**Influence of Ultrasound on Pore and Crack Formation in Laser Beam Welding of Nickel-Base Alloy Round Bars**

**Jan Grajczak 1,\*, Christian Nowroth 2, Sarah Nothdurft 1, Jörg Hermsdorf 1, Jens Twiefel 2, Jörg Wallaschek 2 and Stefan Kaierle 1**


Received: 31 August 2020; Accepted: 25 September 2020; Published: 29 September 2020

**Abstract:** Welding by laser beam is a method for creating deep and narrow welds with low influence on the surrounding material. Nevertheless, the microstructure and mechanical properties change, and highly alloyed materials are prone to segregation. A new promising approach for minimizing segregation and its e ffects like hot cracks is introducing ultrasonic excitation into the specimen. The following investigations are about the e ffects of di fferent ultrasonic amplitudes (2/4/6 μm) and di fferent positions of the weld pool in the resonant vibration distribution (antinode, centered, and node position) for bead on plate welds on 2.4856 nickel alloy round bars (30 mm diameter) with a laser beam power of 6 kW. The weld is evaluated by visual inspection and metallographic cross sections. The experiments reveal specific mechanisms of interaction between melt and di fferent positions regarding to the vibration shape, which influence weld shape, microstructure, segregation, cracks and pores. Welding with ultrasonic excitation in antinode position improves the welding results.

**Keywords:** ultrasound; laser beam welding; excitation methods; melt pool dynamics; nickel base alloy 2.4856
