PSI - Issue 69

C.A. Biffi et al. / Procedia Structural Integrity 69 (2025) 47– 52

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As customary in laser welding, both penetration depth and bead width decrease steadily by increasing scanning speed, as the energy density delivered onto the surface of the workpiece decreases proportionally. It appears that beam shaping has no influence on the bead width, while it appears to affect to some extent the penetration depth. In particular, when a high scanning speed is employed, the use of a non-gaussian power distribution gave rise to shallower beads.

Fig. 4. Evolution of welded bead width (W) and penetration (D) as function of the applied scanning speed and beam shaping. Finally, differential scanning calorimetry was employed to verify how laser beam welding had any effect on the functional performances of the addressed NiTiHf alloy. Figure 5 demonstrates that nor transformation temperatures nor the related enthalpies differ between cast and welded samples. This is likely related to the fact that no selective vaporisation of alloying elements took place during the welding process.

Fig. 5. DSC scans of the laser beam welded and as-cast NiTiHf alloy

4. Conclusions The present work explored for the first time the use of beam shaping during laser beam welding of a NiTiHf high temperature, shape-memory alloy. The alloy displays satisfactory weldability if the correct set of processing parameters are selected: in particular, high welding speeds should be avoided in order not to incur into extensive cracking. Beam shaping is useful in avoiding excessive energy concentration, which may lead to the formation of gas porosities: in this respect, the use of a quasi-uniform laser power distribution may help in obtaining smoother welded beads.