10
S. K. Das et al.
with the AL–Mg alloys instead of the steel plate. Meran and Kovan [34] employed
X155CrMoV12-1 tool steel (cold worked) for welding copper and brass.
1.4.1.2 Tool Materials for Welding High-Temperature Alloys
PCBN Tool
Harder materials (alloys of steel, nickel and titanium) are always difficult to weld, and
selecting proper FSW tool for welding these materials is challenging. PCBN which
is only second in hardness to diamond is the preferred tool material for welding
these materials [52]. A PCBN tool is known to maintain its strength and hardness at
elevated temperature conditions. The wear rate of PCBN is low because of its thermal
and chemical stability which is superior to diamond [52]. It is particularly inert to
iron. Moreover, PCBN has low coefficient of friction (COF) which yields smooth
surface of the weld. However, PCBN tools are very costly due to the requirement of
high pressure and temperature during its manufacturing.
Tungsten Based Tool
Tungsten-based composites are one of the popular choices as the tool material for
FSW of steel. Pure tungsten has very poor toughness at room temperature, and its
wear rate is also high when welding materials, viz. steel and titanium-based alloys.
Thus, researchers have employed variety of tools based on tungsten, viz. W-La 2 O 3 ,
WC–Co, WC, W-Mo and W-Re for FSW of steel and hard material. These materials
possess most of the properties needed for welding of hard materials. The hardness
of WC is ~1650HV, and it has excellent toughness [52]. WC and WLa 2 O 3 have been
utilized as a tool material in most of the investigations for joining sheets of carbon
steel and stainless steel by FSW. W–Re (W-25 wt% Re) tool is the most popular
among W-based tool material. The addition of rhenium enhances the hot strength of
the material, which reduces the deformation of the pin during its insertion into the
workpiece. Re also improves the wear resistance of the material. This material has
less tendency of fracture because of lower ductile to brittle transition temperature
which is approximately 50 °C.
1.4.1.3 Miscellaneous Tool Materials
Superalloys based on cobalt (Co) or nickel (Ni) have been sometimes employed as
tool materials for FSW of steel. Si 3 N 4 is used as the tool material for welding because
it has properties, viz. higher hardness, low coefficient of thermal expansion and higher
thermal conductivity. However, the workpiece material may be contaminated with Si
and N upon using this tool. Thus, Si 3 N 4 tool is provided with a coating of TiC/TiN to
prevent this contamination. Lee et al. [29] successfully carried out FSW of titanium
S. K. Das et al.
with the AL–Mg alloys instead of the steel plate. Meran and Kovan [34] employed
X155CrMoV12-1 tool steel (cold worked) for welding copper and brass.
1.4.1.2 Tool Materials for Welding High-Temperature Alloys
PCBN Tool
Harder materials (alloys of steel, nickel and titanium) are always difficult to weld, and
selecting proper FSW tool for welding these materials is challenging. PCBN which
is only second in hardness to diamond is the preferred tool material for welding
these materials [52]. A PCBN tool is known to maintain its strength and hardness at
elevated temperature conditions. The wear rate of PCBN is low because of its thermal
and chemical stability which is superior to diamond [52]. It is particularly inert to
iron. Moreover, PCBN has low coefficient of friction (COF) which yields smooth
surface of the weld. However, PCBN tools are very costly due to the requirement of
high pressure and temperature during its manufacturing.
Tungsten Based Tool
Tungsten-based composites are one of the popular choices as the tool material for
FSW of steel. Pure tungsten has very poor toughness at room temperature, and its
wear rate is also high when welding materials, viz. steel and titanium-based alloys.
Thus, researchers have employed variety of tools based on tungsten, viz. W-La 2 O 3 ,
WC–Co, WC, W-Mo and W-Re for FSW of steel and hard material. These materials
possess most of the properties needed for welding of hard materials. The hardness
of WC is ~1650HV, and it has excellent toughness [52]. WC and WLa 2 O 3 have been
utilized as a tool material in most of the investigations for joining sheets of carbon
steel and stainless steel by FSW. W–Re (W-25 wt% Re) tool is the most popular
among W-based tool material. The addition of rhenium enhances the hot strength of
the material, which reduces the deformation of the pin during its insertion into the
workpiece. Re also improves the wear resistance of the material. This material has
less tendency of fracture because of lower ductile to brittle transition temperature
which is approximately 50 °C.
1.4.1.3 Miscellaneous Tool Materials
Superalloys based on cobalt (Co) or nickel (Ni) have been sometimes employed as
tool materials for FSW of steel. Si 3 N 4 is used as the tool material for welding because
it has properties, viz. higher hardness, low coefficient of thermal expansion and higher
thermal conductivity. However, the workpiece material may be contaminated with Si
and N upon using this tool. Thus, Si 3 N 4 tool is provided with a coating of TiC/TiN to
prevent this contamination. Lee et al. [29] successfully carried out FSW of titanium