Optimal Processing Window Research Articles

Impact of process parameters and gas atmospheres on density and microstructure of super duplex stainless steel produced by Laser Powder Bed Fusion

Super duplex stainless steel (2507 SDSS) is an alloy renowned for its excellent corrosion resistance and mechanical properties. This unique combination arises from a duplex microstructure characterized by austenite and ferrite. However, when processed using the laser powder bed fusion (LPBF) process, this steel contains only the ferritic phase due to the rapid cooling rates inherent in LPBF, which suppresses the formation of the austenitic phase. This study explores a parameter process optimization for this steel in two different atmospheres, Ar and N, with the latter being an austenite-stabilizing element intended to enhance the formation of the austenitic phase. A comparison of the optimal process windows between the two atmospheres is conducted, and the amount of austenitic content is evaluated as a function of the process parameters and the shielding gas employed. Findings demonstrate that utilizing a nitrogen atmosphere, in conjunction with process parameters that reduce normalized enthalpy and material evaporation, increases austenite content post-manufacture. Additionally, nitrogen as the processing gas effectively minimizes and stabilizes nitrogen content within the samples.

Hot deformation characteristics and microstructural evolution of Ti-900 alloy

Hot deformation behaviour of Ti-900 (Ti-6.5Al-3.2Mo-1.8Zr-0.25Si) alloy has been analyzed by conducting an isothermal hot compression test at 850 °C to 1050 °C temperatures and strain rates between 0.001 s−1 to 10 s−1. The effect of strain rates and deformation temperature on flow stress is investigated. The processing maps are constructed, and constitutive equations are studied to understand the formability of the novel titanium alloy in the different temperatures and strain rates regimes. Results suggest that temperatures and strain rates between 880 °C to 950 °C and 0.001 s−1 to 0.01 s−1 are the optimal processing window for this alloy. The kinetic rate equation indicates that the apparent activation energy for deformation is 531 kJ/mol in the α + β region. Post deformation microstructure formation is also studied.

Obtaining strength and ductility synergy for directed energy deposited Ti17 alloys by machine learning

Recently, obtaining a balance of tensile strength and ductility in direct energy deposited (DED) titanium alloy components has been a major concern, which obstructs their further application. Herein, machine learning (ML) methods were applied to find the optimal process window of DEDed titanium alloy parts from a wide range of possible depositing process variables. Four algorithms were used for ML model training and tensile property prediction of DEDed titanium alloy. The results showed that the prediction ability of the XGBoost model was the best. The optimized ‘laser power’-‘scanning rate’ process window produced DEDed titanium alloy specimens with an ultimate tensile strength (UTS) of 1050 MPa and an elongation (E) of 12.5 %. It was demonstrated that ML methods could promote the discovery of the optimal process window, leading to an outstanding synergy of tensile strength and ductility.

Characterization of Hot Deformation Behavior and Processing Maps Based on Murty Criterion of SAE8620RH Gear Steel

The hot deformation behavior and microstructure evolution of the SAE8620RH gear steel were investigated through a single-pass hot compression test at deformation temperatures between 850 and 1100 °C and strain rates between 0.02 and 8.0 s−1 by 60% reduction. A novel strain compensation constitutive model was developed, and the 2D processing maps were established by Murty’s criterion. Results showed that the relationship between material-related parameters and strain can be mathematically expressed by a highly reliable 8th-order polynomial. The constructed strain compensation constitutive model demonstrated remarkable predictive precision, as evidenced by the correlation coefficient (R) and the absolute values of average relative error (AARE) of 0.978 and 4%, respectively. The flow instability domains considerably expanded towards the high deformation temperature region as the strain increased. Microstructure analysis confirmed the accuracy of the processing map constructed by Murty’s criterion. The most noticeable optimum processing windows for SAE8620RH gear steel at a strain of 0.7 occurred within the temperature range of 1000–1100 °C and the strain rate range of 0.3–1.0 s−1, due to high η values exceeding 0.3 and equiaxial dynamic recrystallization microstructure.

Hot deformation behavior of a Fe3Al–Ta alloy in the B2-order regime

In the present work, the hot deformation behavior and the corresponding microstructure evolution of an Fe–25Al-1.5Ta (at.%) alloy in the B2-phase field were investigated. Uniaxial compression tests were carried out in a strain rate range from 0.0013 s−1 to 1 s−1 and in a temperature range from 800 °C to 850 °C, where an ordered B2–FeAl matrix phase along with a C14 - (Fe, Al)2Ta Laves phase was confirmed by X-ray diffraction. A dynamic material model was applied to predict the safe and damaging processing windows. The underlying flow softening mechanisms were characterized using scanning electron microscopy and electron-backscatter diffraction. The flow stress-strain curves mostly showed a broad maximum followed by a slight decrease in stress until a steady stress was reached. The optimum processing window for the studied alloy was located at 850 °C/0.0013 s−1, where the efficiency of power dissipation (η) and strain rate sensitivity (m) reached 50% and 0.25, respectively. The processing map also showed a domain of flow instability, resulting from cracking, in the range of lower temperatures and higher strain rates (800 °C/1 s−1). The microstructural analyses confirmed a combination of dynamic recovery (DRV) and dynamic recrystallization (DRX) over the entire range of deformation conditions tested. The current study reveals a well-suited parameter range to achieve a high degree of hot deformability in Fe–Al alloys at significantly lower temperatures than those typically used. This may contribute to optimizing the thermomechanical processing of Fe–Al alloys and reducing energy consumption in industrial forging operations.

Fe-Mn-Al-Ni Shape Memory Alloy Additively Manufactured via Laser Powder Bed Fusion

Fe-Mn-Al-Ni is an Fe-based shape memory alloy (SMA) featuring higher stability and low temperature dependency of superelasticity stress over a wide range of temperatures. Additive manufacturing (AM) is a promising technique for fabricating Fe-SMA with enhanced properties, which can eliminate the limitations associated with conventional fabrication and allow for the manufacture of complicated shapes with only a single-step fabrication. The current work investigates the densification behavior and fabrication window of an Fe-Mn-Al-Ni SMA using laser powder bed fusion (LPBF). Experimental optimization was performed to identify the optimum processing window parameters in terms of laser power and scanning speed to fabricate Fe-Mn-Al-Ni SMA samples. Laser remelting was also employed to improve the characteristics of Fe-Mn-Al-Ni-fabricated samples. Characterization and testing techniques were carried out to assess the densification behavior of Fe-Mn-Al-Ni to study surface roughness, density, porosity, and hardness. The findings indicated that using a laser power range of 175–200 W combined with a scanning speed of 800 mm/s within the defined processing window parameters can minimize the defects with the material and lead to decreased surface roughness, lower porosity, and higher densification.

Mechanism and influencing factors analysis of polyethylene oxide electrohydrodynamic printing

AbstractElectrohydrodynamic (EHD) printing is a micro–nano printing technology based on the principles of electric field and fluid dynamics. It is characterized by high resolution, high precision, and high speed, applied to various materials, including metals, ceramics, and organic materials. Compared with traditional printing technologies, EHD printing offers advantages such as low manufacturing cost, simple process, and direct fabrication, making it highly promising in the field of micro–nano manufacturing. Polyethylene oxide (PEO) is a highly water‐soluble polymer that has been widely used in various fields due to its low toxicity and ease of processing. In this study, a finite element simulation model was developed using simulation software to simulate and analyze the mechanisms of focused jetting and deposition of PEO solution under an electric field. Based on the principles of electrohydrodynamics, a self‐built EHD printing system was used to investigate the influence of different solution mass fractions and printing parameters on fiber formation, and the optimal process window of EHD printing PEO solution was obtained. Ultimately, ordered deposition of fiber lines ranging from 1.761 to 6.093 μm was achieved. The simulation results were consistent with the experimental results, validating the effectiveness of the established model in guiding jetting outcomes.Highlights Independently building a low‐cost electrohydrodynamic (EHD) printing system. Finite element simulation of EHD printing process. Mechanism analysis of PEO solution jetting and deposition. Optimal process window for PEO solution EHD printing. Influence of key process parameters on fiber forming width.

Hot Working of an Fe-25Al-1.5Ta Alloy Produced by Laser Powder Bed Fusion

In the present work, hot working was used as a post-processing method for Fe-25Al-1.5Ta (at.%) alloy built using laser powder bed fusion (LPBF) to refine the undesirable columnar microstructure with heterogeneous grain sizes and strong textures in the build direction. The hot deformation behavior and workability were investigated using constitutive modeling and the concept of processing maps. Uniaxial compression tests were conducted up to a true strain of 0.8 at 900 °C, 1000 °C, and 1100 °C with strain rates of 0.0013 s−1, 0.01 s−1, and 0.1 s−1. The constitutive equations were derived to describe the flow stress–strain behavior in relation to the Zener–Hollomon parameter. Processing maps based on a dynamic materials model were plotted to evaluate the hot workability and to determine the optimal processing window as well as the active deformation mechanisms. The microstructure of the deformed specimens was characterized by scanning electron microscopy equipped with an electron backscatter diffraction detector. The results indicated a high degree of hot workability of the LPBF builds without flow instabilities over the entire deformation range tested. The epitaxially elongated grains of the as-built alloys were significantly refined after deformation through dynamic softening processes, and the porosity was reduced due to compressive deformation. The current study revealed a well-suited parameter range of 1000–1080 °C/0.004–0.012 s−1 for the safe and efficient deformation of the LPBF-fabricated Fe-25Al-1.5Ta alloys. The effectiveness of the process combination of LPBF with subsequent hot forming could be verified with regard to microstructure refinement and porosity reduction.

Comparison of Thermal Deformation Behavior and Characteristics of Mg-Gd-Y-Zn Alloys with and without Bulk LPSO Phase.

Alloys Mg-8Gd-4Y-0.6Zn-0.5Zr (referred to as 0.6Zn) without the bulk long-period stacking ordered (LPSO) phase and Mg-8Gd-4Y-1.1Zn-0.5Zr (referred to as 1.1Zn) containing the bulk LPSO phase were prepared and a series of hot compression tests were conducted to examine and evaluate the influence of the bulk LPSO phase on the thermal deformation behavior and characteristics of the Mg-Gd-Y-Zn-Zr alloy. The bulk LPSO phase affects the dynamic recrystallization behavior, resulting in differences in flow stress between two alloys under different conditions. Specifically, in the temperature range of 380~460 °C, compression at lower strain rates is beneficial for the LPSO phase to promote dynamic recrystallization, while compression at a high strain rate inhibits the dynamic recrystallization due to the severe deformation of the bulk LPSO phase to release the stress concentration instead. The increase in temperature helps the LPSO promote dynamic recrystallization. As a result, the LPSO phase promotes dynamic recrystallization at all experimental strain rates at 500 °C. Furthermore, the thermal processing maps of the 0.6Zn and 1.1Zn alloys are established, and their optimal processing windows are located at 500 °C/0.001~0.01 s-1 and 500 °C/0.01 s-1, respectively. In addition, the instability zones for the 1.1Zn alloy are much larger than that for the 0.6Zn alloy, which corresponds to the microcracks generated at the interfaces between α-Mg and bulk LPSO phases.

On the Processability and Microstructural Evolution of CuCrZr in Multilayer Laser-Directed Energy Deposition Additive Manufacturing via Statistical and Experimental Methods

Laser-directed energy deposition (LDED) is a promising technology for coating, repairing, and building near-net-shape 3D structures. However, the processing of copper alloys, specifically, has presented a significant challenge due to their low laser absorptivity at the 1060 nm laser wavelength and high thermal conductivity. This study undertook a methodical examination by employing a 2 kW disk laser, operating at a wavelength of 1064 nm, and a coaxial nozzle head to comprehensively examine the processability of the highly conductive CuCrZr alloy for expanding the range of materials that can be successfully processed using LDED. The investigation focuses not only on optimizing the input process parameters that are the laser power, scanning speed, powder feed rate, and overlap ratio, but also on planning the toolpath trajectory, as these factors were found to exert a substantial influence on processability, geometrical accuracy, and the occurrence of defects such as lack of fusion. The optimal toolpath trajectory discovered involved implementing a zigzag strategy combined with a 90° rotation of the scanning direction. Additionally, a start point rotation was considered between each layer to even out the deposition of the layers. Moreover, a contour with a radial path at the corners was introduced to enhance the overall trajectory. Based on the hierarchal experimental study, the appropriate ranges for the key process parameters that leads to 99.99% relative density have been identified. They were found to be from 1100 up to 2000 W for the laser power (P), and from 0.003 up to 0.016 g/mm for the amount of powder that is fed to the melt pool distance (F/V). Regarding the influence of process parameters on the microstructure of the samples with equal deposition height, it was observed that varying combinations of process parameters within the optimal processing window resulted in variations in grain size ranging from 105 to 215 µm.

Optimization of the Crystallization Process of TFA-MOD ErBCO Films on IBAD-Substrate Under Low-Pressure Conditions via DSD Approach

Crystallization in a sub-atmospheric reactor could achieve higher production rate while dramatically reducing the flow rate of high-purity carrier gas. Due to enhanced supersaturation conditions at low total pressure, it is necessary to find the optimum processing window to avoid misoriented growth. This is extensive and incomplete when using one-factor-at-a-time experiments as significant parameters are often correlated. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">We prepared ErBa₂Cu₃O_7-<i>_δ</i> (ErBCO) films by the TFA-MOD route with low-fluorine solutions on technical IBAD template with CeO₂ top buffer layer in an industrial reel-to-reel furnace. We used a novel design-of-experiment (DOE) technique, the Definitive Screening Design (DSD), to identify significant factors for improving critical temperature and microstructure of the films. Within the investigated range, lower crystallization temperature as well as lower total pressure are beneficial. With the new process window, the self‑field critical current density at 77 K was successfully increased from almost zero to 1 MA/cm². This shows that DSD is an attractive approach to optimize the CSD process under low-pressure conditions to enhance the growth rate or possibly achieve a reduction of carrier gas flow rate by a factor <i>p</i>_tot/<i>p</i>_atm of 3.3 for equal output as the atmospheric reactor. Further improvement of <i>J</i>_c is necessary and possible.

Machine learning-assisted constitutive modeling of a novel powder metallurgy superalloy

The flow behavior and microstructure evolution during thermomechanical processing (TMP) of powder metallurgy superalloys are very important for their service behavior. In this contribution, a machine learning-assisted physical model was proposed to predict the flow stress, dynamic recrystallization (DRX) kinetic, and grain size evolution of a novel FGH4113A superalloy during the TMP. The work hardening and dynamic softening stages were modeled separately to predict the flow stress. The novel aspect of the proposed model is that the strong coupled effects of deformation temperature, strain rate, true stain, and primary γ' precipitates on the DRX kinetic were quantitatively described by the genetic algorithm-based artificial neural network (GA-ANN). Besides, the grain size modeling considered the pinning effect by primary γ' precipitates and the deformation-induced DRXed grain growth. Comparing the experimental and predicted flow curves, DRX fraction, and average grain size reveals that the proposed model has a preferable prediction accuracy than the conventional model. Then the specific DRX kinetic and grain size evolution characteristics were revealed. The promoting effect of strain rate on the DRX degree was gradually increased with the deformation temperature. Finally, the 3D processing map based on the developed model was established to guide TMP's optimized design and microstructure control. Three domains were divided and discussed: grain refinement, constant, and growth. The optimal processing window is defined as 1000–1050 °C/0.001–0.006 s−1 and 1075–1100 °C/0.008–0.01 s−1.

Laser Activation for Highly Boron-Doped Passivated Contacts

Passivated, selective contacts in silicon solar cells consist of a double layer of highly doped polycrystalline silicon (poly Si) and thin interfacial silicon dioxide (SiO2). This design concept allows for the highest efficiencies. Here, we report on a selective laser activation process, resulting in highly doped p++-type poly Si on top of the SiO2. In this double-layer structure, the p++-poly Si layer serves as a layer for transporting the generated holes from the bulk to a metal contact and, therefore, needs to be highly conductive for holes. High boron-doping of the poly Si layers is one approach to establish the desired high conductivity. In a laser activation step, a laser pulse melts the poly Si layer, and subsequent rapid cooling of the Si melt enables electrically active boron concentrations exceeding the solid solubility limit. In addition to the high conductivity, the high active boron concentration in the poly Si layer allows maskless patterning of p++-poly Si/SiO2 layers by providing an etch stop layer in the Si etchant solution, which results in a locally structured p++-poly Si/SiO2 after the etching process. The challenge in the laser activation technique is not to destroy the thin SiO2, which necessitates fine tuning of the laser process. In order to find the optimal processing window, we test laser pulse energy densities (Hp) in a broad range of 0.7 J/cm2 ≤ Hp ≤ 5 J/cm2 on poly Si layers with two different thicknesses dpoly Si,1 = 155 nm and dpoly Si,2 = 264 nm. Finally, the processing window 2.8 J/cm2≤ Hp ≤ 4 J/cm2 leads to the highest sheet conductance (Gsh) without destroying the SiO2 for both poly Si layer thicknesses. For both tested poly Si layers, the majority of the symmetric lifetime samples processed using these Hp achieve a good passivation quality with a high implied open circuit voltage (iVOC) and a low saturation current density (J0). The best sample achieves iVOC = 722 mV and J0 = 6.7 fA/cm2 per side. This low surface recombination current density, together with the accompanying measurements of the doping profiles, suggests that the SiO2 is not damaged during the laser process. We also observe that the passivation quality is independent of the tested poly Si layer thicknesses. The findings of this study show that laser-activated p++-poly Si/SiO2 are not only suitable for integration into advanced passivated contact solar cells, but also offer the possibility of maskless patterning of these stacks, substantially simplifying such solar cell production.

Process window prediction in stainless steel selective laser melting using various energy densities: laser power, scan speed, and defocusing distance

Abstract The process window of selective laser melting (SLM), a set of optimum process parameters, is crucial for producing defect-free components with excellent mechanical properties. This study aims to predict the optimum process window for SLM of stainless steel by varying the defocusing distance (f) which changes the laser beam diameter (d) and using laser power (P) and scan speed (V) as process parameters. The process window was predicted using empirical formulae related to the energy density equations, instead of the conventional approach based on simple experimental results. To predict the process window, we analyzed the melt pool geometry of components with different features, such as depth (D), width (W), layer thickness (t), and hatch distance (h). Using the energy density equation, we correlated the effect of these process variables on the melt pool geometry and derived empirical equations. The upper limit of the process window (D/W) was strongly correlated with local applied energy and expressed as P ≤ 34Vd2. The lower limits, D/t and W/h, showed good correlation with linear energy density and laser energy density, respectively, and expressed as P &gt; 2.16Vd and P &lt; 0.13V. Finally, we used these empirical equations to predict the process window, which was experimentally verified.

Hot Workability Investigation of an Fe-Al-Ta Alloy Using Deformation Processing Maps

Fe-Al-Ta alloys are expected to replace high-alloyed steels in steam turbine blades. However, the mechanical properties of the forged blades are still not optimal due to limited grain refinement during hot forging and the coarse-grained microstructure inherited from the as-cast precursor. It is, therefore, essential to investigate the hot deformation behavior of the alloy to identify the optimum range for the deformation parameters leading to good hot workability with significant grain refinement. The hot deformation behavior and hot workability of an Fe-25Al-1.5Ta (at.%) alloy were investigated in the present work using constitutive modeling and the concept of processing maps. Uniaxial compression tests were conducted in a strain rate range from 0.0013 s−1 to 1 s−1 and in a temperature range from 900 °C to 1100 °C, where a disordered A2 α-(Fe, Al) matrix phase along with a C14-(Fe, Al)2Ta Laves phase were confirmed by X-ray diffraction. The flow stress–strain curves showed a broad maximum followed by a slight drop in stress until a steady state was reached. The optimum processing window for the studied alloy was located at 910–1060 °C/0.0013–0.005 s−1, where the efficiency of the power dissipation (η) and strain rate sensitivity (m) reached 50% and 0.33, respectively. The material underwent a combination of dynamic recovery and dynamic recrystallization over the whole tested deformation range. No flow instabilities were predicted based on Prasad’s flow instability criterion when deformation was performed up to a true strain of 0.5 and 0.8, indicating a high degree of hot workability of the studied alloy over the entire deformation range tested. The current study reveals a well-suited parameter range for the safe and efficient deformation of Fe-Al-Ta alloys, which may contribute to the optimization of the thermomechanical processing of this alloy.

Additive manufacturing process parameter determination for a new Fe-C-Cu alloy

As a potential replacement for stainless steel alloys commonly used to print parts with laser powder bed fusion, a new Cu precipitation strengthened ferrous alloy, with composition Fe-0.2C-6Cu (wt%), was recently developed. This material is Co- and Ni-free, printable, has mechanical properties comparable to that of high strength stainless steels (approximately 1300 MPa UTS), and is cost-advantaged relative to existing low-alloy steels for additive manufacturing of parts with complex shapes. To gain traction for broader application, optimal laser powder bed fusion (LPBF) processing conditions to produce nearly defect-free parts without compromising mechanical strength are needed. Here, an optimal processing window based upon laser speeds that achieve minimal porosity was quantified via comparisons of measured melt pool penetration, scan speeds, printed material density and laser beam energy density on a commercial LPBF unit operating at 350 W, 80 μm hatch spacing, and 50 μm layer thickness based upon optimal parameters for 17-4PH. The window is 300 to 500 mm/s to achieve >99.8 % dense Fe-0.2C-6Cu (wt%) specimens. Other defects such as burning, spatter, and lack of fusion were also avoided in this window. The window was validated with in-situ synchrotron X-ray imaging that enabled visualization of the vapor cavity, melting, and solidification during a single laser track scan on a miniature powder bed sample. In addition, in-situ infrared imaging provided temperature fields, cooling rate and solidification range, and confirmed minimal printing defects and spatter within the processing window.

Multi-Objective Process Optimization of Laser Cladding Co-Based Alloy by Process Window and Grey Relational Analysis

To determine the optimal process parameters for the preparation of a Co-based alloy cladding layer, the experimental research of laser cladding Co-based alloy was carried out based on the optimal process window and grey relational analysis methods with 42CrMo as the substrate. The analysis of variance (ANOVA) was used to explore the influence laws of laser process parameters on the forming characteristics of the cladding layer within the optimal process window range. Furthermore, the optimal process parameter combination was obtained by grey relational analysis, and the experimental verification of the optimization results was conducted. It was found that the process parameter interval determined by the optimal process window was laser power 1300–2100 W, scanning speed 6–14 mm/s, and powder feeding rate 17.90–29.84 g/min. The influence order of each process parameter was: laser power &gt; scanning speed &gt; powder feeding rate. The optimal process parameters of laser power 2100 W, scanning speed 6 mm/s, and powder feeding rate 17.90 g/min were obtained. The experimental verification results of optimal process parameters proved that the grey correlation grade of the optimized parameters was improved by 0.260 compared with the initial parameters and agreed well with the prediction value with an accuracy of 96%. After optimization, the cross-sectional area, the ratio of the width to height, cladding efficiency, and powder utilization rate of the cladding track increased by 4.065 mm2, 1.031, 19.032, and 70.3%, respectively, and the fluctuation ratio decreased by 60.9%. The optimal cladding track was well bonded to the substrate without cracks, holes, and evident element segregation, and included the phases of Cr3C7, CoCx, fcc-Co, and WC.

Evolution of multi-cellular structure on Zr and Er modified Al6Si1Mg alloy fabricated by laser powder bed fusion

The printability of Al6SiMg0·5Er1·0Zr alloy at various laser power, scan speed, and hatch spacing was investigated. The optimal processing window was determined. The relationship between hatch spacing and lack of fusion (LOF) defects and microstructure is discussed. Hatch spacing significantly affects the cellular size, which is formed by eutectic Si network, and medium hatch spacing can achieve the finest microstructure. Samples with high densities and fine microstructures were investigated more carefully. The grain and cellular boundaries have many Al3(Er,Zr) phases. The grain size was refined to 2.64 μm, and the epitaxial growth of columnar crystals was completely suppressed. The cellular structure has been significantly improved. Get the equiaxed - ultrafine equiaxed - columnar multi-cellular structure with dramatically enhanced mechanical properties. The yield strength, tensile strength, and elongation were 373 Mpa, 480 MPa, and 5.5%, respectively. Grain boundary strengthening and Orowan strengthening was the main strengthening mechanisms.

Annular laser metal deposition of Ti-6Al-4V alloy in a semi-open environment: Process optimization, microstructure and mechanical properties

Laser metal deposition (LMD) in open environment is beneficial for the forming of large parts or the online repairing of damaged components. A major challenge in successful deposition of active materials is oxidation. The surface chromatic aberration is adopted to represent the oxidized discoloration. In this paper, response surface methodology (RSM) is used to obtain the process parameters of a single layer of Ti-6Al-4V alloy with low surface chromatic aberration in a semi-open environment, based on annular laser metal deposition (ALMD) process. The results show that low surface chromatic aberration is achieved by appropriately reducing laser power, and increasing powder feeding rate and shielding flow rate. There is good agreement between the predicted and experimental values. The desirability approach is employed for determining the optimal processing window to obtain the deposited layer less than surface chromatic aberration threshold of 5.09 based on oxygen concentration analysis. Furthermore, the microstructure and mechanical properties are investigated. The yield strength of 907 MPa and elongation of 6.5% are achieved at the optimum parameter settings. This study establishes a methodology towards successful deposition of Ti-6Al-4V alloy in a semi-open environment.

Screw Extrusion Additive Manufacturing of Carbon Fiber Reinforced PA6 Tools

The creation of tools by additive manufacturing is becoming increasingly convenient for CFRP one-off and small batch production. Screw extrusion additive manufacturing of thermoplastic polymers has boosted the development of large format manufacturing solutions. Interlayer adhesion and anisotropic properties of a 3D printed part are indisputably key aspects of tool manufacturing process. In this study, thermal and mechanical properties of large format 40% carbon fiber reinforced polyamide 6 3D printed tools were determined. Moreover, the influence on part performance of two main printing parameters, deposition temperature and extruding pressure, was analyzed with respect to polymer melt rheology. The printed material revealed a highly anisotropic thermal and mechanical behavior associated with the alignment of the high carbon fiber content. The optimal process window was identified in terms of substrate deposition temperature. Along the print direction, no major impact on tensile and flexural mechanical properties was detected, while the injection molding values were exceeded by approximately 10%. The layer adhesion was estimated by measuring the stress at break on transversely Z-oriented specimens. Higher deposition temperatures and pressures, combined with lower viscosity, promote wetting and bond formation between layers, ultimately leading to more consistent performances. The best results in the transverse direction were achieved between 140 and 160 °C, reaching roughly a fifth of the longitudinal values. A significant drop in performance was detected below 120 °C, which was identified as the minimum process temperature. A post-process annealing heat treatment was also investigated, no beneficial outcomes were reported.