Exceptional high fatigue strength in Cu-15at.%Al alloy with moderate grain size.

Rui Liu,Zhenjun Zhang,Zhefeng Zhang,Xianghai An,Peng Zhang,Yanzhong Tian

doi:10.1038/srep27433

Rui Liu, Zhenjun Zhang + Show 4 more

Open Access

https://doi.org/10.1038/srep27433

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Abstract

It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue strength of 280 MPa at 107 cycles. This value is much higher than the fatigue strength of 200 MPa for the nano-crystalline counterpart (0.04 μm in grain size) despite its higher tensile strength. The remarkable improvement of fatigue strength should be mainly attributed to the microstructure optimization, which helps achieve the reduction of initial damage and the dispersion of accumulated damage. A new strategy of “damage reduction” was then proposed for fatigue strength improvement, to supplement the former strengthening principle. The methods and strategies summarized in this work offer a general pathway for further improvement of fatigue strength, in order to ensure the long-term safety of structural materials.

Highlights

(b) Relationships between stress amplitude and fatigue life
Cu-15at.%Al alloys with ultrafine grains (UFGs) produced by cold rolling and subsequent annealing processes 29 have been investigated in this study
A trade-off relation between tensile strength and uniform elongation can be readily noticed: by decreasing the average grain size, the tensile strength monotonically increases while the uniform elongation continuously decreases

Summary

Introduction

(b) Relationships between stress amplitude and fatigue life. CG: coarse-grained specimens, HPT: specimens fabricated by high-pressure torsion, CR+AN400/500: specimens fabricated by cold rolling and annealing at 400/500 oC; results of CG and HPT were from the work of An et al.[18]. Comparison with the significant increase of the tensile strength, the range of fatigue strength improvement is rather limited[19]. It is probably due to the original damage (including high-density defects[24] and micro-cracks25) induced by SPD methods[26]. Further studies showed that the annealing process following SPD methods can help diminishing the original damage through recrystallization[27,28]; by cold rolling and annealing process[29], better combination of tensile strength and ductility can be achieved. An α-Cu-Al alloy with high Al content (Cu-15at.%Al, which displayed the best fatigue properties in Ans research18,19) is chosen, with the cold-rolling and annealing process[29] (which brings smaller deformation damage in comparison to SPD methods), aiming at improving fatigue strength a step further

Methods

Results

Conclusion