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| The microstructure and high cycle fatigue property of selective laser melting TA15 titanium alloy |
| CAI Xiaoye，BAI Bing，HU Jiaqi，DONG Dingping，CI Shiwei |
| （State-owned Wuhu Mechinery Factory, Wuhu 241007, China） |
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Abstract Based on the test and analysis of static mechanical properties of TA15 titanium alloy samples formed
by selective laser melting, the fatigue properties of TA15 titanium alloy samples formed by selective laser melting
at room temperature were studied and analyzed. Tensile properties, impact properties and fatigue properties of
TA15 titanium alloy samples at room temperature were tested by universal testing machine, impact testing machine
and fatigue testing machine. Optical microscopy (OM) and scanning electron microscopy (SEM) were used
to analyze the microstructures of the cross-sectional and longitudinal sections, as well as the tensile and fatigue
fractures of the samples. The research shows that the cross section presents a typical checkerboard lattice structure,
and the longitudinal section distributes β columnar crystals penetrate through multiple deposition layers and
grow epitaxially, and acicular martensite is staggered inside the columnar grains. The tensile strength of the transverse
and longitudinal samples after annealing treatment, the strength and yield strength are lower than that of the
as-deposited samples, and the elongation, shrinkage and impact strength are significantly improved, and they are
all better than the TA15 bar index. The fatigue life data has a certain dispersion, which is the main reason for the
fatigue dispersion. It is a selective laser melting and forming process. The metal powder is rapidly melted and
cooled under the action of a high-energy laser, and defects such as poor overlap, pores, and unmelted powder appear
randomly inside the part. The depositional cross section of TA15 titanium alloy formed by selective laser
melting presents a typical checkerboard lattice structure. The longitudinal section is distributed with β columnar
crystals growing epitaxial through several sedimentary layers. The columnar crystals are interleaved with acicular martensite. The ratio of length to width of primary and secondary α phases in annealed microstructure decreases
continuously, and the spicules are coarsened continuously to form strip. After being held at 850 ℃ for 2 h, the
tensile strength and yield strength of the transverse and longitudinal samples of TA15 titanium alloy decrease,
while the elongation, shrinkage and impact strength of the samples are significantly increased, which are better
than those of TA15 sheet. Fatigue life data of annealed TA15 titanium alloy in selective laser melting forming
(stress ratio R=0.06, Kt=2.5) have a certain dispersion. The main reason for the fatigue dispersion is the rapid
melting and cooling of metal powder under the action of high energy laser. Defects such as poor lap joint, air
hole and unmelted powder appear randomly in the parts.
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Received: 20 July 2022
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2023, Vol. 33 
