*2.5. Apparent Shear Strength Determining*

Researchers divide methods for determining adhesion into two groups: the pull-off strength measurement of adhesion and the apparent shear strength of single-lap-joint adhesively bonded specimens. Nowadays there are a number of standardized methods for their determination: ISO 4624:2002, ASTM C633-01, ASTM D7234-05, ASTM D1002-10, ASTM D4541, ISO 9693-1:2012. Mainly these standards were developed for paints and varnishes, for thermal spray coating materials, for rigid plastics, for metal to metal. For metal-ceramic materials, standardized methods have not been found during the study of this issue (except ISO 9693-1:2012). ISO 9693-1:2012 is focused on normal strength, but in the research the focus was on shear strength. It leads from the assumption that surface morphology critically influences shear [32]. Therefore, in this work, an approach to determine the apparent strength is based on the developed standards for adhesively bonded metal specimens. In this regard, for determining the apparent shear strength of the adhesive ceramic layer taken as a basis ASTM D1002-10 (Standard test method for apparent shear strength of single-lap-joint adhesively bonded metal specimens by tension loading) [38]. Similar approach was used in other researches [34–36].

The samples were tested on a universal testing machine UTS 110M-100 (Ivanovo, Russia). The range of measured loads is 0.001–100 kN, load measurement error less than 1% from the statement, up to 1/100 from the value of the permissible load. The test method is to obtain the value of the tensile load of failure of two samples bonded together with ceramics. The forces tending to shift one half of the sample relative to the other showed in Figure 3, strain rate was equal to 1 mm/min. To decrease the bending stresses during the shear test, the thickness of the metal frames was equal to 1.8 mm. Shear strength can be calculated by the following equation:

$$
\pi = \frac{F}{A} \tag{1}
$$

where *F* is the failure load (N), *A* is the area (mm<sup>2</sup> ) of the contact surface (ceramic joint).

**Figure 3.** Sketch of the sample, dimensions and loading scheme: the ceramic layer is highlighted by red; the cobalt-chromium sample is highlighted by green; the centering plates highlighted by magenta; the contact surfaces highlighted by blue. **Figure 3.** Sketch of the sample, dimensions and loading scheme: the ceramic layer is highlighted by red; the cobalt-chromium sample is highlighted by green; the centering plates highlighted by magenta; the contact surfaces highlighted by blue.

Statistical analysis of the data was carried out using the MatLab software. The re-

Samples were prepared according to the study protocol and divided by groups with the following marks: polishing (*n* = 3)—PL; milling (*n* = 3)—MC; abrasive blasting, with an abrasive size of 50 μm (*n* = 12), abrasive size 90 μm (*n* = 3), abrasive size 125 μm (*n* =

During plasma-electrolyte treatment, the surface relief formation occurs due to the combustion of individual microdischarges that melt the surface. For local melting, it is necessary that at the ignition point of the gas discharge, the temperature of the cobalt-chromium alloy S&S Scheftner (Mainz, Germany) becomes higher than the solidus temperature of 1170 °C, preferably above the liquidus temperature of 1390 °C. The melting process is beginning when the solidus temperature is exceeded. A completely liquid metal can be obtained only at temperatures above 1390 °C. It is known that the casting temperature recommended by the manufacturer is 1490–1540 °C. At these temperatures the alloy has good fluidity and there is no burnout of alloying elements. Insufficient invested discharge power will not allow to achieve the required heating of the sample and lead to local melting with the formation of microholes. And a higher power can lead to overheating of the entire sample and its melting with loss of geometry, which is unacceptable. It should also be noted that the treatment proceeds more intensively on sharp and protruding surfaces, this is explained by the greatest intensity of the electric

Thus, when processing samples, it is necessary to take into account their geometry, mass and properties of the alloy. With a sample thickness of a metal plate of 1.8 mm, surface melting occurred at a voltage of U = 220 V and a current strength of I = 12 A, and

3)—AB50, AB90, AB125 respectively; plasma-electrolyte processing (*n* = 16)—PZ.

*3.1. The Surface Microrelief Formation by Plasma-Electrolyte Treatment* 

Nonparametric measurements are given in the following format: median (Me) and interquartile range of 25–75 (Q1–Q2). A normal distribution check was carried out using the Jarque-Bera test. To compare groups two-sample t-test (*p* < 0.05) and Kolmogorov– Smirnov test were used. The interpolation of the data was carried out using the

*2.6. Statistical Processing of Experimental Data* 

least-squares method.

field in these places.

**3. Results** 
