We aim to develop a capability for targeted specialty alloy microstructure design via metal 3D printing. Our approach to generate customised grain boundary networks in stainless steels and superalloys will unlock superior mechanical, corrosion and technological properties, without subsequent thermomechanical treatments. Scientific outcomes are new physical metallurgy knowledge on the targeted selection of desirable interfaces via recrystallisation and coupled segregation-precipitation phenomena. Technological outcomes are processing maps for printing parts with customised microstructures. This will diminish anisotropy, residual stress and defects, benefitting defence, aerospace and energy applications, all vital to the Australian economy.