Modification of alpha morphology in Ti-6Al-4V by thermomechanical processing

Weiss, Isaac; Froes, F. H.; Eylon, D.; Welsch, G.

doi:10.1007/bf02644991

Cited by 325 publications

(96 citation statements)

References 13 publications

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“…Dynamic globularization takes place by penetration of beta phase into newly formed alpha/alpha interface at kinked point and the penetration rate is dependent on diffusion process. 9) In this regard, fraction globularized increases with decreasing strain rate since low strain rate at high temperature is more beneficial to migration of the interface by diffusion. Also, the earlier studies for both thin and thick lamellar microstructures show the fraction globularized increases with decreasing strain rate.…”

Section: Strain Rate Sensitivitymentioning

confidence: 99%

Microstructural Mechanisms during Dynamic Globularization of Ti-6Al-4V Alloy

Park

Shin

et al. 2008

Mater. Trans.

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The microstructural mechanisms during dynamic globularization were investigated for ELI grade Ti-6Al-4V alloy with initial martensite microstructure. For this purpose, compression tests were carried out isothermally at 1073 K up to the strains of 1.0 and 1.4 with the strain rates ranging from 10 À3 s À1 to 1 s À1 . Fully dynamically globularized specimen exhibited higher Vickers hardness values due to the finer grain size and higher dislocation density compared to the conventionally produced one, i.e., partial dynamic globularization by subsequent annealing. The strain rate sensitivity (m) values of the flow stresses at initial stage (" % 0:05) and final stage (" % 1:4) of deformation were %0:15 and %0:36, respectively, leading to the conclusion that deformation was controlled by dislocation glide/climb at low strains and grain boundary sliding at high strains. Also, microstructural evolution during dynamic globularization was rationalized by examining the microstructures associated with kinking and fragmentation of lamellar plates.

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Section: Strain Rate Sensitivitymentioning

confidence: 99%

Microstructural Mechanisms during Dynamic Globularization of Ti-6Al-4V Alloy

Park

Shin

et al. 2008

Mater. Trans.

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“…For example, it was found that the dislocation-evolution-related α recrystallization is the main pattern of substructure formation [16]. However, Weiss et al [17] reported another formation phenomenon via local shear bands during the deformation of Ti-6Al-4V at 955 • C and a constant crosshead speed of 2 × 10 −4 m/s, although no more details were given. Sequentially, acicular α is fragmented gradually by the edging of the β matrix along the interface between substructures, in which the driving force is considered to be the discrepancy of tension between α/α and α/β interfaces [18].…”

Section: Introductionmentioning

confidence: 99%

Relationship between Flow Behavior and Microstructure Evolution during Isothermal Compression of near β Titanium Alloy Ti-55531 with Acicular Starting Microstructure

Zhang

et al. 2018

Metals

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Near β titanium alloy Ti-55531 with an acicular starting microstructure was isothermally compressed at 750-825 • C and 10 −3 −1 s −1 . The microstructure evolution and its influence on the flow behavior of yielding and softening were investigated. Discontinuous or continuous yielding depends on the hindrance to the dislocation motion coming from the β grain boundary or α phase. At higher temperatures, the hindrance mainly comes from the β grain boundary. Its discontinuous action, including the piling-up and subsequent loosening of dislocations at the β grain boundary, leads to discontinuous yielding. At lower temperatures, the continuous hindrance to the dislocation motion, which is exerted by the β grain boundary and acicular α, causes continuous yielding. Sequentially, the substructures in acicular α are evolved from high-density dislocations or local shear bands, which depend on the orientation relationship between β and α. Then, the β matrix edges into the acicular α along substructure boundaries. The higher strain rate decreases the deformation time to carry out the fragmentation of acicular α, while the higher temperature decreases the dislocation density due to the recovery of β, which does not benefit the substructure formation and subsequent fragmentation of acicular α. Therefore, the retardation of acicular fragmentation and the as-resulted decreased flow softening rate are observed.

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“…As aforementioned, globularization of lamellae is known to occur by penetration of the phase through such grooves called 'cusp' during dynamic and/or static recrystallization processes. 9,21) In the case of non-isothermal deformation at 900 C, penetration becomes difficult compared to that at 940 C due to not only the lower temperature but also concurrent cooling of the sample during forging under non-isothermal condition. 22) In addition, although the sample was reheated to forging temperature, the time was not sufficient for globularization.…”

Section: Fc Samplesmentioning

confidence: 99%

“…In addition, it is affected by the processing parameters such as the forging temperature, strain, strain rate, and deformation mode. Accordingly, extensive and intensive investigations have been performed previously on the globularization behavior of the lamellar Ti alloys focusing on the effects of the microstructures [9][10][11][12] and processing parameters. [13][14][15] However, most of the previous studies were conducted under the isothermal deformation condition, and it is rare to find a systematic one carried out under the non-isothermal deformation condition.…”

Section: Introductionmentioning

confidence: 99%

Globularization Behavior of ELI Grade Ti-6Al-4V Alloy during Non-Isothermal Multi-Step Forging

Kim

Park

Shim³

et al. 2008

Mater. Trans.

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The globularization behavior of ELI grade Ti-6Al-4V alloy having different initial lamellar structures during multi-step forging under nonisothermal condition was investigated. The samples with either a thin or thick lamellar structure, which were produced from annealing followed by different cooling conditions, were upset and stretched repeatedly at forging start temperatures of 940 C and 900 C, and subsequently air cooled. The microstructural changes after non-isothermal multi-step forging were analyzed with respect to globularization of lamellae. After multi-step forging at 940 C, the initially thin lamellar structure changed to homogeneous equiaxed globules, but elongated globules with high aspect ratio were obtained from the initially thick lamellar structure. By forging at 900 C, the initially thin lamellar structure was changed to a mixed structure of both equiaxed and elongated globules, while severely deformed lamellae were preserved inside distorted colonies with little globularization for the initially thick lamellar structure. Globularization of the samples by forging at 900 C with both initially thin and thick lamellar structures was less effective compared to that by forging at 940 C. A quantitative microstructural analysis revealed that, in addition to the initial microstructure and forging start temperature, globularization of lamellae was significantly affected by the instantaneous microstructural development by thermal fluctuation during non-isothermal multi-step forging.

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Modification of alpha morphology in Ti-6Al-4V by thermomechanical processing

Cited by 325 publications

References 13 publications

Microstructural Mechanisms during Dynamic Globularization of Ti-6Al-4V Alloy

Microstructural Mechanisms during Dynamic Globularization of Ti-6Al-4V Alloy

Relationship between Flow Behavior and Microstructure Evolution during Isothermal Compression of near β Titanium Alloy Ti-55531 with Acicular Starting Microstructure

Globularization Behavior of ELI Grade Ti-6Al-4V Alloy during Non-Isothermal Multi-Step Forging

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