PSI - Issue 42

Tsanka Dikova et al. / Procedia Structural Integrity 42 (2022) 1520–1528 Tsanka Dikova, Angel Anchev, Vladimir Dunchev, Dzhendo Dzhendov, Yavor Gagov / Structural Integrity Procedia 00 (2019) 000 – 000 3

1522

The new CAD/CAM technologies for production of metal substructures provide stronger adhesion of porcelain to the pure titanium and its alloy Ti6Al4V made by casting (Antanasova et al. (2018)). For the pure titanium, the adhesion strength values are 46.33 MPa for milled samples and 34.17 MPa for casts. It is found that there is no great difference between the adhesion of porcelain to milled pure titanium (45.23 MPa) and Ti6Al4V alloy produced by CAD/CAM technologies (43.18 MPa). The use of sandblasting and bonding agent increase the adhesion strength to Ti6Al4V alloy made by milling and SLM (Antanasova et al. (2020)). The highest values are obtained after combined treatment: 37.3 MPa for milled and 36.7 MPa for SLM samples. Therefore, the manufacturing method in CAD/CAM technologies does not have a significant effect on the adhesion strength. Pre-oxidation has a negative effect on the adhesion strength of Ti6Al4V alloy made by SLM (Antanasova et al. (2021)). Increasing the oxidation temperature leads to the formation of a thicker oxide layer on the surface of the metal and to a lower adhesion strength. To obtain the best adhesion, passivation of the titanium alloy at room temperature and subsequent sandblasting of the surface is recommended. As can be seen, there remain a number of unsolved questions regarding the adhesion strength between the titanium and its alloys on the one hand and dental ceramics on the other. Despite the fact that the newCAD/CAMmanufacturing technologies such as milling and SLM provide successful control of the thickness of titanium oxide on the surface of the metal substructure (Antanasova et al. (2018)), the unsolved questions not only do not decrease, but also increase due to the constant development of new types of dental ceramics. The purpose of the present paper is to investigate experimentally the adhesion strength of a coating of low temperature dental ceramic to Ti6Al4V alloy produced by milling and selective laser melting. Before applying the porcelain, the surface of the titanium samples is treated by sandblasting, application of bonding agent and combined treatment, including sandblasting and a layer of bonding agent. 2. Materials and methods 2.1. Materials and technologies for samples manufacturing Two groups of samples (28 pieces in each group) were made from Ti6Al4V alloy by means of CAD/CAM milling and selective laser melting. The samples were plate-shaped with length of 25+/-1 mm, width of 3+/-0.1 mm and thickness of 0.5+/-0.05 mm according to the standard ISO 9693:2019. A virtual model of the plate was created with the help of SolidWorks software, which was used for the production of all samples using both technologies. CAD/CAM milling The specimens were fabricated from Starbond Ti5 Disc (Ti6Al4V milling Grade 5 “ELI”) for type 4 dental restorations according to ISO 22674 with chemical composition given in Table 1 (Ti Milling Discs). The blank used was in the disk shape with thickness of 10 mm and diameter of 98.3 mm, Ref. 136510. The position of the samples during milling is shown in Fig. 1a. The plates were milled on a CORITEC 650i Loader machine (Imes-Icore GmbH, Eiterfeld, Germany) under constant cooling. •

Table 1. Chemical composition of Ti6Al4V alloy (milling disc - 1 and powder for SLM - 2). Chemical element, (%) → Al C H Fe

N

O

Ti

V

Alloy ↓ 1

Starbond Ti5 Disc CT PowderRange Ti64 F

6.2

<0.4 0.08

<0.4 0.012

<0.4 0.25

<0.4 0.05

<0.4 0.13

89.4 Rest

4

2

5.50-6.50

4.50

• Selective laser melting CT PowderRange Ti64 F powder alloy (Carpenter Additive, Liverpool, UK) with chemical composition given in Table 1 (Technical data sheet (2019), Datasheet (2020)) was used for the SLM samples. They were fabricated on a SYSMA MySint 100 machine (SYSMA S.p.A., Vicenza, Italy) equipped with a fiber laser. The following SLM process parameters were used: laser power 200 W, laser beam spot diameter 55 µm, layer thickness 20 µm, scan step 0.020 mm, protective gas argon. The position of the specimens and supports during SLM is shown in Fig. 1b. In order to relieve the internal stresses, after fabrication, the samples were subjected to annealing according to the manufacturer's instructions.