SEM-picture of a crack surface in a weld, from linked article.
Laser welding and ultrasonics
Laser welding is a promising metal join technique especially for narrow and deep welds. One of the problems that engineers and welders face nowadays with high-alloy metals is hot-cracking of welds. This is usually the result of segregation occurring during the welding process. One of the methods that can minimize the segregation phenomenon is to subject the workpiece to ultrasonic vibrations. I would like to introduce you in an interesting article on the influence of ultrasound on the formation of pores and cracks during welding of nickel-based alloys using a laser beam.