Effect of β phase stability at room temperature on mechanical properties in β-rich α+β type Ti-4.5Al-3V-2Mo-2Fe alloy

Gunawarman, Mitsuo Niinomi, Daniel Eylon, Shiro Fujishiro, Chiaki Ouchi

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)

Abstract

The stability of the β phase at room temperature in various microstructures of a β-rich α+β type Ti-4.5Al-3V-2Mo-2Fe alloy and its relationship with the fracture toughness, hardness and tensile properties were investigated. A variety of microstructures were established by varying solution treatment temperatures in α+β field, cooling rate after solution treatment and the condition of subsequent second-step annealing treatment after air-cooling treatment. These microstructures have β phase with lattice parameters of β phase ranging between 0.3244 nm and 0.3221 nm. The stability of β phase, which is indicated by decreasing lattice parameter of β phase, is increased by either lowering cooling rate or formation of diffusional transformation products (secondary phases) in the β phase. The β phase with lattice parameter of β phase around 0.3242 nm is the minimal instability of unstable β phase at room temperature for attaining deformation-induced martensite in tensile specimens. There exists a proper degree of β phase stability for increasing the fracture toughness, JIC. The relatively higher fracture toughness is obtained at low or high stability of β phase. The high fracture toughness at low stability of β phase (unstable β) is mainly due to the deformation-induced martensite. While, the high fracture toughness at high stability of β phase (stable β) is mainly due to the secondary phase in the β phase that produces a prominent crack deflection toughening mechanism. However, the relatively lower fracture toughness is obtained at high stability of β phase when the β phase contains small amount or no secondary phase. This leads to conclude that, if only the β phase stability is taken into account for explaining fracture mechanism, the fracture toughness would decrease monotonously with increasing stability of β phase. The Vickers hardness is nearly independent of stability of β phase.

Original languageEnglish
Pages (from-to)191-199
Number of pages9
JournalIsij International
Volume42
Issue number2
DOIs
Publication statusPublished - 2002 Feb

Keywords

  • Fracture toughness
  • Hardness
  • Mechanical properties
  • Microstructure
  • Stability of β phase
  • Tensile properties
  • Ti-4.5Al-3V-2Mo-2Fe
  • β-rich α+β titanium alloy

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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