RESUMO
The present paper aims to provide an overview of the current state-of-the-art mechanical surface modification technologies and their response in terms of surface roughness, surface texture, and microstructural change due to cold work-hardening, affecting the surface integrity and corrosion resistance of different Mg alloys. The process mechanics of five main treatment strategies, namely, shot peening, surface mechanical attrition treatment, laser shock peening, ball burnishing, and ultrasonic nanocrystal surface modification, were discussed. The influence of the process parameters on plastic deformation and degradation characteristics was thoroughly reviewed and compared from the perspectives of surface roughness, grain modification, hardness, residual stress, and corrosion resistance over short- and long-term periods. Potential and advances in new and emerging hybrid and in-situ surface treatment strategies were comprehensively eluded and summarised. This review takes a holistic approach to identifying the fundamentals, pros, and cons of each process, thereby contributing to bridging the current gap and challenge in surface modification technology for Mg alloys. To conclude, a brief summary and future outlook resulting from the discussion were presented. The findings would offer a useful insight and guide for researchers to focus on developing new surface treatment routes to resolve surface integrity and early degradation problems for successful application of biodegradable Mg alloy implants.
RESUMO
The fast degradation and consequent loss of mechanical integrity is a major problem of biodegradable Mg alloy, which limits its clinical viability. This paper presents the influence of a synergistic approach combining deep ball burnishing and hydroxyapatite (HA) coating on biomechanical integrity, degradation and immune response of Mg alloy (AZ31B). The burnishing resulted in smooth surface topography, increased hardness from 0.87 to 1.45 GPa and induced microstructural disturbances with deformation twins/twin bands, which enabled formation of a dense and compact platelet-like crystals HA coating of 110 µm thickness. Compared to the untreated and burnished specimens, the burnished + HA coated surface provided remarkably higher corrosion resistance as indicated by lower corrosion current density and smaller mass loss. HA coating and surface integrity enhancement by burnishing were predominantly responsible for improved corrosion resistance. HA coating on the burnished surface exhibited hydrophilic properties and adequate bonding strength. While the modified surfaces promoted cell growth, the burnished + HA surface outperformed in exhibiting less pro-inflammatory and high anti-inflammatory cytokines, demonstrating that the treated surfaces were not posing any threat to immune cells. The findings indicate that the synergistic surface treatment can be a viable means to enhance corrosion resistance and immune response of Mg alloys implants.
