Controlling crystallographic ordering in Mo–Cr–Ti–Al high entropy alloys to enhance ductility

Laube, Stephan; Chen, Hans; Kauffmann, Alexander; Schellert, Steven; Gorr, Bronislava; Müller, Julian; Butz, Benjamin; Christ, H.‐J.; Heilmaier, Martin

doi:10.1016/j.jallcom.2020.153805

Cited by 34 publications

(19 citation statements)

References 42 publications

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“…Our latest works [25], however, revealed a B2-type ordered crystal structureinstead of the A2-type disordered counterpartin several derivatives within the Ta-Nb-Mo-Cr-Ti-Al system. It was concluded that the poor ductility and high brittle-to ductile transition temperatures [22] of some of the alloys studied correlate the appearance of an ordered B2-type phase [25,26].…”

Section: Introductionmentioning

confidence: 99%

Formation of complex intermetallic phases in novel refractory high-entropy alloys NbMoCrTiAl and TaMoCrTiAl: Thermodynamic assessment and experimental validation

Müller

Gorr

Christ

et al. 2020

Journal of Alloys and Compounds

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In this work, we present the results of the thermodynamic assessment of two equiatomic refractory High Entropy Alloys (HEAs), namely TaMoCrTiAl and NbMoCrTiAl, in the temperature range between 700 and 1500°C. Particular attention is paid on the constitution of the intermetallic phases stable in these alloy systems. Thermodynamic calculations were performed using a self-developed thermodynamic database based on the CALPHAD (Calculation of Phase Diagram) approach. The details of the thermodynamic modelling and particular characteristics of the relevant phases within the Ta-Nb-Cr-Ti-Al system are presented. To verify the new database, the phase formation and stability of both quinary alloys in near-equilibrium conditions were studied experimentally by utilizing scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD) as well as X-ray powder diffraction (XRD). Both equiatomic alloys reveal a complex microstructure including several intermetallic phases at intermediate temperatures. The alloy NbMoCrTiAl consists of an ordered B2 phase, Al(Mo, Nb)3 and two polytypes (C14 and C15) of the Cr2Nb Laves phase. Precipitations of Cr2Ta Laves phase (C14, C15 and C36-type) in the B2 matrix were observed in the alloy TaMoCrTiAl. Based on the results of thermodynamic calculations, it was concluded that: (i) Nb stabilizes the AlMo3 A15 phase in the alloy NbMoCrTiAl, (ii) Al and Ti play a crucial role in the formation of the ordered B2 phase in both alloys and (iii) the concentrations of Cr and/or Ta/Nb should be dramatically reduced to decrease the Laves phase volume fraction.

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Section: Introductionmentioning

confidence: 99%

Formation of complex intermetallic phases in novel refractory high-entropy alloys NbMoCrTiAl and TaMoCrTiAl: Thermodynamic assessment and experimental validation

Müller

Gorr

Christ

et al. 2020

Journal of Alloys and Compounds

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“…The fracture effect can be associated on the "order-disorder" transformation as shown from thermodynamic calculations. It is reported that "orderdisorder" creates an imbalance of Young's Modulus between phases [8]. At this stage we can only speculate that this imbalance leads to unhomogenities and results to fracture.…”

Section: Discussionmentioning

confidence: 79%

“…During Α2 → Β2 transformation, decrease of ductility and enhance of yield strength is reported. Additionally, in HEAs with BCC_B2, when the range of ordering decreases, the alloy's total ductility of increases [8].…”

Section: Introductionmentioning

confidence: 99%

Examination of Fracture Mechanisms in two Al – Ti – V – Cr – (Si) High Entropy Alloys

et al. 2021

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This work focuses on the examination of two High Entropy Alloys (HEAs), the AlTiVCr and AlTiVCr–Si7.2, which have been observed to fail in a brittle manner directly after casting. Understanding the failure mechanics is a prerequisite for an alternative enhanced alloy design in order to prevent early failure without loading application. The specimens were produced using the Vacuum Arc Melting methodology in a protective argon atmosphere. The material was re–melted five times in combination with electromagnetic stirring in order to achieve a fully homogenized microstructure. Based on our findings, the failure occurred in the first 10 minutes after casting during slow cooling. Similarly, the same took place during thermal treatment after the third re–melting. The specimens were first prepared for optical (OM) and scanning electron microscopy (SEM) analysis. The material consists of a coarse dendritic microstructure as well as a retained BCC phase, which is the AlTiVCr phase. In the AlTiVCr – Si7.2 alloy a uniformly dispersed, angular intermetallic compound, namely the Ti5Si3, was identified, which increases the failure resistance of the material. Based on these findings the alloy will be redesigned.

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“…Preliminary studies (results not shown here) have revealed that the alloy with the B2 structure can be easily thermomechanically processed by cold rolling and subsequent annealing. Usually, RHEAs with such a structure suffer from brittleness at room temperature [28,29]. However, there are some examples of relatively ductile alloys with nearly a single-phase B2 structure [28,30,31].…”

Section: Discussionmentioning

confidence: 99%

A new refractory Ti-Nb-Hf-Al high entropy alloy strengthened by orthorhombic phase particles

Yurchenko

Panina

Tikhonovsky

et al. 2020

International Journal of Refractory Metals and Hard Materials

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This study reports the structure and mechanical properties of a new refractory Ti 40 Nb 30 Hf 15 Al 15 (at.%) high entropy alloy. The alloy was fabricated by vacuum arc melting and had a density of 7.07 ± 0.03 g/cm 3 . After annealing at 1200°C for 24 h, the alloy possessed a single-phase B2 structure. Further annealing at 600°C for 24 h resulted in the formation of Widmanstatten (Ti, Al)-rich orthorhombic particles (O-phase) in a bcc matrix. The single-phase B2 alloy demonstrated high (> 50%) compressive ductility and a pronounced work hardening capacity. The precipitation of the O-phase particles led to a 50% strength increment at 22 and 600°C, with some sacrificing in the compressive ductility at 22°C. The obtained results suggest new approaches to the development of precipitation-strengthened refractory high entropy alloys with a balanced combination of the room-and hightemperature properties.

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Controlling crystallographic ordering in Mo–Cr–Ti–Al high entropy alloys to enhance ductility

Cited by 34 publications

References 42 publications

Formation of complex intermetallic phases in novel refractory high-entropy alloys NbMoCrTiAl and TaMoCrTiAl: Thermodynamic assessment and experimental validation

Formation of complex intermetallic phases in novel refractory high-entropy alloys NbMoCrTiAl and TaMoCrTiAl: Thermodynamic assessment and experimental validation

Examination of Fracture Mechanisms in two Al – Ti – V – Cr – (Si) High Entropy Alloys

A new refractory Ti-Nb-Hf-Al high entropy alloy strengthened by orthorhombic phase particles

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