Tensile Deformation and Fatigue Strength of DMLS Materials: Light Metals
Tensile Deformation and Fatigue Strength of DMLS Materials: Light Metals*
Todd M. Mower and Michael J. Long
M.I.T. Lincoln Laboratory
244 Wood Street
Lexington, MA 02420
(781) 981-3533 mower@ll.mit.edu
Mechanical behavior of aluminum and titanium alloys fabricated with Direct Metal Laser Sintering (DMLS) was compared to that of similar alloys produced with conventional methods (wrought and machined). The elastic moduli were measured in flexure, stress-strain characteristics were measured in tensile deformation, and fatigue strengths were measured in fully reversed bending. The effects of DMLS fabrication orientation and surface polishing upon mechanical behavior were studied. Both vertically and horizontally-grown DMLS AlSi10Mg materials demonstrated lower yield strength than conventional Al6061, while the strengths of DMLS Ti6Al4V were similar to that of conventional material. The fatigue strengths exhibited by DMLS AlSi10Mg materials were measured to be about 60% of the fatigue strength of Al6061. The fatigue behavior of DMLS Ti6Al4V proved to be drastically inferior to that of conventional material. These lower fatigue strengths appear to be a consequence of multiple fatigue cracks initiating at surface defects, internal voids and microcracks, and growing simultaneously during cyclic loading. Post-processing the DMLS Ti6Al4V with hot isostatic pressure elevated the fatigue strength to about 50% that of conventional material. Measurements of surface roughness with a laser profilometer, metallurgical examinations of the material microstructures, and fractography contribute to an understanding of the mechanical behavior of the DMLS materials.