Effect of Initial Microstructure on the Compatibility of Rapidly Solidified Ti-Rich TiAl Powder

1996 ◽  
Vol 460 ◽  
Author(s):  
M. Nishida ◽  
A. Chiba ◽  
Y. Morizono ◽  
T. Kai ◽  
J. Sugimoto
Keyword(s):  
Grain Boundary ◽  
Orientation Relationship ◽  
Hot Pressing ◽  
Dendritic Structure ◽  
High Energy ◽  
Grain Boundary Sliding ◽  
Al Alloy ◽  
Initial Microstructure ◽  
Boundary Sliding ◽  
Rapidly Solidified

ABSTRACTInitial microstructure dependence of compactibility at elevated temperature in rapidly solidified Ti-rich TiAl alloy powders produced by plasma rotating electrode process (PREP) has been investigated. There were two kinds of powders with respect to the microstructure. The first one had a surface relief of a martensitic phase, which was referred as M powder. The second one had a dendritic structure, which was referred as D powder. α2+γ microduplex and α2/γ lamellar structures were formed in Mand D powders of the Ti-40 at%Al alloy by heat treatment at 1273 K, respectively. The microduplex structure consisted of γ precipitate in the twin related α2 matrix with the usual orientation relationship. It was difficult to compact the D powder by hot pressing at 1273 K under 50 MPa for 14.4 ks. On the other hand, the M powder was compacted easily by hot pressing with the same condition. The twin related α2 and α2 boundary changed to random ones and the α2 and γ phases were lost the usual orientation relationship in the duplex structure during the hot pressing. In other words, the low energy boundaries were changed to the high energy ones suitable for grain boundary sliding. Dislocations were scarcely observed inside of both the α2 and γ crystal grains. It was concluded that the grain boundary sliding was a predominant deformation mode in the M powder during the hot pressing. D and M powders in Ti-45 and 47 at%Al alloys showed the same tendency as those in Ti-40 at%Al alloy during hot pressing.

Cavity growth rate in superplastic 5083 Al and AZ31 Mg alloys

2004 ◽  
Vol 19 (11) ◽  
pp. 3382-3388 ◽  
Author(s):  
Yasumasa Chino ◽  
Hajime Iwasaki ◽  
Mamoru Mabuchi
Keyword(s):  
Growth Rate ◽  
Grain Boundary ◽  
Cavity Growth ◽  
Grain Boundary Sliding ◽  
Mg Alloy ◽  
Al Alloy ◽  
Az31 Mg Alloy ◽  
Boundary Sliding ◽  
Cavity Growth Rate ◽  
5083 Al Alloy

The plasticity-controlled growth rate of cavities during superplastic deformationwas statistically investigated for 5083 Al alloy and AZ31 Mg alloy. When the cavity growth rate was evaluated on the basis of macroscopic strain calculated using the displacement of the specimen, the growth rate for the Al alloy was larger than thatfor the Mg alloy. However, the growth rate of the Al alloy was in agreement withthat of the Mg alloy when the cavity growth rate was evaluated on the basis of the microscopic strain due to grain boundary sliding. The results obtained lead to two conclusions: (i) the rate of cavity growth is not affected by the kind of materials,that is, the nature of the grain boundary, and (ii) the microscopic strain due to grain boundary sliding should be used to evaluate exactly the rate of cavity growth for superplastic deformation.

Superplastic Behavior of Ultrafine Grained Al Alloys Fabricated by Severe Plastic Deformation

2007 ◽  
Vol 345-346 ◽  
pp. 597-600
Author(s):  
Duck Young Hwang ◽  
Kion Kwon ◽  
Dong Hyuk Shin ◽  
Kyung Tae Park ◽  
Young Gun Ko ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Effective Strain ◽  
Deformation Mode ◽  
Grain Boundary Sliding ◽  
Al Alloys ◽  
Deformation Mechanisms ◽  
Al Alloy ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Boundary Sliding

Ultrafine grained (UFG) 5083 Al and 5154 Al alloys were prepared by equal channel angular pressing (ECAP) with an effective strain of ~ 4 or ~ 8. This investigation was aimed at examining the effect of the ECAP strain and post-rolling inducing different microstructure in these alloys on the deformation mechanisms at low temperature superplastic (LTS) and high strain superplastic (HSRS) regimes. The sample after 4 passes (a strain of ∼ 4) did not exhibit LTS, but superplastic elongations were obtained in the sample after 8 passes (a strain of ∼ 8). An analysis of the mechanical data in light of the standard deformation mechanisms revealed that deformation of the sample after 4 passes was governed by dislocation climb while grain boundary sliding attributed to LTS of the sample after 8 passes. In addition, the 5154 Al alloy processed by ECAP and postrolling was capable of enhancing HSRS elongation significantly. An analysis revealed that the deformation mode was changed from dislocation viscous glide to grain boundary sliding by additional ECAP strain and post-rolling.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

INTERNAL FRICTION PEAKS CONNECTED WITH GRAIN BOUNDARY SLIDING IN Al

1983 ◽  
Vol 44 (C9) ◽  
pp. C9-759-C9-764
Author(s):  
E. Bonetti ◽  
A. Cavallini ◽  
E. Evangelista ◽  
P. Gondi
Keyword(s):  
Internal Friction ◽  
Grain Boundary ◽  
Grain Boundary Sliding ◽  
Boundary Sliding
Sign in / Sign up

Export Citation Format

Share Document