A method for manufacturing a metallic article includes providing or obtaining a metallic material in powder form, using an additive manufacturing process, building the metallic article from the powder-form metallic material, layer-by-layer, in a build direction, wherein as a result of the additive manufacturing process, the metallic article comprises columnar grain structures oriented in the build direction, and conveying the metallic article through a gradient furnace in a direction of conveyance from a first area of the gradient furnace to a second area of the gradient furnace to increase a size of the columnar grain structures in the metallic article. The metallic article is conveyed through the gradient furnace in an orientation such that the columnar structures oriented in the build direction are substantially parallel to the direction of conveyance.