Abstract
In this study, the influence of ultrasonic nanocrystal surface modification (UNSM), which was applied as a post-additive manufacturing (AM), in terms of surface, tensile and tribological properties of Ti-6Al-4V alloy by selective laser melting (SLM) was investigated. Ti-6Al-4V alloy was subjected to UNSM at room and high temperatures (RT and HT). It was found that the UNSM enhanced the strength and reduced the roughness of the as-SLM sample, where both increased with increasing UNSM temperature. The UNSM bore influence on tribological properties, where the friction coefficient of the as-SLM sample reduced by about 25.8% and 305% and the wear resistance enhanced by about 41% and 246% at RT and HT, respectively. These are essentially attributed to the enhanced strength, smoothed surface and expelled pores from the surface. Based on SEM images, the damage caused by abrasive wear was the most observed in the wear track of the as-SLM sample than was caused by the highest wear rate. The UNSM temperature-dependent wear mechanisms were comprehensively investigated and elaborated based on the obtained experimental data and observed microstructural images. Indeed, a further investigation is required to improve the characteristics of as-SLM Ti-6Al-4V alloy to the wrought level due to the replacement possibility.
Highlights
Ti-6Al-4V alloy is a metallic material that attracts much attention from many researchers due to its biocompatibility, good corrosion resistance and high specific strength
The initiated cracks are the indication of over-peening leading to an excessive strain hardening, where the amalgamated impact of ultrasonic nanocrystal surface modification (UNSM) and thermal energy resulted in surface degradation, and imposing practical limitation in terms of surface quality rather than strength
An appearance of UNSM-induced isolated cracks can be explained in three stages: (1) the stage of strain hardening that consists of an intensive increase in surface roughness; (2) the stage of saturation, where a plastic shearing takes place leading to a reduction in dislocation density and cracks initiated; (3) the stage of surface damage, the integrity of surface is destroyed leading to an appearance of cracks, where the surface roughness increases
Summary
Ti-6Al-4V alloy is a metallic material that attracts much attention from many researchers due to its biocompatibility, good corrosion resistance and high specific strength. Due to these excellent properties, various components are made of Ti-6Al-4V alloy for biomedical and aerospace applications such as medical implants, aerospace crafts, gas turbines etc. Selective laser melting (SLM) is one of AM that capable of processing a wide range of metals, alloys and metal matrix composites [3] This method is commonly used for fabrication of Ti-6Al-4V alloy components of those industries. Attempts for improving their properties have been a critical subject for researchers for overall properties of SLM fabricated Ti-6Al-4V alloy parts [4].
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