Abstract
Titanium alloy Ti-6Al-4V is known for both its excellent mechanical properties and its low surface hardness. This study explores a two-step process for depositing a hard nanocrystalline coating onto the surface of the Ti-alloy, followed by surface melting, which embeds hard nanoparticles into a thin surface layer of the alloy. The treated surface layer was studied using X-ray diffraction, scanning electron microscopy, and Vicker’s micro-hardness testing. The results of the study show that the surface of the Ti-6Al-4V alloy can be successfully hardened by embedding nanosized Al2O3 particles into the surface using gas tungsten arc welding to melt the surface of the material. Surface melting the Ti-6Al-4V alloy with a 50A welding current produced the maximum microhardness of 701 HV0.2kg. The micro-hardness of the treated surface layer decreased with the increasing size of the nanoparticles, while the roughness of the surface increased with the increasing welding current. The heat input into the surface during the surface melting process resulted in the formation of various intermetallic compounds capable of further increasing the hardness of the Ti-6Al-4V surface.
Highlights
Titanium alloys find application as a structural material used in the manufacturing of engineered components that require properties such as excellent corrosion resistance, good strength-to-weight ratio, toughness, and biocompatibility [1,2,3,4]
Analysis of the treated surface showed that the composition of the coating deposited and the magnitude of the welding current or heat input strongly influence the type of microstructures that formed
The surface texture appears to follow a random configuration; the results show that the surface contained un-melted remains of the coating deposited on the surface at the beginning of the process
Summary
Titanium alloys find application as a structural material used in the manufacturing of engineered components that require properties such as excellent corrosion resistance, good strength-to-weight ratio, toughness, and biocompatibility [1,2,3,4]. The effect of the alloying element is the stabilization of α and β phases. The addition of Al, O, N of C causes stabilization of the α phases while the addition of elements such as V, Mo, Mn, Cr, Ni, resulting in stabilization of the β phase [6]. Hardening of α and β phases of titanium can be achieved by solid solution strengthening of α phases leading to the transformation to α’ of α” martensitic structure. The transformation of the β phase, leads to the formation of a metastable structure with improved mechanical properties [7]
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