Gradient Microstructure Induced by Surface Mechanical Attrition Treatment (SMAT) in Magnesium Studied Using Positron Annihilation Spectroscopy and Complementary Methods.

Konrad Skowron,Ewa Dryzek,Andrzej Baczmański,Paweł Nowak,Marianna Marciszko-Wiąckowska,Manuel François,Benoit Panicaud,Léa Le Joncour,Mirosław Wróbel

doi:10.3390/ma13184002

Abstract

Surface mechanical attrition treatment (SMAT) was used to generate a gradient microstructure in commercial grade magnesium. Positron annihilation lifetime spectroscopy and variable energy positron beam measurements, as well as microhardness tests, electron backscatter diffraction, X-ray diffraction, and electrochemical corrosion tests, were used to investigate the created subsurface microstructure and its properties. It was found that SMAT causes an increase in dislocation density and grain refinement which results in increased hardness of the subsurface zone. The mean positron lifetime values indicate trapping of positrons in vacancies associated with dislocations and dislocation jogs. The increase of the SMAT duration and the vibration amplitude influences the depth profile of the mean positron lifetime, which reflects the defect concentration profile. Electrochemical measurements revealed that the structure induced by SMAT increases the susceptibility of magnesium to anodic oxidation, leading to the enhanced formation of hydroxide coverage at the surface and, as a consequence, to the decrease in corrosion current. No significant effect of the treatment on the residual stress was found.

Highlights

In 2019, primary magnesium production worldwide was estimated at 1.1 million tons/year [1].Global growth in the magnesium market is expected to average 3.4% per year, reaching almost1.2 million tons/year by 2020 [2]
It is known that the extent of the roughness increase in Surface mechanical attrition treatment (SMAT) depends on the ball type and size, the treatment time, and the vibration amplitude [68,69]
The deformed layer created by SMAT in pure magnesium has been investigated

Summary

Introduction

In 2019, primary magnesium production worldwide was estimated at 1.1 million tons/year [1].Global growth in the magnesium market is expected to average 3.4% per year, reaching almost1.2 million tons/year by 2020 [2]. Materials 2020, 13, 4002 steel, titanium, and aluminum alloys It is even lower than the density of most of glass-fiber-reinforced polymers and similar to that of much more expensive carbon–fiber composites [4,5]. Its degradation speed in the body is too fast, and its susceptibility to galvanic corrosion is not acceptable, which was already noticed after its application to leg bone fractures at the end of the 19th century [11,12,13] Both alloying and different treatments are tried to eliminate these drawbacks, i.e., to decrease its degradation speed and increase its strength [14,15,16,17,18]. The demand for short-term non-permanent implants has resulted in the development of a new generation of functional resorbable biomaterials, among them, biodegradable magnesium-calcium alloys tested as a potential material for orthopedic implants [19,20,21]

Methods

Results

Conclusion