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

Wire laser additive manufacturing (WLAM) is an emerging process to build rapidly metal parts of low complexity. In this paper, single beads of low alloy carbon steel, ER120, were welded with a filler on a S355J2 substrate to reproduce the conditions met in WLAM. The impact of the process parameters (power, wire feedrate, travel speed, spot size) on the stability and geometry of the beads were investigated. A configuration with a dual spot was also studied and found to give analogous results to a single, larger spot of the same area. For each bead dimension (height, width, area, depth) a power law relationship with the process parameters is fitted. Descriptors based on volume energy density and enthalpy were proposed to describe the transition from a conduction mode welding to a keyhole stage, which can lead to the creation of pores in the part.

A direct energy deposition (DED) process using wires is considered an additive manufacturing technology that can produce large components at an affordable cost. However, the high deposition rate of the DED process is usually accompanied by poor surface quality and inherent printing defects. These imperfections can have a detrimental effect on fatigue endurance and corrosion fatigue resistance. The aim of this study was to evaluate the critical effect of phase transition and printing defects on the corrosion fatigue behavior of 316L stainless steel produced by a wire laser additive manufacturing (WLAM) process. For comparison, a standard AISI 316L stainless steel with a regular austenitic microstructure was studied as a counterpart alloy. The structural assessment of printing defects was performed using a three-dimensional non-destructive method in the form of X-ray microtomography (CT) analysis. The microstructure was evaluated by optical and scanning electron microscopy, while general electrochemical characteristics and corrosion performance were assessed by cyclic potentiodynamic polarization (CCP) analysis and immersion tests. The fatigue endurance in air and in a simulated corrosive environment was examined using a rotating fatigue setup. The obtained results clearly demonstrate the inferior corrosion fatigue endurance of the 316L alloy produced by the WLAM process compared to its AISI counterpart alloy. This was mainly related to the drawbacks of WLAM alloys in terms of having a duplex microstructure (austenitic matrix and secondary delta-ferrite phase), reduced passivity, and a significantly increased amount of intralayer porosity that acts as a stress intensifier of fatigue cracking. [ABSTRACT FROM AUTHOR]

A cross-scale model of macro-micro coupling is established for the wire laser additive manufacturing process of the TC4 titanium alloy. The model reproduces the dynamic evolution process of the molten pool shape, reveals the temperature change law in the molten pool, and simulates the microstructure and morphology of different regions of the molten pool. Finally, the model is used to quantitatively analyze the effects of process parameters (laser power, scanning speed) on the growth morphology of dendrites during solidification. The research shows that with the increase in laser power and the decrease in scanning speed, the peak temperature of the molten pool increases rapidly, and the size of the molten pool increases gradually. When the laser scanning speed is greater than 5 mm/s, the molten pool length decreases significantly. After solidification, an asymmetrically distributed equiaxed grain structure is formed at the upper part of the molten pool, the bottom of the molten pool is made up of slender columnar crystals, and the columnar-to-equiaxed transition (CET) occurs in the middle of the molten pool. With the decrease in laser power and the increase in scanning speed, the growth rate of dendrites becomes faster, the arm spacing and the overall morphology of dendrites become smaller, and the arrangement of columnar crystals have a tighter microstructure. [ABSTRACT FROM AUTHOR]

A cross-scale model of macro-micro coupling is established for the wire laser additive manufacturing process of the TC4 titanium alloy. The model reproduces the dynamic evolution process of the molten pool shape, reveals the temperature change law in the molten pool, and simulates the microstructure and morphology of different regions of the molten pool. Finally, the model is used to quantitatively analyze the effects of process parameters (laser power, scanning speed) on the growth morphology of dendrites during solidification. The research shows that with the increase in laser power and the decrease in scanning speed, the peak temperature of the molten pool increases rapidly, and the size of the molten pool increases gradually. When the laser scanning speed is greater than 5 mm/s, the molten pool length decreases significantly. After solidification, an asymmetrically distributed equiaxed grain structure is formed at the upper part of the molten pool, the bottom of the molten pool is made up of slender columnar crystals, and the columnar-to-equiaxed transition (CET) occurs in the middle of the molten pool. With the decrease in laser power and the increase in scanning speed, the growth rate of dendrites becomes faster, the arm spacing and the overall morphology of dendrites become smaller, and the arrangement of columnar crystals have a tighter microstructure.

The wire laser additive manufacturing (WLAM) process is considered a direct-energy deposition method that aims at addressing the need to produce large components having relatively simple geometrics at an affordable cost. This additive manufacturing (AM) process uses wires as raw materials instead of powders and is capable of reaching a deposition rate of up to 3 kg/h, compared with only 0.1 kg/h with common powder bed fusion (PBF) processes. Despite the attractiveness of the WLAM process, there has been only limited research on this technique. In particular, the stress corrosion properties of components produced by this technology have not been the subject of much study. The current study aims at evaluating the effect of a slow strain rate on the stress corrosion resistance of 316L stainless steel produced by the WLAM process in comparison with its counterpart: AISI 316L alloy. Microstructure examination was carried out using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis, while the mechanical properties were evaluated using tensile strength and hardness measurements. The general corrosion resistance was examined by potentiodynamic polarization and impedance spectroscopy analysis, while the stress corrosion performance was assessed by slow strain rate testing (SSRT) in a 3.5% NaCl solution at ambient temperature. The attained results highlight the inferior mechanical properties, corrosion resistance and stress corrosion performance, especially at a slow strain rate, of the WLAM samples compared with the regular AISI 316L alloy. The differences between the WLAM alloy and AISI 316L alloy were mainly attributed to their dissimilarities in terms of phase compositions, structural morphology and inherent defects.

Arc-wire or laser-wire additive manufacturing seems promising because it allows large parts to be produced with significant deposition rates (ten times higher than powder bed additive manufacturing), for a lower investment cost. These additive manufacturing techniques are also very interesting for the construction or the repair of parts. A versatile 3D printing device using a Wire Arc Additive Manufacturing (WAAM) station or laser device Wire Laser Additive Manufacturing (WLAM) for melting a filler wire is developed to repair and build large titanium parts. The final objectives of the study are to optimize the process parameters to control the dimensional stability, the metallurgical and mechanical properties of the produced parts. In this paper, an experimental study is carried out to determine the first order process parameter ranges (synergic law, laser power, wire feed speed, travel speed) appropriate for these two techniques, for repair or construction parts on Ti-6 Al-4V.

The wire laser additive manufacturing (WLAM) process is considered a direct-energy deposition method that aims at addressing the need to produce large components having relatively simple geometrics at an affordable cost. This additive manufacturing (AM) process uses wires as raw materials instead of powders and is capable of reaching a deposition rate of up to 3 kg/h, compared with only 0.1 kg/h with common powder bed fusion (PBF) processes. Despite the attractiveness of the WLAM process, there has been only limited research on this technique. In particular, the stress corrosion properties of components produced by this technology have not been the subject of much study. The current study aims at evaluating the effect of a slow strain rate on the stress corrosion resistance of 316L stainless steel produced by the WLAM process in comparison with its counterpart: AISI 316L alloy. Microstructure examination was carried out using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis, while the mechanical properties were evaluated using tensile strength and hardness measurements. The general corrosion resistance was examined by potentiodynamic polarization and impedance spectroscopy analysis, while the stress corrosion performance was assessed by slow strain rate testing (SSRT) in a 3.5% NaCl solution at ambient temperature. The attained results highlight the inferior mechanical properties, corrosion resistance and stress corrosion performance, especially at a slow strain rate, of the WLAM samples compared with the regular AISI 316L alloy. The differences between the WLAM alloy and AISI 316L alloy were mainly attributed to their dissimilarities in terms of phase compositions, structural morphology and inherent defects. [ABSTRACT FROM AUTHOR]

The bead geometry, microstructure and mechanical properties of wire laser additively manufactured (WLAM) Ti–6Al–4V samples reinforced by different contents of micron-sized lanthanum oxide (La 2 O 3) particles were explored. The images attained through high-speed charge coupled device (HCCD) and metallographs showed that the addition of La 2 O 3 changed the morphologies of the weld bead of Ti–6Al–4V alloy to lead to the significant reduction of the width of the deposited weld bead and remarkable growth of the weld penetration. The observation result attained through the scanning electron microscope (SEM) revealed that relative to the condition without the addition of micron-sized La 2 O 3 particles, nano-sized La 2 O 3 particles were uniformly distributed in the matrix after adding micron-sized La 2 O 3 particles; β grains and α phases were both greatly refined. Compared with the primitive La 2 O 3 powders, the morphology of La 2 O 3 in the matrix approximately presented a spherical shape. It indicated that La 2 O 3 particles in the molten pool partly or completely decomposed during WLAM. The dispersedly distributed nano-sized La 2 O 3 particles induced fine grain strengthening and dispersion strengthening. Therefore, the tensile strength and Vickers hardness of the deposit of the Ti–6Al–4V alloy rose with increasing addition amount of La 2 O 3. However, the decomposition of La 2 O 3 particles resulted in the formation of interstitial atoms (such as interstitial O atoms), thus leading to the decrease of the elongation of deposits. Without the addition of La 2 O 3 particles, the deposit of the Ti–6Al–4V alloy fractured in the large-size lamellar α during the tensile test, in which the fracture showed micro-morphology of ductile fracture. After the addition of La 2 O 3 particles, the deposit of Ti–6Al–4V alloy fractured at the grain boundary α phase during the tensile test and both cleavage and ductile morphologies were found at the fracture. [ABSTRACT FROM AUTHOR]