The role of ledges in creep of TiAl alloys with fine lamellar structures

Journal Article · Mon Mar 23 04:00:00 EST 1998 · Acta Materialia

DOI:https://doi.org/10.1016/S1359-6454(97)00434-5· OSTI ID:616244

Wang, J N ^[1]; Nieh, T G ^[2]

---

1. Central South Univ. of Technology, Changsha, Hunan (China). Powder Metallurgy Research Inst.
2. Lawrence Livermore National Lab., CA (United States)

Creep experiments have been conducted on two powder-metallurgy TiAl alloys with fine grains, fine lamellar structures, and compositions of Ti-47Al + 2Cr + 2Nb and Ti-47Al + 2Cr + 1Nb + 1Ta. Results show that the stress exponent n and the activation energy Q decrease with decreasing stress (n {approximately}7--9 to 1.5, Q {approximately}300 kJ/mol to {approximately}150 kJ/mol). Stress reduction led to the occurrence of negative, zero and positive creep at low stresses but only positive creep at high stresses. Thinning and dissolving of {alpha}{sub 2} lamellae and continuous coarsening of {gamma} lamellae were observed at both low and high stresses with cross-twinning being a microstructure exclusive at high stresses. To understand the underlying deformation processes, a ledge creep mechanism is proposed. The mechanism involves bunching and escaping of unit-height ledges into or from multiple-height ledges at interfacial boundaries ({alpha}{sub 2}/{gamma} and {gamma}/{gamma}). It is assumed that the ledge motion, which is diffusion-controlled, causes phase transformation and thus deformation of the sample. Using this mechanism, the experimental results including the stress exponents, activation energies and transient creep behaviors after stress reduction at different stresses are reasonably interpreted.

• Sponsoring Organization: USDOE, Washington, DC (United States); National Natural Science Foundation of China, Beijing, BJ (China)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 616244
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: 6 Vol. 46; ISSN 1359-6454; ISSN ACMAFD
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
CHROMIUM ALLOYS
CREEP
GAS TURBINE ENGINES
MICROSTRUCTURE
NIOBIUM ALLOYS
TANTALUM ALLOYS
TITANIUM ALLOYS
WEIGHT