Weldability Analysis Of Titanium And Titanium Alloys

(1) Embrittlement caused by interstitial element contamination

Titanium has a strong chemical reaction activity at high temperatures. Titanium rapidly absorbs hydrogen above 300°C, oxygen above 600°C, and nitrogen above 700°C. Therefore, if titanium is not effectively protected during the welding process and post-welding cooling process, it will inevitably result in decreased plasticity and increased brittleness. The mass fraction of carbon in general titanium materials is controlled below 0.1%. When carbon exceeds its solubility, the formation of hard and brittle TiC, and a reticulate distribution, easy to produce cracks.

(2) Thermal cracking

Because of the low impurity content of titanium and titanium alloy, it is not easy to produce thermal cracks. However, if the quality of the wire is unqualified, especially if there are cracks, interlayers and other defects in the wire. When there are more impurities, welding hot cracks may occur.

(3) Delayed cracking may occur in the heat affected zone

When welding, hydrogen in the molten pool and base material in the low-temperature zone diffuses into the heat-affected zone, resulting in hydrogen accumulation in the heat-affected zone and cracking under unfavorable stress conditions.

(4) Cavitation

Porosity is the most common defect in titanium and titanium alloy welding. There are generally two kinds of porosity in the middle of the weld and fusion line porosity. When the weld energy is large, the porosity is generally located near the fusion line. The main reason for the formation of weld porosity is that the weld zone, especially the butt end face, is contaminated by moisture and grease.