Laser Molten Pool Research Articles

Role of Cr addition in Ni-based interlayer on strengthening titanium and steel dissimilar bimetallic structures enabled by directed energy deposition with laser beam

For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam (DED-LB), pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work. Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically. The distribution of intermetallic compounds (IMCs) such as β-Ti, Ti2Ni, TiNiFe0.2, Ti2Ni3Si and TiB2 in joints was revealed. The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely. Notably, additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus, leading to fewer IMCs in joints. As a result, both bonding strength and toughness of joints were remarkably improved. The findings emphasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.

Laser resolidification of Al-5Mg-0.1Sc alloy: Growth of cells and banded structures

The versatility of Al-Mg alloys makes them well-suited for applications ranging from everyday items to cutting-edge fields like automotive, microelectronics, and aerospace. Moreover, although Al-Mg alloys hold promise for improved surface features in components, research on their laser surface remelting (LSR) remains scarce, presenting an open opportunity to create novel components with these materials. Understanding the growth modes and morphologies of laser surface remelted products is critical in this context. Using a laser instrument, optical microscopy, SEM, XRD, Vickers hardness and image analysis techniques, a correlative analysis of microstructure features and laser heat input is proposed in this research. Furthermore, the Al-5Mg-0.1Sc (wt%) alloy was remelted using two distinct original substrates, each exhibiting varying degrees of microstructure coarsening. Additionally, four distinct laser heat input conditions were applied to each case. All molten pools regions were formed either by cells or bands, with higher growth rates producing a higher fraction of bands. While the variation in the original microstructure of the substrate did not significantly impact both cellular spacings and band/cellular fractions, the microhardness varied remarkably with the reduction in energy input from 10.0 J/mm to 1.7 J/mm. Kurz and Fisher model provided an accurate prediction of the cell spacings formed at the laser molten pool.

Microstructure and Wear Resistance of Laser-Treated and Slow Cooled AlSi10Mg-(x)Ni Alloys

This study examined the solidification features and wear of AlSi10Mg(-Ni) alloy samples generated under various conditions. Additions were varied from 0 to 3 wt% Ni while maintaining Si and Mg contents. All samples were directionally solidified (DS) and laser treated using surface laser remelting (LSR). Both DS and LSR samples were characterized by a number of methods, including the following: thermal analysis, optical microscopy, stereomicroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), wear tests, and Vickers hardness. Ranges for cooling rates, dendritic spacing and hardness, respectively, were from 0.4 to 13.3 K/s, from 77 to 388 μm, from 71 to 93 HV for the DS samples and from 4.3 × 104 to 8.7 × 104 K/s, from 1.0 to 2.0 μm, and from 114 to 143 HV for the LSR (100 J/mm2). The solidification kinetics had a large impact on the solidified samples, allowing a representative range of microstructures and morphologies to be examined in terms of wear. The 1% Ni alloy had the highest wear resistance among all the DS samples under slow cooling and the short-term wear test (10 min/0.5 N), while the LSR samples showed similar wear resistances regardless of the Ni content. The uniform dispersions of Si and Al3Ni forming intercellular dense walls at the top of the laser molten pool together with their rod-like morphologies and reduced dendrite spacing of less than 2 μm, improved bonding with the matrix, resulting in higher and more consistent wear resistance of the laser treated surfaces.

Microstructure evolution and high temperature wear resistance of in-situ synthesized carbides reinforced NiCoFeCrSiMo high entropy alloy coatings fabricated by laser cladding

In this work, we reported a novel strengthening strategy of NiCoFeCrSiMo high entropy alloy by high density in-situ synthesized carbides. The external WC particles were introduced into the laser molten pool and basically dissolved which facilitate the in-situ reactions of carbides. The microstructure of composite coatings consists of high-density carbides which formed dendrites, while the FCC based solid solution matrix of high entropy alloy filled the inter-dendritic zone. The original added WC particles were almost dissolved in the laser pool and M6C type carbides or M2C carbides were in-situ synthesized. The composite coating was strengthened by dislocation pinning and plugging effects. Notably, the average microhardness of the composite coating can reach as high as 947 HV, while the friction coefficient of high entropy alloy coatings with 50 % WC addition could be as lower as 0.2 at 600 °C. The wear surface morphology analysis shows that the wear mechanism of M6C/FCC composite coating was adhesive wear and abrasive wear. The results in this work may provide some new thoughts for the design of ceramic particles reinforced HEA composite coatings.

Effects of WC Particles on the Microstructure of IN718/WC Composite Coatings Fabricated by Laser Cladding: A Two-Dimensional Phase-Field Study

During the process of laser cladding IN718/WC composite coatings, the dissolution and metallurgical reaction of WC particles significantly influence the microstructures of the coatings. However, the limited experimental methods restrict direct observation and prevent a deep understanding of this complicated process. Therefore, a novel numerical model for the solidification process of IN718/WC composite coatings was proposed. The model was established with the coupled multi-phase-field model and lattice Boltzmann method. Different kinds of microstructure around WC particles were simulated by the model and verified by experiments. Subsequently, microhardness and wear tests were carried out to investigate the improved mechanical properties of IN718 coatings reinforced by WC particles. The results show that the cellular alloy reaction layer, IN718 grains, and eutectic structure are formed, in turn, around WC particles. The convection in the laser molten pool can induce double-tail-like or spindle-like WC convection diffusion bands. The hardness of these bands is higher than that of the IN718 matrix. More importantly, WC convection diffusion bands can inhibit the growth of columnar crystals, because the dissolved WC can decrease the freezing temperature of the melt. Finally, mechanical property tests show that WC particles increase the hardness of the coating and significantly improve its wear resistance.

In-situ reinforced phase evolution and wear resistance of nickel-based composite coatings fabricated by wide-band laser cladding with Nb addition

In this paper, Ni60/WC composite coatings were prepared by wide-band laser cladding technique. The effects of the addition of the strong carbide forming element Nb on the microstructure and properties of the composite coatings were studied by microstructure characterization, phase identification, microhardness, wear resistance, and other properties. The results show that the in-situ synthesized phases in the laser molten pool are mainly composed of γ-Ni solid solution and strengthening phases such as Cr7C3, Cr23C6, Cr5B3, and NbC. With the increase of Nb content in the composite cladding layer, the formation of Cr7C3 is inhibited, the amount of residual WC decreases, while the content of NbC increases, and the morphology of the precipitated phase containing NbC changes from coarse strips to fine needle-like agglomerates and then to blocky. Among them, when the Nb content reaches 3 wt%, the needle-like agglomerated NbC is uniformly distributed and has good adhesion to the substrate, which can effectively reduce the breakage and shedding of the hard phase during the wear process and has the best wear resistance performance. Overall, the alloying effect of Nb changed the composition and morphology of the strengthening phase in the cladding layer of the nickel-based composites, reducing the hardness of the cladding layer but enhancing the microstructure uniformity, resulting in improved wear resistance of the coating.

Study on W/Ni interface reaction and strengthening mechanism of tungsten particle reinforced nickel-based alloys by laser-direct energy deposition

Tungsten (W) particle reinforced nickel-based alloys were fabricated via laser-direct energy deposition, microstructure and mechanical properties of the deposited samples were studied systematically. Results indicated that the deposited samples were composed of W particles, γ-Ni matrix, interfacial reaction phase (Ni, Cr)4W and Laves phase. The W particles and the (Ni, Cr)4W, the (Ni, Cr)4W and the γ-Ni matrix are both semi-coherent relations, which endows the W particles/γ-Ni matrix interface high binding strength. The strong interface enables stress-strain transferred effectively between the W particles and γ-Ni matrix during loading, and the particle reinforcing effect was achieved. In addition, the W atoms dissolved in the laser molten pool played a solid solution strengthening role for the γ-Ni matrix, which improved its tensile strength finally. Owing to the synergy effect of particle reinforcing and solid solution strengthening, the optimal ultimate tensile strength and elongation of the deposited sample was 1379.5 ± 13.9 MPa and 8.1 ± 0.9%, respectively. Fracture mechanisms of the deposited samples were investigated by in-situ tensile test, and cracks were observed initiation and propagation inside the W particles with the increase of tensile loads.

Simulation Analysis of Nanosecond Laser Processing of Titanium Alloy Based on Helical Trepanning

Titanium alloy is a type of high-strength material that is difficult to process. In particular, in the aerospace field, the processing accuracy of titanium alloy is high. Recently, laser processing has emerged as a new technology with high processing precision. However, the laser processing methods have obvious differences in processing accuracy and effect. Among them, the laser spiral scanning method plays an important role in welding and drilling, but owing to the complexity of the laser molten pool behavior, there have been limited studies on the material removal mechanism based on laser spiral scanning. To understand the variable process of titanium alloy melt pool in laser spiral scanning processing, a light heat conduction model with mass transfer source term was simulated. The effects of laser power, scanning speed, and scanning path on the morphology were studied. The simulation results show that the unit energy density was the main factor for material removal, and the distribution of the material temperature affected the size of the recast layer. The experimental and simulation results were compared, and good agreement between them was observed. This study can provide a research foundation for the further application of laser spiral scanning technology.

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.

Laser remelting of AlSi10Mg(-Ni) alloy surfaces: influence of Ni content and cooling rate on the microstructure

AlSi10Mg alloys are widely employed in a variety of industries, including aerospace, automotive, and microelectronics. This is because of its low density, acceptable mechanical properties, acceptable corrosion resistance, and inexpensive application cost. Advantageous fluidity, a short solidification period, and minimal volumetric contraction are beneficial characteristics under processing such alloys. Despite being used as commercial alloys, the mechanical properties of the AlSi10Mg alloys still need to be improved. In line with this, the current focus of Al-based alloy development is mostly on modifying commercially available alloys. Under such context, Ni was used as an alloying element in this study to generate the Al3Ni intermetallics, distinguished by its improved mechanical strength. Furthermore, the thermal stability of the Al3Ni may be a benefit, particularly for high-temperature applications. The present study aims to investigate the solidification under low and high cooling rates of four alloys: AlSi10Mg, AlSi10Mg-1Ni, AlSi10Mg-2Ni, and AlSi10Mg-3Ni (wt.%). Samples were obtained by directional solidification (DS) and laser surface remelting (LSR) processes. The cooling rates were calculated for the DS samples and with extrapolation for LSR samples as well as with the use of a model from the literature. After testing several laser conditions, the results also include an examination of microstructural and hardness changes in the treated and untreated zones. The produced gradient of microstructures is fully characterized as well as used to evaluate cooling rates inside the laser molten pools. For energy densities of 400 J/mm2 and 100 J/mm2, the mean dendritic spacings, λ, of the three Ni-containing alloys at the laser molten pool yielded estimated cooling rates of approximately 1.5 × 104 °C/s and 4.7 × 104 °C/s, respectively. A model explaining the reversion of λ across the molten pool will be outlined.

Laser gas oxidising of Ti–6Al–4V surface: experimental and numerical investigation

ABSTRACT The laser gas oxidising of Ti–6Al–4V surface was studied. Confocal laser scanning microscopy techniques were used to investigate its two- and three-dimensional surface topographies. Gas flow behaviour was simulated to define the minimum O2 concentration required for Ti–6Al–4V to self-sustain combustion. To understand the flow behaviour of the Ti–6Al–4V fluid, a high-speed camera monitored the evolution of the Ti–6Al–4V fluid, and the flow behaviour was simulated. Experimental and simulation results show that Ti–6Al–4V can self-sustain combustion with a high O2 to Ar gas flow ratio, and the oxidising layer is rough with macroscopic cracks, while a low O2 to Ar gas flow ratio results in a smooth oxidising layer without cracks. Ti–6Al–4V can self-sustain combustion when the O2 concentration exceeds 65%. Furthermore, the laser molten pool and self-sustaining combustion zone mix and flow together, and a large self-sustaining combustion zone leads to a low convection velocity.

Research on the influence of laser molten pool flow and evaporation on the bump texture forming of aluminum plate surface

At present, the research of laser texture mainly focuses on the machining quality and its properties, but the forming mechanism of laser bump texture surfaces is relatively less studied. In this paper, a long pulse laser ablation model was established based on the laser molten pool flow and evaporation phenomena by numerical simulation. And the evolution mechanism of bump texture morphology on metal surface during laser irradiation time was studied. The results show that the bump texture morphology shows edge protrusions and central depressions, and in the cooling stage, under the action of surface tension, the concave and convex height will show a rebound phenomenon. At the same time, the influence of laser parameters on the morphology of laser bump texture was studied by experiments. By comparing the numerical simulation with the experimental results, it can be found that when the laser irradiation time is equal to 0.5 ms, the morphology obtained by numerical simulation is close to the experimental results. In addition, the differences of pressure field and velocity of vaporized metal gas at different time and under different laser power are compared. Finally, the plasma on the surface of aluminum during laser machining captured by a high-speed camera indirectly indicates that the evaporated metal gas ionizes and forms a stable plasma layer floating above the target material.

Microstructure evolution and properties of in-situ ceramic particles reinforced Fe-based composite coating produced by ultrasonic vibration assisted laser cladding processing

Ultrasonic vibration assisted laser cladding processing was employed to fabricate ceramic particles reinforced Fe-based composite coatings. The influence of the ultrasonic vibration on the dilution, profile appearance, microstructure characteristics, and high temperature oxidation resistance of the composite coatings were investigated. Experimental results revealed that the profile roughness of the coatings was reduced by ultrasonic vibration during laser cladding processing, but the dilution of the coating was slightly increased. The heat and mass transfer in laser molten pool was improved by the ultrasonic vibration, resulting in the refining of the microstructure and increasing the amount of ceramics, as well as homogenizing the distribution of ceramics. The composite coating produced by 300 W ultrasonic vibration assisted laser cladding processing not only possessed good wear resistance, but also had high oxidation resistance. However, excessive ultrasonic vibration power increased the tendency of cracks in the coating.

Comparison of the Microstructure Evolution and Wear Resistance of Ti6Al4V Composite Coatings Reinforced by Hard Pure or Ni-plated Cubic Boron Nitride Particles Prepared with Laser Cladding on a Ti6Al4V Substrate

Titanium alloy is a major structural material with excellent high specific strength in aerospace applications. Cubic boron nitride (cBN) is a synthetic wear-resistant material with high hardness, similar to that of diamond, that is used in mechanical cutting and grinding. In addition, the thermal stability of cubic boron nitride particles is much better than that of diamond. In order to further enhance the wear resistance of the Ti6Al4V alloy, the laser cladding (LC) technology characteristics of metallurgical bonding were used to prepare cubic boron nitride/Ti6Al4V and Ni-plated cubic boron nitride/Ti6Al4V composite coatings on Ti6Al4V substrates in this paper. However, in the laser molten pool, it is difficult to retain the raw properties of cubic boron nitride particles under laser radiation. Both composite coatings were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The microstructures and interface bonding between cubic boron nitride particles and the Ti6Al4V matrix were examined using SEM, and the wear resistance and the worn track morphology of the composite coatings were evaluated using the ball-on-disc wear test and step profiler (WTM-2E). The results indicated that the Ni-plated cubic boron nitride/Ti6Al4V composite coating showed fewer thermal defects in comparison with the cubic boron nitride/Ti6Al4V coating. The Ni plating on the surface of cubic boron nitride particles was able to avoid the generation of thermal cracking of the cubic boron nitride particles in the composite coating. The TiN reaction layer was formed between the cubic boron nitride particles and Ti6Al4V matrix, which effectively prevented the further decomposition of the cubic boron nitride particles. The XRD and XPS results confirmed that the TiN reaction layer formed between the cubic boron nitride particles and Ti6Al4V. The Ni plating on the surface of the cubic boron nitride particles was also beneficial for increasing the wear resistance of the composite coating.

Surface reinforcements of TA15 titanium alloy with laser induced Co base multiphase composites

Ultrafine particles (UPs)/amorphous phases (APs) reinforced composites was deposited on the TA15 titanium alloy via a laser cladding (LC) of the Co-Al-B4C-CeO2 mixed powders; a LC technique (the laser power 900 W, the scanning speed 2.5 mm/s) favored APs/UPs to be produced owing to the transient existence of the laser molten pool (laser pool), its COF was in a range of 0.390–0.425. Then, the monolayer graphene oxide sheets (MGOSs)/carbon nanotubes (CNTs) reinforced composites were formed on this LC fabricated coating by a mean of LC of Co-Al-B4C-CeO2-(MGOSs/CNTs). Noting that a laser beam irradiated on MGOSs/CNTs also the pre-melted powders, huge amounts of MGOSs/CNTs were melted but kept partial MGOSs/CNTs in the solid states; also lots of UPs were produced in the atomic arrangements of APs/MGOSs, considering that partial UPs could obtain large quantity of the energy from a laser beam, forming lattice distortions. Identification of the synthetic UPs and MGOSs/CNTs in such LC composites, more importantly an UPs’ effect, contributes the theoretical/experimental basis to improve quality of the laser 3D print fabricated composites.

Fabrication and tribological behaviors of Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings by laser cladding for self-lubricating applications

In the work the in-situ synthesis of Ti3SiC2 (MAX) phase and silicide reinforced Ni-based composite self-lubricating coatings from Ti-Si-C system and NiCrBSi powders were carried and initiated by laser cladding with use of 5 kW fiber laser beam with 3 mm spot. The microstructures of the laser-clad in situ synthetic self-lubricating coatings were analyzed by a scanning electron microscope (SEM) equipped with an X-ray energy dispersive spectrometer (EDS). An X-ray diffraction (XRD) spectrometer and an electron back-scattered diffraction (EBSD) were used for determination of the reaction products in the composite coatings. The friction and abrasion behavior of the coatings were evaluated at room temperature by a dry sliding friction tester. The results indicate that in-situ chemical reactions took place between elements Ti, Si and C in the laser molten pool, and the reaction products included Ti3SiC2, Ti5Si3, and TiC ceramics as well as TiNix compound. Finally, three laser-clad Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings with the total thickness about 1 mm were fabricated on Ti6Al4V alloy. The average microhardness of the three coatings was 703.2 HV0.2, 751.9 HV0.2 and 850.6 HV0.2 respectively, which has been significantly improved, compared with the hardness of Ti6Al4V substrate (about 360 HV0.2). The average friction coefficient of the Ti3SiC2/Ti5Si3/TiC/Ni-based composite coating (50 wt% Ni25/50 wt% Ti-Si-C) reduced to 0.33 at room temperature, and it exhibited the wear rate of 13.5 × 10−5 mm3 N−1 m−1. The laser cladding Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings characterized by small amount of adhesive wear, plastic deformation and relatively smooth wear surface could be observed.

Microstructures and mechanical properties of WCP/Ti-6Al-4V composite coatings by laser melt injection and laser-induction hybrid melt injection

To improve the coating thickness and process efficiency of conventional laser melt injection (LMI), we introduced laser-induction hybrid melt injection (LIHMI) to prepare spherical WC particle (WCP)-reinforced metal matrix composite coatings on a Ti-6Al-4V substrate. The laser-induction hybrid melt injected coatings were 2.0–2.2 times thicker than that of the conventional laser melt injected coatings. The microstructure and mechanical properties of the WCP/Ti-6Al-4V composite coatings by LMI, LIHMI with induction preheating (pre-LIHMI) and LIHMI with induction preheating and post heating (pre/post-LIHMI) was investigated systemically. LIHMI inhibited the nucleation of primary TiC dendrites in the laser molten pool between adjacent WCP; therefore, the total amount of TiC in the laser-induction hybrid melt injected coatings was far less than that in the laser melt injected coatings. We found that (5.6–5.8)% TiC, β-Ti, and β-Ti/α-Ti formed in the laser-induction hybrid melt injected coatings, while 23% TiC, (Ti,W)C1-X and β-Ti formed in the laser melt injected coatings. In addition, pre/post-LIHMI led to a drastic WCP/Ti interfacial reaction due to the long dwell time and high temperature of the laser molten pool, which greatly deteriorated the mechanical properties of the coatings. Compared with those of the pre/post-LIHMI samples, the pre-LIHMI samples exhibited a shorter liquid residence time and lower temperature of the laser molten pool and a more moderate WCP/Ti interfacial reaction. In addition, tension strength of pre-LIHMI sample and pre/post-LIHMI sample is 34% and 12% higher than that of LMI sample.

Preparation of TA15 powder reinforced 45CrNiMoY alloy steel with high mechanical property by pre-laid laser cladding technology

Based on the principle of in-situ precipitation strengthening, TA15 powder (Ti-6.5Al-1Mo-1V-1.5Zr) was used as an additive to improve the mechanical properties of 45CrNiMoY alloy steel by pre-laid laser cladding (PLLC) technology. Effects of the content of TA15 powders (0–1.5 wt%) on the microstructure, precipitation mechanism and mechanical property of PLLC 45CrNiMoY alloy steel samples were investigated. Results indicate that TA15 alloy has a significant effect on the microstructure of 45CrNiMoY alloy steel through metallurgical reaction in the laser molten pool. With the increase of TA15 powder content, the granular bainite (GB) microstructure were remarkably refined, the mount of the acicular ferrite (AF) was increased, and in-situ precipitates such as Ti-Y2O3-Zr (TYZ) composite oxide, TiC and ZrC carbide were produced. The 45CrNiMoY alloy steel sample with 1.0 wt% TA15 alloy addition has the best combination of tensile strength (1158 ± 9.7 MPa) and elongation (9.8 ± 0.4%), its microhardness was improved by 25.6% compared with the sample without TA15 powder. The TYZ composite oxides did not only serve as the AF nucleation sites but also spheroidize the detrimental manganese sulfide phase leading to a good elongation of the 45CrNiMoY alloy steel, the TiC and ZrC carbides played a key role in the improvement of the microhardness and tensile strength. The proper addition of TA15 powder can effectively improve the microstructure and mechanical properties of the PLLC 45CrNiMoY alloy steel.

Laser melting deposition of a porosity-free alloy steel by application of high oxygen-containing powders mixed with Cr particles

Laser melting deposition (LMD) of an alloy steel by application of commercial 12CrNi2 powder with O content as high as 0.53 wt% has been investigated. It shows that the LMD alloy steel contains micron-sized pores. The pore formation, which is assumed to result from gas bubbles due to the reaction of carbon and oxygen in the laser molten pool, can be prevented by mixing the alloy steel powder with an appropriate amount of Cr particles. The result is interpreted based on reaction thermodynamics in the molten pool in combination with TEM observation of the microstructure of the LMDed alloy steel.

Effect of powder oxygen content on microstructure and mechanical properties of a laser additively-manufactured 12CrNi2 alloy steel

Two 12CrNi2 alloy steel powders, one with high-O content (5300 ppm) and the other with lower O content (280 ppm), have been used for laser melting deposition (LMD) additive manufacturing. The lower O content powder fed into the laser molten pool forms an alloy steel without porosity but with higher austenite volume fraction, which leads to significant increases in both tensile strength and ductility. The findings are discussed and interpreted.