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This paper studies the effects of different combinations of scanning strategies between layers on the surface quality, tensile properties, and microstructure of samples in a laser beam powder bed fusion (L-PBF) formation experiment of Ti-6Al-4V titanium alloy. The purpose of this experiment was to improve the comprehensive performance of the piece by selecting the optimal combination of scanning strategies. The results show that the surface roughness of the L-PBF specimen was the lowest under the combination of the CHESS scanning strategy, reaching 14 μm. The surface hardness of the samples was generally higher with the LINE scanning strategy and the angle offset of 90°, reaching 409 HV. The overall density of the samples was higher under the combination of CHESS scanning strategies, reaching 99.88%. Among them, the CHESS&45° sample had the best comprehensive properties, with a density of 99.85%, a tensile strength of up to 1125 MPa, a yield strength of 912 MPa, and an elongation of 8.2%. The fractured form was a ductile fracture, with many dimple structures. Compared with the CHESS scanning strategy, the tensile properties of the CHESS&45° samples were improved by 12.8%. The microstructure of the L-PBF sample was mainly composed of the primary β phase and α’ martensite phase. The upper surface of the CHESS scanning strategy combination sample had a clear melt channel, and the distribution of each phase was uniform. A certain number of columnar β crystals were distributed in the longitudinal section of the sample, which was paralleled to the build direction. The columnar β crystals of CHESS&45° were relatively coarse, which enhanced the tensile properties of the sample.

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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