Effect of weld power and interfacial temperature on mechanical strength and microstructure of carbon steel 4130 fabricated by ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state 3D printing technology. Steels can be welded with UAM at reduced ultrasonic power, achieving half the shear strength of bulk material. A higher weld power is demonstrated by using a cobalt-based sonotrode coating, achieving shear strengths comparable to bulk 4130 material. In-situ temperature measurements and fracture surface analyses indicate that higher power input promotes metallurgical bonding through softening and increased plastic deformation. Carbides and ferrite are found at 1 mu m scale at key weld interfaces; no martensite is found due to an increase in critical transformation temperatures associated with high heating rates. (C) 2020 Society of Manufacturing Engineers (SME). Published by Elsevier Ltd. All rights reserved.