110年 - 110 國立清華大學碩士班考試入學試題_工程與系統科學系/甲組:物理冶金#104981

(a) Write down the Burgers vector of the dislocation. (2%)

(b) What is the direction of [u₁ V₁w₁]. (3%)

(c) Describe the position of the dislocation including direction of the dislocation line and the Burgers vector in Fig. 1. (5%)

(d) In fec metals, the dislocations are usually dissociated into an extended dislocation, containing two partial dislocations and a stacking fault. Fig. 2 shows an extended dislocation in fcc lattice. Describe the position of the partial dislocation including the direction of dislocation line and Burgers vectors. (5%)

(e)The strength of an fec metal can be increased by controlling the stacking fault energy. Discuss the strengthening mechanism. (5%)

(a) Identify whether you think the crystal is FCC or BCC (5%), and

(b) explain briefly why in each case (15%).

(a) There is a condition for necking for a true stress-strain curve called Considere's criterion. Derive the Considere's criterion for a true stress-strain curve satisfied a = Kεⁿ, where o is the true stress, s is the true strain, n is the strain hardening exponent, and K is the strength coefficient.(5%)

(b) Discuss why the strain hardening exponent decreascs with increasing stacking fault energy, as shown in the table below (5%)

(c)For fcc and bcc metals, there are different temperature dependence on the flow stress components, as shown in Figs. 6 and 7. Use the Considere's criterion to explain the reasons that cause this difference. (10%)

(a) Refer to Fig. 8 above, and consider the three temperature histories shown. If you are trying to design a steel that best takes advantage of dislocation interactions with a second phase (i.e, strength controlled by bowing), which path is best and why? (10%)

(b) Refer to Fig.9 above, and consider the three temperature histories shown. If you are trying to produce a microstructure that derives strength through load transfer without being brittle, which path is best and why? (10%)

(a) sort out which post-annealing microstructure belongs to which sample, (5%) and

(b) write a short explanation for your choices. (15%)

110年 - 110 國立清華大學碩士班考試入學試題_工程與系統科學系/甲組:物理冶金#104981

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