2 results
Now showing1 - 2 of 2
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Phase separation and up-hill diffusion in the ordered α2 compound of a γ-Ti-Al-Nb alloy(EDP Sciences, 2020-10-12); ; ; ; γ-TiAl alloys are intermetallic materials that are designed for applications in air craft engines. Oftentimes alloying elementsare added to improve the corrosion resistance and mechanical properties. Here we investigate microstructural changes thattake place when Nb is added to a binary γ-TiAl alloy. Previous studies of the alloy Ti-42Al-8.5Nb have shown that uponNb addition the orthorhombic O-phase forms out of the parent α2 phase within the alloy’s microstructure. During annealingNb segregates to the newly formed O-phase while Al and Ti partition to the remaining α2-like matrix phase. The changesthese newly formed O-phase domains undergo with time at elevated temperature are not known. Here we use TransmissionElectron Microscopy techniques to monitor the distribution of Nb and the size of O-phase domains during long-termannealing between 1 week and 4 weeks at 550°C. The results show that the size of O-phase domains shrinks withannealing time. At the same time the Nb concentration remains largely constant or possibly shows a small decrease.Publicationtype: Conference Paper45 82 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Elemental segregation and o-phase formation in a gamma-tial alloyTitanium aluminides based on the L10 ordered γ-phase are promising structural lightweight materials for applications in aircraft engines. Typical compositions for γ-TiAl alloys lie in the range Ti-(44-48)Al (at.-%). For high creep resistance, a two-phase microstructure based on lamellar (α2+γ)-colonies is desirable that may be tuned towards better ductility by introducing pure γ-grains (near lamellar or duplex microstructure). γ-TiAl alloys are often alloyed with niobium for increased oxidation resistance and improved mechanical properties. HEXRD and TEM studies of the alloy Ti-42Al-8.5Nb revealed that the orthorhombic O-phase forms during annealing at 500-650°C. This orthorhombic phase has been known in Nb-rich, Al-lean, α2-based Ti-aluminides since the late 1980ies (Nb> 12.5 at.-%, Al< 31 at.-%) but the finding in γ-based alloys is new. TEM imaging showed that the O-phase is located within α2 lamellae of lamellar (α2 +γ)-colonies. O-phase domains and α2 phase form small columnar crystallites based in the α2 /γ interface. The columnar crystallites grow parallel to the [0001] direction of the α2 phase and appear as facets when observed along this direction. The evolution of domains and facets with annealing time and the chemical homogeneity of the phases are investigated. The results of STEM imaging show that O-phase domains form during annealing at 550 °C for 8hours or 168 hours. After 168 hours of annealing Nb segregations are observed by EDX mapping within O-phase domains. In comparison, no segregation of niobium is detected after 8 hours of annealing.Publicationtype: Conference Paper103