Dynamic globularization kinetics during hot working of a two phase titanium alloy with a colony alpha microstructure

Shih

et al. 2015

Metals

Ultrafine-grained (UFG) Ti-6Al-4V alloy has attracted attention from the various industries due to its good mechanical properties. Although severe plastic deformation (SPD) processes can produce such a material, its dimension is generally limited to laboratory scale. The present work utilized the multi-pass caliber-rolling process to fabricate Ti-6Al-4V bulk rod with the equiaxed UFG microstructure. The manufactured alloy mainly consisted of alpha phase and showed the fiber texture with the basal planes parallel to the rolling direction. This rod was large enough to be used in the industry and exhibited comparable tensile properties at room temperature in comparison to SPD-processed Ti-6Al-4V alloys. The material also showed good formability at elevated temperature due to the occurrence of superplasticity. Internal-variable analysis was carried out to measure the contribution of deformation mechanisms at elevated temperatures in the manufactured alloy. This revealed the increasing contribution of phase/grain-boundary sliding at 1073 K, which explained the observed superplasticity.

Section: Discussionmentioning

confidence: 99%

Manufacturing Ultrafine-Grained Ti-6Al-4V Bulk Rod Using Multi-Pass Caliber-Rolling

Shih

et al. 2015

Metals

“…The second term models the static recovery of dislocations. The third term is related to the reduction of dislocation density due to the globularization of lamellar a, which is mainly achieved through recrystallization [12,27]. More details of the evolution of globularization, S, is given in Section 2.5.…”

Section: Evolution Of Dislocation Densitymentioning

confidence: 99%

“…The mechanism of globularization has been extensively studied and it is found that the globularization is mainly achieved through recrystallization [12,27]. Referring to the dynamic recrystallization models proposed by Lin et al [26] and the globularization equation proposed by Gao et al [23], the evolution of volume fraction of globularization can be formulated as:…”

Section: Modelling Of Dynamic Globularization Of Lamellar Amentioning

confidence: 99%

Unified constitutive modelling for two-phase lamellar titanium alloys at hot forming conditions

Yang

Wang

et al. 2016

Manufacturing Rev.

-In this paper, a set of mechanism based unified viscoplastic constitutive equations have been established for two-phase titanium alloys with initial lamellar microstructure, which models the softening mechanisms of the alloys in hot forming conditions. The dislocation density, rotation and globularization of lamellar a-phase and their effects on flow behaviour can also be modelled. The values of material constants in the equation set have been calibrated, according to stress-strain curves and globularization fractions of lamellar a-phase obtained from compression tests at a range of temperatures and strain rates, using a genetic algorithm (GA) based optimisation method. Based on the determined constitutive equations, flow stress and globularization evolution of Ti-17 and TA15 alloys at different temperatures and strain rates were predicted. Good agreements between the experimental and computed results were obtained.

Journal of Materials Processing Technology

“…The experiments conducted by Song et al (2009) reveal the initiation of globularization between strain levels of 0.42-0.65 around 920-980 • C under strain rate range of 0.01-10 1/s. Song et al (2009) identify the differences between dynamic recrystallization and globularization, stating that for the former, the critical strain is lower and mainly dependent on temperature and strain rate, whereas the latter is not very sensitive to deformation temperature and strain rate since it is controlled by dislocation glide.…”

Section: Introductionmentioning

confidence: 97%

“…Another flow softening mechanism observed in titanium alloys at high temperatures is globularization, which is governed by the alpha to beta transformation and sliding of grain boundaries (Song et al, 2009). The experiments conducted by Song et al (2009) reveal the initiation of globularization between strain levels of 0.42-0.65 around 920-980 • C under strain rate range of 0.01-10 1/s.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependent flow softening of titanium alloy Ti6Al4V: An investigation using finite element simulation of machining

Karpat

2011

135

a b s t r a c tTitanium alloy Ti6Al4V is the most commonly used titanium alloy in the aerospace and medical device industries due to its superior properties. There has been a considerable amount of research to better understand the serrated chip formation mechanism of titanium alloy Ti6Al4V by using finite element simulation of machining. An accurate representation of the behavior of the material is important in order to obtain reliable results from the finite element simulation. Flow softening behavior has been integrated into the material constitutive models to simulate adiabatic shear bands and serrated chips. Flow softening is usually related to the dynamic recrystallization phenomenon which initiates after a critical temperature. The aim of this study is to investigate the influence of various flow softening conditions on the finite element simulation outputs for machining titanium alloy Ti6Al4V. For this purpose, a new flow softening expression, which allows defining temperature-dependent flow softening behavior, is proposed and integrated into the material constitutive model. The influence of flow softening below the critical temperature, as adopted in recent studies, is also investigated. Various temperature-dependent flow softening scenarios are tested using finite element simulations, and the results are compared with experimental data from the literature. The results showed that the flow softening initiating around 350-500• C combined with appropriate softening parameters yields simulation outputs that agree well with the experimental measurements.