Peculiar Transformation Behavior and Microstructure Evolution with Tempering of Ti-4Fe-7Al Alloy

Takemoto, Yoshito; Fujii, Kazuya; Nakastuka, Shou; Senuma, Takehide

doi:10.2320/jinstmet.j2013027

Cited by 10 publications

(5 citation statements)

References 15 publications

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“…When the temperature was raised to 200°C, the profile approached that of the ¢ single phase. When compared with the ex-situ, room temperature XRD profile 11) of the sample tempered at 200°C for 5 min, the peaks measured at 200°C are very diffuse. This result could be an effect of the higher measurement temperature, which would increase the crystal lattice vibration and therefore the peak widths; it is also possible that a fine ¡AA iso had been generated.…”

Section: Methodsmentioning

confidence: 99%

“…7) The second type of ¡AA phase, commonly referred to as ¡AA iso , 8,9) is a needle-like product a few hundred nanometers in size, which forms during isothermal aging at relatively high temperatures (approximately 400°C). ¡AA iso is a diffusion transformation product generated and grown by thermal activation 10,11) and is distinctly different from martensite. The structure of ¡AA iso varies with alloy composition, aging temperature, and aging time; the axial ratio b ¡AA /a ¡AA of this phase has a value of ffiffi ffi 2 p < b ¡ 00 =a ¡ 00 < ffiffi ffi 3 p .…”

Section: Introductionmentioning

confidence: 99%

“…6) The ¡AA iso phase is produced rapidly and leads to significant hardening after a few seconds to a few minutes of higher-temperature aging. 11,12) During ¡AA iso formation, specific ¡AA iso variants are preferentially formed in response to slight strains in the matrix phase, resulting in a peculiar phenomenon, in which the sample shape and surface change significantly. 10,1315) For example, a thin STQ plate bent into a U-shape at room temperature will continue to bend with increasing temperature.…”

Section: Introductionmentioning

confidence: 99%

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Formation Mechanism of Tempering-Induced Martensite in Ti–10Mo–7Al Alloy

et al. 2022

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The formation mechanism of ¡AA-martensite (¡AA Mt ) induced by tempering at 450550°C for a short time was investigated using Ti10Mo 7Al alloy. The solution treated and quenched (STQ) sample was composed of ¢ phase and a small amount of ¡AA Mq , and a large amount of ¡AA Mt was generated by rapid tempering at 550°C for 3 s using a salt bath. However, ¡AA Mt was completely transformed into a single ¢ phase by aging at 200°C for 3 min. Reversibility was observed between the ¡AA Mt transformation and the ¢ reverse transformation. In-situ high-temperature X-ray diffraction measurements revealed that ¡AA Mq ¼ ¢ reverse transformation occurred at 200°C and that a thermally activated ¡AA iso was generated at 450°C due to the slow heating rate. In-situ optical microscopic observation of STQ sample with rapid lamp heating revealed that ¡AA Mt was formed during heating process. However, ¡AA Mt did not generate under following conditions; that is, a slow heating rate, thin sample plate, and a small temperature difference until tempering by preheating. On the other hand, rapid tempering using thick plate from liquid nitrogen (¹196°C) to 250°C was performed to ensure a sufficient temperature difference, but ¡AA Mt was not generated at all.From the cross-sectional observation of the STQ plate, it was found that ¡AA Mq was hardly formed on the surface of the sample, but was formed abundantly inside the sample. On the other hand, in the rapidly tempered plate, a large amount of ¡AA Mt was distributed in the surface layer than inside sample. These results suggest that the thermal compressive stress induced by rapid heat treatment contributes to the formation of ¡AA M .

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Formation Mechanism of Tempering-Induced Martensite in Ti–10Mo–7Al Alloy

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“…Symbols of (△) 2) show hardness evolution with isothermal tempering at 450°C after the direct water quenching from 1050°C. (Fig.…”

Section: 緒言mentioning

confidence: 99%

Microstructure of Ti-4Fe-7Al Alloy Quenched in a Salt Bath after Solution Treatment

Ijiri

Akira

Ishikawa

et al. 2016

J. Japan Inst. Metals and Materials

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The Ti 4Fe 7Al alloy exhibits some interesting phenomena upon tempering. The noteworthy features are rapid hardening and shape change in a U shaped specimen with heating, which are caused by the b(bcc)→a″(orthorhombic) transformation at elevated temperature. The transformation behavior on the TTT (time temperature transformation) diagram estimated from the age hardening at various temperatures indicated a C curve with a nose at 450°C, which means that the transformation occurs through a thermal activation process. However, STEM EDS analysis of a″revealed that the transformation had occurred without atom diffusion. In this study, every solution treatment was carried out at 1050°C for 30 min under a vacuum, then the specimen was quenched into a salt bath of 200 550°C and held for a certain period prior to water quenching. These treated specimens were compared with the quenched and tempered specimens with respect to the microstructure and the hardening behavior. The hardness of the specimens held at 200 500°C (30 s) increased with increasing holding temperature. The maximum hardness, 610Hv, which was almost the same as that of a tempered specimen, was obtained at around 450°C. The microstructure of the specimen held at 450°C (30 s) showed a common morphology composed of acicular martensite variants, except for the size. Because the several variants would cancel the transformation strain of each other, no severe unevenness of the surface was generated, unlike the tempered specimen. On the other hand, the hardness of the specimen held at 550°C (30 s) decreased drastically owing to the phase separation to a＋b, and the TiFe precipitates were generated from b upon the extension of the holding time.By the TEM observation of the electropolished thin foil of the specimen held at 450°C (30 s), unreasonable microstructure that was different from the XRD result was obtained. Just after the electropolishing, the SAD patterns showed that the a″  structure has a commensurate relation with the b lattice. However, a″turned spontaneously into an incommensurate relation after one year. On the other hand, TEM observations of the foil prepared by FIB (focused ion beam) were consistent with the XRD result. It was suggested that the hydrogen absorption during electropolishing caused a structural transition of a″ martensite.[doi:10.2320/jinstmet.J2016032] (Received May 11, 2016; Accepted July 26, 2016; Published October 25, 2016) Keywords: a″  martensite transformation, variant, electropolishing, hydrogen absorption

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“…(hcp)となる．αAA iso の組成変化は低温時効や生成直後ではほとんど見られないが 10,12) ，時効に伴って β 安定化元素濃度が 11,12) ．また，αAA iso が生成する際，母相のわずかなひずみに A d v a n c e…”

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Formation Mechanism of Tempering-Induced Martensite in Ti-10Mo-7Al Alloy

嘉利

実希子

雅基

et al. 2021

J. Japan Inst. Metals and Materials

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The formation mechanism of αAA-martensite (αAA Mt ) induced by tempering at 450-550℃ for a short time was investigated using Ti-10Mo-7Al alloy. The solution treated and quenched (STQ) sample was composed of β phase and a small amount of αAA Mq , and a large amount of αAA Mt was generated by rapid tempering at 550℃-3 s using a salt bath. However, αAA Mt was completely transformed into a single β phase by aging at 200℃ for 3 min. Reversibility was observed between the αAA Mt transformation and the β reverse transformation. In-situ high-temperature X-ray diffraction measurements revealed that αAA Mq → β reverse transformation occurred at 200℃ and that a thermally activated αAA iso was generated at 450℃ due to the slow heating rate. In-situ optical microscopic observation of STQ sample with rapid lamp heating revealed that αAA Mt was formed during heating process. However, αAA Mt did not generate under following conditions; that is, a slow heating rate, thin sample plate, and a small temperature difference until tempering by preheating. On the other hand, rapid tempering using thick plate from liquid nitrogen (−196℃) to 250℃ was performed to ensure a sufficient temperature difference, but αAA Mt was not generated at all.From the cross-sectional observation of the STQ plate, it was found that αAA Mq was hardly formed on the surface of the sample, but was formed abundantly inside the sample. On the other hand, in the rapidly tempered plate, a large amount of αAA Mt was distributed in the surface layer than inside sample. These results suggest that the thermal compressive stress induced by rapid heat treatment contributes to the formation of αAA M .

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Peculiar Transformation Behavior and Microstructure Evolution with Tempering of Ti-4Fe-7Al Alloy

Cited by 10 publications

References 15 publications

Formation Mechanism of Tempering-Induced Martensite in Ti–10Mo–7Al Alloy

Formation Mechanism of Tempering-Induced Martensite in Ti–10Mo–7Al Alloy

Microstructure of Ti-4Fe-7Al Alloy Quenched in a Salt Bath after Solution Treatment

Formation Mechanism of Tempering-Induced Martensite in Ti-10Mo-7Al Alloy

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