Effect of trace boron addition on microstructures, textures, mechanical properties and fracture behaviors of near α titanium alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 772; p. 138749
• Main Authors: Ma, X.Z., Xiang, Z.L., Ma, M.Z., Tan, C., Yang, Z.A., Shen, G.L., Chen, Z.Y., Shu, Q.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 20.01.2020; Elsevier BV
• Subjects: B-containing alloy; Boron; Cleavage; Dimpling; Ductile fracture; Dynamic recrystallization; Forging; Fracture behaviors; Grains; High temperature; Mechanical properties; Room temperature; Skull melting; Texture; Textures; TiB whiskers; Titanium alloys; Titanium base alloys; Voids; Whiskers (metals); B-containing alloy; Mechanical properties; TiB whiskers; Fracture behaviors; Textures
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2019.138749

B-free and B-containing near α titanium alloys were fabricated by induction skull melting method. Microstructures, textures, mechanical properties and fracture behaviors were investigated. Observations of as-casted microstructures revealed that prior β grains and α colonies were obviously refined after adding trace boron element, and widmannstatten structure of B-free alloy transformed to basket-weave structure of B-containing alloy. For as-forged alloys, prior β grains were broken and squashed, and they stretched along direction perpendicular to forging direction. TiB whiskers promoted dynamic recrystallization behavior, which led to the precipitation of more equiaxed α grains around them. Texture intensity of overall α phase obviously decreased after the addition of trace boron element, which manifested that TiB whiskers prohibited texture formation and improved microstructure homogeneity. B-containing alloy exhibited excellent combination of room temperature (RT) and high temperature (650 °C) mechanical properties. Fracture characteristics of B-free and B-containing alloys were dominant by abundant dimples and cleavage fracture of α lamellas during RT tensile processes. At 650 °C, the cleavage fracture of α lamellas was replaced by dimples, illustrating ductile fracture characteristics. Longitudinal and transverse fracture of TiB whiskers existed no matter at RT or at 650 °C for B-containing alloy. By observations of lateral surfaces, cracks and voids were easier to generate at boundaries between grains and colonies with large size for B-free alloy. For B-containing alloy, comparing with macro-zones in matrix, voids were inclined to generate around interfaces of TiB whiskers and matrix due to strain mismatch. It illustrated TiB whiskers accelerated the fracture of alloy. Voids, transverse fracture of TiB whiskers and lateral abhesion of TiB whiskers were detected at RT, while lateral abhesion of TiB whiskers was seldom discovered during 650 °C tensile process. •Prior β grains and α colonies are obviously refined after boron addition.•TiB phase promotes dynamic recrystallization behavior.•TiB whiskers prohibit the formation of texture and improve the homogeneity of microstructure during forging process.•B-containing alloy exhibits excellent combination of RT and 650 °C tensile mechanical properties.•Strain mismatch between TiB whiskers and matrix is more easier to cause the formation of voids comparing with macro-zones in matrix.