Microstructural evolution of precipitation-hardened beta-type titanium alloy through high-pressure torsion

作者：Yilmazer H^*; Niinomi M; Cho K; Nakai M; Hieda J; Sato S; Todaka Y

来源：Acta Materialia, 2014, 80: 172-182.

DOI：10.1016/j.actamat.2014.07.041

• Titanium alloys
• Precipitation
• Nanostructured materials
• Dislocation structure
• High-pressure torsion

In order to elucidate the microstructural refinement mechanism and the effect of secondary phase on the microstructural evolution of beta-type titanium alloy, severe plastic deformation was conducted on samples of a precipitation-hardened Ti-29Nb-13Ta-4.6Zr (TNTZ). Specifically, TNTZ that was precipitation-hardened through an aging treatment (TNTZAT) was subjected to high-pressure torsion (HPT) processing (TNTZ(AHPT)). The microstructure of TNTZ(AHPT), which has been evaluated as a function of the torsional rotation number, N, exhibits ultrafine elongated beta grains. The needle-like alpha precipitates in TNTZ(AT), which exhibit a diameter of approximately 12 nm, are homogeneously distributed within the beta grains. The dislocation density and subgrain diameter, estimated by X-ray line profile analysis, saturate at approximately 4.2 x 10(16) m(-2) and 12.2 nm, respectively, at N %26gt;= 10. The beta grains contain nanostructured subgrains having non-uniform morphologies surrounded by blurred and wavy boundaries. A saturated hardness distribution at approximately 450 HV indicates that microstructural homogeneity has been achieved at N %26gt;= 10. The alpha precipitates enhance the beta grain refinement and microstructural homogeneity is achieved in TNTZ(AHPT) at N %26gt;= 10, whereas this occurs at later stages (N %26gt; 20) in TNTZ which is solution-treated and therefore does not contain any alpha precipitates.

• 出版日期2014-11