ti-55Al-7.5Nb alloy via direct laser deposition (DLD) is proposed and studied. The oriented grain growth in Ti-55Al-7.5Nb alloy is successfully achieved by using laser additive manufacturing (AM) without interlayer pause during the laser scaning back and forth. AM features a rapid cooling rate while Ti-55Al-7.5Nb alloy owns a narrow L → α and α → γ phase transformation temperature window, and then enabling the TiAl liquid phase directly transform into a γ single-phase, which is confirmed by the combination of experiments and thermodynamic calculations. The heat treatment in the AM thermal cycles induces a thermal gradient, promoting the new recrystallized grains growing base on the preferred growth of [111]γ along the heat flow during the DLD solidification stage. The AM Ti-55Al-7.5Nb alloy exhibits continuous γ single-phase columnar grains, meanwhile, accompanied by the twins growing along the building direction.

Laser additive manufacturing of microchannel array structure inspired by lobster eyes: Forming ability and optical focusing performance

After millions of years of evolution, nature has evolved materials and structures with excellent performance and has provided a source of inspiration for designing high-performance structures. The bionic lobster eye structure (BLES) is a typical example of imitating the good light-focusing performance of lobster eyes. Here, the BLESs with different structural parameters were designed and fabricated by laser powder bed fusion (LPBF). The experimental results demonstrated that the highest relative density of 99.98% can be obtained at a laser power of 400 W and scanning speed of 2200 mm/s, and the upper profile in each microchannel formed under this parameter was regular. All BLESs exhibited a bright central focal facula with a diffuse background on the focus plate. The light-collecting ability of LPBF-processed BLES was decreased with the increase of the upper width of microchannel (UWM), and samples with a small UWM (1.0 mm and 1.25 mm) had a good light-focusing ability. The light intensity on the analysis surface increased as the analysis surface was away from the center of BLES (optical axis), which was detrimental to the optical focusing performance. The BLES could potentially be applied to satellites to improve the efficiency of light collection of the satellite while reducing the probability of being detected.

Smart laser controlling mixed-mode state

It is desirable to control the mode states of a laser to stabilize it under the influence of environmental factors as well as to tailor the laser beam. Here, we demonstrate mixed-mode-state control in a photonic crystal surface-emitting laser at the chip level by leveraging the mechanism of mutual injection locking via dynamic control of the current injection distribution. We also demonstrate smart control, in which deep learning is applied to accurately predict the current injection distribution required to achieve a targeted beam pattern owing to manipulation of the mixed-mode state, and vice versa. These results could enable smart laser sources essential for advanced laser processing and additive manufacturing applications.