Failure of Porcelain Coating on Milled and SLM Fabricated Titanium Alloy with Different Surface Treatment

Abstract

The present paper aimed at investigating the influence of surface treatment on the failure of porcelain coating on Ti6Al4V alloy fabricated by milling and selective laser melting (SLM). The titanium alloy surface was treated by three different ways: sandblasting, application of a layer of bonding agent and combined (sandblasting and subsequent bond layer). A coating of ultra-low fusing ceramic was fabricated on one surface of the samples. The adhesion of the porcelain to the titanium alloy was investigated by standard 3-point bending test and the failure of the coating was evaluated by optical microscopy. It was found that the type of surface treatment of the titanium alloy affects the failure mechanism of porcelain coating on its surface. In case of all samples, the fracture of the ceramics was observed to occur by a mixed adhesion-cohesion mechanism with a difference in the layer of adhesive or cohesive failures. These differences are greater for the milled alloy compared to its SLM-treated counterpart. In the milled sample, adhesive failure occurs along the metal/oxide layer interface and cohesion through the oxide layer. After sandblasting, both adhesion and cohesion fractures were observed between the oxide layer and the porcelain. In the bond-treated samples, adhesive and cohesive failures were found to occur mainly between the oxide layer and the bond. Most of the specimens treated in a combined way failed cohesively by cracking the ceramic coating. In the control and sandblasted subgroups of the SLM-processed alloy, the porcelain coating was destroyed through adhesive-cohesive route: adhesive along the metal/oxide layer interface, and cohesive through the porcelain. Ceramic fracture in the bond- and combined treated subgroups was observed to occur adhesively along the bond/porcelain interface, and cohesively through the bond and porcelain.