Lakhasly

Microhardness measurements were conducted at room temperature conditions in two directions, along the axial direction and the interface, over+-4.5 mm. The measurements taken along the axial direction provide information about the material characteristics of the welded joint, while those taken at the interface illustrate the softening and hardening along that interface.This can be explained by the larger grain size structure in the peripheral region compared to the centerline [2].The regional speed and temperature at the peripheral region are higher than those at the central region [39].Therefore, the friction between the two surfaces at the interface through the FW process, under the efect of pressure, encourages bulky plastic deformation that leads to fne grain and is the frst reason for the microhardness amplifcation at the weld centerline.Figure 5a shows the microhardness profle for the axial direction, with elevation values related to AISI 316 at the weld centerline.

Microhardness measurements were conducted at room temperature conditions in two directions, along the axial direction
and the interface, over±4.5 mm. The measurements taken
along the axial direction provide information about the material characteristics of the welded joint, while those taken at
the interface illustrate the softening and hardening along that
interface. Figure 5a shows the microhardness profle for the
axial direction, with elevation values related to AISI 316 at
the weld centerline. The hardening region has a dimension
of 500 µm and an average value of 300 Hv0.1, although there
is non-symmetric distribution of microhardness attenuation
in the adjacent regions to the weld centerline, with average
values of 240 Hv0.1 in these softening regions.
It is evident that grain refnement increases the microhardness of the material. Therefore, the friction between the
two surfaces at the interface through the FW process, under
the efect of pressure, encourages bulky plastic deformation
that leads to fne grain and is the frst reason for the microhardness amplifcation at the weld centerline. The attenuation along the axial direction from the centerline toward the
base metal is due to the grain growth in the thermo-mechanically afected zone (TMAZ) and heat-afected zone (HAZ)
that were produced. While recrystallization may be very
limited in TMAZ, there is no recrystallization in HAZ [5].
Figure 5b illustrates the microhardness along the interface
with a homogeneous distribution of microhardness along the
interface. It is noteworthy that the maximum hardness value is
located nearby the weld interface [38], and there is a gradual
decrease in the hardness level when moving from the weld
centerline toward the peripheral. This can be explained by the
larger grain size structure in the peripheral region compared
to the centerline [2]. The increase in microhardness is due to
the high temperature and forge pressure in the weld zone. The
regional speed and temperature at the peripheral region are
higher than those at the central region [39].