Ultrahigh-temperature Nbss/Nb5Si3 fully-lamellar microstructure developed by directional solidification in OFZ furnace

2011 ◽  
Vol 19 (4) ◽  
pp. 460-469 ◽  
Author(s):  
Yulong Li ◽  
Seiji Miura ◽  
Kenichi Ohsasa ◽  
Chaoli Ma ◽  
Hu Zhang
Keyword(s):  
Directional Solidification ◽  
Lamellar Microstructure ◽  
Ultrahigh Temperature ◽  
Fully Lamellar

A Mechanism of Polycrystallization in Fully Lamellar Ti-48Al-8Nb Single Crystal Alloy Aged at Elevated Temperatures

2002 ◽  
Vol 753 ◽  
Author(s):  
Yukinori Yamamoto ◽  
Masao Takeyama ◽  
Takashi Matsuo
Keyword(s):  
Growth Rate ◽  
Diffusion Coefficient ◽  
Single Crystal ◽  
Grain Growth ◽  
Elevated Temperatures ◽  
Volume Diffusion ◽  
Activation Enthalpy ◽  
Lamellar Microstructure ◽  
Aged Sample ◽  
Fully Lamellar

ABSTRACTPolycrystallization mechanism of a fully lamellar microstructure during aging at 1473 and 1273 K has been examined using Ti-48Al-8Nb fully lamellar single crystal, which consists mostly of γ/γ interfaces (variant, perfect-twin and pseudo-twin boundaries). After a certain period of aging, a few γ grains are formed within the lamellae and the lamellar microstructure collapses rapidly to become a γ grained microstructure at both temperatures. An EBSP analysis for aged sample revealed that most of the grains follow the orientation of variant domains in the lamellar microstructure. A kinetic analysis of the grain growth during aging revealed that the activation enthalpy of the growth rate is estimated to be 390 kJ/mol, which is very close to that for volume diffusion coefficient of Al and Nb in γ-TiAl. Based on the results, it is concluded that the formation of the grains is attributed to coarsening of variant domains within the lamellar plates and coalescence of the same variant domains across the lamellae, leading to a γ grained microstructure following the orientation of variant domains. These reactions also make the number of the variant domains decrease during aging, which remains only two variant domains with perfect-twin relationship.

C11b/C40 Lamellar Structure in a Ta-added Molybdenum Disilicide

2000 ◽  
Vol 646 ◽  
Author(s):  
Fu-Gao Wei ◽  
Yoshisato Kimura ◽  
Yoshinao Mishima
Keyword(s):  
Mechanical Properties ◽  
Orientation Relationship ◽  
Binary Alloy ◽  
Lamellar Structure ◽  
Molybdenum Disilicide ◽  
Lamellar Microstructure ◽  
Polycrystalline Alloys ◽  
Lamellar Interface ◽  
Fully Lamellar ◽  
Microstructural Control

ABSTRACTC11b/C40 fully lamellar microstructures, similar to the well-known TiAl/Ti3Al lamellae, were obtained in Ta- and Nb-added MoSi2 polycrystalline alloys in a previous work. In the present study, the crystallography of the lamellar structure is investigated in a MoSi2-15mol%TaSi2 pseudo-binary alloy after homogenized at 1400°C for 168h, in order to provide some useful parameters for microstructural control to improve mechanical properties. The orientation relationship between C11b and C40 phases and its three distinct variants were identified. Coherency of the lamellar interface is analyzed in comparison with the TiAl/Ti3Al lamellae. Approach to modify the C11b/C40 lamellar microstructure to increase its coherency is discussed based on the results obtained.

Producing fine fully lamellar microstructure for cast γ-TiAl without hot working

2020 ◽  
Vol 120 ◽  
pp. 106728 ◽  
Author(s):  
Jae-Kwon Kim ◽  
Jong-Hun Kim ◽  
Ji-Young Kim ◽  
Sung-Hyun Park ◽  
Seong-Woong Kim ◽  
...  
Keyword(s):  
Lamellar Microstructure ◽  
Hot Working ◽  
Fully Lamellar

Creep Mechanisms in Equiaxed and Lamellar Ti-48Al

2000 ◽  
Vol 646 ◽  
Author(s):  
G. B. Viswanathan ◽  
S. Karthikeyan ◽  
V. K. Vasudevan ◽  
M. J. Mills
Keyword(s):  
Applied Stress ◽  
Binary Alloy ◽  
Lamellar Microstructure ◽  
Active Volume ◽  
Equiaxed Microstructure ◽  
Creep Mechanisms ◽  
Deformation Structures ◽  
Experimental Values ◽  
Fully Lamellar ◽  
Rate Controlling Step

ABSTRACTMinimum creep rates as a function of stress have been obtained for Ti-48Al binary alloy with a near gamma and a fully lamellar microstructure. TEM investigation reveals that deformation structures in both microstructures are dominated by jogged screw 1/2[110] dislocations in γ phase. A modif ied jogged screw model is adopted to predict minimum creep rates where the rate controlling step is assumed to be the non-conservative motion of 1/2[110] unit dislocations. In the case of equiaxed microstructure where the deformation was mostly uniform, the creep rates predicted by this model were in agreement with experimental values. Conversely, deformation in lamellar microstructures were highly inhomogeneous where the density of jogged 1/2[110] unit dislocations were seen in varying proportions depending on the width of the γ laths. The creep rates and stress exponents in these microstructures is explained in terms of active volume fractions of γ laths participating in deformation for a given applied stress.

The Effect of Heat Treatment on the Microstructure of Ti-45Al-5Nb-0.3Y Alloy

2009 ◽  
Vol 614 ◽  
pp. 55-59
Author(s):  
Fan Tao Kong ◽  
Yu Yong Chen
Keyword(s):  
Heat Treatment ◽  
Phase Transformation ◽  
Lamellar Microstructure ◽  
Air Cooling ◽  
Water Cooling ◽  
Different Temperatures ◽  
Combined Action ◽  
Average Size ◽  
Equiaxed Grains ◽  
Fully Lamellar

Effects of heat treatment on the microstructure of as-cast and as-forged Ti-45Al-5Nb-0.3Y alloy are discussed. The as-cast Ti-45Al-5Nb-0.3Y alloy exhibits a microstructure consisting of fine equiaxed grains which average size is almost 100μm. Phase transformation of as-cast Ti-45Al-5Nb-0.3Y alloy greatly depends upon cooling rate. During furnace cooling, the alloy transform to fully lamellar microstructure. During air cooling, massive transformation predominates. During oil cooling, extremely fine fully lamellar microstructure is formed. During water cooling, ordering α2 phases are primary. Thermo-mechanical treatments, through combined action of hot canned forging and heat treatment, were performed on a Ti-45Al-5Nb-0.3Y alloy to investigate their effect on the microstructure of the alloy. The as-forged Ti-45Al-5Nb-0.3Y alloy is comprised of a large number of dynamic recrystallization (DRX) γ grains, curved and broken lamellae, and a small amount of remnant lamellae. And three different microstructures, duplex (DP), nearly lamellar (NL) and fine fully lamellar (FFL), have been obtained through heat treatment at different temperatures (1320-1370°C), respectively.

Microstructure of Rolled Ti-46.5Al-4(CrNb,Ta,B)

1998 ◽  
Vol 552 ◽  
Author(s):  
B. J. Inkson ◽  
H. Clemens
Keyword(s):  
Phase Field ◽  
Boron Content ◽  
Sheet Material ◽  
Lamellar Microstructure ◽  
Heat Treatments ◽  
Grain Structure ◽  
Α Phase ◽  
Heat Treated ◽  
B2 Phase ◽  
Fully Lamellar

ABSTRACTAn industrial Ti-46.5A1–4(CrNb,Ta) alloy, with and without boron additions, has been successfully rolled to sheet 1.5mm thick. The microstructure of the sheet material has been characterised as a function of boron content and subsequent heat treatments. It is observed that rod-like (Ti-Ta)B precipitates are effective in refining the grain structure in both as-rolled and subsequently heat treated material. As-rolled microstructures rapidly cooled from the α + γ phase field contain unstable α2, which transforms to B2 phase on annealing below the α + γ tranus. Annealing in the α-phase field can result in a designed fully lamellar microstructure.

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