Laser Engineered Net Shaping Research Articles

Fatigue Behaviour of Additively Manufactured Ti-6Al-4 V

Fatigue behaviour of Ti-6Al-4V specimens additively-manufactured via Laser Engineered Net Shaping (LENS) is investigated in this study. Additive manufacturing provides the opportunity to fabricate complex geometries layer-by-layer from 3D computer aided drawings. As the mechanical behaviour of metallic materials depends on their microstructure, which is affected by the time-temperature history, additive-manufactured components are expected to have different properties than those of their wrought counterparts. Ti-6Al-4V rods were fabricated by LENS using two different sets of process parameters and machined into ‘dog-bone’ fatigue specimens with dimensions in conformance to ASTM standards. The fatigue behaviour and microstructural features of the LENS Ti-6Al-4V samples were characterized and compared with wrought Ti-6Al-4V. Fractography of the fractured specimen surfaces was performed using Scanning Electron Microscopy (SEM) to determine the failure mechanism and realize the effects of porosity on fatigue resistance and data scatter of LENS Ti-6Al-4V. The fatigue lives of the LENS Ti-6Al-4V materials were found to be lower than those of the wrought Ti-6Al-4V, and driven by the porosity and microstructure of the samples.

Microstructure Evolution, Tensile Properties, and Fatigue Damage Mechanisms in Ti-6Al-4V Alloys Fabricated by Two Additive Manufacturing Techniques

Additive Manufacturing (AM) technology is capable of building 3D near-net-shaped functional parts directly from computer models, using unit materials, such as powder or wire. AM offers superior geometrical flexibility with significantly reduced manufacturing lead time, energy, and material waste. These benefits make AM desirable for critical transportation applications, providing that structural integrity and performance requirements are met or exceeded. In this study, structural materials fabricated by two AM techniques were investigated: Laser Engineered Net Shaping (LENS) and Electron Beam Melting (EBM). Ti-6Al-4V alloys were produced using both methods and various processing conditions, which resulted in different microstructures and mechanical properties given their unique thermal histories. Characteristic microstructures were determined for all cases. Room temperature tensile and fatigue crack growth (FCG) properties were also evaluated and compared in different orientations with respect to the deposition direction. The effects of post-deposition heat treatment on tensile and FCG properties were determined. The results are systematically presented and discussed from both the material/process optimization, as well as structural design and fatigue life prediction perspectives.

影响激光近净成形残余应力的关键参数的多元回归分析

影响激光近净成形残余应力的关键参数的多元回归分析

Thin wall tubes with Fe3Al/SS316L graded structure obtained by using laser engineered net shaping technology

In the present paper, designing, technological and material aspects of the Laser Engineered Net Shaping (LENS) manufacturing process of functionally graded materials (FGMs) components based on the Fe–Al intermetallic alloys, have been described in details. The presented results are divided into two parts as follows: in the first part a model and a LENS manufacturing process of the selected FGMs component (the Fe3Al/314L steel tube) have been developed. In the second part, an experimental verification of the model and the process has been carried out. It is shown that, automatically generated code does not allow programming variation of the chemical composition perpendicularly to the wall of the tube. However, applied modification of the code results in a successive direct fabrication of the 316L/Fe3Al FGM tubes. Directly fabricated FGM tubes were characterized by a smooth transition between both components (the 316L steel and the Fe3Al alloy), a high metallurgical quality and a good reproduction of the designed model’s shape.

Power prediction for laser engineered net shaping of Al2O3 ceramic parts

Abstract Laser-aided additive manufacturing technique is a competitive method for direct fabrication of ceramic components. However, the optimal processing parameters are difficult to find because defects are easy to generate for ceramic parts. This paper proposes a mathematical model for predicting required laser power in direct fabrication of Al 2 O 3 ceramic parts by laser engineered net shaping (LENS). The laser power model, which is derived based on energy balance of one deposition layer, reveals the relationship between laser power and other process conditions, such as powder flow rate, nozzle travel speed and physical properties of deposited material. The proposed model was then verified through a fabrication experiment of several single-bead wall Al 2 O 3 ceramic parts with different laser power. Experimental results indicate that the laser power predicted by the model is accurate for different processing conditions. This model provides a new yet simple method for predicting required laser power accurately during LENS processes.

Laser-Deposited In Situ TiC-Reinforced Nickel Matrix Composites: 3D Microstructure and Tribological Properties

A new class of Ni-Ti-C based metal matrix composites has been developed using the laser engineered net shaping (LENS) process. These composites consist of an in situ formed and homogeneously distributed titanium carbide (TiC) phase reinforcing the nickel matrix. Additionally, by tailoring the Ti/C ratio in these composites, an additional graphitic phase can also be engineered into the microstructure. The microstructure of these composites has been characterized in detail in three dimensions, via serial-sectioning in a dual-beam focused ion beam instrument followed by appropriate 3D reconstructions, to determine the true morphology and spatial distribution of the TiC and graphite phases as well as the phase evolution sequence. These three-phase Ni-TiC-C composites exhibit excellent tribological properties, in terms of extremely low coefficient of friction while maintaining a relatively high hardness, and these will be discussed in the presentation.

Microstructure and hydrogen storage properties of a TiZrNbMoV high entropy alloy synthesized using Laser Engineered Net Shaping (LENS)

Laser Engineered Net Shaping (LENS) with laser powers of 300 W and 1 kW was used to synthesize the TiZrNbMoV high entropy alloys (HEA) from a blend of elemental powders. The morphology of the elemental powders was investigated using a scanning electron microscope (SEM) and an infrared particle size analyzer. The chemical composition and microstructure of the synthesized TiZrNbMoV alloys were investigated using an X-ray diffractometer (XRD) and SEM coupled with an energy-dispersive X-ray spectrometer (EDS). The hydrogen absorption and desorption properties of the synthesized TiZrNbMoV alloys were investigated using a Sieverts-type apparatus.After synthesis using a low laser power, the TiZrNbMoV alloy exhibited a two-phase dendritic matrix with some unmelted Mo particles and dendrites of a bcc solid solution surrounded by an orthorhombic NbTi4-type phase. The alloy that was deposited using a laser power of 1 kW and remelted three times possessed a multi-phase microstructure with a Mo-rich matrix containing Zr-rich precipitates and no dendritic segregation. The influence of the technological parameters employed during laser deposition on the microstructure and hydrogen storage properties of the synthesized TiZrNbMoV alloys will be presented and discussed.

Laser surface modification of 316 L stainless steel with bioactive hydroxyapatite

Laser-engineered net shaping (LENS™), a commercial additive manufacturing process, was used to modify the surfaces of 316L stainless steel with bioactive hydroxyapatite (HAP). The modified surfaces were characterized in terms of their microstructure, hardness and apatite forming ability. The results showed that with increase in laser energy input from 32J/mm2 to 59J/mm2 the thickness of the modified surface increased from 222±12μm to 355±6μm, while the average surface hardness decreased marginally from 403±18 HV0.3 to 372±8 HV0.3. Microstructural studies showed that the modified surface consisted of austenite dendrites with HAP and some reaction products primarily occurring in the inter-dendritic regions. Finally, the surface-modified 316L samples immersed in simulated body fluids showed significantly higher apatite precipitation compared to unmodified 316L samples.

Novel Forming of Ti-6Al-4V by Laser Engineered Net Shaping

Titanium alloys offer important weight and performance advantages, but are relatively expensive. Traditional “subtractive” manufacturing causes up to 95% material waste, which makes the manufacturing of titanium components even more expensive. Laser Engineered Net Shaping (LENS) is an effective method of “additively” making components layer-wise, directly from unit materials, based on 3D digital models. Parts fabricated by LENS are net/near-net shape, and therefore, this process minimizes, or even eliminates massive machining costs and material waste. In this study, as-fabricated LENS Ti-6Al-4V test specimens were investigated. The resulting microstructures were extensively characterized and correlated to processing parameters. In addition, room temperature tensile tests were conducted to obtain static mechanical properties and to understand the behaviour at LENS deposition-substrate interface. These results will be presented and discussed.

Combinatorial synthesis of alloy libraries with a progressive composition gradient using laser engineered net shaping (LENS): Hydrogen storage alloys

The laser engineered net shaping technique was applied as a fast synthesis method for preparing libraries of binary and ternary alloys. Compositional gradient libraries of Fe–Ti alloys and four different FeTiNi samples were fabricated from elemental powders. A continuous gradient sample and discrete gradient samples (25 and 188 samples) were deposited. Ternary alloys were prepared from pre-blended powder mixtures. Chemical composition measurements showed that samples of different compositions can be synthesized. XRD phase analysis indicated that structures close to equilibrium or occasionally quenched are obtained after the process. The microstructure of the prepared samples was analyzed. The hydrogen storage properties of the selected samples were investigated. After laser deposition, the samples were found to absorb significant quantities of hydrogen with just a simple activation. The method was determined to be very useful for discovering new ternary and multicomponent alloys for hydrogen storage.

Structure and hydrogen storage properties of a high entropy ZrTiVCrFeNi alloy synthesized using Laser Engineered Net Shaping (LENS)

In this work, the ZrTiVCrFeNi high entropy alloy was successfully synthesized from elemental powders near the equimolar ratio using Laser Engineered Net Shaping (LENS). The prepared alloy exhibited good chemical composition after laser deposition, compared to the nominal composition, which was further improved using high-temperature annealing at 1000 °C for 24 h. Better powder quality and the optimization of the LENS parameters are still necessary for obtaining the improved chemical homogeneity of the alloy after synthesis. The alloy exhibited a two-phase structure, i.e., the dominant C14 Laves phase matrix with a minor amount of the α-Ti solid solution, after synthesis and annealing. The PCT isotherms were measured up to 100 bar of hydrogen pressure at 50 °C after activation of the alloy by annealing at 500 °C for 2 h under vacuum. The obtained maximum hydrogen capacity was 1.81 wt.% after synthesis and 1.56 wt.% after additional annealing. The equilibrium pressure of hydrogen desorption was too low for a complete desorption reaction, resulting in the presence of a C14 hydride phase in the alloy after PCT tests.

First demonstration on direct laser fabrication of lunar regolith parts

PurposeThe purpose of this paper is to evaluate the feasibility of direct fabrication of lunar/Martian regolith simulant parts, in a freeform environment, using Laser Engineering Net Shaping (LENS™) – an additive manufacturing technology.Design/methodology/approachBulk lunar regolith simulant structures were fabricated using a LENS™‐750. Dense parts without any macroscopic defects were produced at a laser power of 50W, a scan speed of 20 mm/s, and a powder feed rate of 12.36 g/min. The laser processed parts were characterized using X‐ray diffraction, differential scanning calorimetry, scanning electron microscope and X‐ray photoelectron spectroscopy to evaluate the influence of laser processing on the microstructure, constituent phases and chemistry of lunar regolith simulant.FindingsA combination of laser parameters resulting in a 2.12 J/mm2 laser energy appeared to be ideal for generating a melt pool necessary for lunar regolith powder deposition without excessive liquid pool spreading and cracking of solidified parts. The results show that LENS™ based laser processing transformed crystalline regolith into nanocrystalline and/or amorphous regolith structures as a result of complete melting followed by resolidification. Laser processing also resulted in marginal changes in the composition of the regolith.Originality/valueEstablishment of a lunar/Martian outpost necessitates the development of methods to utilize in situ mineral resources for various construction and resource extraction applications. Fabrication technologies are critical for habitat structure development, as well as repair and replacement of tools and parts at the outpost. Current experimental results presented in the paper clearly demonstrate that net shape regolith simulant parts can be fabricated using LENS™ by exploiting its capabilities.

MgO-Doped Tantalum Coating on Ti: Microstructural Study and Biocompatibility Evaluation

Pure and MgO incorporated Ta coatings were prepared on Cp-Ti substrate using laser engineered net shaping (LENS), which resulted in diffuse coating-substrate interface. MgO was found along the Ta grain boundaries in the Ta matrix that increased the coating hardness from 185 ± 2.7 HV to 794 ± 93 HV. In vitro biocompatibility study showed excellent early cellular attachment and later stage proliferation in MgO incorporated coatings. The results indicated that although Ta coatings had higher biocompatibility than Ti, it could further be improved by incorporating MgO in the coating, while simultaneously improving the mechanical properties.

Initial cellular response to laser surface engineered biomaterials

Abstract

Estimation of Melt Pool Dimensions, Thermal Cycle, and Hardness Distribution in the Laser-Engineered Net Shaping Process of Austenitic Stainless Steel

Laser engineered net shaping (LENS) and other similar processes facilitate building of parts with freeform shapes by melting and deposition of metallic powders layer by layer. A-priori estimation of the layerwise variations in peak temperature, build dimension, cooling rate, and mechanical property is requisite for successful application of these processes. We present here an integrated approach to estimate these build attributes. A three-dimensional (3-D) heat transfer analysis based on the finite element method is developed to compute the layerwise variation in thermal cycles and melt pool dimensions in the single-line multilayer wall structure of austenitic stainless steel. The computed values of cooling rates during solidification are used to estimate the layerwise variation in cell spacing of the solidified structure. A Hall–Petch like relation using cell size as the structural parameter is used next to estimate the layerwise hardness distribution. The predicted values of layer widths and build heights have depicted fair agreement with the corresponding measured values in actual deposits. The estimated values of layerwise cell spacing and hardness remain underpredicted and overpredicted, respectively. The slight underprediction of the cell spacing is attributed to the possible overestimation of the cooling rates that may have resulted due to the neglect of convective heat transport within the melt pool. The overprediction of the layerwise hardness is certainly due to the underprediction of corresponding cell spacing. The application of Hall–Petch coefficients, which is strictly valid for wrought and annealed grain structures, to estimate the hardness of as-solidified cellular structures may have also contributed to the overprediction of the layerwise hardness.

Analysis of the bullet nose of an aero-engine for bird impact through virtual and rapid prototyping

Flying was inspired by birds. But ironically bird strikes are a menace. Therefore, aero-engines have to be designed to survive these strikes. The design of the bullet nose of an aero-engine during a bird strike is presented in this paper. A Finite Element Analysis (FEA) model was developed for this purpose. It was then fine-tuned through experiments on bullet noses built using Laser-Engineered Net-Shaping (LENS). Through this approach, several design alternatives could be evaluated virtually and only a few physical experiments were required for validation. The outcome is not only a rapid and safe bullet nose design but also a realistic FEA model.

Laser-Based Additive Manufacturing of Metals

For making metallic products through Additive Manufacturing (AM) processes, laser-based systems play very significant roles. Laser-based processes such as Selective Laser Melting (SLM) and Laser Engineered Net Shaping (LENS) are dominating processes while Laminated Object Manufacturing (LOM) has also been used. The paper will highlight key issues without going into details and try to present comparative pictures of the aforementioned processes. The issues included are machine, materials, applications, comparison, various possibilities and future works.

Fabrication of SS316L/Ni25 Functionally Gradient Materials Using Laser Engineered Net Shaping

Functionally gradient materials(FGMs) were successfully fabricated with compositions gradually changed from 100% stainless steel 316L to 100% Ni25 alloy using laser engineered net shaping(LENS) technology. The microstructure characterization, composition analysis and microhardness along the gradient direction are investigated. Meanwhile, the defects in the sample such as cracks and pores are analyzed. The results indicated that the microstructure evolves from columnar dendrite to cellular-crystal or equiaxed dendrite.

Bulk nickel–carbon nanotube nanocomposites by laser deposition

Nickel–carbon nanotube (CNT) nanocomposites have been processed in a bulk form using a laser deposition technique, commercially known as the laser engineered net shaping (LENS) process. Mechanical milling of the powder feedstock consisting of nickel powders and CNTs before laser deposition has resulted in not only a more homogeneous distribution of the nanotubes in the nickel matrix, but also two distinct scales of reinforcements within the composite. The larger reinforcement scale consists of submicrometre to micrometre sized bundles of CNTs while the smaller scale consists of individual (or cluster of a few) CNTs within the nickel matrix. High resolution transmission electron microscopy studies indicate that the nickel/CNT interface is well bonded without the presence of any significant interfacial reaction product. The degree of disorder and defects in the CNT bundles in the nickel matrix varied as a function of bundle size as revealed by Raman spectroscopy results.

Microstructural evolution in laser deposited nickel–titanium–carbon in situ metal matrix composites

Laser deposition of a mixture of elemental nickel, titanium, and carbon (graphite) powders via the laser engineered net shaping (LENS) process results in an in situ titanium carbide reinforced nickel metal matrix composites. The composites have been characterized in detail using X-ray diffraction, scanning electron microscopy (including energy dispersive spectroscopy mapping), Auger electron spectroscopy, and transmission (including high resolution) electron microscopy. Both primary and eutectic titanium carbides, observed in this composite, exhibited the FCC-TiC structure (NaCl-type). Detailed characterization of the nickel/titanium carbide interface was carried out using high resolution TEM with the orientation relationship between the phases being 〈1 0 0〉 TiC//〈1 1 0〉 Ni and (0 0 2) TiC//( 1 ¯ 1 1 ) Ni. Mechanical and tribological testing determined that the composites exhibited a relatively high hardness of 370 VHN and a steady-state friction coefficient of ∼0.5, both improvements in comparison to LENS deposited pure Ni.