The effect of local composition on defect structure in a near-γ-TiAl alloy with duplex microstructure

2001 ◽  
Vol 81 (11) ◽  
pp. 2653-2664
Author(s):  
S. H. Chen, G. Schumacher, D. Mukherji
Keyword(s):  
Defect Structure ◽  
Tial Alloy ◽  
Duplex Microstructure ◽  
Local Composition

The effect of local composition on defect structure in a near-γ-TiAl alloy with duplex microstructure

2001 ◽  
Vol 81 (11) ◽  
pp. 2653-2664 ◽  
Author(s):  
S. H. Chen ◽  
G. Schumacher ◽  
D. Mukherji ◽  
G. Frohberg ◽  
R. P. Wahi
Keyword(s):  
Defect Structure ◽  
Tial Alloy ◽  
Duplex Microstructure ◽  
Local Composition

On the role of mechanical twinning in creep of a near-γ TiAl-alloy with duplex microstructure

1998 ◽  
Vol 39 (8) ◽  
pp. 1023-1029 ◽  
Author(s):  
Birgit Skrotzki ◽  
Mahinur Ünal ◽  
Gunther Eggeler
Keyword(s):  
Tial Alloy ◽  
Mechanical Twinning ◽  
Duplex Microstructure

Elemental Segregation and O-Phase Formation in a Gamma-TiAl Alloy

2018 ◽  
Vol 941 ◽  
pp. 741-746 ◽  
Author(s):  
Heike Gabrisch ◽  
Tobias Krekeler ◽  
Uwe Lorenz ◽  
Marcus Willi Rackel ◽  
Martin Ritter ◽  
...  
Keyword(s):  
Tial Alloy ◽  
Titanium Aluminides ◽  
Orthorhombic Phase ◽  
Aircraft Engines ◽  
Duplex Microstructure ◽  
Two Phase ◽  
Chemical Homogeneity ◽  
Phase Form ◽  
Tial Alloys ◽  
O Phase

Titanium aluminides based on the L10 ordered g-phase are promising structural light-weight 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.

Microstructure Evolution at the Diffusion Bonding Interface of High Nb Containing TiAl Alloy

2015 ◽  
Vol 817 ◽  
pp. 599-603 ◽  
Author(s):  
Xian Sheng Qi ◽  
Xiang Yi Xue ◽  
Bin Tang ◽  
Chuan Yun Wang ◽  
Hong Chao Kou ◽  
...  
Keyword(s):  
Diffusion Bonding ◽  
Tial Alloy ◽  
Nucleation And Growth ◽  
Bonding Process ◽  
Bonding Interface ◽  
Duplex Microstructure ◽  
Hot Press ◽  
Bonding Quality ◽  
Microstructure Observation ◽  
Evolution Of Microstructure

A series of diffusion bonding tests were conducted on high Nb containing TiAl alloy with duplex microstructure, the evolution of microstructure at bonding interface was investigated. Bonding process was performed by using vacuum hot press furnace at the temperature range from 850 to 1150°C with the pressure of 30MPa for 45min. The microstructure observation indicates that sound joint without unbounded area can be obtained when bonded above 950°C. Recrystallization happens in bonding interface when bonded at 1150°C and the recrystallized grain prior nucleated at bonding interface between the lamella colonies. Nucleation and growth of recrystallized grains promote migration of bonding interface and thus improve bonding quality. Besides, the post-bonding heat treatment (PBHT) was also performed to promote the evolution of bonding interface. The experimental results reveal that the bonding interface disappears after PBHT at 1135°Cfor 12h, and exhibits near gamma microstructure.

Electron Microscope Observations of Mechanical Metamorphism in Iron Meteorites

1970 ◽  
Vol 28 ◽  
pp. 488-489
Author(s):  
D. Faulkner ◽  
G.W. Lorimer ◽  
H.J. Axon
Keyword(s):  
Electron Microscope ◽  
Defect Structure ◽  
Shock Loading ◽  
List Type ◽  
Iron Meteorites

It is now generally accepted that meteorites are fragments produced by the collision of parent bodies of asteroidal dimensions. Optical metallographic evidence suggests that there exists a group of iron meteorites which exhibit structures similar to those observed in explosively shock loaded iron. It seems likely that shock loading of meteorites could be produced by preterrestrial impact of their parent bodies as mentioned above.We have therefore looked at the defect structure of one of these meteorites (Trenton) and compared the results with those made on a) an unshocked ‘standard’ meteorite (Canyon Diablo)b) an artificially shocked ‘standard’ meteorite (Canyon Diablo) andc) an artificially shocked specimen of pure α-iron.

A new type of defect structure in 124-superconducting oxide revealed by HREM

1991 ◽  
Vol 49 ◽  
pp. 1092-1093
Author(s):  
R. Sharma ◽  
B.L. Ramakrishna ◽  
N.N. Thadhani ◽  
D. Hianes ◽  
Z. Iqbal
Keyword(s):  
Shock Wave ◽  
Defect Structure ◽  
Neutron Radiation ◽  
Weak Links ◽  
Defect Structures ◽  
New Materials ◽  
New Type ◽  
Current Densities ◽  
Processing Techniques ◽  
Microstructural Studies

After materials with superconducting temperatures higher than liquid nitrogen have been prepared, more emphasis has been on increasing the current densities (Jc) of high Tc superconductors than finding new materials with higher transition temperatures. Different processing techniques i.e thin films, shock wave processing, neutron radiation etc. have been applied in order to increase Jc. Microstructural studies of compounds thus prepared have shown either a decrease in gram boundaries that act as weak-links or increase in defect structure that act as flux-pinning centers. We have studied shock wave synthesized Tl-Ba-Cu-O and shock wave processed Y-123 superconductors with somewhat different properties compared to those prepared by solid-state reaction. Here we report the defect structures observed in the shock-processed Y-124 superconductors.

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