Controlled Grain Refinement of Biodegradable Zn-Mg Alloy: The Effect of Magnesium Alloying and Multi-Pass Hydrostatic Extrusion Preceded by Hot Extrusion

Anna Jarzębska,Łukasz Maj,Martyna Strąg,Krzysztof Sztwiertnia,Daniel Wojtas,Magdalena Bieda,Sylwia Przybysz,Bartosz Sułkowski,Robert Chulist,Wacław Pachla

doi:10.1007/s11661-020-06032-4

Abstract

To satisfy the most stringent criteria in terms of new cardiovascular stents, pure Zn was alloyed with 1 wt pct of Mg and subsequently subjected to plastic deformation, using conventional hot extrusion followed by multi-pass hydrostatic extrusion. A detailed microstructural and textural characterization of the obtained materials was conducted, and mechanical properties were assessed at each pass of deformation process. In contrast to pure Zn, hydrostatically extruded low-alloyed Zn is characterized by a remarkable increase in strength and ductility (YS = 383 MPa, E = 23 pct), exceeding the values needed for stents. Such behavior is associated with a dual microstructure containing fine-grained Zn, alternatively arranged with bands of a fragmented eutectic. Extensive grain refinement was achieved due to the process of continuous dynamic recrystallization. Hydrostatic extrusion changes the initial langle 10bar{1}0rangle fiber texture to a 〈0002〉 and langle 10bar{1}1rangle double fiber texture in which the 〈0002〉 component decreases with each pass of hydrostatic extrusion. The gradual evolution of texture components was simulated using a visco-plastic self-consistent model, which confirmed that, during hydrostatic extrusion, secondary slip systems were activated involving mostly the pyramidal one.

Highlights

BIODEGRADABLE metals are a new generation of materials which may be used in medical devices to improve patients’ lives significantly
The materials were subjected to a main plastic deformation in the form of multi-pass hydrostatic extrusion performed in four consecutive steps at room temperature with a cumulative true strain (e)[23] equal to 3.6 and the final diameter of the extruded rods being 5 mm
Replacement of the hard h0002i orientation by the h1011i component is suitable for plastic deformation, since it makes the material less prone to strain localization and to brittle failure. These results show that the application of multi-pass hydrostatic extrusion instead of one operation is more beneficial for better grain refinement, greater elongation and suppression of the recrystallization processes.[21]

Summary

Introduction

BIODEGRADABLE metals are a new generation of materials which may be used in medical devices to improve patients’ lives significantly They can be used for producing temporary implants, which will dissolve in a human body after completing their mission of supporting the healing process of damaged tissue.[1]. An example of an implant that does not require a long-term presence in a patient’s body is a stent This small meshed tube used, among other things, in cardiovascular interventions supports artery walls and keeps the lumen open.[2] Specialized application needs a number of properties such as biocompatibility, a steady corrosion rate, and the appropriate combination of mechanical strength and plasticity.[3] Pure Zn fulfils most of the aforementioned requirements, which makes it a very promising material for biodegradable stents.[4,5,6] as-cast pure Zn has poor mechanical properties (i.e., yield strength, ultimate tensile strength, elongation to failure). It is of great importance to improve the strength and plasticity of pure Zn

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Conclusion