Laser Engineered Net Shaping Research Articles

Laser engineered net shaping of antimicrobial and biocompatible titanium-silver alloys.

Post-surgery infection is one of the main causes of orthopedic implant failure. This paper presents a powder-feed 3D printing strategy for fabrication of silver (Ag) incorporated titanium (Ti) alloys as an antimicrobial solution for orthopedic implants. Alloys with various Ag concentration, ranging from 0.5% to 2% by weight, were fabricated through laser engineered net shaping (LENS) process. The composition and surface of the fabricated alloys were characterized through X-ray diffraction, energy-dispersive X-ray spectroscopy, and 3D surface profiling. The mechanical properties, antimicrobial performance, and biocompatibility of the alloys were also investigated. Results showed that LENS fabricated TiAg alloys had a marginally higher microhardness and a lower ductility compared to pure Ti. Within only 3 h, TiAg alloys significantly reduced the bacterial attachment of both gram-positive and gram-negative strains by one to four orders of magnitudes. These alloys also demonstrated excellent in-vitro biocompatibility to human osteosarcoma cells. For the first time, laser engineered net shaping (LENS) of TiAg alloy has been explored as an antimicrobial solution for orthopedic applications and showed great potential for biomedical instrumentation.

Research progress on 3D printing metal powders used in cranio-maxillofacial prosthesis

With the rapid development of 3D printing, it is widely used in the field of cranio-maxillofacial surgery. Through the individualized production of 3D printing, the backward mode of traditional production relying on manual shaping has been changed to meet the needs of different patients. However, as no clear specification exists for the performance requirements of 3D printing metal powder for cranio-maxillofacial surgery, its long-term development is not feasible. In this paper, the preparation technologies of 3D printing metal powder for cranio-maxillofacial prostheses (i.e., gas atomization, rotating electrode atomization, and radio frequency plasma spheroidization) and 3D printing forming technologies (i.e., selective laser melting, electron beam selective melting, and laser-engineered net shaping) are introduced. The performance requirements of 3D printing metal powder for cranio-maxillofacial prostheses are then summarized according to the characteristics of the preparation and forming technologies described.

An analysis of phase stresses in additively manufactured 304L stainless steel using neutron diffraction measurements and crystal plasticity finite element simulations

Combined in-situ neutron diffraction measurements during post-processing heat treatment and thermo-mechanical crystal plasticity finite element (CPFE) simulations were utilized to study the residual phase stress development in the two-phase microstructure of an additively manufactured (AM) 304L stainless steel. The steel, fabricated via the laser engineering net shaping technique, has a microstructure comprising primarily of the austenite phase, with ∼ 2.5% ferrite phase by volume fraction. The post-build material was heated to greater than 1300 K and neutron diffraction data was recorded during heating and cooling. Specifically, the evolution of lattice strains in the individual phases were measured with temperature and the corresponding coefficients of thermal expansion (CTEs) calculated. The dislocation densities, phase fractions and textures, before and after heat treatment, were also measured. CPFE simulations were performed to study the interplay of the stress-free thermal strains and the mechanical strains in inducing inter-granular residual stresses in individual phases. The simulations confirmed the presence of process induced inter-granular residual stress primarily in the ferrite phase of the as-built AM material. Comparison of the relevant simulation data with experiments indicate that model predictions of the lattice strains and CTEs in both phases, as well as the inter-granular residual phase stress and pressure in the ferrite phase are in qualitative agreement with the experimental measurements and calculations.

Evaluation of the mechanical and wear properties of titanium produced by three different additive manufacturing methods for biomedical application

Commercially pure titanium, as a widely used metallic biomaterial, was fabricated using dissimilar additive manufacturing (AM) methods, namely selective laser melting (SLM), laser engineered net shaping (LENS) and wire arc additive manufacturing (WAAM). Microstructures as well as mechanical and wear properties of the produced titanium samples were studied. Diverse microstructural features were related to the different linear energy densities and cooling rates induced by each AM method. Tensile testing evaluation indicated the highest yield and ultimate tensile strengths as well as elastic energy for titanium produced by SLM. However, the maximum ductility was obtained in the WAAM-fabricated titanium due to its larger grain size and slightly higher densification. All the mechanical properties obtained were either superior or comparable to those of cast and powder metallurgy produced titanium. Fracture surface analysis showed the presence of mainly coarse and fine dimples for WAAM and SLM-produced samples, respectively. This was consistent with the grain size of each sample. Wear performances and mechanisms were also examined and the results were in agreement with the values obtained from the hardness to elastic modulus ratios (H/E and H3/E2).

Directed Energy Deposition versus Wrought Ti‐6Al‐4V: A Comparison of Microstructure, Fatigue Behavior, and Notch Sensitivity

Laser Engineered Net Shaping (LENS), a Direct Energy Deposition (DED) additive manufacturing process is a 3D manufacturing process generally used to produce fully dense parts or to repair/add additional material to an existing component. The main aim of this work is to evaluate the fatigue behavior of LENS specimens in the presence of geometrical discontinuities and to compare its performance to the one obtained from wrought specimens. For this aim, axial fatigue tests are carried out on three sets of specimens namely, smooth, semi‐circular and V‐notched specimens to determine the fatigue strength and notch sensitivity of the LENS and wrought Ti‐6Al‐4V materials. The LENS material shows higher fatigue strength and notch sensitivity compared to wrought material which is attributed to the unique microstructural features leading to different fatigue failure mechanisms. Further, the fatigue data is assessed by use of strain energy density as a failure criterion.

Effects of Al and Heat Treatment on the Microstructure and Hardness of Ti–Al Synthesized via In Situ Melting using LENS

Producing alloys via in-situ laser alloying approach is becoming very easy and a topical issue in the field of laser additive manufacturing. Several studies have emerged, accompanied by a statement by Gasper et al. (2017), who reported the economic benefits and cost savings that can be related to 3D printing of the additive manufacturing (AM) structure using the said in situ synthesis approach. They studied the laser in situ reactive synthesis of producing titanium aluminide (Ti–Al) from elemental powders using the laser materials deposition (LMD) process. This paper highlights how the functional grade Ti–Al alloys can be produced in a single flight using the 850-R Optomec Laser Engineering Net Shaping (LENS) system. The effects of the Al content in the as-built and heat-treated samples were investigated. The as-built samples were cracked, inhomogeneous, and had visible inter-layer boundaries due to the segregation of the alloying elements and different heat profiles that are typically experienced during 3D printing. These characteristics led to wavy hardness profiles. Heat-treated samples were the least hard when compared to the as-built samples and had a homogenized microstructure. Samples with a duplex microstructure were, in particular, the least hard, indicating that they would have better ductility than others. The outcomes of this study show that a structure with different composition can be fabricated with the LENS system. This would lead to adaptive structures being used, especially in the high temperature applications where a structure would have to withstand low and high temperatures during use.

Influence of energy density on macro/micro structures and mechanical properties of as-deposited Inconel 718 parts fabricated by laser engineered net shaping

In the present study, the influence of laser energy density (LED) on geometrical characteristics, mechanical properties and microstructure of Inconel 718 parts fabricated by laser engineered net shaping (LENS) were investigated. Thin walls and block specimens were designed and fabricated under a total of 25 different energy density combinations. The material properties, including part dimensional shrinkage, surface roughness, surface hardness, and microstructures, including, porosity, geometrical dilution, average grain size and dendrite arm spacing (DAS), were evaluated. The results of this investigations indicate that with the increase of LED, the part shrinkage and surface roughness present a down and up trend, whereas the porosity, geometrical dilution, grain size and DAS increase with increasing of LED and there is no statistically significant effect of LED on the surface micro hardness. Taking account of the material characterization results, the energy density window for LENS process of Inconel 718 is suggested between 98.21 J/mm2 to 107.14 J/mm2. The outputs of this study could provide an insightful view of the effects of energy input on mechanical and microstructural properties of as-deposited Inconel 718 alloy by LENS process.

Laser Based Manufacturing of Ti6Al4V: A Comparison of LENS and Selective Laser Melting

The laser engineered net shaping (LENS) system was used for the laser based manufacturing of a test geometry used to assess the performance of additive manufacturing systems. This system was preferred over a selective laser melting (SLM) system due to certain inherent benefits that would promote the manufacture of the test geometry where the SLM system had failed due to part delamination. The test geometry was successfully manufactured on the LENS system and machined to produce test specimen for mechanical testing and microstructural evaluation. Investigations revealed that the α-β lamellar microstructure was formed via in situ martensitic decomposition of the α’ structure. This resulted in promising yield and tensile strengths in excess of 900 MPa and high tensile elongation up to 13%.

Microstructure characterization and mechanical properties of laser additive manufactured oxide dispersion strengthened Fe-9Cr alloy

Oxide dispersion strengthened (ODS) alloys are attractive material candidates for advanced fission and fusion reactor application owing to their excellent radiation tolerance and high temperature creep strength but traditional manufacturing process encounters some difficulties in producing complex components. An ODS Fe-9Cr alloy with nominal composition of Fe-9Cr-1.5W-0.3Ti-0.3Y (wt%) were manufactured by laser engineered net shaping (LENS) method with different laser power. Equiaxed martensitic grains together with micro-pores were observed in the as-deposited alloys. With the increase of laser power, the density and size of pores decrease, the grain size of the alloys increases while the number density of nanoscale oxides decreases due to the formation of thicker Y-Ti-O-enriched and Al-O-enriched slag layer in the block surface. Hot isostatic pressing (HIP) processing of the as-deposited ODS alloy with low laser power reduces significantly the density of and the size of micro-pores, refines the grain size, and precipitates higher density of nanoscale oxides (Y2TiO5 and Y2Ti2O7), which improves significantly the tensile properties that is comparable at room temperature and is better at 873 K than ODS EUROFER steel produced by conventional powder metallurgy.

Nanostructured Al2O3-YAG-ZrO2 ternary eutectic components prepared by laser engineered net shaping

The present work proposed a novel 3D printing approach for fabricating ternary eutectic ceramics (Al2O3-YAG-ZrO2, or AYZ in short) using laser engineered net shaping (LENS) technique. Highly dense (≥98%) thin wall components with refined eutectic microstructures were successfully fabricated. The as-fabricated ceramic eutectics mainly consist of cellular eutectics with three phases interpenetrated. In each deposited layer, the solidified microstructure changes from planar to cellular along building direction. The evolution of characteristic dimension of microstructure can be well interpreted using Jackson-Hunt relationship. Irregular interpenetrating to regular fibrous eutectic structure transition occurs at boundary region of LENSed specimens, primarily due to much higher solidification rate. The texture of <0001>Al2O3//<001>YAG//<001>ZrO2 is recognized at the interior region of LENSed eutectic part along building direction, but gradually tilts from central to edge due to change of cellular growth direction. The LENSed AYZ samples exhibit almost isotropic property, and have mechanical performances comparable to those fabricated using conventional direction solidification methods.

Emergy-based life-cycle assessment (Em-LCA) for sustainability assessment: a case study of laser additive manufacturing versus CNC machining

Sustainability of laser additive manufacturing needs to be evaluated for finding an optimal compromise between technical development and sustainable performance. The emergy-based life-cycle assessment (Em-LCA) methodology is applied to investigate the sustainability of laser engineered net shaping (LENS) by comparing that of the computer numerical control (CNC) machining for gear manufacturing. Based on the emergy accounting methodology, the emergy-based sustainability index (ESI) is constructed to indicate the sustainability of the two technologies. In addition, contributions of different processes in the two manufacturing options to the final sustainability have been identified for future improvement. The results indicate that Em-LCA offers a practical sustainability assessment tool. The sustainability of the LENS process is much higher than that of the CNC machining. In the end, several countermeasures are proposed to improve the sustainability of the manufacturing technologies.

Surface engineering of LENS-Ti-6Al-4V to obtain nano- and micro-surface topography for orthopedic application

Two distinct surface topographies consisting of micro- and nano-surface were developed using laser texturing (LT) and anodization process respectively and their effect on the surface-related properties of Ti-6Al-4V fabricated using Laser Engineered Net Shaping (LENS) were determined. The topographies developed using laser texturing (25, 50 and 75% overlap) were examined using 3D profilometer, whereas, Field Emission Scanning Electron Microscopy (FE-SEM) was used to analyze Titania NanoTubes (TNT) formed using anodization. Though all the surface modified specimens exhibited hydrophilic behavior, least contact angle values were observed for the specimen surface modified with TNT. 25LT and 50LT specimens offered about 8 fold higher corrosion resistance than TNT specimens. All the surface modified samples exhibited non-toxicity to blood cells as well as to the mesenchymal stem cells (hMSCs) with a higher rate of proliferation and differentiation hMSCs observed on 75LT specimens and TNT specimen.

Surface properties and cytocompatibility of Ti-6Al-4V fabricated using Laser Engineered Net Shaping

Direct laser deposition (DLD) is one of the rapidly emerging laser-based additive manufacturing (LBAM) process. Laser Engineered Net Shaping (LENS) is one such DLD technique which was employed to fabricate one of the widely used Ti–6Al–4V implant material with enhanced surface-related properties compared to the wrought sample (commercially available). Wear and corrosion behavior of LENS fabricated Ti–6Al–4V (L-Ti64) was characterized using low-frequency reciprocatory wear tester and potentiostat. Sample hardness was determined using Vickers's microhardness test. Adhesion and morphology of Human mesenchymal stem cells (hMSCs) on the samples were examined using Scanning Electron Microscopy (SEM) and fluorescence microscope whereas the quantification of live cells was determined using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) assay. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was used to determine the concentration of leached-out metal ions during wear test. All the above mentioned surface-related properties were compared to that of wrought Ti-6Al-4V (W-Ti64) to standardize the efficiency of LENS-fabricated materials (L-Ti64) when compared to its wrought counterpart. The results clearly indicated stable passive behavior of L-Ti64, which was evident from the lower corrosion rate and high passive range obtained. L-Ti64 exhibited improved hardness level than W-Ti64 by 8% which enhanced the wear resistance and also prevented the release of wear debris. However, in presence of FBS, coefficient of friction (COF) increased by about 21 and 33% for L-Ti64 and W-Ti64 respectively, which inturn accelerated the wear rate of both the samples. Low cytotoxicity and well spread morphology of human Mesenchymal Stem Cells (hMSC's) affirmed higher level of biocompatibility of both the samples. However, no significant differences in the cellular behaviors were observed.

Structural representation of additively manufactured 316L austenitic stainless steel

Three 316L stainless steel materials are studied and reported upon; wrought, as-built additively manufactured (AM), and heat-treated AM material. The AM material was produced from the laser engineered net shaping (LENS) process. Macroscopic uniaxial compression stress-strain curves were obtained for all three materials. The curves were similar for the wrought and heat-treated AM materials but the as-built AM material demonstrated approximately 1.7 times greater flow stress at any given level of strain than the other two materials. Electron-backscatter diffraction analysis of the materials also showed that the microstructures of the three materials differed; with complex grain morphology for the as-built AM material. The mean grain size of each of the three materials also differed. The initial dislocation density was also measured with neutron diffraction and line-profile analysis for both wrought and as-built AM materials with the density in the AM material approximately 2.5 times greater. A single crystal model was proposed to represent the essential features of the three FCC materials accounting for dislocation interactions and representation of grain size via a simple Hall-Petch type term. The strength of this term is evaluated through independent experimental results on traditionally manufactured materials. The model was applied to each of the three materials by simulation of the uniaxial compression experiments by direct numerical simulation of electron-backscatter diffraction images. This allowed for representation of the size of each grain in the simulations. The results suggest that the difference in initial dislocation density of the three materials is the primary factor causing the difference in stress-strain response. Although the differences in grain size contribute to a higher stress for the as-built AM material, the effect is small. Other factors such as internal stress and grain morphology could play a role in mechanical behavior difference and these two factors are also discussed.

Yttria stabilized zirconia (YSZ) thin wall structures fabricated using laser engineered net shaping (LENS)

Yttria stabilized zirconia (YSZ) thin wall components were fabricated using laser engineered net shaping (LENS) technique. It was found that after LENS processing, the monoclinic (m) phase in as-received YSZ powders transformed to tetragonal (t) and cubic (c) phases with the lenticular shaped t-ZrO2 embedded in the c-ZrO2 matrix. The relative density of the parts reached up to 98.7%. Our investigation showed that micro cracks within the wall structure were reduced by judiciously choosing laser power parameter. The fabricated parts have surface roughness values that ranged from 20 to 40 μm. The maximum hardness and elastic modulus achieved from the LENSed YSZ parts were 19.8 GPa and 236.1 GPa, respectively. We also demonstrated that dark brown color of the LENSed parts could be removed via heat treatment.

Effects of Composition and Post Heat Treatment on Shape Memory Characteristics and Mechanical Properties for Laser Direct Deposited Nitinol

Nitinol structures were synthesized in a fully dense form using a laser direct deposition method. The pure elemental metal powders of nickel and titanium were used and powder ratios were controlled to arrive at the prescribed final chemical compositions of Nitinol. The transformation temperatures of synthesized Nitinol samples with different chemical composition and post heat treatment conditions were systematically analyzed and compared with those of conventional Nitinol. Compared to Nitinol parts produced by other techniques, the laser engineered net shaping (LENS) created the least amount of secondary phase, indicating the possibility of high corrosion resistance. Two step post processing of solution heat treatment and aging heat treatment was carried out to improve the homogeneity of the microstructure and to investigate its effects on phase transformation temperatures. The resultant phase transformation temperatures could be controlled by the heat treatment parameters. Compression test results showed mechanical properties of synthesized Nitinol samples are largely affected by its post heat treatment history while the effect of initial chemical composition was negligible.

Characteristics of laser metal deposited titanium aluminide

The unique properties of titanium and its alloys make them a continuous area of interest for the material researchers and high profile material industries. Titanium and its alloys possess high strength-to-weight ratio and excellent corrosion resistance properties which made them very useful for high temperature applications especially in areas such as energy generation, automobile and aeronautic industries. In this paper, the effect of deposition parameters on the properties of laser fabricated titanium aluminide alloy was studied. Titanium aluminide powder (Ti-4822-4) was deposited on pure titanium substrate using laser engineered net shaping (LENS) technique of additive manufacturing. Processing parameters like the laser power, scanning speed and powder flow rate were varied. Laser power was varied between 300 to 500 W, scanning speed varied between 3.174 to 7.406 mm s−1 and powder flow rate varied between 4.09 to 7.12 g min−1. The design and analysis of the results was carried out using design expert 6.0.8 software. The trends in deposits cracks, heights and microhardness in relation to the deposition parameters have been studied. The outcome of the study showed that cracks in the deposits reduced as the laser power increases and scanning speed reduces. It was also revealed that the overall microhardness increases as the laser power, scanning speed and powder flow rate increases. The height of the deposits increases as the laser power increases, scanning speed decreases and powder flow rate increases. Microscopic images of the deposits revealed massive presence of γ-TiAl and isolated lamellar region of γ-TiAl and Ti3Al.

Effects of deposition variables on molten pool temperature during laser engineered net shaping of Inconel 718 superalloy

The molten pool temperature during laser engineered net shaping (LENS) could directly affect the microstructure and phase compositions of materials in the molten pool, thereby affecting the mechanical properties of the fabricated parts. To achieve a well-built solid structure, the research on fundamentals and methods of molten pool thermal behavior monitoring is of great significance. Using a high-resolution infrared camera, this paper realized real-time temperature tracking of Inconel 718 deposition in the LENS process. The effects of deposition variables, such as laser power and scanning speed, on the molten pool temperature and cooling rate have been investigated. In addition, the effects of the molten pool temperature on the molten pool depth and dendrite arm spacing (DAS) have been analyzed. The results suggest that the molten pool temperature increases with increasing of the laser power while it drops first and then rises with increasing of the scanning speed. The molten pool temperature increases nonlinearly with increasing of the number of layers during the material deposition process.

Microstructure and mechanical property of TiB reinforced Ti matrix composites fabricated by ultrasonic vibration-assisted laser engineered net shaping

PurposeThe purpose of this paper is to identify if the implementation of ultrasonic vibration in laser engineered net shaping (LENS) process can help to reduce internal weaknesses such as porosity, coarse primary TiB whisker and heterogeneous distribution of TiB reinforcement in the LENS-fabricated TiB reinforced Ti matrix composites (TiB-TMC) parts.Design/methodology/approachAn experimental investigation is performed to achieve the results for comparative studies under different fabrication conditions through quantitative data analysis. An approach of microstructural characterization and mechanical testing is conducted to obtain the output attributes. In addition, the theoretical analysis of the physics of ultrasonic vibration in the melting materials is presented to explain the influences of ultrasonic vibration on the microstructural evolution occurred in the part fabrication.FindingsBecause of the nonlinear effects of acoustic streaming and cavitation induced by ultrasonic vibration, porosity is significantly reduced and a relatively small variation of pore sizes is achieved. Ultrasonic vibration also causes the formation of smaller TiB whiskers that distribute along grain boundaries with a homogeneous dispersion. Additionally, a quasi-continuous network (QCN) microstructure is considerably finer than that produced by LENS process without ultrasonic vibration. The refinements of both reinforcing TiB whiskers and QCN microstructural grains further improve the microhardness of TiB-TMC parts.Originality/valueThe novel ultrasonic vibration-assisted (UV-A) LENS process of TiB-TMC is conducted in this work for the first time to improve the process performance and part quality.

Deformation of honeycomb cellular structures manufactured with Laser Engineered Net Shaping (LENS) technology under quasi-static loading: Experimental testing and simulation

The paper presents a methodology investigation of honeycomb cellular structures deformation process in quasi-static compression tests. Two honeycomb topologies with different elementary cells were designed and manufactured from Ti-6Al-4 V alloy powder with the use of Laser Engineered Net Shaping (LENS) system and compressed using a universal strength machine. To simulate the deformation process with LS-Dyna software, the mechanical properties of the material were assessed and correlated. An elasto-visco-plastic material model (Mat_Plasticity_With_Damage) was used for predicting the material behavior. The results of experimental tests and numerical simulations were compared. A reasonable agreement between deformation, failure and force histories was obtained. Additionally, both the topologies were compared for their energy absorption capabilities. The validated numerical modelling with the adopted constitutive model will be used in the further studies to analyze different cellular structures topologies subjected to dynamic loading.