Composite structure of α phase in metastable β Ti alloys induced by lattice strain during β to α phase transformation

Hua, Ke; Zhang, Yudong; Kou, Hongchao; Li, Jinshan; Gan, Weimin; Fundenberger, Jean-Jacques; Esling, Claude

doi:10.1016/j.actamat.2017.04.051

Cited by 85 publications

(9 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is an already well-established route for material engineers to strengthen β-stabilized Ti-alloys [31][32][33] . Due to its importance and relatively easy triggerability it is being widely researched from experimental and theoretical (modelling) point of views 5,20,27,34,35 .…”

Section: Resultsmentioning

confidence: 99%

Routes to control diffusive pathways and thermal expansion in Ti-alloys

Bönisch

Stoica

Calin

2020

Sci Rep

View full text Add to dashboard Cite

β-stabilized Ti-alloys present several unexplored and intriguing surprises in relation to orthorhombic α″ phases. Among them are (i) the diffusion-controlled formation of transitional α″ iso , α″ lean and α″ rich phases and ii) the highly anisotropic thermal expansion of martensitic α″. Using the prototypical Ti-Nb system, we demonstrate that the thermodynamic energy landscape reveals formation pathways for the diffusional forms of α″ and may lead to a stable β-phase miscibility gap. In this way, we derive temperature-composition criteria for the occurrence of α″ iso and resolve reaction sequences during thermal cycling. Moreover, we show that the thermal expansion anisotropy of martensitic α″ gives rise to directions of zero thermal strain depending on Nb content. Utilizing this knowledge, we propose processing routes to achieve null linear expansion in α″ containing Ti-alloys. These concepts are expected to be transferable to other Ti-alloys and offer new avenues for their tailoring and technological exploitation. β-stabilized Ti-alloys provide the basis for a multitude of future applications in biomedicine and aeronautics 1,2. Their low elastic moduli, shape memory and superelastic effects, blended with pronounced hardenability and attractive ductility captivates the attention of engineers and material scientists alike. Despite their seemingly simple phase diagrams β-stabilized systems, such as Ti-Nb (Fig. 1) show a vast array of phase transformations and transient states, attributed to the extensive α-β two-phase field. The ensuing exceptionally pronounced metastability necessitates large diffusional compositional changes and extended aging durations (up to many weeks or months) to reach (meta)stable equilibrium. The nature of compositional fluctuations decisively influences the refinement of precipitation products 3-5 and the β ↔ α″ martensitic transformation 6. For instance, detailed (micro)structural studies uncovered non-conventional transformation pathways for α-precipitation 3,7-9. Of particular note is the discovery of transitional α″-like structures (α″ iso , α″ lean , α″ rich) during martensite decomposition and prior to α precipitation 7-11. Furthermore, recently extraordinarily large anisotropic thermal expansion was revealed in α″ martensite of the Ti-Nb system 9,12. The successful development of novel structural and functional Ti-alloys with bespoke mechanical and shape memory behaviour depends critically on accurate descriptions of precipitation and decomposition processes. In addition, key for dimension critical components is the ability to control thermal expansion 13,14. Nowadays, the core challenge in developing new Ti-alloys lies in unravelling the complexity of phase reactions and in deriving robust thermodynamic and structural descriptions to assist the alloy design process. Empirical trial-and-error methods still prevail today, nevertheless systematic attempts are made to develop and employ predictive capabilities through ab-initio 15-19 , phase-field 20,21 and CALPHAD 22-27 methods. The...

show abstract

Section: Resultsmentioning

confidence: 99%

Routes to control diffusive pathways and thermal expansion in Ti-alloys

Bönisch

Stoica

Calin

2020

Sci Rep

View full text Add to dashboard Cite

show abstract

“…That is, the three variants are interrelated by a 60 • rotation around the common <11.0> axis. Such a configuration is believed to result from the accommodation of the transformation strain of one variant by others, and is helpful in reducing elastic energy concentration in one direction [15][16][17]. All of this evidence demonstrates the occurrence of local variant selection.…”

Section: Elementmentioning

confidence: 87%

Characterization of a New Microstructure in a β-Solidifying TiAl Alloy after Air-Cooling from a β Phase Field and Subsequent Tempering

Chen

Liu

Sun

et al. 2018

Metals

Self Cite

View full text Add to dashboard Cite

In this study, we found that well-developed α 2 martensite was formed in a Ti-40Al-10V (atomic percent or at.%) alloy after air-cooling from a β phase field, rather than the traditional α 2 /γ lamellar colonies. The martensitic laths were produced according to the Burgers orientation relationship (OR), the same as those during quenching. Local variant selection detected that three (or six) α 2 variants sharing one (or two) common [11.0] α2 axes were predominant, while no global variant selection was observed. Subsequent to the martensitic transformation, the retained β phase was decomposed mainly via a β→γ transformation. The γ laths always nucleated at the α 2 /β interface according to a Blackburn orientation relationship. In order to stabilize the microstructure, the air-cooled samples were tempered at 800-1000 • C. During tempering, the microstructure decomposed mainly via an α 2 →γ transformation. The martensite was almost completely transformed after tempering at 1000 • C for 4 h, and hence a fine β-γ microstructure was obtained. Such a treatment resembling the quenching-tempering in steels may be a new strategy for the microstructural design of TiAl alloys, while an unexpected quenching process can be avoided.

show abstract

“…Ahmed et al [16] reported various sizes and volume fractions of secondary α phase during aged at 500–725 °C in a commercial near β titanium alloy Ti-10V-2Fe-3Al. Hua et al [17] reported that the αWGB appeared after being solution treated at 900 °C for 0.5 h followed by aging at 700 °C for 5 min in β titanium alloy Ti-7Mo-3Nb-3Cr-3Al. However, the effect of αWGB on mechanical properties was not discussed in their work.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Secondary α Phase during Aging Treatment in Novel near β Ti-6Mo-5V-3Al-2Fe Alloy

et al. 2018

View full text Add to dashboard Cite

Evolution of secondary α phase during aging treatment of a novel near β titanium alloy Ti-6Mo-5V-3Al-2Fe(wt.%) was studied by OM, SEM, and TEM. Results indicated that size and distribution of secondary α phase were strongly affected by aging temperature and time. Athermal ω phase formed after super-transus solution treatment followed by water quenching, and promoted nucleation of needle-like intragranular α in subsequent aging process. When aged at 480 °C, fine scaled intragranular α with small inter-particle spacing precipitated within β grains and high ultimate tensile strength above 1500 MPa was achieved. When the aging temperature increased, the size and inter-particle spacing of intragranular α increased and made the strength reduce, but the ductility got improved. When aging temperature reached as high as 600 °C, ω phase disappeared and intragranular α coarsened obviously, resulting in serious decrease of strength. While mutually parallel Widmanstätten α laths formed at the vicinity of β grain boundaries and grew into the internal area of β grains, and significant improvement of ductility was achieved. As the aging time increased from 4 h to 16 h at 600 °C, the intragranular α grew slightly and brought about minor change of mechanical properties.

show abstract

Composite structure of α phase in metastable β Ti alloys induced by lattice strain during β to α phase transformation

Cited by 85 publications

References 39 publications

Routes to control diffusive pathways and thermal expansion in Ti-alloys

Routes to control diffusive pathways and thermal expansion in Ti-alloys

Characterization of a New Microstructure in a β-Solidifying TiAl Alloy after Air-Cooling from a β Phase Field and Subsequent Tempering

Evolution of Secondary α Phase during Aging Treatment in Novel near β Ti-6Mo-5V-3Al-2Fe Alloy

Contact Info

Product

Resources

About