ESR as a fast technique to dissolve nitrogen-rich inclusions in titanium

Nitrogen-rich inclusions can lead to a reduction in fatigue life of highly stressed titanium-alloy components (found in the compressor sections of power generation gas turbines, turbine sections of power generation steam turbines, wing sections of aircraft air frames, and compressor and fan sections of aircraft jet engines, for example). It is the ”crack starting” nature of the nitrogen-rich inclusions that is the problem, not the presence of nitrogen in the system, per se. This paper covers the theory and laboratory experiments used to evaluate ESR (electro-slag refining) as an alternative technique for rapid dissolution of nitrogen-rich inclusions in titanium and titanium alloys. Five variations of melt rate, slag temperature and inclusion type were evaluated. One variant showed complete dissolution of the inclusions. Several of the other variants showed partial dissolution of the inclusions. The kinetics were observed to occur at a rate 100 to 1000 times faster than the rate of dissolution of nitrogen-rich inclusions by immersion in liquid titanium.