Microstructure development and hardness of a powder metallurgical multi phase γ-TiAl based alloy

Abstract

a b s t r a c tA b-solidifying TiAl alloy with a nominal composition of Tie43.5Ale4Nbe1Moe0.1B (in at.%), termed TNMÔ alloy, was produced by a powder metallurgical approach. After hot-isostatic pressing the microstructure is comprised of fine equiaxed g-TiAl, a 2 -Ti 3 Al and b o -TiAl grains. By means of two-step heat-treatments different fine-grained nearly lamellar microstructures were adjusted. The evolution of the microstructure after each individual heat-treatment step was examined by light-optical, scanning and transmission electron microscopy as well as by conventional X-ray and in-situ high-energy X-ray diffraction. The experimentally evaluated phase fractions as a function of temperature were compared with the results of a thermodynamical calculation using a commercial TiAl database. Nano-hardness measurements have been conducted on the three constituting phases a 2 , g and b o after hot-isostatic pressing, whereas the hardness modification during heat-treatment was studied by macro-hardness measurements. A nano-hardness for the b o -phase is reported for the first time.

Dependency of microstructure and microhardness on withdrawal rate of Ti-43Al-2Cr-2Nb alloy prepared by electromagnetic cold crucible directional solidification

“…The variation of HV was mainly attributed to the change of phases and interlamellar spacing. Firstly, as reported in references [16,17], B2 phase and α 2 phase are harder than the γ phase. In this case, increase of B2 phase and α 2 phase would result in the increase of Vickers microhardness of CCDS Ti-43Al-2Cr-2Nb alloy.…”

Powder Metallurgical Production of Innovative High-Temperature Materials

“…Wegen der sehr hohen anfänglichen Kühlrate bei der Erstarrung der Teilchen, nach Referenz [8] ca. 2 ⋅ 10 5 K/s für ein 45 µm großes Pulverteilchen, liegt nach der Erstarrung ein sehr feinkörniges und homogenes Gefüge vor, dessen Phasenanteile weit vom thermodynamischen Gleichgewicht entfernt sein können [8,10]. Da die auftretenden Seigerungen nur an den Korngrenzen sind, können sie durch den anschließenden Kompaktierungsprozess, z.…”

“…Bei der Wahl der HIP-Parameter ist darauf zu achten, dass die ehemaligen Pulverkorngrenzen nicht mehr erkennbar sind, da sie mit Sauerstoff angereicherte Zonen darstellen. Das Gefüge ist dann feinkörnig und sehr homogen, und die auftretende Phasenfraktion entspricht jener des thermodynamischen Gleichgewichts [10]. An dieser Stelle sei angemerkt, dass die Gefügehomogenität geHIPter TiAl-Pulver deutlich höher ist als jene von gegossenen und geschmiedeten TiAlLegierungen.…”

In Situ Characterization Techniques Based on Synchrotron Radiation and Neutrons Applied for the Development of an Engineering Intermetallic Titanium Aluminide Alloy

“…It might have been too high to fully reach thermodynamic equilibrium, especially as the β phase, stabilized by slowly diffusing elements Nb and Mo, exhibits a prolonged dissolution behavior. Nevertheless, Schloffer et al [75] showed that phase fractions retrieved from light-optical microscopy, conventional XRD and in situ HEXRD are in good agreement, at least up to the dissolution temperature of the γ phase (T γ,solv ).…”