Corrosion behaviour of the new gas turbine alloy 2100 GT in hot gases and combustion products

Not only excellent high temperature mechanical properties are needed to est ablish a new gas turbine alloy, but also a very good oxidation behaviour, t ogether with good resistance to so-called "hot corrosion". This paper descr ibes experimental studies on the corrosion behaviour in hot gases and combu stion products of a new Ni-Cr-Ta alloy 2100 GT in comparison to the commerc ially established alloys 230, C-263 and 617. Alloy 2100 GT is a newly developed cobalt, tungsten and molybdenum free Ni- base superalloy of Krupp VDM. It contains as major alloying elements 25 wt. -% chromium, 8 wt.-% tantalum, 2.4-3 wt.-% aluminium and 0.2-0.3 wt.-% carb on. High temperature strength is achieved by the addition of tantalum, resu lting in significantly increased solid solution strengthening, carbide hard ening due to the formation of primary precipitated tantalum carbides, and g amma'-precipitation hardening by aluminium and tantalum. The isothermal oxidation tests showed that the parabolic rate constant of a lloy 2100 GT is similar to that of alumina-forming alloys. This is achieved by the remarkably high aluminium content for a wrought alloy. Additions of yttrium improve the spalling resistance under thermal cycling by the forma tion of very thin and tightly adherent oxide layers. No deleterious effect caused by the addition of tantalum could be found. In the cyclic oxidation tests performed at temperatures between 700 degreesC and 1200 degreesC allo y 2100 GT showed the lowest mass change of all the alloys investigated. Na2SO4 has been found to be a dominant component of alkali salt deposits on gas turbine components at elevated temperatures. Combustion gases contain SO2 because of the impure nature of the fuel. To investigate the hot corros ion behaviour of alloy 2100 GT, tests were performed with salt deposits con taining 0.1 mol Na2SO4 and a test gas comprising air and 0.1% SO2. Test tem peratures were 600 degreesC, 700 degreesC, 850 degreesC and 950 degreesC. A lloy 2100 GT exhibited the best performance at all test temperatures. It wa s the only alloy which did not suffer any fluxing of the oxide layer and on ly slight internal sulphidation was observed.