Effects of nanofeatures induced by severe shot peening (SSP) on mechanical, corrosion and cytocompatibility properties of magnesium alloy AZ31

Abstract

The application of biodegradable magnesium-based materials in the biomedical field is highly restricted by their low fatigue strength and high corrosion rate in biological environments. Considering the sensitivity of both fatigue strength and corrosion rate to the surface characteristics of the material, apposite surface treatments could address these challenges. As a low cost and versatile severe plastic deformation technique aimed at inducing surface grain refinement, severe shot peening has been effective in enhancing mechanical properties and promoting cellular interactions on non-degradable biocompatible metallic materials. Herein, we treated the surface of a biocompatible magnesium alloy AZ31 by severe shot peening in order to evaluate the potential of surface grain refinement to enhance its functionality in a biological environment. The AZ31 samples were studied in terms of a wide variety of micro/nanostructural, mechanical, and chemical characteristics in addition to cytocompatibility properties. The evolution of surface grain structure and surface morphology were investigated using optical as well as scanning and transmission electron microscopy. Surface roughness, wettability and chemical composition, as well as in depth-microhardness and residual stress distribution, and corrosion resistance were investigated. Successive light surface grinding was used after severe shot peening to eliminate the effect of surface roughness and separately investigate the influence of grain refinement alone. Cytocompatibility tests with osteoblasts (or bone forming cells) were performed using sample extracts. Results revealed for the first time that severe shot peening can significantly enhance mechanical properties without causing adverse effects to the growth of surrounding osteoblasts. The corrosion behavior, on the other hand, was not improved by severe shot peening; nevertheless, slight grinding of the rough surface layer with a high density of crystallographic lattice defects, without removing the entire nanocrystallized layer, provided a good potential for improving corrosion characteristics after severe shot peening and thus, this method should be studied for a wide range of orthopedic applications in which biodegradable magnesium is used.

Integrated Numerical-Experimental Assessment of the Effect of the AZ31B Anisotropic Behaviour in Extended-Surface Treatments by Laser Shock Processing

“…It is attractive for the biomedical industry in implant design, since it is degradable, with outstanding mechanical properties in comparison with polymers [3][4][5]. This has led to a great number of studies regarding mechanical properties enhancement [6][7][8], corrosion resistance [5,[7][8][9][10][11] and microstructure modifications [12][13][14], among others. Single Mg crystal responses to shock loading in various conditions and orientations is also documented, including the study of the spall fracture [15], confirming the main mechanisms of hexagonal-closed-packed (hcp) crystals subject to uniaxial shock compression.…”

Tailoring biomineralization and biodegradation of Mg–Ca alloy by acetic acid pickling

“…Though Ca was effective to inhibit degradation rate, its higher concentration can cause detrimental effects by accelerating the degradation [17]. The various surface modifications attempted include conversion coatings [18], deposition of thin films by various coating techniques [19][20][21][22] and mechanical processing of the surfaces [23][24][25]. The mechanical methods have a demerit of causing surface impurities that accelerate degradation by creating galvanic couples in the sample surface [26,27].…”

Corrosion behavior and mechanical degradation of as‐extruded Mg–Gd–Zn–Zr alloys for orthopedic application

“…Controlling degradation and providing mechanical support are very important aspects of biodegradable Mg alloys during use (Erinc, Sillekens, Mannens, & Werkhoven, ; Zheng, Gu, & Witte, ). However, achieving satisfactory levels of these is difficult because most Mg alloys undergo localized corrosion that can easily lead to undesired corrosion and premature loss of mechanical integrity (Bagherifard et al, ; Virtanen, ).…”