Titanium alloys are active metals and are widely used in aerospace, petrochemical and atomic energy industries. The main characteristics of titanium and titanium alloys brazing are as follows:
The surface of the oxide film stability, titanium and its alloy and oxygen affinity, the surface is easy to produce a very stable layer of oxide film, so that the solder wetting and spreading, brazing must be removed.
(2) has a strong suction tendency, titanium and its alloys in the heating process of hydrogen, oxygen and nitrogen absorption tendency, and the higher the temperature, the more serious absorption, so that the plastic and toughness of titanium metal sharply reduced, so brazing should be carried out in a vacuum or inert atmosphere.
(3) easy to form intermetallic compounds, titanium and its alloy with most of the needle reaction, brittle compounds, resulting in brittle joints. Therefore, the solder used for brazing other materials is generally not suitable for brazing active metals.
Organization and performance are easy to change. Titanium and its alloys undergo phase transition and grain coarsening when heated. The higher the temperature, the more severe the coarsening. Therefore, the temperature of high-temperature brazing should not be too high.
In conclusion, the brazing heating temperature must be paid attention to when brazing titanium and its alloys. Generally speaking, the brazing temperature should not exceed 950-1000, the lower the brazing temperature, the smaller the influence on the base material properties. For quenching aging alloys, brazing can also be done under the condition of aging temperature. In order to prevent oxidation, oxygen absorption and hydrogen absorption reaction of brazing joint, titanium and titanium alloy brazing is carried out in vacuum and emotional atmosphere, generally do not use flame brazing. When brazing in vacuum or argon, high frequency heating and furnace heating can be used, which can make the heating speed faster and the holding time shorter, the compound in the interface area is thinner, and the joint performance is better. Therefore, it is necessary to control the brazing temperature and holding time so that the filler can fill the gap.
The reason why titanium and titanium alloys are best brazed in vacuum and argon is that during vacuum brazing, although titanium has a great affinity for oxygen, titanium can obtain a smooth surface at 13.3Pa vacuum, which is caused by the oxide film on the surface that can dissolve into titanium.
In titanium alloys, there are cadmium and zinc based filler metals, such as s-cd95ag5 / s-zn58sn40cu2, etc. The brazing metal has silver base, titanium base and aluminum base.
When brazing under the protection of argon, the brazing temperature range is 760~927℃. In order to prevent the discoloration of titanium, high-purity argon is required. Liquid argon in refrigerated storage containers is generally used because of its high purity.
