Banca de DEFESA: FÁBIO GUSTAVO LIMA PEREIRA

PROCESSING OF NICKEL-BASED ALLOYS HARDENED BY OXIDE DISPERSION VIA MECHANICAL ALLOY AND PLASMA SINTERIZATION IN AN ABNORMAL REGIME

lloys reinforced by oxide dispersion; Mechanical Alloyng; DC electrical discharge sintering

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 particles, rich in Y-Ti-O, dispersed along the microstructures of these materials. The traditional method of processing ODS alloys is via mechanical alloying, followed by consolidation by hot isostatic pressing. Recently, a new technique for sintering materials from powder using pulsed DC electrical discharge was developed by LabMat of the Universidade Federal de Santa Catarina. This technique consists of heating the compact through the bombardment of ionic particles and fast neutral chemical species. In the present work, nickel-based alloys were processed by MA in a
spex mill and sintered in a conventional furnace using a DC electric discharge technique. Furthermore, the nickel-based ODS alloys were developed from the addition of 1.2%𝑌2𝑂3 in a matrix with Ni-20Cr composition. Initially, the properties of starting and milled powders were evaluated using techniques such as x-ray diffraction and scanning electron microscopy, in addition to investigating the effects of processing parameters: milling time (0h, 1h and 2h), temperature (1000 ∘C and 1200 ∘C) and sintering time (30 and 60min) on the microstructural characteristics, density and microhardness of the Nickel based alloy Ni-20Cr-1.2𝑌2𝑂3. Subsequently, 5% by weight of 𝐴𝑙2𝑂3 was added to the alloy Ni-20Cr-1.2𝑌2𝑂3, in order to analyze the effect
of load transfer hardening . The microstructural characteristics of the consolidated alloys were examined using SEM-FEG, while the mechanical properties were evaluated using the Vickers microhardness test. The densities of the sintered samples were determined using the Archimedes principle. Densities between 6.3 and 7.14 g/𝑐𝑚3 were found and microhardnesses between 114 and 266 HV. The surface porosity of the Ni-20Cr-1.2𝑌2𝑂3 alloy was investigated using the image analysis method, considering parameters such as mean pore diameter, shape factor and elongation factor. All microstructural aspects, surface porosity and mechanical properties suggest that plasma sintering processes in abnormal DC glow discharge and in conventional tube
furnace are similar.