178
T. Sano
Fig. 5.14 Results of fatigue tests for the base material (BM) and as-welded specimens (with and
without reinforcement) before and after DryLP treatment [55]
Fig. 5.15 TEM images of weld material (WM) microstructures in laser-welded specimens (with
reinforcement) a before and b after DryLP treatment
as the darker areas. The dislocation density was estimated using Keh’s equation,
ρ =
n 1
L 1 + n 2
L 2
t, where ρ is the dislocation density, n 1 and n 2 is the number
of intersection points between the dislocation lines and the vertical and horizontal
grid lines drawn on the TEM image, respectively, L 1 and L 2 is the total length of
the vertical and horizontal grid lines, respectively, and t is the thickness of the TEM
sample [112]. The dislocation densities of these samples before and after DryLP
treatment were estimated as 1.0 × 10
14 m
−2 and 5.1 × 10
14 m
−2 , respectively.
This indicates that DryLP plastically deformed the WM, resulting in hardening and
inducing compressive residual stress.