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 pow er generation gas turbines, turbine sections of power generation steam turb ines, wing sections of aircraft air frames, and compressor and fan sections of aircraft jet engines, for example). It is the "crack starting" nature o f the nitrogen-rich inclusions that is the problem, not the presence of nit rogen in the system, per se. This paper covers the theory and laboratory ex periments used to evaluate ESR (electro-slag refining) as an alternative te chnique for rapid dissolution of nitrogen-rich inclusions in titanium and t itanium alloys, Five variations of melt rate, slag temperature and inclusio n type were evaluated. One variant showed complete dissolution of the inclu sions. Several of the other variants showed partial dissolution of the incl usions. The kinetics were observed to occur at a rate 100 to 1000 times fas ter than the rate of dissolution of nitrogen-rich inclusions by immersion i n liquid titanium.