Nowadays, there is a great manufacturing trend in producing higher quality net-shape components of challenging geometries. One of the major challenges faced by additive manufacturing (AM) is the residual stresses generated during AM part fabrication often leading to unacceptable distortions and degradation of mechanical properties. Therefore, gaining insight into residual strain/stress distribution is essential for ensuring acceptable quality and performance of high-tech AM parts. This research is aimed at comparing microstructure and residual stress built-up in Ti-6Al-4V AM components produced by Wire + Arc Additive Manufacturing (WAAM) and by laser cladding process (CLAD). 2 Introduction Additive manufacturing, often called 3D printing is nowadays among the most studied processes. AM is a key technique of a great potential in reducing high cost of producing conventional components made from relatively expensive materials such as titanium alloys. The worldwide Ti component production is constrained due to the high cost of Ti in comparison to other materials. Therefore, AM techniques aiming towards zero waste manufacturing are identified as potential prosperous routes in broadening Ti parts fabrication that are usually affected by often difficult and extensive machining. Ti is very broadly used in space, aerospace, nuclear, marine and chemical industries by virtue of its desirable properties such as high specific strength combined with excellent corrosion and oxidation resistance [1]. Although Ti is a very cherished material, its use in AM processes is also relatively challenging because of its low thermal conductivity which results in drawbacks such as uneven temperature field and poor interlamination integration [2]. Avoiding extensive machining by a near netshape successive layers fabrication can reduce the Ti parts production cost significantly. The buy-tofly ratio for a part machined from forged billet is typically 10-20 [3] and can potentially drop to nearly 1 when produced by AM techniques. There are numerous AM techniques that are capable of producing complex geometries close to their net-shape. Simply, AM techniques can be classified according to feeding technique, heat source or feedstock material. Powder bed, blown power and wire feed are the main AM techniques using heat sources such as electron beam, laser or electric arc, while the most common feedstock materials are powder or wire. Despite the similarity of AM

This paper presents the results of functionally graded Ti6Al4V-Mo alloy manufactured with directed energy deposition called CLAD ® (Construction Laser Additive Direct) process. Single track width sample with five gradients of composition, from 0 to 100 wt.% Mo, was manufactured using a coaxial nozzle. Both Ti6Al4V and Mo ratios were modified with a 25 wt.% increase or decrease in the chemical composition of each gradient. A two-powder feeder was used to input the correct ratio of each powder, so as to obtain the desired chemical composition. XRD analysis allowed to define the phases present in each deposition, as well as the lattice parameter. SEM observations showed microstructural evolution from 25 wt% Mo on, namely where the ␤-phase becomes dominant. Moreover, dendrites appear from 50 wt.% Mo on. Microhardness analysis revealed variation along the deposition depending on the chemical composition. The homogeneity of the powder mixture under laser beam was highlighted thanks to tomography on the manufactured samples, which validates the processability of functionally graded material (FGM) by CLAD ® process.

The aim of this paper is twofold: firstly, to compare the microstructural and the mechanical properties of Ti-44Nb samples manufactured pre-alloyed powder and differential injection, and secondly, to demonstrate the feasibility of the differential injection method included in the DED-CLAD ® process, to manufacture functionally graded Ti-Nb alloys. Functionally graded materials (FGM) are promising new materials which are perfectly adapted to custom-made parts with various properties for specific applications. In FGMs, titanium and niobium ratios were modified in different steps to create the variation in alloy composition owing to a double-powder feeder. Mechanical analysis and SEM observations show the variation along the deposition depending on the chemical composition. Chemical analysis revealed the homogeneous repartition of the powder mixture as well as the nominal composition of each deposition. Mechanical tests showed a decrease of the microhardness with the increase of Nb content. The elastic modulus was found to be the lowest for Ti-40Nb.

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Directed Energy Deposition (DED) Additive Manufacturing process for metallic parts are becoming increasingly popular and widely accepted due to their potential of fabricating parts of large dimensions. The complex thermal cycles obtained due to the process physics results in accumulation of residual stress and distortion. However, to accurately model metal deposition heat transfer for large parts, numerical model leads to impractical computation time. In this work, a 3D transient finite element model with Quiet/Active element activation is developed for modeling metal deposition heat transfer analysis of DED process. To accurately model moving heat source, Goldak’s double ellipsoid model is implemented with small enough simulation time increment such that laser moves a distance of its radius over the course of each increment. Considering thin build-wall of Stainless Steel 316L fabricated with different process parameters, numerical results obtained with COMSOL 5.6 Multi-Physics software are successfully validated with experiment temperature data recorded at the substrate during the fabrication of 20 layers. To reduce the computation time, elongated ellipsoid heat input model that averages the heat source over its entire path is implemented. It has been found that by taking such large time increments, numerical model gives inaccurate results. Therefore, the track is divided into several sub-tracks, each of which is applied in one simulation increment. In this work, an investigation is done to find out the correct simulation time increment or sub-track size that leads to reduction in computation time (5–10 times) but still yields sufficiently accurate results (below 10% of relative error on temperature). Also, a Correction factor is introduced that further reduces computation error of elongated heat source. Finally, a new correlation is also established in finding out the correct time increment size and correction factor value to reduce the computation time yielding accurate results.