Sinterização a plasma e propriedades de ligas Ni-Cr endurecidas por dispersão de óxidos

Abstract

Oxide Dispersion Reinforced Alloys (ODS) are known for their high application potential as structural materials in power generation systems or in the petrochemical industry, mainly due to their highly stable microstructure and high creep resistance. These characteristics are associated with the presence of a high density of dislocations and grain boundaries that are effectively anchored by ultrafine oxide particles dispersed along the microstructures of these materials. In the present study, Nickel-based ODS alloys were processed via high-energy ball milling for 1 and 2 hours. The milled powders were compacted at 600 MPa and subsequently sintered in a tubular furnace and in a plasma furnace under abnormal conditions at temperatures of 1000 ∘C, 1100 ∘C, 1150 ∘C e 1200 ∘C. Ni-Cr alloys with the compositions Ni-20Cr, Ni-20Cr-1,2𝑌2𝑂3 and Ni-20Cr-1,2𝑌2𝑂3-5𝐴𝑙2𝑂3 were developed and characterized. The effects of the composition and the processing parameters milling time, sintering temperature and sintering time on the microstructural characteristics, density and microhardness of the milled powders and consolidated alloys were then investigated. The microstructural aspects of the sintered alloys were analyzed using Electron Backscatter Diffraction (EBSD), X-ray diffraction, and Energy Dispersive Spectroscopy (EDS) techniques, while the mechanical properties were evaluated using the Vickers microhardness test and the density using the Archimedes principle. Higher sintering temperatures resulted in alloys with higher microhardness and density (7,181 g/𝑐𝑚3 e 260 HV, 7,09 g/𝑐𝑚3 e 255 HV, for samples sintered in tubular and plasma furnaces, respectively. The addition of 1.2% 𝑌2𝑂3 to the Ni-20Cr matrix significantly reduced the grain size of the alloy. The highest microhardness was found for the Ni-20Cr-1.2𝑌2𝑂3-5𝐴𝑙2𝑂3 alloy (339 HV) and was attributed to the combined effect of dispersion and composite strengthening mechanisms. All the microstructural aspects and mechanical properties suggest that the plasma sintering in abnormal discharge and tube furnace sintering are similar processes.