Free-form laser consolidation for producing metallurgically sound and functional components

Functional metallic components can be built layer by layer from a computer-aided design model, by using an optical fiber coupled Nd:YAG laser beam along with the simultaneous delivery of desired metal/alloy powders through a nozzle into the molten pool. Building of shapes using various alloys, including 316 L stainless steel, Ni-base IN-625 superalloy, and M4 tool steel, have been investigated. The components built using the free-form laser consolidation are metallurgically sound, free of cracks and porosity. Surface finish on the order of 1-2 mu m (R-a) can be obtained on the consolidated samples. The microstructure of the laser-consolidated samples is similar to the rapidly solidified materials. Under certain conditions, directionally solidified microstructure can also be obtained. X-ray diffraction analysis reveals that laser-consolidated material maintains the same phase structure as the original powder. The tensile properties of the laser-consolidated IN-625 alloy and 316 L stainless steel are comparable to the respective wrought materials. The microhardness of the consolidated M4 tool steel reaches to approximately Hv 1000. The polarization testing results indicate that laser-consolidated IN-625 alloy and 316 L stainless steel show a similar corrosion resistance as the respective wrought material in 3.5% NaCl solution. (C) 2000 Laser institute of America. [S1042-346X(00)00504-0].