Deep Understanding of the Influence of the Process Parameters During Linear Friction Welding on the Joint Quality and the Microstructural Changes of Two Mono-Material Titanium Alloy Joints: The β-Metastable Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) and the Near-α Ti-6Al-2Sn-4Zr-2Mo (Ti6242)

Linear friction welding (LFW) of near-α Ti-6Al-2Sn-4Zr-2Mo (Ti6242) and β-metastable Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) was studied through eight sets of process parameters. Varying the main LFW process parameters revealed that: (1) increasing the ratio between the normal pressure and local flow stress shortens the duration of friction phase (III); this ratio is influenced by the normal pressure and/or heat generated by the longitudinal deformation conditions, the latter being driven by the oscillation parameters (amplitude and frequency); (2) the joint and PAZ extents can be drastically lowered by favoring the extrusion of the heated material through higher normal pressures; (3) the presence of defects is mostly due to contaminant layers initially present on the contact surfaces; these defects can be dissipated into the bulk with the help of an enhanced recrystallization and/or material blending; (4) the two-component {110}〈111〉 β texture intensity is mostly influenced by the amplitude and degree of recrystallization. Subjecting three significantly different Ti17 joints to β-annealing resulted in similar homogenized microstructures and defect dissolution. The different material responses of Ti17 and Ti6242 to LFW showed the necessity of defining optimized sets of process parameters depending on the welded materials and initial microstructures.