SAM

Experimental and numerical analysis of the selective laser sintering (SLS) of PA12 and PEKK semi-crystalline polymers

ROUCHAUSSE, Yann — Thu, 01 Jan 2015 00:00:00 GMT

Experimental and numerical analysis of the selective laser sintering (SLS) of PA12 and PEKK semi-crystalline polymers ROUCHAUSSE, Yann; PEYRE, Patrice; DEFAUCHY, Denis; REGNIER, Gilles A dual experimental-numerical approach was carried out to estimate thermal cycles and resulting fusion depths obtained during the selective laser sintering (SLS) of two polymers: PA12 and PEKK. The validation of thermal cycles was obtained by considering fusion depths on single layers for different experimental conditions and temperature measurements with IR thermal camera. It was shown that a simple Beer-Lambert’s heat deposit equation incorporating an extinction coefficient determined experimentally, and an efficiency ratio including both laser absorption and diffusion in the powder bed were sufficient for determining accurately fusion depths, and heat cycles for the two polymers. This allowed determining optimum process conditions for manufacturing additive layers on a specifically-designed SLS set-up.

Direct keyhole laser welding of aluminum alloy AA5754 to titanium alloy Ti6Al4V

TOMASHCHUK, Iryna — Wed, 01 Jan 2014 00:00:00 GMT

Direct keyhole laser welding of aluminum alloy AA5754 to titanium alloy Ti6Al4V TOMASHCHUK, Iryna; SALLAMAND, Pierre; CICALA, E; PEYRE, Patrice; GREVEY, D The tensile strength of direct AA5754/Ti6Al4V joints performed by high speed Yb:YAG laser welding is found to be determined by morphology and phase content of dissimilar interface formed between contacting Al-rich and Ti-rich melted zones. Three types of contact interfaces were observed: (1) thin (<20 μm thick) interface composed mostly by TiAl and formed under 0.2 mm beam shift to Al side and linear energy of welding ≥37.5 kJ/m; (2) cracked interface (190–300 μm thick) composed by Al3Ti and other Al–Ti intermetallics and formed under beam shift at 0.2 mm to Ti side and linear energy ≥37.5 kJ/m; (3) malaxated interface composed of layers and isles of Ti3Al and TiAl forming in other tested conditions and favored by welding speed >10 m/min. Maximal linear tensile force (220 N/mm for 2 mm thick weld) can be attained when thin contact interface is formed. In this case, the fracture starts in intermetallics-rich zone but propagates mainly in Al-rich melted zone, when in other cases it occurs in brittle intermetallic layers.

Influence of a pulsed laser regime on surface finish induced by thedirect metal deposition process on a Ti64 alloy

GHARBI, Myriam — Wed, 01 Jan 2014 00:00:00 GMT

Influence of a pulsed laser regime on surface finish induced by thedirect metal deposition process on a Ti64 alloy GHARBI, Myriam; PEYRE, Patrice; GORNY, Cyril; MORVILLE, Simon; LE MASSON, Philippe; CARRON, Denis; FABBRO, Rémy; CARIN, Muriel tThe direct metal deposition (DMD) laser technique is a free-form metal deposition process, which allowsgenerating a prototype or small series of near net-shape structures. Despite numerous advantages, oneof the most critical issues of the technique is that produced pieces have a deleterious surface finish whichrequires post machining steps. Following recent investigations where the use of laser pulses instead of acontinuous regime was successful to obtain smoother DMD structures, this paper relates investigationson the influence of a pulsed laser regime on the surface finish induced by DMD on a widely used titaniumalloy (Ti64). Findings confirm that using high mean powers improves surface finish but also indicate aspecific effect of the laser operating mode: using a quasi-continuous pulsed mode instead of fully-cw laserheating is an efficient way for surface finish improvement. For similar average powers, the use of a pulsedmode with large duty cycles is clearly shown to provide smoothening effects. The formation of larger andstable melt pools having less pronounced lateral curvatures, and the reduction of thermal gradients andMarangoni flow in the external side of the fusion zone were assumed to be the main reasons for surfacefinish improvement. Additional results indicate that combining the benefits from a pulsed regime and auniform laser irradiation does not provide further reduction of surface roughness.

Finite element analysis of laser shock peening of 2050-T8 aluminum alloy

HFAIEDH, Neila — Thu, 01 Jan 2015 00:00:00 GMT

Finite element analysis of laser shock peening of 2050-T8 aluminum alloy HFAIEDH, Neila; PEYRE, Patrice; SONG, Hongbin; POPA, Ioana; JI, Vincent; VIGNAL, Vincent Laser shock processing is a recently developed surface treatment designed to improve the mechanical properties and fatigue performance of materials, by inducing a deep compressive residual stress field. The purpose of this work is to investigate the residual stress distribution induced by laser shock processing in a 2050-T8 aeronautical aluminium alloy with both X-ray diffraction measurements and 3D finite element simulation. The method of X-ray diffraction is extensively used to characterize the crystallographic texture and the residual stress crystalline materials at different scales (macroscopic, mesoscopic and microscopic). Shock loading and materials’ dynamic response are experimentally analysed using Doppler velocimetry in order to use adequate data for the simulation. Then systematic experience versus simulation comparisons are addressed, considering first a single impact loading, and in a second step the laser shock processing treatment of an extended area, with a specific focus on impact overlap. Experimental and numerical results indicate a residual stress anisotropy, and a better surface stress homogeneity with an increase of impact overlap. A correct agreement is globally shown between experimental and simulated residual stress values, even if simulations provide us with local stress values whereas X-ray diffraction determinations give averaged residual stresses.

Generation and characterization of T40/A5754 interfaces with lasers

PEYRE, Patrice — Wed, 01 Jan 2014 00:00:00 GMT

Generation and characterization of T40/A5754 interfaces with lasers PEYRE, Patrice; BERTHE, Laurent; POUZET, Sébastien; SALLAMAND, Pierre; TOMASHCHUK, Iryna; DAL, Morgan Laser-induced reactive wetting and brazing of T40 titanium with A5754 aluminum alloy with 1.5 mm thickness was carried out in lap-joint configuration, with or without the use of Al5Si filler wire. A 2.4 mm diameter laser spot was positioned on the aluminum side to provoke spreading and wetting of the lower titanium sheet, with relatively low scanning speeds (0.1 to 0.6 m/min). Process conditions did not play a very significant role on mechanical strengths, which were shown to reach 250-300 N/mm on a large range of laser power and scanning speeds. In all cases considered, the fracture during tensile testing occurred next to the TiAl3 interface, but in the aluminum fusion zone. In a second step, we have investigated the interfacial resistance with the LASAT bond strength tester, based upon the generation and propagation of laser-induced shock waves. This allowed us estimating a uniaxial bond strength of 0.68 GPa for the T40/A5754 interface under dynamic loading conditions.

Analysis of laser–melt pool–powder bed interaction during the selective laser melting of a stainless steel

GUNENTHIRAM, Valérie — Sun, 01 Jan 2017 00:00:00 GMT

Analysis of laser–melt pool–powder bed interaction during the selective laser melting of a stainless steel GUNENTHIRAM, Valérie; PEYRE, Patrice; COSTE, Frédéric; FABBRO, Rémy; DAL, Morgan; SCHNEIDER, Matthieu The laser powder bed fusion (LPBF) or powder-bed additive layer manufacturing process is now recognized as a high-potential manufacturing process for complex metallic parts. However, many technical issues are still to overcome for making LPBF a fully viable manufacturing process. This is the case of surface finish and the systematic occurrence of porosities, which require postmachining steps. Up till now, the porosity origin remains unclear but is expected to be related to the stability of the process. As a LPBF part is made by the accumulation of hundreds of meters of small weld beads, it also appears to be important to understand all the phenomena that occur during the laser-powder-melt pool (MP) interaction for each single track. For this reason, in the first part of our study, using an instrumented LPBF setup and a fast camera analysis (>10 000 image/s), single tracks were fabricated and analyzed in real time and postmortem. Spatters ejections and powder denudation phenomena were observed together with variations of melt pool dimensions and melt-pool instabilities. In turn, the physical origin of this powder denudation and the dynamics of the MP were investigated and discussed.

Aluminum to titanium laser welding-brazing in V-shaped grooveI

TOMASHCHUK, Iryna — Sun, 01 Jan 2017 00:00:00 GMT

Aluminum to titanium laser welding-brazing in V-shaped grooveI TOMASHCHUK, Iryna; SALLAMAND, Pierre; MÉASSON, A.; CICALA, E; DUBAND, M; PEYRE, Patrice Laser assisted joining of AA5754 aluminum alloy to T40 titanium with use of Al-Si filler wires was carried out. Continuous Yb:YAG laser beam was shaped into double spot tandem and defocalized to cover larger interaction zone in V shaped groove. Experimental design method was applied to study the influence of operational parameters on the tensile properties of the joints. Microstructure examination and fractography study were carried out to understand the relation between local phase content and fracture mode. Within defined window of operational parameters, statistically important factors that influenced the strength of T40 to AA5754 joints in V groove configuration were Si content in the filler metal and groove opening angle on T40 side. The best quality joint showed joint coefficient of 90% (or 200 MPa of apparent UTS). Tensile strength of the joints was found to be determined by the proportion between well-developed and under-developed reaction zones of T40/melted zone interface. The formation of 2–25 μm thick Si-rich interlayers composed by Ti5Si3 and τ2 proved to enhance the strength of brazed interface. The creation of very thin (<0.5 μm) Si-rich layers at the bottom of the groove was found not sufficient to establish mechanical continuity of the joint and thus should be avoided.

Simplified numerical model for the laser metal deposition additive manufacturing process

PEYRE, Patrice — Sun, 01 Jan 2017 00:00:00 GMT

Simplified numerical model for the laser metal deposition additive manufacturing process PEYRE, Patrice; POUZET, Sébastien; CASTELNAU, Olivier; DAL, Morgan The laser metal deposition (LMD) laser technique is a free-form metal deposition process, which allows generating near net-shape structures through the interaction of a powder stream and a laser beam. A simplified numerical model was carried out to predict layer heights together with temperature distributions induced by the (LMD) process on a titanium alloy, and a metal matrix composite. Compared with previously developed models, this simplified approach uses an arbitrary Lagrangian Eulerian free surface motion directly dependent on the powder mass feed rate Dm. Considering thin wall builds of Ti-6Al-4V titanium alloy, numerical results obtained with comsol 4.3 Multiphysics software were successfully compared with the experimental data such as geometrical properties of manufactured walls, fast camera molten pools measurements, and thermocouple temperature recordings in the substrate during the manufacturing of up to 10 LMD. Even if the model did not consider coupled hydraulic-thermal aspects, it provides a more realistic local geometrical description of additive layer manufacturing walls than simpler thermal models, with much shorter calculation times than more sophisticated approaches considering thermocapillary fluid flow. In a second step, microstructures (equiaxed or columnar) were predicted on Ti-6Al-4V walls using microstructural map available in the literature, and local thermal gradients G (K/m) and solidification rate R (m/s) provided by the FE calculation near the solidification front. © 2017 Laser Institute of America.

Laser offset welding of AZ31B magnesium alloy to 316 stainless steelG

CASALINO, Giuseppe — Sun, 01 Jan 2017 00:00:00 GMT

Laser offset welding of AZ31B magnesium alloy to 316 stainless steelG CASALINO, Giuseppe; GUGLIELMI, P; LORUSSO, V.D.; MORTELLO, Michelangelo; SORGENTE, D; PEYRE, Patrice In this paper, the feasibility of using a fiber laser to perform a dissimilar metal joining was explored. AZ31B magnesium and 316 stainless steel were autogenously joined in butt configuration. The weldability between different materials is often compromised by a large difference in thermal properties and poor metallurgical compatibility. Thus, the beam was focused onto the top surface of the magnesium plate, at a certain distance from the interfaces (offset), and without using any interlayer or groove preparation. Such a method was called laser offset welding (LOW). Results proved a very good capability. The ultimate tensile strength exceeded the value of 100 MPa, since a resistant and thin layer of hard intermetallic compounds is formed within the fusion zone. The rupture was observed within the magnesium side, far from the centerline. The metallurgy of fusion zone indicated the effectiveness of phases coalescence, without mixing at liquid states. LOW was demonstrated to be a promising technique to join dissimilar metal welds, being capable to produce an effective bonding with good tensile strength.

Multiphysics Simulation and Experimental Investigation of Aluminum Wettability on a Titanium Substrate for Laser Welding-Brazing Process

PEYRE, Patrice — Sun, 01 Jan 2017 00:00:00 GMT

Multiphysics Simulation and Experimental Investigation of Aluminum Wettability on a Titanium Substrate for Laser Welding-Brazing Process PEYRE, Patrice; DAL, Morgan The control of metal wettability is a key-factor in the field of brazing or welding-brazing. The present paper deals with the numerical simulation of the whole phenomena occurring during the assembly of dissimilar alloys. The study is realized in the frame of potential applications for the aircraft industry, considering the case of the welding-brazing of aluminum Al5754 and quasi-pure titanium Ti40. The assembly configuration, presented here, is a simplification of the real experiment. We have reduced the three-dimensional overlap configuration to a bi-dimensional case. In the present case, an aluminum cylinder is fused onto a titanium substrate. The main physical phenomena which are considered here are: the heat transfers, the fluid flows with free boundaries and the mass transfer in terms of chemical species diffusion. The numerical problem is implemented with the commercial software Comsol Multiphysics™, by coupling heat equation, Navier-Stokes and continuity equations and the free boundary motion. The latter is treated with the Arbitrary Lagrangian Eulerian method, with a particular focus on the contact angle implementation. The comparison between numerical and experimental results shows a very satisfactory agreement in terms of droplet shape, thermal field and intermetallic layer thickness. The model validates our numerical approach.