About the titanium foil using in the brazed construction of small windows for the transmission of radiant energy

Abstract

The aim of this work was to miniaturize the design of a brazed joint of a thin non-metallic disk with a hollow thin-walled metal cylinder for operation as part of a vacuum device in a wide temperature range. For brazing a non-metallic disk with a glass tube-shaped device body, when choosing a metal filler, the fragility of glass, its low mechanical strength in bending and tensile and a lower thermal coefficient of linear expansion than metal fillers must be taken into account. Therefore, the use of low-temperature plastic solders based on tin, indium, lead etc., which are alloyed with titanium, is preferable. However, the disadvantages of these fillers include a significant decrease in mechanical strength when the brazed unit is heated to relatively low temperatures, especially if there is a gas inside the device under excessive pressure. The option of brazing a leucosapphire disk with a glass tube was also considered. A design has been proposed to determine how a disk is connected to a titanium body. This design has increased the heat resistance of the leucosapphire lens, which is connected to the body of the product made of titanium alloy or covar. Such connection can be used as pyrometer windows installed directly in the body of an internal combustion engine or gas turbine engine. The main feature of this development was the creation of a brazed joint structure in which the shell covering the disk is made of non-metal, in this case of leucosapphire, made of titanium foil with a thickness of 100 and in some cases 50 μm. Brazing modes were set and brazed windows were made. Tests on the vacuum density after different modes of thermal cycling of brazed samples showed high performance of this structure of the brazed joint. It was shown that the use of titanium foil makes it possible to obtain high-quality heat-resistant brazed joints. The relatively small stresses that lead to plastic deformation of the foil make it possible to increase the inconsistency of the thermal coefficient of linear expansion (TCLE) of materials that were brazed. It shout be noted that the foil material can also be other metals which had chemical active towards non-metallic materials or their components, for example, zirconium, niobium, tantalum, etc. Keywords: structures of brazed joints, brazing of non-metals, non-metallic materials, leucosapphire, glass tube, adhesive-active filler metals, fillers, titanium.