Recent progress in the high-cycle fatigue behaviour of <i>γ</i>-TiAl alloys

Edwards, Thomas Edward James

doi:10.1080/02670836.2018.1463614

Cited by 21 publications

(24 citation statements)

References 145 publications

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“…Instead, here, at both 25 ºC and 700 ºC, such localised plasticity, identified in microcompression samples by a combination of DIC and TEM, was attributed to longitudinal slip occurring 30 -50 nm away from lamellar interfaces, and longitudinal twinning propagating from the interfaces, without cracking. These two latter deformation mechanisms maintain material cohesion and may produce equivalent surface steps as previously identified by AFM [6], have the same appearance in BSE imaging as the features reported to be microcracks and interfacial sliding [50], and, furthermore, microplasticity may generate acoustic emissions [51], similarly to microcracking, as remarked by Appel et al [46].…”

Section: Location Of Plasticity Occurring Below the General Yield Stresssupporting

confidence: 56%

Deformation of lamellar γ-TiAl below the general yield stress

et al. 2019

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The occurrence of plasticity below the macroscopic yield stress during tensile monotonic loading of nearly lamellar Ti-45Al-2Nb-2Mn(at%)-0.8vol% TiB 2 at both 25 °C and 700 °C, and in two conditions of lamellar thickness, was measured by digital image correlation strain mapping of a remodelled Au surface speckle pattern. Such initial plasticity, not necessarily related to the presence of common stress concentrators such as hard particles or cracks, could occur at applied stresses as low as 64 % of the general yield stress. For a same applied strain it was more prominent at room temperature, and located as slip and twinning parallel to, and near to or at (respect.

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Section: Location Of Plasticity Occurring Below the General Yield Stresssupporting

confidence: 56%

Deformation of lamellar γ-TiAl below the general yield stress

et al. 2019

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“…The similar behavior of the two highest deformed conditions is attributed to their almost identical microstructure, as shown in Figure 1 c,d. At RT, the γ-phase is prone to micro-plastic deformation through dislocation movement [ 47 , 55 , 56 , 57 ]. The generated strain accumulation leads to crack initiation at the boundaries of the relatively soft and globular γ-grains [ 58 , 59 ].…”

Section: Resultsmentioning

confidence: 99%

“…The generated strain accumulation leads to crack initiation at the boundaries of the relatively soft and globular γ-grains [ 58 , 59 ]. Consequently, the coalescence of these early defects leads to the formation of a pre-crack at the grain boundaries, which propagates further by stable crack growth [ 56 , 58 , 60 ].…”

Section: Resultsmentioning

confidence: 99%

“…These cracks typically possess a dimension comparable to the size of the present (α 2 /γ) col and exhibit steps, which are exemplary marked by an arrow within Figure 4 b. Thus, unfavorable orientated colonies were cleaved by interlamellar fracture [ 56 , 62 ]. Crack initiation was observed not to occur at surface defects, but at colonies located just below the sample surface.…”

Section: Resultsmentioning

confidence: 99%

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An Advanced TiAl Alloy for High-Performance Racing Applications

Burtscher

Klein

Lindemann³

et al. 2020

Materials

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Requirements and strict regulations for high‑performance racing applications involve the use of new and innovative lightweight structural materials. Therefore, intermetallic γ‑TiAl-based alloys enable new opportunities in the field due to their lower density compared to commonly used Ni‑base superalloys. In this study, a β‑solidifying TiAl alloy was examined toward its use as structural material for inlet and outlet valves. The nominal composition of the investigated TNM alloy is Ti–43.5Al–4Nb–1Mo–0.1B (in at%), which enables an excellent formability at elevated temperatures due to the presence of bcc β‑phase. Different hot‑extrusion tests on an industrial scale were conducted on the cast and hot isostatic pressed material to determine the ideal microstructure for the respective racing application. To simulate these operation conditions, hot tensile tests, as well as rotational bending tests, at room temperature were conducted. With a higher degree of deformation, an increasing strength and fatigue limit was obtained, as well as a significant increment of ductility. The fracture surfaces of the rotational bending test specimens were analyzed using scanning electron microscopy, revealing the relationship between crack initiation and microstructural constituents. The results of this study show that the mechanical performance of extruded TiAl material can be tailored via optimizing the degree of hot-extrusion.

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“…Hence, it is important to investigate their fracture behavior during high-cycle fatigue (HCF) for improving the service property of TiAl alloys. Most of the previous researches have been focused on fatigue crack growth [12][13][14][15]. It was demonstrated that the low ductility and toughness of TiAl alloys result in a low tolerance to fatigue crack growth and a relatively steep slope of the Paris region [16,17].…”

Section: Introductionmentioning

confidence: 99%

Effect of Microstructure on the High-Cycle Fatigue Behavior of Ti(43-44)Al4Nb1Mo (TNM) Alloys

Tang

Zhu

et al. 2019

Metals

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To investigate the high-cycle fatigue (HCF) behavior of TNM alloys, three different microstructures were designed and obtained by different heat treatments. Staircase tests and fatigue tests in a finite life-region were performed to evaluate the fatigue properties. Then, the fracture surfaces were analyzed to study the fracture behavior of TNM alloys with different microstructures. Results showed that the TNM alloys with duplex microstructure possesses the highest fatigue strength and fatigue life, followed by near lamellar TiAl alloys. HCF failure exhibited cleavage fracture morphologies, and multiple facets were generated in the crack initiation region of different TNM alloys. Two different crack initiation modes, subsurface crack nucleation and surface origin, were observed. Both crack initiation modes appeared in near lamellar alloys, while only subsurface crack initiation were obtained in the duplex (DP) alloy. It contributes to the high scatter of S-N data. The HCF failure of TNM alloys was dominated by crack nucleation rather than crack propagation. These findings could provide guidance for optimizing the microstructure and improving the HCF properties of TiAl alloys.

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Recent progress in the high-cycle fatigue behaviour of γ-TiAl alloys

Cited by 21 publications

References 145 publications

Deformation of lamellar γ-TiAl below the general yield stress

Deformation of lamellar γ-TiAl below the general yield stress

An Advanced TiAl Alloy for High-Performance Racing Applications

Effect of Microstructure on the High-Cycle Fatigue Behavior of Ti(43-44)Al4Nb1Mo (TNM) Alloys

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