Powder characteristics blending and microstructural analysis of a hot-pack rolled vacuum arc-melted γ-tial-based sheet

Abstract

In the quest for cost-effective fabrication processes capable of producing sound γ-TiAl products, the microstructure and mechanical properties of a modified second-generation hot-rolled γ-TiAl-based alloy with nominal composition Ti-48Al-2Nb-0.7Cr-0.3Si were investigated in this work. The alloy was fabricated using a processing route that involved uniaxial cold-pressing of powders and vacuum arc re-melting. Prior to the cold pressing, the elemental powder characteristics, such as particle sizes and morphologies, were blended to minimise porosity in the compact that might be inherited by the final ingot. A hot-pack rolling process was carried out directly from the melted button-ingot using a conventional two-high rolling mill to produce a 4 mm-thick sheet. The relative density results of both as-compacted and as-melted alloy parts showed a significant reduction of porosity in the alloy. In addition, both the optical and the scanning electron microscopy micrographs of the rolled sheet revealed a typical 'duplex' microstructure with a mean grain size of about 9 urn. Moreover, the results from a room-temperature indentation plastometry test of the hot-rolled sheet indicated good mechanical properties with recorded yield strength of about 600 MPa, an ultimate tensile strength of about 850 MPa, and a true plastic strain of about 3%.

In 'n soektog na koste-effektiewe vervaardigingsprosesse wat in staat is om goeie γ-TiAl-produkte te produseer, is die mikrostruktuur en meganiese eienskappe van 'n gemodifiseerde tweedegenerasie warmgewalste γ-TiAl-gebaseerde legering met nominale samestelling Ti-48Al-2Nb-0.7Cr-0.3Si ondersoek. Die legering is vervaardig deur gebruik te maak van 'n verwerkingsroete wat eenassige koue pers van poeiers en vakuumbooghersmelting behels. Voor die koue pers is die elementêre poeierkenmerke, soos deeltjiegroottes en morfologieë, vermeng om porositeit in die kompak te minimaliseer wat deur die finale steen geërf kan word. 'n Warmpak-walsproses is direk vanaf die gesmelte knoppiesblok uitgevoer met behulp van 'n konvensionele twee-hoë walswerk om 'n 4 mm-dik plaat te vervaardig. Die relatiewe digtheidsresultate van beide as-saamgepakte en as-gesmelte legeringsdele het 'n beduidende vermindering van porositeit in die legering getoon. Daarbenewens het beide die optiese en die skandeer-elektronmikroskopie mikrograwe van die gerolde vel 'n tipiese "dupleks" mikrostruktuur met 'n gemiddelde korrelgrootte van ongeveer 9 urn geopenbaar. Boonop het die resultate van 'n kamertemperatuur inkepingsplastometrietoets van die warmgewalste plaat goeie meganiese eienskappe met aangetekende vloeisterkte van ongeveer 600 MPa, 'n uiteindelike treksterkte van ongeveer 850 MPa en 'n ware plastiese vervorming van ongeveer 3% aangedui.