Laser Metal Deposition Technique Research Articles

Experimental and Computational Thermal Analysis of Ti-Based Alloy Produced by Laser Metal Deposition Technique

AbstractA Ti-Fe-Si-Cr-Nb alloy was fabricated using laser metal deposition (LMD) technique. The laser power and scanning speed were varied during fabrication to optimize the processing parameters. The thermal behavior during LMD processing was modeled and simulated by means of COMSOL Multiphysics 6.0 software. The samples produced were characterized using an optical microscope, X-ray diffractometer, and scanning electron microscope coupled with energy dispersive spectroscopy. The microhardness and wear behavior of the alloy were tested using a diamond indenter and ball-on-disk wear machine. The results obtained showed that the alloys exhibited similar dendritic microstructure for all processing parameters. The formation of cracks and pores were evident mainly in samples that were produced at high scanning speed and low laser power. A decrease in microhardness was noticed when the laser power was increased, while an increase in scanning speed yielded samples with high microhardness values. The alloy showed good tribological behavior, but no clear relationship between the wear resistance of the alloy and the variation of the laser processing parameters could be established.

A comprehensive study of A357 alloy printability via laser metal deposition

Laser metal deposition (LMD) is one of the most important techniques in additive manufacturing (AM) thanks to the high flexibility of the process, which makes the production of free-form shapes possible. However, working with some materials presents some challenges. This is the case with aluminum alloys due to their reflectivity and their very high thermal conductivity. On the other hand, aluminum and its alloys are quite important in several industrial fields, including aerospace, among others, due to their mechanical properties with low density. In this work, LMD is applied on an A357 aluminum alloy. The techniques are investigated moving from a single-track approach up to multi-pass and multi-layer strategies. Densities, microstructures and mechanical performance are investigated as a function of process parameters. Porosities are reduced, resulting in overall densities of over 97% and microhardness values are in the range of 80–100 HV. Differences in mechanical performance are analysed considering different building directions, showing a dependency on loading direction and the distance from the substrate. Tensile tests reveal a promising performance for further investigation with the LMD technique. The obtained evidence is interesting for future trends where large and light components are required while maintaining the mechanical performance of traditional manufacturing methods. Moreover, a comprehensive study is done for the first time on A357 alloy that is deeply used in the aerospace and automotive fields. The investigation and definition of the best process parameters open the possibility of exploiting LMD technology in the production of wide components or for adding features to already existing components overcoming some limits of other AM technologies.

Nano mechanical study on a single layer TiC/TI6Al4V-ELI composite manufactured with laser metal deposition

This study investigated the nano mechanical properties of Ti6Al4V-ELI embraced with TiC particles, synthesized with in situ laser metal deposition technique. The 3.85% feed ratio fraction TiC/Ti6Al4V-ELI composite samples were manufactured at four varying energy densities. The beta grain boundary and the acicular alpha primary matrix were found to have diverse morphologies of carbide particles due to the in-situ reaction. The effect of energy density is observed on the microstructure and nano mechanical properties. An average off set of 650 nm was recorded after the nano-indentation in the matrix at a maximum load of 400 mN.

Effects of substrate heating on the microstructure and hardness of TiB/Ti6Al4V-ELI during laser in-situ metal deposition

This work investigated the influence of heating temperature (°C) on the microstructure and microhardness of TiB/Ti6Al4V-ELI composite clads that were produced via in-situ alloying using laser metal deposition technique. The samples were produced on a Ti6Al4V base plates which were heated at different temperatures (25°C, 200°C, 300°C, 400°C and 500°C) before they were characterised for microstructure and hardness. It was found that the TiB/Ti6Al4V-ELI sample that was produced on a non-pre-heated base plate was characterized by TiB particles and had the lowest hardness of 511 ± 66 HV. Base plate heating resulted in the formation of TiB whiskers that were dispersed within the titanium matrix. 200°C led to a microstructure with clusters of TiB whiskers hence it had an increased hardness of 651 ± 40 HV. A fine microstructure with homogeneous distribution of the TiB whiskers was obtained at 500°C base plate heating temperature and had hardness of 565 ± 14 HV.

Influence of γ/γ′ morphology evolution on the mechanical properties of Ni-based single crystal superalloys formed by laser metal deposition

The variation in hardness and tensile properties of Ni-based single crystal (SX) superalloy DD6 during laser metal deposition processing has been investigated, and the effects of laser scanning velocity and post heat-treatment on the evolution of microstructure and its interaction with mechanical properties of deposited region were determined. It is found that the microstructure of as-deposited Ni-based single crystal superalloy mainly consists of columnar dendrite epitaxially growing from the substrate. The fine γ′ phase microstructure and dense γ/γ′ phase interfaces contribute more to the microstructural evolution and mechanical properties of deposited part formed by laser metal deposition. Furthermore, the heat treatment reduces the mechanical properties of deposited sample due to the introducing of stray grains that destroys the original single crystallinity. The mechanism unraveled here could shed light on the reliability evaluation and parameter selection of the laser metal deposition technique and other directed energy deposition technology.

Effects of energy density on the microstructure evolution of TiC/Ti6Al4V-ELI metal composite fabricated with laser metal deposition

This study investigated the microstructural evolution of Ti6Al4V-ELI reinforced with TiC, fabricated via in-situ laser metal deposition technique. The 3.85% volume fraction TiC/Ti6Al4V-ELI metal composite samples were fabricated at two different energy densities (ED). It was observed that in-situ reaction resulted in various morphologies (unmelted or partially melted, chain-shaped eutectic, granular eutectic, granular primary eutectic, and dendritic primary) of TiC embedded with the beta grain boundary and the acicular alpha prime matrix. The size of dendritic structures decreases with respect to ED. Additionally, the hardness average of 457.59 ± 39.73 and 455.08 ± 18.03 HV0.3 for 96 and 102 J/mm2 ED respectively.

A review on additive manufacturing of alloys using laser metal deposition

Manufacturing technologies related to additive processing permit quick and reliable fabrication of parts, components, thereby enabling savings with respect to economy and time. Moreover, as the technology of additive based fabrication is free from usage of tools, it provides flexibility in multiple degrees of freedom. With the objective of improving certain hindrances present in the additive based fabrication and to expand its potential to next level, design and principle of operation oriented rethinking is essential. LMD (Laser metal deposition), an recently evolved next dimension of additive based manufacturing, not only permits fabrication of parts with intricate shapes and dimensions, but makes it possible to repair and recoat the worn-out components, parts relevant to the industrial sectors of construction of turbines, nuclear power plants, tool manufacturing, aerospace engines, submarines etc. At the same time, the employment of this LMD technique in fabrication of intricate parts require extensive proficiency of its parameters and their control. Fabrication of superior quality components can be attained using the technique of LMD, only by carrying out the process in a completely regulated environment, as extensive number of supplementary factors must be taken into account. Therefore, this review paper throws an insight about the strategies being adopted and the combination of process related parameters being employed by several researchers and investigators during the fabrication of alloys of stainless steel, Inconel, titanium etc., using the technique of LMD.

An approach towards energy and material efficient additive manufacturing: Multi-objective optimization of stellite-6 deposition on SS304

Energy and material saving in additive manufacturing (AM) has become the main concern in recent times for sustainable manufacturing. In this study, a 2 kW fiber laser was used in the direct laser metal deposition technique to deposite stellite-6 powder on SS304. Laser power (400–800 W), laser deposition speed (400–800 mm/min) and powder feed rate (10–20 g/min) were considered as input process parameters; whereas laser energy efficiency (LEE), powder deposition efficiency (PDE) and dilution (D) were taken as output responses. An empirical study has been carried out to analyse the combined effect of input process parameters on outputs. Three recently developed multi-objective optimization algorithms were used to maximize LEE and PDE with an optimum dilution, in which Multi-objective bonobo algorithm provided the best Pareto-surface. An improvement of 10% in LEE with maximum PDE was obtained. Microstructure of deposited clad was found to have fine-homogeneous dendrite and inter-dendritic eutectics, which mainly consisted of cobalt phases and carbides. The hardness of the deposited track was found to be three times of that of the substrate, due to the presence of carbides and high cooling rate. The wear rate of the deposited coating was found to be 7.61 × 10–5 mm3/N-m, which was improved 6.6 times to the substrate. A decrease in the pile-up during wear was observed on the deposited surface, which was found to have a correlation with the rheological factor. The ratio of volumetric wear rate to hardness for stellite-6 coating was 1.28 × 10–7 mm3 /N-m/HV (20 times less as substrate), which indicated an excellent tribological performance of the coating. A stable friction-wear time curve was observed for stellite-6 coating and the coefficient of friction was found out to be 0.33.

Plastic Behavior of Laser-Deposited Inconel 718 Superalloy at High Strain Rate and Temperature

Nickel-based superalloys have several applications for components exposed to high temperatures and high strain rate loading conditions during services. The objective of this study was to investigate the tensile properties of Inconel 718 produced using the laser metal deposition technique. Specimens with different heat treatments were investigated. Experimental tests were performed at the DYNLab at Politecnico di Torino (Italy). The temperature sensitivity was investigated between 20 °C and 1000 °C on a Hopkinson bar setup at a nominal strain rate of 1500 s−1. The specimens heating was obtained by means of an induction heating system, and the temperature control was performed by thermocouples, an infrared pyrometer, and a high-speed infrared camera. The thermal images were analyzed to check the uniformity of the heating and to investigate the presence of adiabatic self-heating. The results showed that the materials strength exhibited a significant drop starting from 800 °C. The strain rate influence was investigated at room temperature, and limited sensitivity was found covering six orders of magnitude in the strain rate. A preliminary analysis of the fracture mode was performed. Finally, different solutions for the strength material modeling were proposed and discussed with the aim of identifying models to be used in finite element simulations.

Effect of Initial Temperature on the Microstructure and Properties of Stellite-6/Inconel 718 Functional Gradient Materials Formed by Laser Metal Deposition.

Stelite-6/Inconel 718 functionally gradient materials (FGM) is a heat-resisting functional gradient material with excellent strength performance under ultra-high temperatures (650–1100 °C) and, thus, has potential application in aeronautic and aerospace engineering such as engine turbine blade. To investigate the effect of initial temperature on the microstructure and properties of laser metal deposition (LMD) functional gradient material (FGM), this paper uses the LMD technique to form Stelite-6/Inconel 718 FGM at two different initial temperatures: room temperature and preheating (300 °C). Analysis of the internal residual stress distribution, elemental distribution, microstructure, tensile properties, and microhardness of 100% Stelite-6 to 100% Inconel 718 FGM formed at different initial temperatures in a 10% gradient. The experimental results prove that the high initial temperature effectively improves the uneven distribution of internal residual stresses. Preheating slows down the solidification time of the melt pool and facilitates the escape of gases and the homogeneous diffusion of elements in the melt pool. In addition, preheating reduces the bonding area between the gradient layers, enhancing the metallurgical bonding properties between the layers and improving the tensile properties. Compared with Stellite-6/Inconel 718 FGM formed at room temperature, the mean yield strength, mean tensile strength, and mean elongation of Stellite-6/Inconel 718 FGM formed at 300 °C are increased by 65.1 Mpa, 97 MPa, and 5.2%. However, the high initial temperature will affect the hardness of the material. The average hardness of Stellite-6/Inconel 718 FGM formed at 300 °C is 26.9 HV (Vickers hardness) lower than that of Stellite-6/Inconel 718 FGM formed at 20 °C.

Laser deposition of graded γ-TiAl/Ti2AlNb alloys: Microstructure and nanomechanical characterization of the transition zone

Additive manufacturing (AM) is a transformative technology to the aerospace industry. As one of the AM techniques, laser metal deposition (LMD) enables the fabrication of engine blades and a disk, as a single component, known as blisk. In this study, we use the LMD technique to fabricate a γ-TiAl/Ti2AlNb graded metallic alloy by depositing γ-TiAl powder on a Ti2AlNb alloy substrate. High-resolution scanning electron microscope (SEM) and high-speed nanoindentation are employed to characterize the microstructure and mechanical properties of the transition zone from the Ti2AlNb substrate (disk) to the γ-TiAl alloy (blade). The results show that the transition zone includes three layers (I, II and III) with gradient compositions and phases: (I) mainly β/B2 matrix with randomly distributed α2 and γ phases, (II) (α2 + γ) lamella with γ and β/B2 phases, and (III) similar microstructure with Layer II but finer γ and β/B2 phases. The results of nanoindentation mapping show good correlations between the mechanical properties (nanohardness and elastic modulus) and microstructure in the transition zone. Attributing to the rule of mixtures, the nanohardness and elastic modulus gradually increase from the substrate Ti2AlNb to Layer I, and gradually decrease from Layer I to γ-TiAl. This work demonstrates that the microstructure and phase analysis in combination with high-speed nanoindentation offers a new opportunity to study graded materials made using LMD.

Microstructural and Mechanical Properties of Laser Deposited Ti-6Al-4V Alloy: A Review

Laser Metal Deposition (LMD) is known to be an Additive Manufacturing (AM) technique which produces parts by depositing materials layer by layer. Its quality is reliant on the process parameters, which need to be optimised to attain improved mechanical properties. This article reviewed the mechanical properties (microstructure and tensile strength) of LMD Ti6Al4V alloy published by different authors and relates these mechanical properties with the effects of some of the processing parameters required for additive manufacturing of titanium alloys. Furthermore, the article summaries important findings and proffer suggestions for future research in the area of machine part repair using LMD technique.

In-process monitoring of the melt-pool motion during continuous-wave laser metal deposition

Abstract In the field of additive manufacturing (AM), the implementation of real-time monitoring systems is essential to guarantee the quality and repeatability of the manufactured parts. Particularly in the laser metal deposition technique, the dynamics and stability of the molten pool, both geometrically and thermally, have an impact on the microstructural properties and the formation of defects. This article presents a novel technique to track the molten pool in real-time. A middle wavelength infrared (MWIR) camera is used, with a spectral range between 3 and 5 μm. The acquired frames are processed to reduce their dimension using a new strategy based on Superpixels. Traditional pixels are grouped into block-structures that are similar in temperature, optical flow, and spatial position. This guarantees a better adherence to the edges improving the segmentation task. Then, the optical flow of the molten pool is calculated. Throughout this tracking, geometric and thermal features are extracted. The proposed method was evaluated using qualitative and quantitative criteria. The performance of the proposal is compared against benchmark algorithms using standard metrics such as Sub-segmentation Error, Compactness, and Achievable Segmentation Accuracy obtaining better results. The proposal presented is robust to the number of superpixels generated as well as the size of the images. Which provides better performance for in situ monitoring tasks. Our proposal has significant industrial potential for monitoring additive manufacturing processes, as it requires minimal modifications to commercially available industrial machines.

Investigation of copper/stainless steel multi-metallic materials fabricated by laser metal deposition

The feasibility of fabricating a single component with a copper and stainless steel multi-material structure can broaden its functional properties and offer significant value in engineering design. In an effort to join copper with 304L stainless steel (SS304L) using the laser metal deposition technique, pure copper was deposited on SS304L both directly and via interlayers of a nickel-based alloy Deloro 22 (D22). The microstructure, elemental distribution, bonding strength, microhardness profile, and thermal conductivity/diffusivity of the multi-metallic structures were investigated. The transition zone of the Cu-SS direct joint shows numerous SS304L globules and separated Cu-rich and Fe-rich islands. Tensile testing of the Cu-SS shows poor bonding strength. By adding D22 interlayers, a well bonded and defect-free Cu-D22-SS structure was achieved. Evidence of strong bonding at the Cu-D22 and D22-SS was obtained by tensile testing where samples broke in either the copper or D22 regions. The Cu-D22-SS results in a hardness of 228.7 ± 19.5 HV at the D22 layers. Ascending to the copper layers, a gradual drop of hardness to a steady value of 52.9–56.1 HV was observed. The theoretical prediction shows there is a ~100% increase in thermal conductivity and a ~370% increase in thermal diffusivity of the Cu-D22-SS system when compared with pure SS304L.

Microstructural, mechanical and electrochemical properties of AlCrFeCuNiWx high entropy alloys

AlCrFeNiCuWx high entropy alloys were fabricated on 316 L stainless steel substrate using laser metal deposition technique. The microstructural and mechanical characteristics of these alloys were studied by advanced characterization techniques. The results revealed that the alloys exhibited a dual phase structure with BCC (body centered cubic) and FCC (face centered cubic) solid solution phases. The presence of tungsten (W) particles in the HEA matrix changed the shape of grains from columnar to aquiaxed. The alloys that contained W possessed higher plasticity at maximum compressive stress. They also showed better performance when they were evaluated for wear and corrosion.

High-performance Ti-6Al-4V with graded microstructure and superior properties fabricated by powder feeding underwater laser metal deposition

Abstract It is challenging to apply laser metal deposition (LMD) in underwater environment to realize on-site repair of marine equipment due to the potential impact of water. In the present work, we report an innovative underwater repair technique termed underwater laser metal deposition (ULMD) which can overcome the challenges. This new technique renders both technical and theoretical advancements from the following aspects: (1) A special in-house designed drainage nozzle was integrated with the laser cladding head to create local dry cavity which ensured the successful manufacturing of titanium alloy Ti-6Al-4V in underwater environment; (2) Unique microstructure formation/evolution mechanisms have been revealed for the ULMD process, which significantly differ from those of the in-air LMD process; (3) The hydrogen content has been well controlled during ULMD, which can effectively prevent the formation of hydrogen-induced cracks; (4) The mechanical properties of the ULMD Ti-6Al-4V parts were equal or even better than that fabricated by in-air LMD or SLM technique. In the meantime, a systematically parametric study was performed for this new technique and the experimental results showed that a high laser power (1600 W), a reasonable scanning velocity (800 mm/min) and a cross-hatching strategy were essential for achieving minimum metallurgical defects and full densification, which can provide very helpful guidance for the future research in this area. This research work opens a new avenue which makes underwater 3D-printing an applicable tool when coping with the fabrication and repair of customized components or complex shape parts in underwater environment.

Effect of heat treatment on the microstructure, microhardness, and wear characteristics of AlCrFeCuNi high-entropy alloy

The comprehensive properties exhibited by dual-phase high-entropy alloys (HEA) increase their prospects of finding use in engineering applications. However, the distribution of the phases that are present in the alloys has a significant effect on their mechanical performance. Therefore, the homogeneity of microstructure in these alloys remains critical for the improvement of their mechanical properties. In this study, AlCrFeCuNi HEA was fabricated by a direct laser metal deposition technique. The effect of heat treatment on the microstructure, microhardness, and wear performance of the alloy was investigated. The microstructural analysis revealed that the alloy was characterized by a dendritic microstructure with a dual-phase (BCC + FCC) composition. Microstructural changes were achieved at all heat treatment temperatures with grain growth starting to occur at 950 °C and dissolution of the BCC phase happening at 1100 °C. Good anti-wear characteristics were obtained for alloy heat treated at 950 °C.

Effect of Nb addition on the microstructural, mechanical and electrochemical characteristics of AlCrFeNiCu high-entropy alloy

AlCrFeNiCuNbx (x = 0.05, 0.15, and 0.26) high-entropy alloys (HEAs) were successfully fabricated using the laser metal deposition technique. The laser power of 1600 W and scanning speed of 1.2 m/min were used during laser processing of the alloys. The microstructural, mechanical, and electrochemical characteristics of the alloys were evaluated using various advanced characterization techniques. Results showed that the alloys exhibited a dual-phase structure with dendritic grains. The inclusion of Nb in the AlCrFeNiCu alloy matrix promoted the formation of fine eutectic structures and changed the shape of the grains from columnar to equiaxed. The Cu content decreased with the increase in the content of Nb, whereas the Al content increased with the increase in the content of Nb. The findings indicated that the presence of Nb in the alloy promoted the formation and enhanced the stability of the body-centered cubic (bcc) phase. All of the alloys that contained Nb also exhibited high hardness, compressive strength, and wear resistance. Furthermore, the low current density and positive shift in potential exhibited by HEAs with appropriate addition of Nb highlighted the superior anticorrosive properties.

Material characterization and corrosion behavior of hybrid coating Ti−Al−Si−Cu/Ti−6Al‐4V composite

AbstractTitanium alloy grade 5 is a grade of the titanium material that is in‐demand in the marine, aerospace, biomedical and turbo machinery industries. It offers great properties such as being light weight, good corrosion performance and great strength. However, some of the other properties, namely: its low hardness and poor tribological performance, has limited its various industrial application. Developments have focused on the enhancement of the surface properties without altering the bulk of the material. This has led to the laser metal deposition technique categorized under the additive manufacturing processes. It is a feasible technique that operates on layer‐by‐layer additive processing to manufactures whole parts or repair local damages in components. This study aims to ascertain the optimum processing conditions of the process by varying the laser intensity and scanning speed between 0.9 kW–1 kW and 1.0 m/min–1.2 m/min, respectively, while maintaining all the other process parameters. The specimens were produced by utilizing the ytterbium laser system to conduct laser surface alloying of Ti−Al−Si−Cu/Ti‐6Al‐4 V. Metallographic preparations, characterizations to conduct laser metal deposition (LMD), microhardness and corrosion test were conducted. It was deduced that Ti‐9Si‐3Cu alloy had the best optimum performance at 1 kW and 1.0 m/min. The hardness and corrosion were optimum improved at reduced scan speeds and increased laser power.

Tribological and corrosion properties of laser additive manufactured AlCrFeNiCu high entropy alloy

High entropy alloys (HEAs) are new class of materials with a high potential to find use in structural applications where high corrosion and wear resistance are required. Their high configurational entropy, sluggish diffusion, cocktail effect and ability to form stable solid solutions structures make them to exhibit unique physical and mechanical properties which are desirable for these applications. In this work, AlCrFeNiCu high entropy alloy was produced using laser metal deposition technique. The laser power was varied from 1600 to 2000 W while the scanning speed was kept constant at 13.3 mm/s. Microstructural analysis were conducted using scanning electron microscope and x-ray diffractometer. Corrosion performance of the alloy was evaluated in 0.5 M sulphuric acid solution using potentiodynamic polarization. Ball on disk tribometer was used to test for the wear resistance of the alloy. Microstructural analysis revealed that the alloy exhibited a dendritic microstructure consisting of dual phase (bcc + fcc) solid solutions. The wear resistance of the alloy decreased with the increase in laser power. The worn out surfaces showed that the nature of wear was adhesive. However, no relationship between laser power and corrosion resistance of the samples was established.