Effects of copper insert layer on the properties of friction welded joints between TiAl and AISI 4140 structural steel

Friction welding characteristics between TiAl and AISI 4140 have been investigated in this study. In spite, many trials were applied to achieve the sound weld zone of direct bonding between TiAl and AISI 4140 without crack under various friction welding conditions, a micro and large crack occurred through the interface due to the brittle nature of reaction products and the martensite transformation resulted in volume expansion near the weld zone. The formation of crack resulted in a lower tensile strength of joints relative to those of other welding technique. Therefore, to prevent crack formation at the interface, pure copper was used as insert metal for stress relief buffer layer. In the view point of tensile strength, the highest tensile strength between TiAl and AISI 4140 was acquired by using pure copper as insert metal. Fracture occurred at the TiAl base metal under optimum friction welding condition.