Low-cycle fatigue behaviour of titanium-aluminium-based intermetallic alloys : a short review

DATA AVAILABILITY STATEMENT: Data sharing not applicable.Over the past decade, relentless efforts have brought lightweight high-temperature γ-TiAl-based intermetallic alloys into real commercialisation. The materials have found their place in General Electric’s (GE) high bypass turbofan aircraft engines for the Boeing 787 as well as in the PW1100GTF engines for low-pressure turbine (LPT) blades. In service, the alloys are required to withstand hostile environments dominated by cyclic stresses or strains. Therefore, to enhance the fatigue resistance of the alloys, a clear understanding of the alloys’ response to fatigue loading is pivotal. In the present review, a detailed discussion about the low-cycle fatigue (LCF) behaviour of γ-TiAl-based alloys in terms of crack initiation, propagation and fracture mechanisms, and the influence of temperature and environment on cyclic deformation mechanisms and the resulting fatigue life has been presented. Furthermore, a comprehensive discussion about modelling and prediction of the fatigue property of these alloys with regard to the initiation and propagation lives as well as the total fatigue life has been provided. Moreover, effective methods of optimising the microstructures of γ-TiAl-based alloys to ensure improved LCF behaviour have been elucidated.Thuthuka National Research Foundation and the APC was funded by the Council of Scientific and Industrial Research (CSIR).https://www.mdpi.com/journal/metalsMaterials Science and Metallurgical EngineeringSDG-07:Affordable and clean energySDG-09: Industry, innovation and infrastructur

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

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.Presented at the 23rd Annual International Conference of the Rapid Product Development Association of South Africa (RAPDASA) Institute for Industrial Engineering, held from 9 to 11 November 2022 in Somerset West, South Africa.The Council of Scientific and Industrial Research.http://sajie.journals.ac.zaam2023Materials Science and Metallurgical Engineerin

Vacuum melting of compressed powders and hot rolling of the as-cast Ti-48Al-2Nb-0.7Cr-0.3Si intermetallic alloy : mechanical properties and microstructural analysis

The amalgamated effect of hot-rolling, rapid cooling and heat treatment on the grain refinement and the resultant mechanical properties of an intermetallic sheet of nominal composition Ti-48Al-2Nb-0.7Cr-0.3Si was investigated. The sheet of 4 mm thickness was fabricated by hot-pack rolling from the vacuum arc remelted (VAR) ingot using a conventional two-high rolling mill. After the final rolling pass, the canned specimen was rapidly cooled in the air to room temperature followed by heat treatment in the α + γ region. The scanning electron microscopy (SEM) micrographs of the as-rolled sheet revealed slightly elongated grains of a typical “duplex (DP)” microstructure with a mean grain size of about 3 μm which grew to about 4 μm and became more equiaxed and homogeneous after heat treatment. Moreover, the EBSD micro-texture indicated a weak cube texture in the rolled + heat-treated sheet. Furthermore, the results from the profilometry-based indentation plastometry of the rolled + heat treated specimen illustrated the balanced and improved mechanical properties compared to the as-cast and as-rolled samples, and also those of similar alloy systems found in the literature.The Council of Scientific and Industrial Research, the University of Pretoria and Mintek.https://www.elsevier.com/locate/manpro2024-07-11hj2023Materials Science and Metallurgical Engineerin