National University of Science and Technology MISiS, Moscow, Russia:

N. I. Polushin, Head of Scientific-Research Laboratory “Super-hard materials”
I. Yu. Markova, Junior Researcher of Scientific-Research Laboratory “Superhard materials”
A. I. Laptev, Chief Researcher of Scientific-Research Laboratory “Super-hard materials”, e-mail: laptev@misis.ru
M. N. Sorokin, Senior Researcher of Scientific-Research Laboratory “Superhard materials”

The purpose of this paper is to determine the composition of solder for soldering of PCD composites to a steel casing during the production of PDC bits. Two solders were chosen to be researched: silver PSr40 and brass P47, widely used for soldering of carbide tools. The paper presents the results of experimental studies on the strength of soldering when using these 0,45 C steel brazing alloys with the WC – 15Co hard alloy. The soldering was carried out by the HD method on the VCH-25AV unit and by using the PV284X flux. The PSr40 and P47 solders were used to limit the soldering temperature, which should not exceed the temperature of thermal resistance of PCD diamond composite materials. The research results showed that during the brazing process with the P47 solder, the latter was chemically interacting with hardalloy cobalt and formed the Co₃ZnC_x compound, which led to destruction of the brazed samples during the rupture test on the carbide. This was due to a decreased level of cobalt and a decreased strength of its surface zone. The study of the solder joints WC – 15Co and P47 with a field emission scanning electron microscope showed that the depth of a hard-alloy cobalt etching in the undisturbed part of the sample equals 0.05–0.1 mm. In the samples with PSr40 soldering, a fracture occurs, as a rule, partially on the solder (hard alloy interface), and partly along the body of the solder. The etching of hard-alloy cobalt did not change, which is explained by a lower soldering temperature of the PSr40. The results of both breaking and shearing test on the welded specimens are presented. The tensile tests showed that the strength of solderbonded samples, welded with the PSr40, is significantly higher than (approximately by a factor of 2) the strength of the samples, welded with the P47 solder. According to the results of the tensile and shearing tests, silver solders (silver level is higher than 40%) can be recommended for use in the production of diamond tools made from hard-alloy composite materials such as PCD, including the manufacture of PDC bits. According to this, soldering of PCDcutting elements with the PSr40 solder at the temperatures up to 700 °C does not decrease their performance.

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