Abstract
In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition.
Highlights
The development of nano- or ultrafine-structured materials (NSMs or USMs) is an important issue of materials research due to their outstanding high strength compared to coarse-grained counterparts, as indicated by the well-known Hall-Petch relationship, and a large number of NSMs and USMs have been developed in Ti, Fe, Zr, Cu, Ni- and Al-based alloys[1,2,3,4,5,6]
As the Cu content increases from the Co-Cr-Mo ternary eutectic alloy (CCM), the peak intensity corresponding to the γ-Co phase becomes stronger and the peak intensity of the Co7Mo6 phase decreases along with the finding that the width of the reflections becomes broader, indicating microstructural refinement
This suggests that the addition of Cu leads to an increased volume fraction of γ-Co and refined Co7Mo6 without change of the constituent phases observed for the Co-Mo-Cr ternary eutectic alloy
Summary
The development of nano- or ultrafine-structured materials (NSMs or USMs) is an important issue of materials research due to their outstanding high strength compared to coarse-grained counterparts, as indicated by the well-known Hall-Petch relationship, and a large number of NSMs and USMs have been developed in Ti-, Fe-, Zr-, Cu-, Ni- and Al-based alloys[1,2,3,4,5,6]. Typical ultrafine-eutectic alloys (UEAs) exhibit poor plasticity because these materials are deformed mainly by highly localized shear bands and show catastrophic failure following highly limited plasticity similar to NSMs or USMs7–9 These restrictions such as limited ductility and low deformability etc. It can be suggested that the deformation of materials exhibiting a lower n value is more dominated by dislocations than that for higher n values, which is responsible for high hardness at low loading conditions[19,20] Along with this line, Das et al have reported that the dislocation-based deformation mechanisms including dislocation-lamellae interaction and slip transfer across the lamellae interfaces are still important factors for improving the global plasticity as well as for controlling shear bands in Ti-Fe-(Sn) UEAs18,19. The microscopic deformation mechanisms will be systemically discussed, revealing that the mechanical properties of eutectic alloys can be improved by the multiple mechanisms involved in the TWIP, TRIP, and lamellar interfacial interaction
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