A method of forming an article includes forming a layer of a mixture of at least two distinct metal powders selected such that when combined they are chemically in the proportions of a superalloy containing a gamma prime phase, and fusing the powders locally without diffusion to define the shape of a part of the article such that the materials of the distinct metal powders remain substantially chemically segregated forming regions of different chemical composition. The method further includes repeating the forming and fusing until the derived article is formed, and heat treating the finished article such that at least one of the distinct separate materials diffuses to form a gamma prime phase containing superalloy with the other.