In this paper, five grading functional gradient lattice structures with a different density perpendicular to the loading direction were proposed, and the surface morphology, deformation behavior, and compression properties of the functional gradient lattice structures prepared by selective laser melting (SLM) with Ti-6Al-4V as the building material were investigated. The results show that the characteristics of the laser energy distribution of the SLM molding process make the spherical metal powder adhere to the surface of the lattice structure struts, resulting in the actual relative density of the lattice structure being higher than the designed theoretical relative density, but the maximum error does not exceed 3.33%. With the same relative density, all lattice structures with density gradients perpendicular to the loading direction have better mechanical properties than the uniform lattice structure, in particular, the elastic modulus of LF, the yield strength of LINEAR, and the first maximum compression strength of INDEX are 28.99%, 16.77%, and 14.46% higher than that of the UNIFORM. In addition, the energy absorption per unit volume of the INDEX and LINEAR is 38.38% and 48.29% higher, respectively, than that of the UNIFORM. Fracture morphology analysis shows that the fracture morphology of these lattice structures shows dimples and smooth planes, indicating that the lattice structure exhibits a mixed brittle and ductile failure mechanism under compressive loading. Finite element analysis results show that when the loading direction is perpendicular to the density gradient-forming direction, the higher density part of the lattice structure is the main bearing part, and the greater the density difference between the two ends of the lattice structure, the greater the elastic modulus.

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The tensile properties and microstructure of Ti6Al4V titanium (TC4) alloy specimens fabricated by SLM under five scanning strategies were studied. They are the bidirectional scanning with a 67° rotation (R-scan) strategy, bidirectional scanning along with x-axis (X-scan) strategy, bidirectional scanning along with y-axis (Y-scan) strategy, bidirectional scanning with a 90° rotation in each layer (XY-scan) strategy, and the filled scanning strategy with homocentric squares (H-scan) strategy. Through the tensile experiments of specimens fabricated by different scanning strategies, it is found that the fabricated specimens by the XY-scan strategy show the best tensile properties. Compared with the R-scan strategy, the maximum tensile strength of the specimens prepared by the XY-scan strategy increased by 17.3%, and the maximum tensile strength reached 919.55 MPa. The tensile experiment of the fabricated specimens by the angle offset XY-scan strategy shows that the tensile property is the best when the offset angle is 45°. Compared with the XY scanning strategy, the maximum tensile strength of the specimens prepared by the angle-shifted XY scanning strategy was increased by 46.1%, and the maximum tensile strength reached 1343.27 MPa. The fracture surfaces of the specimens are mainly composed of cleavage cracks and dimple cracks. The tensile properties are the worst when the fracture cracks are mainly cleavage cracks and the tensile properties are the best when the cracks are mainly dimple cracks. When the α′-phase direction of acicular martensite inside and outside the β-phase of columnar crystal is parallel to the tensile direction, the tensile properties of specimens are improved. When the secondary α′-phase direction is parallel to the tensile direction, the tensile property is further improved.

To optimize the microstructure and properties of TC4 specimens formed by selective laser melting (SLM), the test program of formed specimens by the variable parameter forming process (VPFP) was designed based on the quantitative parameter forming process (QPFP). The purpose of this study is to explore the influence of the VPFP on the surface morphology, tensile properties, and microstructure of the specimens. The test results show that the surface morphology and tensile properties of the specimens were better formed by the VPFP. The internal holes of the specimens formed by the VPFP were small in volume and occupied a relatively small proportion, and the density could reach 99.7%. When the laser power was 300 W–260 W and equally divided into six hierarchies, the tensile strength could reach 1185.214 MPa by VPFP, but the elongation had no obvious change. The number of secondary acicular martensite α’ phases was decreased in the microstructure of the specimens formed with VPFP. With the superposition of the hierarchy, the length of the primary acicular martensite α’ phase became shorter, the width became larger, and the width of the columnar crystal β phase became smaller. The VPFP is used to change the inherent method of forming specimens with the same parameters, which provides a new idea for SLM-forming structures; the test provides data and yields a theoretical research basis for forming the specimens process method.

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