NIMS and Osaka University researchers succeeded in fabricating a nickel single crystal with only a very few crystalline defects, irradiating nickel powder with a large-radius, flat-top laser beam. The technique may be useful in fabricating single-crystalline materials such as heat-resistant materials for jet engines and gas turbines.
Previously, this technique required expensive equipment and the need for a vacuum; both limited its widespread use. When a raw metal powder material is irradiated with a laser beam, it melts, forming a solid-liquid interface. Growing grains near the interface in the same direction was challenging, as was preventing the formation of strain-inducing defects caused by their solidification.
The research team succeeded in fabricating single crystals using a flat-top laser beam, forming a flat melt pool surface on the nickel powders. Individual crystalline grains grew in the same direction with fewer strain-inducing defects. Single crystals without grain boundaries that are susceptible to cracking are very strong at high temperatures. This new technique minimizes strain generation and cracking of crystals during their solidification and does not require seed crystals, simplifying additive manufacturing processes.
Because single crystals are more robust than polycrystals at high temperatures, their practical use as heat-resistant materials is promising. Global R&D efforts to achieve this using cheaper and widely used laser additive manufacturing technology are expected to intensify rapidly. This research was published in Additive Manufacturing Letters, an open-access journal.