PSI - Issue 42

Tsanka Dikova et al. / Procedia Structural Integrity 42 (2022) 1520–1528

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4 Tsanka Dikova, Angel Anchev, Vladimir Dunchev, Dzhendo Dzhendov, Yavor Gagov / Structural Integrity Procedia 00 (2019) 000 – 000

Fig. 1 (a) Virtual model of the disk for CAD milling with samples located in it; (b) As-received samples on the working table of the SLM machine.

• Surface treatment The samples from each group were divided into 4 subgroups (7 pieces per subgroup) depending on the treatment of their surfaces. The first subset of samples were without surface treatment and served as a control group. The plates of the second subgroup were subjected to sandblasting of only one surface. Sandblasting was performed with Al 2 O 3 (110 µm) under pressure of two bars for time of 10 s. The sample was located at 10 mm distance from the nozzle at an angle of 45°. After sandblasting, the samples were cleaned with steam-jet and air dried. One layer of VITA NP BOND PASTE bonding agent (VITA Zahnfabrik H. Rauter GmbH & Co.KG, Bad Sackingen, Germany) was applied to the surface of the samples from the third group. It was fired at a temperature of 960 °C for 1 min according to the manufacturer's instructions (VITA NP BOND Paste, Instructions for use). The samples of the fourth group were subjected to combined treatment: at first, their surfaces were sandblasted and then bonding agent was applied according to the modes indicated above.

• Porcelain coating A coating of VITA LUMEX AC porcelain (VITA Zahnfabrik H. Rauter GmbH & Co.KG, Bad Sackingen, Germany) with thickness of 1.1±0.1 mm and length of 8±0.1 mm was manufactured according to ISO 9693:2019 in the middle of the treated surface along the entire width of the samples. Four layers of ceramic were sequentially applied and fired according to the manufacturer's instructions (Table 2) (VITA LUMEX AC, Instruction for use).

Table 2. Regimes of porcelain firing. Layer Porcelain

Firing temperature, ( o C)

Time, (s)

1 2 3 4

Opaque Dentin Enamel

800 760 755 750

1 1 1 1

Glaze

2.2. Samples characterization

• Adhesion strength test The experimental study of the adhesion strength of the porcelain coating to the titanium alloy was carried out by means of 3-point bending test according to the standard ISO 9693:2019 "Dentistry. Compatibility testing of metal ceramic and ceramic-ceramic systems". A special device was designed for this purpose (Fig. 2). The tests were performed on a combined static and dynamic testing machine ZWICK Roell Vibrophore 100 (ZWICK Roell, Germany). A static bending test was implemented with loading speed of 1.5 mm/min until a displacement of 0.2 mm was reached. A force/displacement diagram was result of the conducted tests, on which a load drop was registered at the moment of debonding the ceramic layer. The adhesion strength is calculated on formula (1) (ISO 9693:2019): = ∗ (1) Where: is the adhesion strength of the coating (the stress at which a crack occurs or the coating detaches from the metal base); is the load at which the coating is destroyed; k is coefficient, that depends on the thickness and modulus of elasticity of the metal substrate.