TY - JOUR

T1 - Fracture behavior of novel biomedical Ti-based high entropy alloys under impact loading

AU - Gurel, S.

AU - Yagci, M. B.

AU - Canadinc, D.

AU - Gerstein, Gregory

AU - Bal, B.

AU - Maier, Hans-Jürgen

N1 - Funding Information: In the case of the TiTaHfMoZr HEA, mainly quasi-cleavage fracture features with flat facets, river patterns and Chevron marks that can be observed on the fracture surface, indicating a brittle behavior (Fig. 7). Moreover, both intercrystalline and transcrystalline fracture are facilitated with limited crack propagation (Fig. 7(a), (b) and (c)). Tongue formation, which is a result of small-scale height elevations, can also be observed (Fig. 7(b)), which can be attributed to twinning [78], where the twin boundary fracture [79] may lead to the formation of the ladder-like structures with an elevation difference as illustrated by the yellow dashed lines in Fig. 7(c). In addition, the ladder-like formations (Fig. 7(c) and (d)) due to cleavage fracture and striations that are directed gradually along shear forces (Fig. 7(e)) indicate a rapid fracture. Furthermore, flat regions with striations due to rapid fracture dominate the fracture surface of the TiTaHfMoZr HEA (Fig. 7). Therefore, cleavage fracture dominates the fracture surface of the TiTaHfMoZr HEA, and the material exhibits a much more brittle behavior than TiTaHfNb and TiTaHfNbZr with the lowest recorded impact energy of 0.1 J. These findings are also supported by the stereoscopic microscopy images presented in Fig. 8: the fracture surface of the TiTaHfNb exhibits mainly cup and cone structures, indicating ductile behavior (Fig. 8 (a) and (b)), while the flat regions and intergranular cracking with small dimples on the fracture surface of the TiTaHfNbZr HEA clearly evidence its mixed fracture mode with higher brittleness (Fig. 8 (c) and (d)). As for the TiTaHfMoZr alloy, cleavage surfaces were observed under the stereoscopic microscope, supporting the aforementioned brittle response of this alloy under impact loading (Fig. 8 (e) and (f)).This study was supported by the BAGEP Award of the Science Academy. B. Bal acknowledges the AGU-BAP [grant number FAB-2017-77]. Financial support by the German Research Foundation (DFG, grant MA 1175/79-1 and grant 316923185) is also gratefully acknowledged. The authors also thank Mr. Mehmet Fazil Kapci for his help with the compression experiments.

PY - 2021/1/28

Y1 - 2021/1/28

N2 - This paper focuses on the mechanical properties and fracture behavior of newly developed body-centered-cubic-structured TiTaHfNb, TiTaHfNbZr and TiTaHfMoZr high entropy alloys (HEAs) under impact loading as part of an effort to evaluate their potential utility as implant materials. The experimental findings showed all three Ti-based HEAs have lower Young's modulus as compared to the conventionally used implant materials. Fractography analysis revealed that the TiTaHfNb HEA demonstrated significant ductility with the highest energy absorption capacity, while the TiTaHfNbZr and the TiTaHfMoZr alloys exhibited mixed mode fracture with relatively low ductility. Specifically, the reduction of ductility and energy absorption capacity under impact loading was attributed to the addition of Zr and Mo into Ti-based HEA system, which facilitates formation of additional dislocations in the microstructure due to increased lattice distortion. The current findings demonstrate that, from a mechanical point of view, the TiTaHfNb HEA could be considered as an alternative implant material for applications demanding high wear and corrosion resistance, such as hip or knee implants, and thus, warrant further investigation of the biomedical performance of this alloy.

AB - This paper focuses on the mechanical properties and fracture behavior of newly developed body-centered-cubic-structured TiTaHfNb, TiTaHfNbZr and TiTaHfMoZr high entropy alloys (HEAs) under impact loading as part of an effort to evaluate their potential utility as implant materials. The experimental findings showed all three Ti-based HEAs have lower Young's modulus as compared to the conventionally used implant materials. Fractography analysis revealed that the TiTaHfNb HEA demonstrated significant ductility with the highest energy absorption capacity, while the TiTaHfNbZr and the TiTaHfMoZr alloys exhibited mixed mode fracture with relatively low ductility. Specifically, the reduction of ductility and energy absorption capacity under impact loading was attributed to the addition of Zr and Mo into Ti-based HEA system, which facilitates formation of additional dislocations in the microstructure due to increased lattice distortion. The current findings demonstrate that, from a mechanical point of view, the TiTaHfNb HEA could be considered as an alternative implant material for applications demanding high wear and corrosion resistance, such as hip or knee implants, and thus, warrant further investigation of the biomedical performance of this alloy.

KW - Fracture

KW - High entropy alloy

KW - Impact response

KW - TiTaHfMoZr

KW - TiTaHfNb

KW - TiTaHfNbZr

UR - http://www.scopus.com/inward/record.url?scp=85096405398&partnerID=8YFLogxK

U2 - 10.1016/j.msea.2020.140456

DO - 10.1016/j.msea.2020.140456

M3 - Article

AN - SCOPUS:85096405398

VL - 803

JO - Materials Science and Engineering A

JF - Materials Science and Engineering A

SN - 0921-5093

M1 - 140456

ER -