tailieunhanh - Kinetics of Materials - R. Balluff_ S. Allen_ W. Carter (Wiley_ 2005) Episode 6

Tham khảo tài liệu 'kinetics of materials - r. balluff_ s. allen_ w. carter (wiley_ 2005) episode 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 206 CHAPTER 8 DIFFUSION IN CRYSTALS The hysteresis loop will therefore appear as a line of negligible width and slope 1 Sr as in Fig. . Negligible internal friction therefore occurs. Figure c CUT 1. Frequency dependence of anelastic behavior a CUT ịí 1. b CUT 1. b When cut 1 1 Su o and 2 0 The hysteresis loop will therefore appear again as a line of negligible width but with a larger slope as in Fig. . Negligible internal friction occurs. c When cut 1 _ _ Sr Su _ ISr St 1 ----------- To and 2 ------ To The hysteresis loop will therefore appear as in Fig. . The slope of the dashed line is 77 A wo Si bfí bí7 2 and the width of the loop at CT 0 is 2 2 Sr - Su ơa Also because the strain lags behind the stress the direction of traversal of the loop must be as indicated. In this situation maximum internal friction occurs. Describe in detail how to determine the diffusivity of c in . Fe using a torsion pendulum. Include all of the necessary equations. See Section and Fig. where c atoms in sites 1 2 and 3 expand the crystal preferentially along X y and z respectively. Solution. Using a torsion pendulum find the anelastic relaxation time T by measuring the frequency of the Debye peak Up and applying the relation cUpT 1. Having T the relationship between T and the c atom jump frequency r is found by using the procedure to find this relationship for the split-dumbbell interstitial point defects in Exercise . Assume the stress cycle shown in Fig. and consider the anelastic relaxation that occurs just after the stress is removed. A c atom in a type 1 site can jump into two possible nearest-neighbor type 2 sites or two possible type 3 sites. Therefore -4r ci 2T c2 2r c3 at Because Cl C2 C3 ctot constant f 2-t __. ctot z __ -6r ci- - at 3 EXERCISES 207 which may be integrated to obtain ctotl Ci t - o ctotỊ -er t C1 O V e The relaxation time is then T 1 6T and because the total .

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