The influence of interstitial impurities on true grain-boundary sliding of titanium in coarse-grained and submicrocrystalline states

HCP metals show new dislocation creep at temperatures below 0.3 Tm with stresses below σ0.2, while FCC metals show it above σ0.2. In the former, grain boundaries absorb the dislocations through slip-induced grain-boundary sliding, while in the latter dislocations are accommodated by cross slip at cell walls. The difference comes from the difference in the crystal symmetry. In UFG-Al at low temperatures, it is anticipated that grains without cell structure lead creep deformation similar to CG HCP metals rather than CG Al. UFG Al specimens were fabricated by ARB method. They showed remarkable creep behavior at less than σ0.2 similary to CG HCP metals. It posseses stress exponent of about three, grain-size exponent of almost zero, and very low apparent activation energy of 20 kJ/mol, and also grain boundary sliding behavior is obserbed by AFM.

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Influence of Interstitial Impurities on Deformational Behavior and Fracture Mechanism of Submicrocrystalline Titanium at Room and Elevated Temperatures

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1013.138 ◽

2014 ◽

Vol 1013 ◽

pp. 138-145 ◽

Cited By ~ 1

Author(s):

Evgenii Dudarev ◽

Galina Bakach ◽

Aleksandr I. Potekaev ◽

Yurii Kolobov ◽

Oleg Kashin ◽

...

Keyword(s):

Plastic Deformation ◽

Elevated Temperatures ◽

Grain Boundary Sliding ◽

Interstitial Impurity ◽

Coarse Grained ◽

Interstitial Impurities ◽

Localization Of Plastic Deformation ◽

Deformational Behavior ◽

Boundary Sliding ◽

High Degree

General trends and other aspects of the deformational behavior, localization of plastic deformation on the macroscale level, and fracture of submicrocrystalline and coarse-grained titanium with different interstitial impurity levels are established. It is shown that for the submicrocrystalline structure as well as for the coarse-grained structure, strengthening by interstitial impurities decreases with increase of the deformation temperature. Experimental data are presented which indicate that in the development of grain-boundary sliding in submicrocrystalline titanium with simultaneous onset of recrystallization, a high degree of plastic deformation is reached before fracture occurs, where the deformational behavior and localization of plastic deformation on the macroscale level are analogous to the same processes under superplastic flow.

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Superplasticity and Deformation Mechanism of LD10 Aluminium Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.2941 ◽

2005 ◽

Vol 475-479 ◽

pp. 2941-2944

Author(s):

Hong Zhen Guo ◽

Chunyan Duan ◽

Ze Kun Yao ◽

Wei Zhang

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Annealing Temperature ◽

Tensile Deformation ◽

Liquid Mixture ◽

Grain Boundary Sliding ◽

Coarse Grained ◽

Recrystallization Annealing ◽

Boundary Sliding ◽

Solid Liquid

The commercial hot-rolled bars of LD10 alloy (grain size 25~75µm) are pretreated via proper recrystallization annealing (temperature 380°C, 420°C and 460°C) and solution annealing (temperature 500°C). The average elongation is increased from 158% to 270%, 223%, 219% and 233% respectively and the maximum elongation is 321% (500°C, 3.3×10-4s-1). The test results show that the alloy can present certain superplasticity owing to structural effect of dynamic recrystallization refining during superplastic deformation of coarse-grained LD10 alloy. Large and deep cavities form in grain boundaries and result in intergranular fracture after larger superplastic tensile deformation. And a large amount of metal filaments appear on grain surfaces. The formation of filaments is attributed to viscous flow of solid-liquid mixture in grain boundaries caused by grain-boundary sliding. The appearance of solid-liquid mixture makes grain-boundary sliding easier.

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Examination of Fracture Interfaces in Silicon Nitride

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113925 ◽

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.

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