Papers by Keyword: Laser Deposition

Abstract: Titanium and its alloys are commonly used for biomedical implants and therefore should have good biocompatibility, suitable levels of strength, fracture toughness, fatigue resistance, and low elastic modulus. Alloying Ti with β-stabilizing elements (Ta, Mo, Nb and V) allows obtaining alloys with elastic modulus closer to that of bone (10-30 GPa), thus minimizing the tendency for stress shielding and bone resorption. A combinatorial method, based on variable composition laser-assisted deposition, has been used for synthesizing Ti-Ta alloys. The alloys were characterized in composition and microstructure by XRD, SEM, and EDS, and mechanical properties were assessed using depth-sensing ultramicroindentation tests. As the Ta content increases from 3 wt% to 36 wt%, the elastic modulus of the alloys decreases from 120 GPa to about 45 Gpa, corresponding to a region formed of the predominant α” (orthorhombic) phase. The lowest value of elastic modulus (45 GPa) was obtained for the Ti-36Ta (wt%) alloy, which is considerably lower than those of commercial Ti alloys currently used (above 110 GPa). Based on these results, volumetric samples of Ti-40Ta alloy were produced by laser deposition, presenting the predominance of the α” (orthorhombic) phase, elastic modulus as (80±12) GPa, and nanohardness as (4.2±0.6) GPa with H_it/E_it equal to 0.052±0.015, which reinforces the viability of using this composition with potential application as a biomaterial.

Abstract: Titanium and its alloys could have good biocompatibility, suitable levels of strength, fracture toughness, fatigue resistance and low elastic modulus, which are requirements for metallic materials used as biomaterials. Implants of commercially available Ti alloys show excessive levels of stiffness that cause stress shielding and often lead to bone resorption and failure. For better biomechanical performance, it is necessary to redesign biomaterials with lower elastic modulus. Alloying Ti with β-stabilizing elements (Ta, Mo, Nb) allows obtaining alloys with Young´s modulus closer to that of bone (10-30 GPa), minimizing the tendency for stress shielding and bone resorption. A combinatorial method, based on variable composition laser deposition, has been used for synthesizing alloys with a gradient of composition along a single clad track and scanning for the most interesting compositions. This study reports results on laser synthesis of alloys in the Ti-5Mo-xNb system, in search for compositions with microstructure and properties optimized for use as biomaterials. The alloys were then characterized in composition and microstructure by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The mechanical properties were assessed using depth-sensing ultramicroindentation tests. Their microstructures consist of the orthorhombic α’ phase with martensitic morphology, and untransformed β. The alloys indentation hardness increased with the Nb content from 2.79 ± 0.02 GPa to 3.7 ± 0.8 GPa, due to solid solution strengthening. The same trend was observed in the elastic moduli that increased from 38.8 ± 8.1 GPa to 76 ± 13 GPa, and in addition the H/E ratio was greater than 0.04 for all samples which indicates good wear resistance. Despite being dual phase (α’+β) all compositions present elastic modulus that are considerably lower than those of commercial Ti alloys currently used (above 100 GPa).

Abstract: The work is devoted to the development of the technology for the formation of the required microrelief of the optical surfaces of glass-ceramic substrates. The solution of the problem using a controlled local deposition of silicon dioxide on the polished surface by laser pyrolysis of tetraethoxysilane vapor in the presence of ozone is shown. The characteristics of the experimental samples, their comparison with the data of mathematical modeling of the results of technological processes are presented. The possibility of using the developed technology for the production of substrates of optical parts with a defined wedge-shaped value is shown.

Abstract: Additive technologies, in particular, wire-feed laser deposition, can significantly reduce the production cycle of manufacturing large-sized parts or parts of complex shape due to partial or complete elimination of technological operations such as casting, machining and welding. The aim of the work is to develop an analytical model of heating and melting of the filler wire during wire-feed laser deposition. The heat conduction problem was solved by the functional-analytical methods. The practical effectiveness of the functional-analytical methods with respect to computational time is several orders of magnitude higher than numerical ones. Obtained analytical solution made it possible to determine the temperature field for heat flux arbitrarily distributed on the filler wire surface. It is established that at a higher feed rate, the wire tip is completely melted at a greater distance from the laser axis. The shape of the melting surface also depends on the feed rate. At a slow feed rate, a more uniform heating of the wire over the cross section occurs. The melting surface has a small angle of inclination.

Abstract: Laser deposition is an advanced manufacturing technology capable of enhancing service life of engineering components by hard-facing their functional surfaces. There are quite a number of parameters involved in the process and also desirable output characteristics. These output characteristics are often independently optimised and which may lead to poor outcome for other characteristics, hence the need for multi-objective optimisation of all the output characteristics. In this study, a laser deposition of Ti-6Al-4V wire and tungsten carbide powder was made on a Ti-6Al-4V substrate with a view to achieve a metallurgical bonded metal matrix composite on the substrate. Single clads were deposited with a desire to optimise the composite clad characteristics (height, width and reinforcement fraction) for the purpose of surface coating. Processing parameters (laser power, traverse speed, wire feed rate, powder feed rate) were varied, the experiment was planned using Taguchi method and output characteristics were analysed using principal component analysis approach. The results indicated that the parameters required for optimised clad height, width, and reinforcement fraction necessary for surface coating is laser power of 1800 W, traverse speed of 200 mm/min, wire feed rate 700 mm/min and powder feed rate of 30 g/min. The powder feed rate was found to most significantly contribute 43.99%, followed by traverse speed 39.77%, laser power 15.87% with wire feed rate having the least contribution towards the multi-objective optimisation. Confirmation results showed that clad width and reinforcement fraction were significantly improved by the optimised parameters. The multi-objective optimisation procedure is a useful tool necessary to identify the process factors required to enhance output characteristics in laser processing.

Abstract: The paper presents the results of an investigation of additive technology of direct growth from aluminum wire using various thermal sources-a laser and a combined laser arc. In the course of the work, the parameters of the regimes are selected, which ensure an even-dimensional formation of a thin wall during successive layering. The results are presented on the measurement of microhardness and chemical analysis.

Abstract: In this paper, the microstructural evolution of the composite formed by fibre laser deposition of Ti-6Al-4V wire and WC-W₂C powder was investigated and reported. Nine single tracks were deposited using combinations of four laser processing parameters (laser power, traverse speed, wire feed rate and powder feed rate) with each having three levels based on Taguchi design of experiments. The samples of the deposited composites were subjected to microstructural examinations using scanning electron microscopy with energy dispersive spectroscopy and X-ray Diffractometry, and microhardness tests. The resultant microstructure is characterised by uniform distribution of the reinforcement particles (WC-W₂C) and dispersion of in-situ synthesised TiC and W solid solution precipitates in a β-stabilised Ti matrix. The TiC precipitates have blocky and fine eutectic morphologies, while the W solid solution precipitates have blocky and leaf-like equiaxed morphologies. The retained W composition in the β-Ti was found to range from 7.5-9 at%, and it helped to β-stabilise the matrix which was considered beneficial for the composite matrix to retain its ductility. Increasing laser power was found to decrease the amount of W retained in the Ti matrix which resulted in a lower cooling rate, favourable for the nucleation of W solid solution. The uniform dispersion of the TiC and W solid solutions in the β-Ti matrix phase has significantly enhanced its hardness which ranged from 455-543 HV_0.3. It is anticipated that the composite formed will possess excellent wear resistance and contact deformation characteristics.

Abstract: This paper presents some experimental research followed by setting industrial criteria for evaluation of titanium screw dental implants coated with layers of carbon doped with silver and silicon. Coating was done by three laser deposition methods. The coatings were studied related to the laser deposition method, friction coefficient and adherence to titanium substrate. As well, a DEFORM 2D™ simulation of screw dental implant fixture is presented. Research was done in the framework of CarLa M-ERA.NET project. Only research done by Romanian partners is presented.

Abstract: RETRACTED PAPER: High entropy alloys have attracted great interest due to their flexibility in composition accompanied with very interesting properties, which make these materials candidates for further research. The formation of single solid solution phases as a preference to complex mixtures of intermetallic phases leads to good mechanical and thermal properties. Additive manufacturing in the form of Laser deposition presents us with a very unique way to manufacture near net shape metallic components with advanced materials. The present study focusses on the characterization of High entropy alloys manufactured through laser deposition. The alloy system considered for this study is (AlFeCoCrNi). The ratio of aluminum to nickel was decreased to observe the transition of the solid solution from a BCC structure to a FCC structure. The lattice parameter increased from .288 nm to .357 nm and the hardness decreased from Hv 670 to Hv 149 respectively. The effect of composition on thermodynamic variables, microstructure and mechanical properties were analyzed.

Abstract: Additive Manufacturing using laser deposition has a great deal of attractiveness as a fabrication technique for metals and alloys. The combination of a high heat input, small molten volume, and incremental addition also is well suited for the production of high performance alloys and composites. The high cooling rates inherent in the process produces refined microstructures, leading to excellent as-deposited mechanical properties in conventional alloys. The high heating rates and cooling rates potentially lends itself to structurally amorphous alloys, functionally gradient materials, and nanostructured materials, among other more exotic metallic materials. By monitoring the process a map of the quality of the build can be recorded for quality assurance and validation. Flaws detected during fabrication can then be repaired in-situ. Realizing this potential will require a combination of modeling, experimental validation, and new design paradigms. Together this will lead to the greatest properties and functionalities in future products.