Improvement of the Oxidation Resistance of Dispersion Strengthened Nickel-Chromium Alloys

The cyclic dynamic oxidation and hot corrosion behavior at 2000F (1093C) and 2200F (1204C) of Ni/Cr/ThO2 alloys modified by additions of 5 w/o aluminum and 0.2 w/o yttrium or 3 - 5 w/o manganese were measured. Alloys of the composition Ni/16-20Cr/5Al/2ThO2 exhibited the best oxidation resistance having a smaller weight change and less damage by spalling or erosion than the manganese-modified alloys. A thermomechanical procedure was defined to produce a coarse grain microstructure in the aluminum-modified alloys. The procedure consists of primary working by extrusion followed by secondary working by swaging or rolling. The resulting coarse grained alloys have good stress-rupture strength at 2000F (1093C) but the ultimate tensile strength is low. A coarse thoria size resulting during processing of the powder through the consolidation step was believed to have contributed to the low tensile strengths at 2000F (1093C). (Author)