Deep Understanding of the Influence of the Process Parameters During Linear Friction Welding on the Joint Quality and th
- PDF / 3,415,210 Bytes
- 16 Pages / 593.972 x 792 pts Page_size
- 118 Downloads / 225 Views
TION
TI alloys are now largely used for structural applications in the aeronautic industry because of their advantageous performance-to-density ratio combined with fairly good thermal expansion and electro-chemical compatibility with carbon-fiber reinforced plastics (CFRPs). However, welding Ti alloys using common fusion techniques can be challenging since detrimental atmospheric pollution might occur if sufficient gas shielding is not used; solidification defects and/or pores can also be present. Indeed, oxygen can cause a change from good ductility at low oxygen concentration (0.07 wt pct) to total brittleness at 0.65 wt pct[1]; pores due to
DORICK BALLAT-DURAND, SALIMA BOUVIER, and MARION RISBET are with the Sorbonne Universite´s, Universite´ de Technologie de Compie`gne, Laboratoire Roberval de Me´canique, UMR-CNRS 7337, CS 60319 Rue Roger Couttolenc, 60203 Compiegne Cedex, France. Contact e-mail:[email protected] Manuscript submitted May 13, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
hydrogen and CO2 pollution were also identified within Ti joints obtained by electron beam welding.[2] Solidstate joining processes such as linear friction welding (LFW) are believed to prevent the Ti alloy assemblies from being subjected to these issues. Indeed, the literature review of friction welding suggested that Ti alloy LFW joints remained below the liquidus in the b domain, plus only for a very short time, thus avoiding the formation of typical fusion welding defects (i.e., excessive interstitial enrichment or retained pores).[3] In LFW, the heat induced by friction at the rubbing surfaces ultimately results in joining under an appropriate set of axial pressure and oscillating motion contingent upon the geometries and materials constituting the welded parts. LFW configurations are defined by a specific power input parameter and four characteristic process phases[4]:
Contact stage I: The two parts are brought into contact initially resting on surface asperities followed by an increase in the contact area due to asperity flattening.
Initial stage II: Large particles are expelled from the
interface, and the friction on the asperities leads to a local heating forming hot spots initiating material joining and axial shortening. Friction stage III: The heat and joining extend up to the entire contact interface leading to severe local shear stresses and consistent deformation heating; the joint is no longer able to handle the axial load leading to the material extrusion and consistent axial shortening. Forging stage IV: Once the axial shortening threshold is reached, the oscillation stops and the weld is consolidated by holding the axial pressure; fast cooling is ensured by heat diffusion within each welded part.
Previous work performed by the authors of this article already characterized the microstructures of mono-material LFW joints using Ti17 and Ti6242.[5,6] These studies showed that remarkable gradients of thermo-mechanical loads were present within the weld-enhancing phase transformations and recrys
Data Loading...
