Ti6242 alloy is a near-alpha titanium alloy with extensive applications in biomedical, automotive, and aviation industries. Compared to the more widely used Ti64 alloy, Ti6242 exhibits superior thermal resistance, making its processing via conventional methods challenging. Consequently, recent efforts have focused on additive manufacturing, particularly powder bed fusion (PBF), techniques for producing components from this alloy. PBF methods, which involve selective melting of a pre-prepared powder bed using laser or electron beams, are among the primary techniques for additive manufacturing of metal components. Achieving desirable properties in Ti6242 components produced through PBF for the aforementioned applications requires optimization of the manufacturing process and modification of the resultant microstructures through suitable post-processing techniques, such as heat treatment. Given the limited research on this topic, the present study investigates the effects of annealing heat treatment on the microstructure and properties of Ti6242 alloy produced via electron beam PBF. Examination of the fabricated samples revealed that the porosity levels were within the acceptable ranges for PBF processes. The as-built microstructure consisted of columnar primary β grains containing lamellar α+β phases with Widmanstätten and basketweave morphologies. Annealing heat treatment was performed at three temperatures, i.e. 950, 1005, and 1050 °C, for durations of 1, 3, 5, and 7 hours. The resulting microstructure, phase composition, and mechanical properties of the treated samples were subsequently eva‎luated and compared. The selected temperatures correspond to regions below, near, and above the α-to-β phase transformation temperature of the alloy, respectively. The results indicated that the microstructure at 950 °C was similar to that of the as-built sample but with coarser microstructural features. Prolonged heat treatment at this temperature further increased the size of these features. Heat treatment at 1005 °C and 1050 °C transformed the microstructure from columnar to equiaxed grains. Equiaxed β grains at these temperatures contained large α colonies. Williamson-Hall plots derived from X-ray diffraction patterns showed higher lattice microstrain in the heat-treated samples compared to the as-built condition. After heat treatment, fraction of the β phase increased at 950 and 1050 °C but decreased at 1005 °C. Hardness of the heat-treated samples ranged between 350 and 365 HV which was lower than that of the as-built sample, but comparable to those of conventionally fabricated samples (340–360HV). Ultimate shear strength of the samples decreased after heat treatment at 950 and 1050 °C, while their ductility improved. However, heat treatment at 1005 °C resulted in a significant reduction in both ultimate shear strength and ductility, attributed to excessive reduction in the β phase fraction.

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مسعود عطاپور , احمد رضائيان