22.08.2015   Comprehensive nuclear materials

Thermal Creep

Thermal creep is a potential factor which can deter­mine the upper operation limit of vanadium alloys.

Подпись: 500 |tm Подпись: Intergranular fracture-' Подпись: 50 |tm

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Figure 7 Cross-section of W coating on V-4Cr-4Ti after bending tests. Fracture started in the W coating layer.

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W coating by plasma spraying Laser weld joint

Oxygen level (wppm) Nitrogen level (wppm)

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Previously, uniaxial tensile creep tests and biaxial pressurized creep tube tests were carried out in vac­uum for evaluation of the creep deformation charac­teristics. Figure 11 shows summary of the creep deformation rate as a function of applied stress.3 In this plot, the creep data were described by a power — law equation24:

de/dt = A{DGb/kT){a/G)n

where de/dt is the creep rate, s is the applied stress, D is the lattice diffusion coefficient, G is the shear modulus, b is the Burgers vector, k is the Boltzmann constant, T is the absolute temperature, and A is a constant. The exponent of the function (n) changed from <1 to >10 with the increase in the stress.

A new apparatus for biaxial creep testing in Li provided opportunities for examining creep

surface hardening during exposure to Li. Further investigation is necessary for understanding the envi­ronmental effects on impurity redistribution and creep performance.

Microstructural observations of the creep tube specimens tested at 1123 K showed free dislocations and dislocation cell at 100 and 150 MPa, respectively. This change of dislocation structure can cause the change in power-law creep behavior.27

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Figure 10 Tensile deformation curves of V-4Cr-4Ti at various temperatures.

 

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Figure 11 Thermal creep deformation rate of V-4Cr-4Ti as a function of applied stress for uniaxial and biaxial tests. The definition of the terms and the function from which n is extracted are indicated in the text. Reproduced from Kurtz, R. J.; Abe, K.; Chernov, V. M.; Hoelzer, D. T.;

Matsui, H.; Muroga, T.; Odette, G. R. J. Nucl. Mater.

2004, 329-333, 47-55.