Laser Additive Manufacturing Techniques Research Articles

Recent progress in carbide‐based composite materials fabricated by laser additive manufacturing processes

AbstractFabricating and introducing new materials with new features is one of the most important goals for many scientific groups. Today, additive manufacturing (AM) is known as one of the new production methods, which can create an excellent opportunity for achieving this goal. As one of the ongoing production processes, the laser AM (LAM) methods have the proper capacity for producing new advanced materials like carbide, nitride, and boride‐based materials. Hence, this work aims to review carbide‐based materials produced by LAM techniques with the composite viewpoint. These materials can act as a matrix, reinforcement, or tertiary component in advanced composites. With this viewpoint, these composite materials were introduced in eight separate sections, which are tungsten carbide, titanium carbide, silicon carbide, niobium carbide, chrome carbide, vanadium carbide, and boron carbide, as well as high entropy alloy composites.

Microstructure and magnetocaloric effect in nonequilibrium solidified Ni-Mn-Sn-Co alloy prepared by laser powder bed fusion

Additive manufacturing (AM) enables complex structures of Ni-Mn-X Heusler alloys to be utilized in solid state refrigeration systems. Here, the laser powder bed fusion (L-PBF) technique was used to fabricate a Ni-Mn-Sn-Co magnetic shape memory alloy with sophisticated geometries. Relative densities ranging from 96.12 to 97.04% were attained. L21–ordered austenite and an average structure of 5-layered modulated (5 M) martensite were observed at ambient temperature. The nonequilibrium solidification condition and repeated remelting processes during L-PBF gave rise to a strong 〈001〉A texture in austenite with epitaxial columnar grains along the build direction and dendrites related to microsegregation. Furthermore, the austenite exhibited nanodomains in its matrix and the martensite possessed stacking-mediated structures with 4–7 layers of atoms randomly stacked within the twin substructures. The combined influence of relatively homogeneous composition and specific microstructures yielded a competitive magnetization difference of 81.0 A·m2·kg–1 and a maximum magnetic entropy change of about 14 J·kg–1·K–1 with a working temperature interval of about 22 K under the external field change of 5.0 T without any heat treatment. The as-built state alloy is expected to facilitate the development of new laser AM techniques for Ni-Mn-X alloys.

Evaluation of functionally graded YSZ - IN625 clad without bond coat using laser directed energy deposition

M-CrAlY or M-Cr-based bond coats are used as a buffer layer to apply ceramic thermal barrier coatings (TBCs) to metal turbine blades. However, due to oxygen diffusion, thermally grown oxides grow over the bond coat material, leading to coating failure in the components. Therefore, this study attempts to fabricate a novel TBC-coated IN625 without bond coat material using a Functional grading approach. The findings from this study may pave the way for processing functionally graded ceramic materials using Laser Additive manufacturing techniques. This study also evaluates the performance of functional grading in joining dissimilar materials using small spot-size laser sources. In the present study, samples were fabricated for three sample conditions: S1: direct clad, S2: 25% linear grading, and S3: 50% linear grading. The interface between Yttria Stabilized Zirconia (YSZ) and IN625 for the S1 sample showed discontinuous and horizontal cracks along the interface due to steep variations in thermal properties. However, the interface of S2 and S3 samples showed good adhesion and a smooth transition in microstructure between IN625 and YSZ as a result of functional grading. SEM micrographs showed homogeneous YSZ distributions without segregation within the IN625 matrix. This was attributed to strong Marangoni flow as a result of the small spot-size laser beam used in this study.

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.

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

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

Laser additive manufacturing of ductile Fe-based bulk metallic glass composite

• Fe-based BMGCs with high strength and record-breaking ductility was fabricated via LAM technique. • An appropriate amount of stainless steel can effectively ductile the Fe-based BMG without seriously sacrificing strength. • Dual-phase structure was achieved by simply transporting the second phase into laser molten pool in the form of powder during LAM process. Laser additive manufacturing (LAM) is a promising technology for processing bulk metallic glass (BMG) with freeform geometries or unlimited size. However, the inherently brittle Fe-based BMGs produced by LAM have always been plagued by the micro-cracking induced by the large thermal stresses during the LAM process. To solve this dilemma, 316L stainless steel (SS) with excellent toughness and similar elemental composition was carefully selected as the second phase to form Fe-based BMG composites (BMGCs). The obtained Fe-based BMGCs are equipped with a heterogeneous structure, i.e., the 316L SS phase is wrapped by the metallic glass and forms a unique "fishbone" structure with a micron - scale. Excitedly, the special structure nicely improves a plastic strain of the Fe-based BMGC with a strength of 2355 MPa to ∼17%, achieving a record-breaking achievement among Fe-based amorphous with critical dimensions over 1mm.

Effect of C addition on microstructure and mechanical properties of laser micro-alloying Ti–Al–V–C titanium matrix composites

Most research activities involving the in-situ synthesis of TiC reinforced titanium matrix composites (TMCs) using laser additive manufacturing (LAM) focus on Ti and C interactions; however, interactions between other elements within the same context remain unexplored. This work details the design of a novel laser processing experiment called the laser micro-alloying (LMA) for depositing the Ti–Al–V-xC (0 ≤ x ≤ 1.0, wt.%) alloys, which was then used to elucidate the solid solution relationships between C, Al, and V in various matrices and the effect of C on the TiC in-situ precipitation behavior. The effect of C addition on the matrix microstructure was also elucidated to determine the alloying mechanism. It was confirmed that the solid solubility of C in the matrix decreases as Al and V contents increase. The TiC precipitation increases with increasing C content in the Ti alloy matrix, while the TiC morphologies in the samples evolved from feathery to clavate, then dendritic. It was noted that 0.12 wt.% C addition in Ti–4Al–3V resulted in a significant decrease in prior β grain size and α laths’ width, while further increasing C content had a negligible effect. Also, solid solution strengthening of C and continuous precipitation of TiC increased the indentation hardness, elastic modulus, and yield strength, with the increase being most significant when the C content is 0.12 wt.%. The work will lay a foundation for designing optimized TMCs used for LAM and other laser processing techniques.

Microstructure and Corrosion Behavior of Iron Based Biocomposites Prepared by Laser Additive Manufacturing.

Iron (Fe) has attracted great attention as bone repair material owing to its favorable biocompatibility and mechanical properties. However, it degrades too slowly since the corrosion product layer prohibits the contact between the Fe matrix and body fluid. In this work, zinc sulfide (ZnS) was introduced into Fe bone implant manufactured using laser additive manufacturing technique. The incorporated ZnS underwent a disproportionation reaction and formed S-containing species, which was able to change the film properties including the semiconductivity, doping concentration, and film dissolution. As a result, it promoted the collapse of the passive film and accelerated the degradation rate of Fe matrix. Immersion tests proved that the Fe matrix experienced severe pitting corrosion with heavy corrosion product. Besides, the in vitro cell testing showed that Fe/ZnS possessed acceptable cell viabilities. This work indicated that Fe/ZnS biocomposite acted as a promising candidate for bone repair material.

2D numerical model for heat transfer on a laser deposited high entropy alloy baseplate using Comsol Multiphysics

In an optimization study, cracks were observed in the microstructures of laser-deposited HEAs on a steel baseplate from residual stresses, thus, the optimization of crack-free microstructures was achieved by the optimization of the laser parameters by baseplate preheating attributed to the lowering of the thermal gradients of the deposition process. This study reports the finite element analysis on the temperature distribution by the moving laser modelled to achieve process optimization with the necessary boundary conditions. Simulation has been reported as a facilitating tool in predicting the behaviour of materials during process optimization. Comsol Multiphysics 4.4, was used to create a 2D transient heat transfer time-dependent model to simulate the temperature distribution and the laser heating of the A301 steel baseplate surface and determine the effect of temperature on the optimization process of the alloys. Gaussian profiles were used as the heat source distributed per time. The results are presented in terms of thermal fields and Gaussian temperature profiles. Which show the temperature distribution that occurred in the steel baseplate during fabrication and the high cooling rate of the laser additive manufacturing technique restricted thermal stresses, improving adhesion and facilitating the optimization process.

Insights into high thermal stability of laser additively manufactured Al2O3/GdAlO3/ZrO2 eutectic ceramics under high temperatures

Laser additive manufacturing techniques have been considered to be the most promising methods to fabricate melt-grown Al 2 O 3 -based eutectic ceramics which are potential candidates for high temperature structural applications. In this paper, Al 2 O 3 /GdAlO 3 /ZrO 2 ternary eutectic ceramic was additively manufactured based on one-step melt-growth by laser directed energy deposition, and its thermal stability under high temperatures was studied. The results indicate that the as-solidified eutectic composite consists of ultrafine phases of α-Al 2 O 3 , GdAlO 3 and t-ZrO 2 , and presents an irregular eutectic morphology with amounts of terminations and branches. The 3D-printed eutectic ceramic exhibits a superior thermal stability that no mass variation and no phase transition occur even after annealed at 1500 °C for 200 h. In addition, the submicron-scaled eutectic microstructure and the polished surface topography can maintain stability up to 1400 °C which is higher than 80% of its melting point (>0.8 T m ). With further increasing the temperature, obvious microstructure coarsening, and surface holes formation occur, leading to the severely deterioration of the mechanical property. The hardness of the as-deposited eutectic ceramic rapidly decreases from 15.84 ± 0.61 GPa to 13.01 ± 0.40 GPa after 200 h annealed at 1500 °C. The results indicate that the additively manufactured Al 2 O 3 -based eutectic ceramics have great potential to be long-time high-temperature structural materials applied at elevated temperatures. • Highly dense Al 2 O 3 /GdAlO 3 /ZrO 2 eutectic ceramic is 3D-printed based on melt growth. • Thermal stability of the additively manufactured eutectic ceramic is studied under high temperatures. • Critical transition temperature from stability to instability is determined, and the instability mechanism is revealed.

Laser Shock Peening of Ni-Ti Bulk Structures Developed by Laser Additive Manufacturing

Three different compositions of bulk Ni-Ti samples fabricated by laser additive manufacturing technique are subjected to laser shock peening with multiple shots of 1 GW/cm2 irradiance. A numerical simulation is implemented to predict the amount of residual stress to be generated on the sample surface to optimize the processing parameters. The experimental results reveal the number of shots to be three, in order to achieve the desired amount of residual stress from the chosen power density for processing. LSP yields a total increase in the residual stress by 40-45% on the surface of the samples. To investigate the nature of samples, after LSP several characterizations are done to study the mechanical, microstructure, phase transformation and crystalline properties. The scanning electron microscopy images reveal the surface morphology of the samples, to be roughened in nature by the effect of LSP. Also, the enhancement in the microhardness by 20% vividly shows improvement in the mechanical properties. X-ray diffraction shows a substantial fluctuation in peak intensity and peak positioning post LSP. The peak diminishing is observed after LSP in the XRD graph, which confirms the amorphization induced in the samples. Differential scanning calorimetry shows an increase in the phase transformation temperature by 20-30 °C for the NiTi50 sample. The study reveals the composition of NiTi50 fabricated by LAM was able to sustain the pressure generated by LSP by withholding its physical and chemical nature.

Rare earth improves strength and creep resistance of additively manufactured Zn implants

Poor mechanical strength and creep resistance limit the orthopedic application of biodegradable Zinc (Zn). In present work, cerium (Ce) was alloyed with Zn using laser additive manufacturing technique. As one kind of rare earth element, Ce possessed high surface activity, which effectively interrupted the grain growth and caused the formation of stable intermetallics, thus contributing to grain refinement strengthening and precipitate strengthening. More significantly, Ce alloying activated more pyramidal slip by means of reducing the critical resolved shear stress during plastic deformation, and resultantly formed the sessile dislocations, which caused the accumulated strain hardening and improved the creep resistance. As a result, Zn-Ce alloy exhibited a considerably improved ultimate tensile strength of 247.4 ± 7.2 MPa, and a reduced creep rate of 1.68 × 10−7 s−1. Moreover, it exhibited strong antibacterial activity, as well as favorable cytocompatibility and hemocompatibility. All these results demonstrated the great potential of Zn-Ce alloy as a candidate for bone repair application.

Titanium-Silicon on CoCr Alloy for Load-Bearing Implants Using Directed Energy Deposition-Based Additive Manufacturing.

Cobalt-chromium (CoCr) alloys offer outstanding wear resistance when compared to other biocompatible metallic materials and are extensively used in articulating surfaces of total hip and knee arthroplasty. However, CoCr alloys' biocompatibility is known to be inferior to titanium (Ti). Wear- and corrosion-induced metal-ion release from CoCr alloys has been reported to cause cancer and negative physiological impacts. In this study, CoCr alloy was coated with commercially pure Ti (CpTi) and CpTi-Silicon (CoCrTi-Si) with the specific objective of reducing Co and Cr ion release during articulation, without degrading the excellent wear resistance of the CoCr alloy. Directed energy deposition (DED), a blown powder-based laser additive manufacturing technique, was utilized to process CpTi- and CpTi-Si-based coatings on Stellite 6B commercial CoCr alloy. Scanning electron microscopy (SEM), X-ray diffraction (XRD) analyses, and hardness testing found that refined carbides and titanium silicides increased the hardness from 321 ± 13 to 758 ± 48 HV0.5. Tribological studies determined a comparable wear rate between Stellite 6B alloy and CoCrTi-Si in DI water but a statistically significant reduction in Dulbecco's Modified Eagle Medium (DMEM). The wear rates for Stellite 6B were 8.5 ± 0.8 × 10-5 and 12.9 ± 0.4 × 10-5 mm3/Nm in DI water and DMEM, respectively. While the wear rates for CoCrTi-Si were 9.1 ± 0.5 × 10-5 and 8.9 ± 0.8 × 10-5 mm3/Nm in DI water and DMEM, respectively. Contact resistance acquisition displayed the presence of a passive film formation during tribological testing. ICP-MS results for Stellite 6B and CoCrTi-Si concluded a reduction of Co ions release in DI water from 149.8 ± 66.7 to 17.5 ± 0.7 ppb and a reduction in Cr ions release from 66.7 ± 32.4 to 18.0 ± 0.5 ppb, respectively. In DMEM media, Co ion release for Stellite 6B and CoCrTi-Si reduced from 10.1 ± 1.4 to 4.1 ± 0.2 ppb and Cr ion release for Stellite 6B and CoCrTi-Si reduced from 8.7 ± 0.2 to 5.0 ± 0.7 ppb, respectively. The current study revealed a new mode of manufacturing for CoCr alloy-based load-bearing implants that can reduce toxic metal ions release due to wear- and corrosion-induced damages.

Heating Conditions Influence on Solidification of Inconel 625-WC System for Additive Manufacturing.

In this study, an Inconel 625–tungsten carbide (WC) composite system was investigated by means of microstructure changes affected by both heating rate and WC content. In order to investigate how the system behaves while exposed to fast thermal processing, controlled melting using a differential thermal analysis (DTA) apparatus was performed on the powders. Two WC powders with different average grain size were used to obtain six compositions of Inconel 625–WC powder mixtures (10, 20, and 30 wt.% WC). They were analyzed under 10 and 30 °C/min heating rate in order to obtain composite samples. Results from DTA together with SEM/energy-dispersive X-ray spectroscopy (EDS) microstructural observations allowed observing material changes during solidification. Because of the extensive microsegregation of alloying elements to liquid and their reactions with C, which derived from dissolved WC, the formation of secondary phases with improved microhardness was possible. The collected results provide a better understanding of material behavior during intensive thermal processing which can be useful when designing materials for the laser additive manufacturing technique.

Hot Corrosion and Mechanical Performance of Repaired Inconel 718 Components via Laser Additive Manufacturing.

Hot corrosion is one of the crucial failure modes of Ni-based superalloy components operating at high temperatures, which inevitably affects the subsequent mechanical properties of the alloys. In this research, damaged Inconel 718 alloy components with a pre-made trapezoid groove are repaired using laser additive manufacturing technique, and the change mechanisms of the microstructure and tensile properties of the repaired Inconel 718 alloy due to the hot corrosion in the salt mixture of 87.5 wt.% Na2SO4 + 5 wt.% NaCl + 7.5 wt.% NaNO3 at 650 °C for different durations are investigated. The results show that oxidation and Cr-depletion occur on the repaired components due to the hot corrosion, and the corrosion products are mainly composed of Cr2O3, Fe3O4, and Ni3S2. The tensile strength and elongation of the as-repaired specimens are 736.6 MPa and 12.5%, respectively. After being hot corroded for 50 h, the tensile strength increases to 1022.9 MPa and elongation decreases to 1.7%. However, after being hot corroded for 150 h, both tensile strength and elongation of the repaired specimens drop to 955.8 MPa and 1.2%, respectively. The mechanical performance alteration is highly related to thermal effects instead of the molten salt attack.

Microstructure characterization and micro-hardness of Fe-9Cr ODS alloy produced by laser powder bed fusion

Oxide dispersion strengthened (ODS) alloys have been considered as the promising candidates for advance Generation-IV fission reactor application due to excellent radiation tolerance and high temperature mechanical properties but traditional manufacturing process is complex. A 9Cr-ODS alloy with nominal composition of Fe-9Cr-1.5W-0.3Ti-0.3Y2O3 (wt %) was produced by laser powder bed fusion (LPBF) which is a laser additive manufacturing technique. The microstructure and nanoscale oxide particles were characterized by using optical microscope (OM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The micro-hardness was tested by hardness tester. The results showed that the equiaxed grains with an average size of 3.8 μm were obtained. The dispersed oxide particles with 10-20 nm were observed in LPBFed 9Cr-ODS alloy. The micro-hardness of built sample was about 460 HV.

Modeling of thermal and solidification behavior during laser additive manufacturing of AlSi10Mg alloy powders and its experimental validation

In the present era, the laser additive manufacturing process is widely adopted in the manufacturing sector to produce near net shape components with minimum wastage of raw materials. Direct metal laser sintering (DMLS) is one of the laser additive manufacturing techniques which has received the most attention, as it builds the parts directly from metal or alloy powders. However, the quality of the components produced by DMLS has hindered its use on a larger scale. The process parameters in the DMLS process directly influence the quality of the building part. So, a better understanding of the influence of process parameters on build parts can provide insight to get high-quality products. In the present study, a three-dimensional transient heat transfer model was developed to simulate the temperature field and molten pool profile using the ansys 17.0 platform. The temperature distribution, melt pool dimension, solidification rate, cooling rate, and structural morphology are investigated with the variation of input laser energy. From the investigation, it was observed that the temperature of the powder bed and melt pool dimensions such as length, width, and depth increases with an increase in input laser energy. The cooling rate also increases with a decrease in laser energy input. Further, the developed model is validated to verify the accuracy and the simulated results are quite agreed with the analytical as well as experimental results.

Study of microstructure evolution and preference growth direction in a fully laminated directional micro-columnar TiAl fabricated using laser additive manufacturing technique

In this study, a fully laminated Ti-48Al-2Nb-2Cr alloy plate with no cracks and aluminum loss is successfully fabricated using laser additive manufacturing technique. A well-aligned micro-columnar microstructure is expected to grow along the deposition direction. Attributed to the rapid cooling, micro-segregation between interdendritic and dendrite areas is observed in the fabricated alloy. Meanwhile, rapid cooling results in existence of B2 phases in the center of dendrites, which will then decompose with the gradual coarsening of α2/γ lamella under subsequent thermal cycling. Additionally, dominant growth of 〈1 1 0〉β during solidification of molten pool is predicted, which is the preference growth direction of primary β phase.

Effects of build orientation on fatigue behavior of Ti-6Al-4V as-built specimens produced by direct metal laser sintering

Additive Manufacturing (AM) is undoubtedly of high potential to fulfil the needs of modern digital manufacturing, however, the failure prediction of the components made by this technique is still a challenging task due to uncertainty in their structural properties. Different geometries and build orientation of AM parts results in various surface roughness and residual stresses and consequently various mechanical properties. Regardless of the type of laser AM technique (Direct Energy Deposition (DED), Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), etc.), the AM components are usually subjected to heat treatments in order to eliminate the residual stress and improve metallurgical characteristics, and to surface treatments to decrease their roughness. Although rarer, the cases in which the specimens are tested as-built, are considered extremely necessary in order to quantify the quality of machine molding and the set of parameters used, as well as the validity of any other subsequent treatment. For these reasons, the following work aims to examine the experimental results of the fatigue behavior for as-built specimens produced with Ti-6Al-4V powders through the DMLS additive production technique with optimized parameters, using two different build directions. The two different behaviors will be compared. In particular, attention will be focused not only on the results obtained from the experimental fatigue tests but, through a scanning electron microscope (SEM), the single fracture surfaces will be investigated and in conclusion considerations on the residual stress state will be made. All the results will be use in order to determine and correlate the causes to the different fatigue behavior. The results obtained can be used as a starting point for the performance quantification of subsequent treatments or more simply be used in the design phase.

激光增材制造镁合金的研究现状及展望

激光增材制造镁合金的研究现状及展望