Abstract
Research and development of alloys based on the intermetallic γ-TiAl phase is experiencing a renewed interest since powder metallurgical approaches provide new near-net-shape processing options. In this work, the manufacturing via spark plasma sintering was facilitated, a straightforward manufacturing technique to consolidate gas atomized pre-alloyed TiAl powder for microstructural and mechanical evaluation. Two alloys, the so-called BMBF3 alloy (Ti-47.4Al-5.6Nb-0.4W, in at.%) and the BMBF2 alloy (Ti-48.6Al-4.1Nb-0.7W-0.4Si-0.5C-0.1B, in at.%) were microstructurally designed via a heat treatment into a mechanically balanced nearly lamellar γ microstructure, i.e. γ appears in globular and lamellar morphology, as well as a creep resistant fully lamellar one. The latter exhibits high creep strength up to 850 °C, especially due to the formation of p-Ti 3AlC carbides. A heat treatment study upon this fully lamellar microstructure of the C-containing alloy links carbide formation and growth kinetics to the mechanical response of the microstructure. Thus, a stabilization heat treatment at 800 °C leads to the formation of finest carbides which are homogeneously distributed and increase the strength of the microstructure due to lower dislocation mobility. The two investigated alloys can be addressed as either a ductile TiAl alloy employable up to 750 °C (BMBF3), while the BMBF2 alloy is considered useable up to 850 °C.
| Originalsprache | Englisch |
|---|---|
| Aufsatznummer | 107316 |
| Seitenumfang | 10 |
| Fachzeitschrift | Intermetallics |
| Jahrgang | 138.2021 |
| Ausgabenummer | November |
| Frühes Online-Datum | 31 Aug. 2021 |
| DOIs | |
| Publikationsstatus | Veröffentlicht - Nov. 2021 |
Bibliographische Notiz
Funding Information:Two TiAl alloys, the so-called BMBF3 and BMBF2 alloy, were manufactured via SPS. The alloy nomenclature refers to the project ”NextTiAl” (03XP0088A) funded by the German Federal Ministry of Education and Research (BMBF). The chemical compositions of the starting powders are Ti-47.4Al-5.6Nb-0.4W and 800 m. ppm O for BMBF3 as well as Ti-48.6Al-4.1Nb-0.7W-0.4Si-0.5C-0.1B and 800 m. ppm O for BMBF2. The concentrations of the elements Ti, Al, Nb, and W were determined by means of X-ray fluorescence (XRF) spectroscopy while Si, C, and B were measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). For analyzing the O content, carrier gas hot extraction (CGHE) was used [ 34 ]. The powders were produced via electrode induction melting gas atomization (EIGA) [ 35 ] by TLS Technik GmbH & Co. Spezialpulver KG, Germany. The ingots for the EIGA process were produced according to Refs. [ 36 , 37 ] by GfE Metalle und Materialien GmbH, Germany. The powders < 150 µm were consolidated in a graphite die to cylindrical discs with a diameter of either 20 or 80 mm and a height of 14 mm with a SPS unit of the type HP D 25 from FCT Systems GmbH, Germany, at the Technische Universität Bergakademie Freiberg, Germany. The heating of the SPS device is done by pulsed electric current, whereas the cooling is achieved by natural convection (NC) [ 38 ]. Therefore, the cooling rate is dependent on the geometry and the size of the sintered part. An evaluation of the cooling rate for the 20 and 80 mm diameter revealed a rate of 300–450 K/min and around 90 K/min, respectively, between 1200 and 1000 °C as measured by a thermocouple in the center of the graphite die. The applied pressure was 50 MPa.
Funding Information:
The research work was conducted within the framework of the BMBF project 03XP0088C, Germany. The multi-annual BMBF project is focusing on alloy development of γ-TiAl based alloys. The support of the project partners is gratefully acknowledged. Furthermore, the work received support from the Austrian Research Promotion Agency (FFG) in the project 3DnanoAnalytics (FFG-no. 858040 ).
Funding Information:
The research work was conducted within the framework of the BMBF project 03XP0088C, Germany. The multi-annual BMBF project is focusing on alloy development of ?-TiAl based alloys. The support of the project partners is gratefully acknowledged. Furthermore, the work received support from the Austrian Research Promotion Agency (FFG) in the project 3DnanoAnalytics (FFG-no. 858040).
Publisher Copyright:
© 2021 The Author(s)
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