Microstructural evolution and mechanical properties of in-situ as-cast beta titanium matrix composites

[EN] The aim of this research is to investigate the effects of B4C additions on microstructure refinement and mechanical properties, due to in-situ formation of TiB and TiC in a matrix of beta titanium by casting process. Researches have been done on the individual effects of TiC and TiB compounds in titanium composites, however, their hybrid effect has been scarcely explored in beta titanium alloys. The effects on lattice parameter were investigated by Rietveld refinement and EDS analysis. The beta lattice parameters increased due reaction between Ti and B4C. DTA analysis revealed the sequence of phase formation on heating and cooling around the melting point, being confirmed by investigation of orientation relationship between phases by EBSD and pole figure analysis. Orientation relationships are {312}(TiB)//{112}(beta), {112}(TiC)//{112}(beta) for the smallest addition of B4C, {113}(TiC)//{112}(beta) for the remaining composites, and {010}(Ti)(B)//{011}(T)(i)(c) between the particles. Grain size reduced by half with 0.5% addition of B4C, while 3% addition made grains 25 times smaller than the alloy. Young's modulus and hardness increased with the addition of boron carbide. An analysis of the hardness of the materials was carried out from a nano to a macro scale. The as-cast composite materials have a refined structure with improved mechanical properties in comparison to the commercial alloy. (C) 2018 Elsevier B.V. All rights reserved.The authors gratefully acknowledge the Brazilian research funding agencies CNPq (National Council for Scientific and Technological Development) and CAPES (Federal Agency for the Support and Evaluation of Graduate Education) for their partial financial support of this work.Rielli, VV.; Amigó, V.; Contieri, RJ. (2019). Microstructural evolution and mechanical properties of in-situ as-cast beta titanium matrix composites. Journal of Alloys and Compounds. 778:186-196. https://doi.org/10.1016/j.jallcom.2018.11.093S18619677

γʹ and γ″ co-precipitation phenomena in directly aged Alloy 718 with high δ-phase fractions

Co-precipitation of γ′ and γ′′ is the main strengthening mechanism that provides superior high-temperature strength in directly aged Alloy 718 aerospace parts. Control of their morphology, fraction, and configuration might allow exposure to more demanding operation environments in next-generation aircraft engines. The density of geometrically necessary dislocations introduced during hot deformation has been shown to significantly affect the co-precipitate morphology of γ′ and γ′′ in materials free of the δ-phase. However, the combined effects of geometrically necessary dislocation density and lower Nb content due to higher δ-phase fractions on co-precipitation behaviour and strengthening remain unknown. We verify these effects by hardness testing as a proxy for high-temperature strength in materials with 4.1 % δ-phase fraction. Deformation at 950 °C yields a remarkable increase of 12 % in hardness after direct ageing, explained by the prevalence of complex co-precipitate configurations. Deformation at 1000 °C decreases the δ-phase fraction and geometrically necessary dislocation density but achieves up to 19 % volume fractions of γ″, leading to a predominance of monoliths and duplet co-precipitates and a better direct ageing response. Atom probe microscopy reveals the flux of elements during co-precipitation. We recommend a δ-annealing treatment before the final forging step for manufacturing stronger Alloy 718 aerospace parts

Single step heat treatment for the development of beta titanium composites with in-situ TiB and TiC reinforcement

[EN] Titanium matrix composites have been attracting great interest from aerospace industry due to favorable properties like thermal stability, high specific strength, corrosion, and wear resistance. Optimal relation between mechanical properties demands complex processing routes and, in this context, the effects of a single-step processing route on microstructure and mechanical properties of ß titanium matrix composites was placed on focus in this study. The commercial TIMETAL Beta 21S alloy and its modification with the addition of B4C were developed, allowing in-situ formation of TiB and TiC particles in a ß matrix. The composites presented highest values of mechanical strength and hardness, and the addition of 3% of B4C provided a significant reduction in grain size, and compressive yield strength and ultimate compressive strength values of 1205 MPa and 1636 MPa, respectively, with a maximum deformation of 20.5%. An orientation relationship investigation provided in- formation about some unconventional relation between the present phases.The authors are grateful for the funding provided by the Brazilian research agencies FAPESP (State of Sao Paulo Research Foundation) and CAPES (Federal Agency for the Support and Evaluation of Graduate Education). The authors also gratefully acknowledge the use of experimental facilities at Brazilian Nanotechnology National Laboratory (LNNano), and the Electron Microscopy Service and Materials Technology Institute at the Universitat Politecnica de Valencia.Rielli, VV.; Amigó, V.; Contieri, RJ. (2020). Single step heat treatment for the development of beta titanium composites with in-situ TiB and TiC reinforcement. Materials Characterization. 163:1-10. https://doi.org/10.1016/j.matchar.2020.11028611016