Molar volumes of bcc, hcp, and orthorhombic Ti-base solid solutions at room temperature

Yan, Jia-Yi; Olson, Gregory B.

doi:10.1016/j.calphad.2016.01.003

Cited by 30 publications

(6 citation statements)

References 60 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…x 0 and that hexagonal α′ and orthorhombic α″ do generally not coexist 23,[39][40][41][42] . In contrast, the transition from β to α″ around β α − ″…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

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

“…x 0 and that hexagonal α′ and orthorhombic α″ do generally not coexist 23,[39][40][41][42] . In contrast, the transition from β to α″ around β α − ″…”

Section: Resultsmentioning

confidence: 99%

“…x 0 involves a strong disruption in crystal symmetry that carries forward an expansion of the specific volume 23,42 . Thus, an accurate thermodynamic depiction of the experimentally observed (dis)continuity requires a smooth behaviour (equal slopes) of α G and α″ G at α α − ″…”

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

“…Unlike the 3-4% level in steels, the martensi c transforma on dilata on is typically less than 1% in tanium alloys, which is comparable to the uncertainty of current molar volume model [25]. The comparison between predic on and measurement of molar volume for α" and β is shown in Figure 4(b).…”

Section: Computa Onal Design Integra Onmentioning

confidence: 83%

“…As quan fied in previous steel research, transforma on toughening effect is sensi ve to martensi c transforma on dila on. In order to calculate the transforma on dilata on for TRIP alloy design, room temperature molar volumes of β, α', and α" phases were modeled as func ons of chemical composi on in the CALPHAD framework with literature data and supplemental x-ray diffrac on measurements for tanium based solid solu ons [25]. The molar volume V m was expressed as the sum of a linear mixture of pure elements and regular-solu on interac on terms as represented in Equa on 6, where x i is the molar frac on of component i, V i is the component volume, and Ω ij is the binary interac on parameter.…”

Section: Transforma On Dilata On Modelmentioning

confidence: 99%

TRIP Titanium Alloy Design

Meng

Yan²,

Olson

2020

MATEC Web Conf.

Self Cite

View full text Add to dashboard Cite

Building on successful development experience of transformation induced plasticity (TRIP) steels, an analogous concept was taken to design high performance titanium alloys. This article describes a computational design framework of novel near-α TRIP titanium alloys with both high yield strength and fracture toughness for naval structural applications using a systems design approach integrating processing/structure/properties/performance relations. Predictive models including a transformation stability model based on Olson-Cohen heterogeneous martensite nucleation theory for titanium alloys was proposed. Integration of the models with CALPHAD software and databases enables parametric design optimization to meet design objectives. The developed models were calibrated with experimental measurements.

show abstract

“…Considering the crystallographic fit between the parent BCC and transformed O crystalline cell, one can notice a misfit between the expected and the observed lattice parameters of the transformed Ti-α″ phase. For a “perfect” fit between the parent Ti-β phase, with a lattice parameter of a β = 0.329 nm, and the transformed Ti-α″ phase, the Ti-α″ phase should possess lattice parameters close to a α″ = 0.288 nm, b α″ = 0.526 nm and c α″ = 0.473 nm [ 67 , 68 ]. The observed misfit shows an increase in the lattice parameter a α″ from the expected value of 0.288 nm to the observed value of 0.298 nm, and a decrease in both b α″ and c α″ lattice parameters from 0.526 nm to 0.492 nm and 0.473 nm to 0.463 nm, respectively.…”

Section: Resultsmentioning

confidence: 99%

Evolution of Microstructural and Mechanical Properties during Cold-Rolling Deformation of a Biocompatible Ti-Nb-Zr-Ta Alloy

et al. 2022

View full text Add to dashboard Cite

In this study, a Ti-32.9Nb-4.2Zr-7.5Ta (wt%) titanium alloy was produced by melting in a cold crucible induction in a levitation furnace, and then deforming by cold rolling, with progressive deformation degrees (thickness reduction), from 15% to 60%, in 15% increments. The microstructural characteristics of the specimens in as-received and cold-rolled conditions were determined by XRD and SEM microscopy, while the mechanical characteristics were obtained by tensile and microhardness testing. It was concluded that, in all cases, the Ti-32.9Nb-4.2Zr-7.5Ta (wt%) showed a bimodal microstructure consisting of Ti-β and Ti-α″ phases. Cold deformation induced significant changes in the microstructural and the mechanical properties, leading to grain-refinement, crystalline cell distortions and variations in the weight-fraction ratio of both Ti-β and Ti-α″ phases, as the applied degree of deformation increased from 15% to 60%. Changes in the mechanical properties were also observed: the strength properties (ultimate tensile strength, yield strength and microhardness) increased, while the ductility properties (fracture strain and elastic modulus) decreased, as a result of variations in the weight-fraction ratio, the crystallite size and the strain hardening induced by the progressive cold deformation in the Ti-β and Ti-α″ phases.

show abstract

Molar volumes of bcc, hcp, and orthorhombic Ti-base solid solutions at room temperature

Cited by 30 publications

References 60 publications

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

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

TRIP Titanium Alloy Design

Evolution of Microstructural and Mechanical Properties during Cold-Rolling Deformation of a Biocompatible Ti-Nb-Zr-Ta Alloy

Contact Info

Product

Resources

About