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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.

Laser engineered net shaping (LENS™) has been used to create dense WC–12%Co composite coatings on stainless steel substrates. Low heat input and controlled atmosphere with oxygen content less than 10 ppm resulted in minimum interface dilution, carbide dissolution and uniform carbide distribution. Under present experimental conditions, coatings produced at laser energy input of 365 and 465 J/mm 3 showed similar phase constituents, hardness and wear rate. The coating hardness varied between 1171 and 1181 HV with an average dry sliding specific wear rate in the range of 3 × 10 −6 mm 3 /Nm and 6.5 × 10 −6 mm 3 /Nm against Si 3 N 4 ball. Deformation and extrusion of cobalt phase followed by fracture and removal of carbide particles was found to be a predominant material removal mechanism in the present laser deposited WC–Co coatings. The influence of laser energy input on the microstructural and wear properties of WC–12%Co composites coatings are reported in this article.

Laser engineered net shaping has been used to create a Ti–SiC composite layer on Ti to improve its wear resistance. The influences of laser power and scanning speed on the microstructure and wear resistance of the coatings were examined. Laser parameters were found to have a strong influence on the dissolution of SiC, leading to the formation of Ti5Si3 and TiC with a high amount of SiC on the surface. The composite coatings with hardness between 976 and 1167 HV exhibited average wear rate between 5.91 and 6.60 × 10−4 mm3 (N m)−1.

Laser Engineered Net Shaping (LENS™) has been used to fabricate dense, net shape melt-cast structures of lead zirconate titanate (PZT), in a single step, directly on a metallic substrate by complete melting and resolidification of PZT powders. From our results, it appears that reasonable dielectric properties can be obtained in LENS™ processed PZT structures without post-fabrication heat treatments. Our results also demonstrate potential application of LENS™ towards direct fabrication of PZT based embedded sensors and transducers on structural components.

The relatively high cost of manufacturing and the inability to produce modular implants have limited the acceptance of tantalum, in spite of its excellent in vitro and in vivo biocompatibility. In this article, we report how to process Ta to create net-shape porous structures with varying porosity using Laser Engineered Net Shaping (LENS) for the first time. Porous Ta samples with relative densities between 45% and 73% have been successfully fabricated and characterized for their mechanical properties. In vitro cell materials interactions, using a human fetal osteoblast cell line, have been assessed on these porous Ta structures and compared with porous Ti control samples. The results show that the Young's modulus of porous Ta can be tailored between 1.5 and 20 GPa by changing the pore volume fraction between 27% and 55%. In vitro biocompatibility in terms of MTT assay and immunochemistry study showed excellent cellular adherence, growth and differentiation with abundant extracellular matrix formation on porous Ta structures compared to porous Ti control. These results indicate that porous Ta structures can promote enhanced/early biological fixation. The enhanced in vitro cell-material interactions on the porous Ta surface are attributed to its chemistry, its high wettability and its greater surface energy relative to porous Ti. Our results show that these laser-processed porous Ta structures can find numerous applications, particularly among older patients, for metallic implants because of their excellent bioactivity.

Special microstructures of the newly developed Laser Engineered Net Shaping (LENS™)-processed steel induce a new variability in fatigue damage formation and evolution mechanisms. The microporosity and mechanism of fatigue damage formation and growth were invested using X-ray computed tomography and scanning electron microscopy. Systematic observations were made of the variations in the fracture surfaces according to three fatigue damage evolution stages: fatigue crack formation (incubation), microstructurally/physically small cracks, and long cracks. The fatigue crack was formed almost exclusively at the relatively large pores located at or near the specimen surface, with rare cases at incompletely melted power particles on the surface. Distributed cracks from large interior pores coalesced with each other in the microstructurally small crack regime to form the major critical crack that eventually fractured the specimen. This coalescence accelerated the fatigue crack growth, which in turn decreased the fatigue life but not significantly. In the long-crack regime, the fracture surface was rougher, but the overall surface tended to be perpendicular to the loading direction, indicating a Mode I type fracture. Cyclic strain-softening, with reduced strain-hardening, was also observed. The multistage fatigue model of McDowell et al. was used to capture the microstructure effects in the three fatigue damage evolution regimes, and the upper and lower bounds for the strain–life are predicted.

Recently tantalum is gaining more attention as a new metallic biomaterial as it has been shown to be bioactive and biologically bonds to bone. However, the relatively high cost of manufacture and an inability to produce a modular all Ta implant has limited its widespread acceptance. In this study we have successfully deposited a Ta coating on Ti using laser engineered net shaping (LENS) to enhance the osseointegration properties. In vitro biocompatibility study, using human osteoblast cell line hFOB, showed excellent cellular adherence and growth with abundant extracellular matrix formation on the Ta coating surface compared with the Ti surface. A six times higher living cell density was observed on the Ta coating than on the Ti control surface by MMT assay. A high surface energy and wettability of the Ta surface were observed to contribute to its significantly better cell-material interactions. Also, these dense Ta coatings do not suffer from low fatigue resistance due to the absence of porosity and a sharp interface between the coating and the substrate, which is a major concern for porous coatings used for enhanced/early biological fixation.

The water-atomized ATOMET 28, 1001, 4701, and 4801 powders, manufactured by Rio Tinto Metal Powders, were used for additive manufacturing by a laser engineered net shaping (LENS) technique. Their overall morphology was globular and rounded with a size distribution from about 20 to 200 µm. Only the ATOMET 28 powder was characterized by a strong inhomogeneity of particle size and irregular polyhedral shape of powder particles with sharp edges. The powders were pre-sieved to a size distribution from 40 to 150 µm before LENS processing. One particular sample—LENS-fabricated from the ATOMET 28 powder—was characterized by the largest cross-sectional (2D) porosity of 4.2% and bulk porosity of 3.9%, the latter determined by microtomography measurements. In contrast, the cross-sectional porosities of bulk, solid, nearly cubic LENS-fabricated samples from the other ATOMET powders exhibited very low porosities within the range 0.03–0.1%. Unexpectedly, the solid sample—LENS-fabricated from the reference, a purely spherical Fe 99.8 powder—exhibited a porosity of 1.1%, the second largest after that of the pre-sieved, nonspherical ATOMET 28 powder. Vibrations incorporated mechanically into the LENS powder feeding system substantially improved the flow rate vs. feeding rate dependence, making it completely linear with an excellent coefficient of fit, R2 = 0.99. In comparison, the reference powder Fe 99.8 always exhibited a linear dependence of the powder flow rate vs. feeding rate, regardless of vibrations.

Laser Engineered Net Shaping (LENS) is an advanced manufacturing technology, but it is difficult to control the depositing height (DH) of the prototype because there are many technology parameters influencing the forming process. The effect of main parameters (laser power, scanning speed and powder feeding rate) on the DH of single track is firstly analyzed, and then it shows that there is the complex nonlinear intrinsic relationship between them. In order to predict the DH, the back propagation (BP) based network improved with Adaptive learning rate and Momentum coefficient (AM) algorithm, and the least square support vector machine (LS-SVM) network are both adopted. The mapping relationship between above parameters and the DH is constructed according to training samples collected by LENS experiments, and then their generalization ability, function-approximating ability and real-time are contrastively investigated. The results show that although the predicted result by the BP-AM approximates the experimental result, above performance index of the LS-SVM are better than those of the BP-AM. Finally, high-definition thin-walled parts of AISI316L are successfully fabricated. Hence, the LS-SVM network is more suitable for the prediction of the DH.

Metallic biomaterials are widely used to restore the lost structure and functions of human bone. Due to the large number of joint replacements, there is a growing demand for new and improved orthopedic implants. More specifically, there is a need for novel load bearing metallic implants with low effective modulus matching to that of bone in order to reduce stress shielding and consequent increase in the in vivo life-span of the implant. In this study, we have fabricated porous Ti6Al4V alloy structures, using Laser Engineered Net Shaping (LENS™) to demonstrate that advanced manufacturing techniques such as LENS™ can be used to fabricate low-modulus, tailored porosity implants with a wide variety of metals/alloys, where the porosity can be designed in areas based on the patient's need to enhance biological fixation and achieve long-term in vivo stability. The effective modulus of Ti6Al4V alloy structures has been tailored between 7 and 60 GPa and porous Ti alloy structures containing 23 to 32 vol. % porosity showed modulus equivalent to human cortical bone. In vivo behavior of porous Ti6Al4V alloy samples in male Sprague-Dawley rats for 16 weeks demonstrated significant increase in calcium within the implants indicating excellent biological tissue ingrowth through interconnected porosity. In vivo results also showed that total amount of porosity plays an important role in tissue ingrowth.

Brass coating was applied to AISI410 steel using high power laser in a laser engineered net shaping (LENS™) system. The influence of laser treatment on interfacial microstructure and thermal performance was evaluated as a function of coating thickness. Laser deposition resulted in a diffused and metallurgically sound interface between metallurgically incompatible brass coating and AISI410 steel substrate. The thermal conductivity of AISI410 steel increased from 27 W/mK to a maximum of 37 W/mK depending on the coating thickness, almost 50% gain. The absence of sharp interface between the coating and the substrate, as a result of laser processing, resulted in a low interfacial thermal contact resistance. Thermal performance tests showed that the brass coating can enhance the heat transfer rate of stainless steel substrate. These results show that novel and efficient feature based coatings can be exploited using laser-based advanced manufacturing technologies for various industrial applications.

The effect of the laser engineered net shaping (LENS) process on the microstructure and mechanical properties of (Ti,W)C–Ni solid solution cermets was investigated. Nano-(Ti,W)C–Ni powder was synthesised, spray dried and densified by two different processes: sintering and LENS. Furthermore, all results were compared with conventional micrometre sized TiC–WC–Ni cermets. Solid solution (Ti,W)C–Ni cermets made by sintering resulted in a coreless and ultra fine microstructure, while the LENS processed specimens revealed inhomogeneous microstructure and particle coarsening. The hardness values of the LENS processed specimens range from 15 to 20 GPa, which is higher than for the ultra fine and conventional sintered composites (∼12 GPa). The measured toughness values show greater variability.

The use of rapid prototyping (RP) technology for rapid tooling and rapid manufacturing has given rise to the development of application-oriented composites. The present paper furnishes succinct notes of the composites formed using main rapid prototyping processes such as Selective Laser Sintering/Melting, Laser Engineered Net Shaping, Laminated Object Manufacturing, Stereolithography, Fused Deposition Modeling, Three Dimensional Printing and Ultrasonic Consolidation. The emphasis of the present work is on the methodology of composite formation and the reporting of various materials used.

Laser Engineered Net Shaping (LENSTM) is attracting the attention of the researchers because of its ease in operation and wide variety of material acceptance. Tensile specimens of Co-Cr-Mo alloy are prepared using LENS process as per JIS standards. Laser power, powder feed rate and laser scan speed are the process parameters used. All the specimen samples are tested for their tensile strength. The samples fabricated with high laser power, low powder feed rate and high laser scan speed have exhibited highest tensile strengths (both yield strength and ultimate tensile strength) among the samples tested. The tensile properties of the LENS deposited samples are compatible with or superior than the as-cast Co-Cr-Mo alloy samples.

Designing load bearing implants with the desired mechanical and biological performance and to fabricate net shape, functional implants with complex anatomical shapes is still a challenge. In addition, patient specific load bearing implants with the possibilities of guided tissue regeneration are gaining significant interest in orthopedics. Novel design approaches and fabrication technologies that can achieve balanced mechanical and functional performance in mono-block implants are necessary to accomplish these objectives. In this article we give an overview of our novel design concepts for load bearing metal implants and demonstrate the manufacturing of unitized implant structures with and/or without porosity using laser engineered net shaping (LENS™) — a solid freeform fabrication technique. We have fabricated porous metal implants with designed porosities up to 70 vol.% in various biomedical metals/alloys, such as Ti, Ti6Al4V, NiTi and CoCrMo, and tailored their effective modulus to suit the modulus of human cortical bone, thus eliminating stress-shielding. Unitized structures with functionally graded CoCrMo alloy coating on porous Ti6Al4V alloy have been fabricated using LENS™ to minimize wear induced osteolysis. Finally, this technology can also be used to fabricate porous, net shape implants with functional gradation in structure and/or composition to mimic natural bone. Since the LENS™ fabrication does not change the chemistry of the biocompatible alloys the inherent in vitro and in vivo biocompatibility will remain the same and therefore, we have not provided any biocompatibility results in this article. This article provide an insight into the important aspects of LENS™ fabrication and properties of CoCrMo alloy structures, which can potentially eliminate long standing challenges in load bearing implants such as total hip prosthesis to increase their in vivo life time.

Laser deposition is being used for the fabrication of net shapes from a broad range of materials, including tungsten carbide–cobalt (WC–Co) cermets (composites composed of a metallic phase and a hard refractory phase). During deposition, an unusual thermal condition is created for cermets, resulting in rather complex microstructures. To provide a fundamental insight into the evolution of such microstructures, we studied the thermal behavior of WC–Co cermets during laser deposition involving complementary results from in situ high-speed thermal imaging and three-dimensional finite element modeling. The former allowed for the characterization of temperature gradients and cooling rates in the vicinity of the molten pool, whereas the latter allowed for simulation of the entire sample. By combining the two methods, a more robust analysis of the thermal behavior was achieved. The model and the imaging results correlate well with each other and with the alternating sublayers observed in the microstructure.

Implant related infections are of great concern in modern surgery. In order to improve the implant performance and to reduce implant related infections, titanium (Ti) surface was modified to simultaneously improve cell- materials interactions and antimicrobial activity. Ti surface was first coated with tricalcium phosphate (TCP) using Laser Engineered Net Shaping (LENS™) to improve biocompatibility. Silver (Ag) was then electrodeposited from different concentrations of silver nitrate (AgNO(3)) solutions to improve the antimicrobial activity. The Ag-TCP coatings were tested for cytotoxicy with human osteoblast cells. The antimicrobial activities of the Ag-TCP coatings were evaluated using Pseudomonas aeruginosa and Staphylococcus aureus bacteria. In vitro bacterial adhesion study indicated a significant reduction in bacterial colony on Ag-TCP coated surfaces when compared to TCP coated surface.

Nanostructured WC–10 wt.% Co powder was used to make thick wall samples by the Laser Engineered Net Shaping (LENS ® ) process. During this process, a Nd:YAG laser was applied to create a molten pool on a stainless steel substrate and to deposit WC–Co into bulk cermets, the shape of which was controlled by a pre-programmed computer-aided design (CAD) model. Microstructure characteristics were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that working distance and relative location of the focal plane of the laser beam play an important role in controlling sample microstructures, in addition to other common process parameters such as laser power, traverse speed and powder feed rate. Thermal behavior leading to the observed microstructures that result from the variations in working distance was also investigated in this work.

This article has a twofold purpose. The first part deals with introduction of innovative high technology laser engineered net shaping (LENS) that offers a breakthrough in manufacturing, maintaining, and repairing products. It also presents many possibilities for the use of LENS technology, especially in the tool-making industry and for medical purposes. The second part presents a comparison of a product manufactured by conventional technologies and the same product manufactured by LENS technology. The product is a titanium alloy medical implant.

Surface modification of AISI 410 martensitic stainless steel was carried out by laser surface-melting using laser engineered net shaping (LENSTM). The microstructures of laser surface-melted specimens showed varying amount of retained austenite depending on the processing parameters. The refinement and high strength of austenite as a result of increased scan speed and decreased laser power resulted in high amount of retained austenite in the final microstructure. Laser surface-melting of AISI 410 martensitic stainless steel at optimized processing parameters resulted in fine martensite with minimum retained austenite, leading to a 55% increase in the surface hardness compared to the hardness of conventionally heat treated samples. The inherent advantage of laser surface-melting using LENSTM is to control simultaneously both location and microstructure leading to better service performance of components.

In this article, the laser-engineered net shaping (LENS) process is implemented to fabricate net-shaped Fe-based Fe-B-Cr-C-Mn-Mo-W-Zr metallic glass (MG) components. The glass-forming ability (GFA), glass transition, crystallization behavior, and mechanical properties of the glassy alloy are analyzed to provide fundamental insights into the underlying physical mechanisms. The microstructures of various LENS-processed component geometries are characterized via scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The results reveal that the as-processed microstructure consists of nanocrystalline α-Fe particles embedded in an amorphous matrix. An amorphous microstructure is observed in deposited layers that are located near the substrate. From a microstructure standpoint, the fraction of crystalline phases increases with the increasing number of deposited layers, effectively resulting in the formation of a functionally graded microstructure with in-situ-precipitated particles in an MG matrix. The microhardness of LENS-processed Fe-based MG components has a high value of 9.52 GPa.

Tungsten carbide–cobalt (WC–Co) has been extensively employed as an abrasion/wear protective material. However, carbon loss (decarburization) of WC–Co powders during processing reduces the efficiency of the material against abrasive wear. This paper examines the efficiency of three consolidation processing techniques to obtain coatings and bulk samples from WC–Co powder. In this work, high velocity oxy-fuel (HVOF) spray forming and laser engineered net shaping (LENS®) were applied to make WC–Co coatings; spark plasma sintering (SPS) was used to produce bulk WC–Co samples for comparison. The microstructures of two types of coatings and one bulk sample were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) to recognize material modification. In addition, porosity and tribological properties of the WC–Co samples were tested. The ultra-microindentation technique was applied to measure the universal hardness and the elasto-plastic properties of the samples. Experiments using a tribometer (ball on disc configuration) under dry conditions have been performed in order to evaluate the friction and wear properties of the different systems.

Metal-matrix composites consisting of a complex quaternary Ti-35Nb-7Zr-5Ta alloy reinforced by borides have been successfully deposited from a powder feedstock consisting of a blend of elemental titanium, niobium, zirconium, tantalum, and, titanium diboride (TiB2) powders, using the laser engineered net-shaping (LENS™) 1 process. The microstructures of the as-deposited composites have been characterized using scanning electron microscopy, orientation microscopy, and, transmission electron microscopy. Both primary and eutectic boride precipitates, exhibiting the orthorhombic B27 structure, are observed in these as-deposited composites. The complex primary borides exhibit an unusual compositional variation within the same precipitate, which has been investigated in detail using site-specific characterization with a transmission electron microscope. The ability to form near-net shape components using the Laser Engineered Net Shaping process makes these laser-deposited composites promising candidates for wear-resistant applications in biomedical implants.

PurposeThe paper seeks to investigate the laser engineered net shaping (LENS) of metal thick‐wall parts from Ni‐based alloy powders.Design/methodology/approachThe composition of Ni‐based alloy powders was determined from phase diagram, which was 84Ni14.4Cu1.6Sn. The powders were prepared by gas atomization. Deoxygenation and screen separation were applied to the powders to improve the sintering ability and narrow the particle size distribution before shaping. Thick‐wall metal parts were built by LENS under different conditions. The microstructures, surface morphologies of the prepared parts were characterized.FindingsThe gas atomized powders were almost uniformly spherical after sieving. Most of oxygen contained in the alloy powders could be removed in H2 atmosphere for heating at 550°C for 2 h. These nickel‐based alloy powders with 150‐200 mesh size were suitable for powder feed system. And these powders were shaped successfully by LENS. Thick‐wall parts with thickness ranged from 20 to 25 mm were fabricated. The thickness of each layer was between 400 and 600 μm by scanning electron microscope. Metallographs revealed that dendritic structures with different characteristics were grown on XY‐, YZ‐ and XZ‐section.Research limitations/implicationsThe present experiments were limited by the atmosphere control during the LENS process. The oxide at the interface between two neighbor layers could decrease the mechanical properties if without good inert gas protection, such as a protective atmosphere chamber.Originality/valueThis paper describes a refined experimental program that is needed to resolve the remaining technical issues in LENS of thick‐wall parts. The nickel‐based alloy powders suitable for the LENS process were studied and prepared. After pretreatment, the self‐made powders have good shaping ability. Microstructure features were first discussed with the variation of the face orientation. The dendrite arm distance obtained by this experiment is between 8 and 20 μm, well conforming to the theory. The thick‐wall parts with dense structures were fabricated successfully to widen the field of application of LENS.

Porous NiTi alloy samples were fabricated with 12–36% porosity from equiatomic NiTi alloy powder using laser engineered net shaping (LENS™). The effects of processing parameters on density and properties of laser-processed NiTi alloy samples were investigated. It was found that the density increased rapidly with increasing the specific energy input up to 50 J/mm3. Further increase in the energy input had small effect on density. High cooling rates associated with LENS processing resulted in higher amount of cubic B2 phase, and increased the reverse transformation temperatures of porous NiTi samples due to thermally induced stresses and defects. Transformation temperatures were found to be independent of pore volume, though higher pore volume in the samples decreased the maximum recoverable strain from 6% to 4%. Porous NiTi alloy samples with 12–36% porosity exhibited low Young's modulus between 2 and 18 GPa as well as high compressive strength and recoverable strain. Because of high open pore volume between 36% and 62% of total volume fraction porosity, these porous NiTi alloy samples can potentially accelerate the healing process and improve biological fixation when implanted in vivo. Thus porous NiTi is a promising biomaterial for hard tissue replacements. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009

In an attempt to relate the laser-engineered net shaping (LENS) process parameters, laser power and laser travel speed, to the quality of LENS-produced parts, strain measurements were taken at several predetermined points within seven LENS AISI 410 thin plates using the neutron diffraction method. The residual stresses at these points were then calculated using the measured strain values to ascertain how the internal stress varies as a function of the input parameters and location. It is found that the component of the stress in the vertical direction (i.e., perpendicular to the raster direction of the laser/powder nozzle) is dominant, in agreement with previous reports, and relatively insensitive to variations in process parameters. This was confirmed with numerical simulations performed with a thermomechanical model developed using the commercial program SYSWELD. The simulations also showed a good qualitative agreement with the measured simulated stresses.

The Laser Engineered Net Shaping (LENS ® ) technology is an extension of rapid prototyping technologies into the direct fabrication of metal parts. Bulk dense tungsten carbide–cobalt (WC–Co) cermets were produced without any molds using the LENS ® technology, starting from granules consisting of nanostructured WC crystallites in a Co matrix. Thermal behavior of the LENS ® process, shape change and coarsening of WC crystallites were investigated in this work to study the mechanisms of microstructural evolution of the cermets. Microstructures with alternating layers were observed, which is relevant to the thermal behavior of the LENS ® process. Variations in hardness result from the change in cooling rate along the specimen height.

Laser Engineered Net Shaping (LENS™) is a laser-assisted manufacturing process that offers the possibility of producing metallic coatings and components with highly nonequilibrium microstructures. In this work, the microstructure developed by LENS deposition of Cu47Ti33Zr11Ni8Si1 powder on a bulk metallic glass substrate, with nominal composition Zr58.5Nb2.8Cu15.6Ni12.8Al10.3, is investigated. Single-layer deposition results in the formation of an inhomogeneous but partially amorphous layer above a crystalline heat-affected zone. Elemental analysis of the deposited layer indicates incomplete mixing of the powder with the melt pool. The as-deposited alloy exhibits a single glass transition event and its primary crystallization event is consistent with the first crystallization temperature of the Cu-based powder. Subsequent remelting of this layer results in a still partially amorphous deposit with a uniform composition of (Zr + Nb)51.8Cu24.7Ti3.4Ni16.4Al3.7. The remelted layer exhibits a structural rearrangement immediately prior to the primary crystallization event, possibly associated with the formation of a quasicrystalline phase.

Tungsten carbide–cobalt (WC–Co) cermets have been widely used because of their high hardness and excellent wear-resistant properties. In this study, the environmental burdens related to WC–Co component fabrication were evaluated to compare the Laser Engineered Net Shaping (LENS ® ) process and the conventional powder metallurgy (P/M) process. Sensitivity analysis revealed that choice of weighting scheme does not significantly affect the final result; the LENS ® process is more preferable if powder recycling is applied, part size is small, or part shape is complex; and the P/M process provides more benefits to produce large parts of simple shape.

Laser-engineered net shaping (LENS) is a rapid direct manufacturing process. The LENS process can be analyzed as a sequence of discrete events, given that it is a layer-by-layer process. The thermal history associated with the LENS process involves numerous reheating cycles. In this article, the thermal behavior during laser deposition with LENS is simulated numerically by using the alternate-direction explicit (ADE) finite difference method (FDM). The simulation results showed that deposited material experiences a significant rapid quenching effect during the initial stages of deposition and can attain a very high cooling rate. With an increase in deposit thickness, the rapid quenching effect decreases and eventually disappears. The effects of the processing parameters on the thermal behavior of deposited materials were also simulated and analyzed. The objective of this study is to provide insight into the thermal history during the LENS process, where the ability to correlate process parameters to microstructural evolution is a motivating force.

The thermal behavior during laser-engineered net shaping (LENS) processing was numerically simulated using the alternate direction explicit finite difference method in Part I of this work. In this article, Part II, the numerical simulation results were compared to experimental results obtained with LENS-deposited 316L stainless steel. In particular, the cooling rate that is present during LENS deposition was established on the basis of dendrite arm spacing (DAS) measurements with and without a melt pool sensor (MPS) and a Z-height control (ZHC) subsystem. The microstructure of the deposited materials was characterized and analyzed, and the corresponding microhardness was measured as a function of distance from the substrate. The influence of thermal history on microstructure evolution was analyzed and discussed based on both modeling and experimental results. The results discussed in this article suggest relatively good agreement between experiments and modeling.

Fabrication of net shape load bearing implants with complex anatomical shapes to meet desired mechanical and biological performance is still a challenge. In this article, an overview of our research activities is discussed focusing on application of Laser Engineered Net Shaping (LENS™) toward load bearing implants to increase in vivo life time. We have demonstrated that LENS™ can fabricate net shape, complex metallic implants with designed porosities up to 70 vol.% to reduce stress-shielding. The effective modulus of Ti, NiTi, and other alloys was tailored to suit the modulus of human cortical bone by introducing 12–42 vol.% porosity. In addition, laser processed porous NiTi alloy samples show a 2–4% recoverable strain, a potentially significant result for load bearing implants. To minimize the wear induced osteolysis, unitized structures with functionally graded Co–Cr–Mo coating on porous Ti6Al4V were also made using LENS™, which showed high hardness with excellent bone cell–materials interactions. Finally, LENS™ is also being used to fabricate porous, net shape implants with a functional gradation in porosity characteristics.

Application of rapid prototyping (RP) in ceramics manufacturing is motivated by advances in engineering ceramics where attaining complex shapes using traditional processing is difficult. Laser Engineered Net Shaping (LENS™), a commercial RP process, is used to fabricate dense, net-shaped structures of α-Al 2 O 3 . Shapes such as cylinder, cube, and gear have been fabricated successfully with 10-25 mm section sizes. As-processed structures show anisotropy in mechanical properties with a high compressive strength normal to the build direction and columnar grains along the build direction. Heat treatment did not alter strength and anisotropy, but increased the grain size from 6 to 200 μm and hardness from 1550 to 1700 Hv.

As a layer additive rapid manufacturing process, laser engineered net shaping (LENS) can fabricate three-dimensional components directly from a computer-aided design (CAD) model. In this work, the LENS process was employed to fabricate Ti6Al4V metal matrix composites using powder mixtures of gas-atomized Ti6Al4V powder and varying volume fractions of Ni nanocoated TiC particles. The as-fabricated microstructures were studied using scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), differential thermal analyzer (DTA), and transmission electron microscopy (TEM) techniques. The interfaces between the metal matrix and ceramic particles were examined. The presence of intermetallic phases and resolidified TiC particles was rationalized on the basis of the thermal field during deposition. The influence of LENS parameters on the microstructure evolution and mechanical behavior of the metal matrix composites (MMCs) was also discussed.

A three-dimensional finite element model was developed and applied to analyze the temperature and phase evolution in deposited stainless steel 410 (SS410) during the Laser Engineered Net Shaping (LENS ®,1 ) rapid fabrication process. The effect of solid phase transformations is taken into account by using temperature and phase dependent material properties and the continuous cooling transformation (CCT) diagram. The laser beam is modeled as a Gaussian distribution of heat flux from a moving heat source with conical shape. The laser power and translational speed during deposition of a single-wall plate are optimized in order to maintain a steady molten pool size. It is found that, after an initial transient due to the cold substrate, the dependency of laser power with layer number is approximately linear for all travel speeds analyzed. The temperature distribution and cooling rate surrounding the molten pool are predicted and compared with experiments. Based upon the predicted thermal cycles and cooling rate, the phase transformations and their effects on the hardness of the part are discussed. © 2007 Elsevier B.V. All rights reserved.

There is a growing interest in metal-on-metal bearing surfaces for orthopedic implants. Although some success has been achieved in applications like hip implants which involve a large contact area, non-conforming joints, such as knees, have proved more difficult. The current work examines the applicability of a novel additive manufacturing process, Laser Engineered Net Shaping (LENS®, the registered trademark and service mark of Sandia National Laboratories and Sandia Corporation), for producing CoCrMo implants. A series of experiments were conducted to determine the optimum parameters for deposition of CoCrMo. Microstructural studies, hardness tests, and dry sand/rubber wheel abrasive wear tests were conducted on the LENS® deposits. The results showed that metallurgically sound deposits can be produced using the LENS® process under optimized conditions. The hardness of the LENS® deposited CoCrMo was found to be comparable to that of standard CoCrMo wrought material; however, wear tests indicated that LENS® deposits were considerably less resistant to abrasive wear than wrought CoCrMo. The reasons for this behaviour are discussed based on microstructural observations.

The Laser Engineered Net Shaping (LENS™) method was used to fabricate porous Ti implants. Porous Ti structures with controlled porosity in the range of 17–58 vol.% and pore size up to 800 μm were produced by controlling LENS™ parameters, which showed a broad range of mechanical strength of 24–463 MPa and a low Young’s modulus of 2.6–44 GPa. The effects of porous structure on bone cell responses were evaluated in vitro with human osteoblast cells (OPC1). The results showed that cells spread well on the surface of porous Ti and formed strong local adhesion. MTT assay indicated LENS™ processed porous Ti provides a preferential surface for bone cell proliferation. Porous Ti samples also stimulated faster OPC1 cell differentiation compared with polished Ti sheet, which could be due to the change in cell morphology within the pores of Ti samples. More extracellular matrix and a higher level of alkaline phosphatase expression were found on the porous samples than on the Ti sheet. This can be beneficial for faster integration of porous implant with host bone tissue. The results obtained also indicated that a critical pore size of 200 μm or higher is needed for cell ingrowth into the pores, below which OPC1 cells bridged the pore surface without any growth in the pores.

Fully dense, compositionally graded yttria-stabilized zirconia coatings have been developed using LENS™. Due to high thermal gradients and cooling rates in LENS™, a fine coating microstructure with a hardness in the range of 1700–2000 Hv is produced. The rapid heat loss through the substrate resulted in the directional growth of grains along the thickness direction. The inherent advantage of this approach is its ability to simultaneously control composition and micron level features to produce feature-based thermal barrier coatings.

Fabrication of bulk NiTi alloy parts by conventional processing contains undesirable intermetallic phases in varying proportions depending on the composition and requires postfabrication heat treatments, which necessitate development of new processing routes. We have fabricated net-shape samples, with and without designed porosity, from equiatomic NiTi alloy powders using laser engineered net shaping (LENS), a commercially available rapid prototyping technique. Laser-processed NiTi samples retained the desired phases of initial powder and showed higher hardness due to the retention of high-temperature cubic B2 phase. Thermally induced stresses and defects, due to high cooling rate in laser processing, increased the reverse transformation temperatures of laser-processed samples. LENS-processed samples also showed high compressive strengths (plastic flow stress) in the range of 890 to 1,050 MPa due to finer grain size. This article discusses the influence of laser parameters on microstructure, mechanical properties, and phase transformation behavior of fully dense NiTi parts produced via LENS.

Laser Engineered Net Shaping (LENS®) is a Direct Laser Deposition (DLD) additive manufacturing technology that can be used for directly building complex 3D components from metal powders in a combined deposition/laser-melting process. In this study, the effect of LENS process parameters, such as laser power, powder feed rate and traverse speed, on the resultant microstructure, hardness and tensile strength of Ti-6Al-4V components is experimentally investigated. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) are used to characterize the microstructure in terms of grain size and morphology. Relationships between process parameters and the microstructural/mechanical properties are provided. Results indicate that the scale of columnar grains increases with slower laser traverse speeds while other process parameters are maintained constant. The size of the α and β laths increases with higher laser powers and slower traverse speeds. The ultimate tensile and yield strengths of the LENS specimens were found to be higher than those of cast and wrought materials, and this can be generally attributed to the different cooling rates inherent to LENS — which impacts grain size. The percent elongation to failure, however, was consistently lower than that of the wrought material.Copyright © 2015 by ASME

During the past few years, metal based additive manufacturing technologies have evolved and may enable the direct fabrication of heterogeneous objects with full spatial material variations. A heterogeneous object has potentially many advantages and in many cases can realize appearance and/or functionality that homogeneous objects cannot achieve. In this work we employ a preprocess computing combined with a multi-objective optimization algorithm based on the modeling of the LENS deposition of multiple materials to optimize the fabrication process. The optimization methodology is applied to the fabrication of cermet composite (using Inconel 718 and ceramic powders) with prescribed material feeding rates. The multi-objective optimization considers that the energy consumption and the material waste during the fabrication process should be minimized, while the probability of the melting of the powders should be maximized. The optimization software modeFRONTIER® is used to drive the computation procedure with a MATLAB code. The results show the design and objective spaces of the Pareto optimal solutions, and enable the users to select preferred setting configurations from the set of optimal solutions.Copyright © 2015 by ASME

The impact of the surface convection generated by argon shielding gas used during Laser Engineered Net Shaping (LENS) on the deposited part is investigated. LENS generates complex thermal histories in the build that are dependent upon the material, part geometry, laser heat input, mass feed rate, and radiative as well as convective cooling. It has been shown that the deposition track and final part quality are subject to many of these considerations; however, no investigation has been undertaken to understand the impact of surface convection resulting from changing the argon shielding gas flow rate. A thermo-mechanical finite element analysis with measurement-based convection models is used to study the effects from different argon shielding flow rates on the temperature history, distortion, and residual stress of thin wall Ti-6Al-4V structures. The results from three cases show that reducing the shielding flow rate by half increases the temperature by 5% to 13%, while decreasing the deflection and residual stress.Copyright © 2015 by ASME

The isothermal oxidation of Fe-28Al-5Cr (at%) intermetallic alloy microalloyed with Zr and B (&lt, 0.08 at%) in air atmosphere, in the temperature range of 1000 to 1200 °C, was studied. The investigation was carried out on the thin-walled (&lt, 1 mm) elements prepared by Laser Engineered Net Shaping (LENS) from alloy powder of a given composition. Characterization of the specimens, after the oxidation, was conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM, with back-scatter detector (BSE) and energy-dispersive X-ray spectroscopy (EDS) attachments). The investigation has shown, that the oxidized samples were covered with a thin, homogeneous α-Al2O3 oxide layers. The intensity of their growth indicates that the material lost its resistance to oxidation at 1200 °C. Structural analysis of the thin-walled components’ has not shown intensification of the oxidation process at the joints of additive layers.