Laser metal deposition (LMD) is of the directed energy deposition (DED) process which is widely used for producing large-scale, dense, and functional parts in the field of additive manufacturing (AM). This research work investigates the microstructure and mechanical properties of PH 13–8 Mo martensitic stainless-steel parts produced via LMD. The workshop trials were conducted using an LMD system collaborated with a robotic arm to deposit single-track thin walls and horizontal blocks. The microstructural characteristics of the additively manufactured parts were analyzed using an optical microscope. The mechanical properties were evaluated through hardness measurements and uniaxial tensile tests. The influence of energy density and powder deposition density on the characteristic geometry of straight walls was also investigated. The microstructural analysis showed that the microstructure consisted of columnar dendrites that grew epitaxially from the substrate, with primary austenite cells containing intercellular ferrite and martensite laths that were roughly parallel with the retained austenite. When the energy density increased from 43 to 86 J/mm 2 (a doubling of energy density), there was an increase in secondary dendritic arm spacing (SDAS) by approximately 250% in the first layer and approximately 90% in the top layer. The difference in SDAS change between the first and top layers can be attributed to the difference in cooling rates experienced by each layer during the additive manufacturing process. Increasing powder deposition density from 0.5 to 1 g/min results in a decrease in porosity from 3% to less than 1% and an increase in strength from 800 to over 1000 MPa. The hardness of the deposits was found to range from 300 to 400 HV. This variation in hardness can be attributed to differences in microstructure resulting from changes in cooling rates at different heights.

Porous structures have been used in many areas particularly in medical, transportation, space and defense applications. The building of porous structure is formed by the lattices which have many unusual and interesting features that make them candidates for innovative designs. Such designs include creating porosity variation in structures and the aim is to achieve exceptional mechanical and biological efficiencies in terms of strength, stiffness, energy absorption capacity, and stimulating tissue ingrowth. In this paper, a design approach for uniform and graded porous structures is proposed to be produced by additive manufacturing. Pores were radially graded inside to outside by changing the lattice strut thickness, and vice versa. The additively manufactured structures were characterized by laboratory tests in the scope of producibility, morphological, chemical, and mechanical performance via caliper, precision scales, uniaxial compression test, optical light, and scanning electron microscope. The findings confirm that the wide range of porosities (60- up to 80 %) were achieved by using different strut thickness. Besides, porous structures with a wide range of density ratio from 0.88 to 1.22 g/ cm3 were revealed by applying porosity variation strategies. The graded porous structures were evaluated based on their specific compressive strengths. The results have also shown that the density of struts, which increased radially inward to outward facilitated a 6% improvement. Deformation mechanism and failure behavior of the structures were strongly affected by the porosity variation strategy. The graded porous structures were found to exhibit distinct deformation behavior when compared to a uniform porous structure, where the energy absorption capacity is higher in graded porous structures compared to uniform structures.

Ti-6Al-4V is one of the most promising alloys for electron beam melting (EBM) of structural parts due to its outstanding properties and its extensive use in the aerospace, automotive, and energy industries. In this study, we report a detailed and systematic micromechanical characterization of additively manufactured Ti-6Al-4V parts produced via EBM. The specimens were characterized by microhardness, nanoindentation, micropillar compression, and microscratch measurements. The results show that the Ti-6Al-4V exhibits a strong indentation size effect and higher strain rate sensitivity compared to those obtained from macroscale measurements. The high scratch resistance and the high hardness of the alloy at small indentation depths suggest that the EBM-produced Ti-6Al-4V parts can provide good performance in service under sliding wear conditions.