材料科学导论试卷B-2013-1-4

南昌航空大学2012—2013学年第一学期期末考试

课程名称：材料科学导论 闭卷 B 卷 120 分钟

一、 名词解释（每小题3分，共15分）

1.

Performance

2. Precipitation hardening

3. Steady diffusion

4. Fatigue limit

5. Schottky defect

二、简答题（共27分）

metals with HCP crystal structure. (7分)

2. Cite types of short-circuit diffusion and explain why shortcircuit contributions to the overall bulk diffusion flux are insignificant(不重要) in most situations. (10分)

3. Briefly describe in your own words the strengthening mechanisms about solid solution strengthening.(10分)

三、相显微结构分析题（18分）

1. Briefly describe their microstructure difference and formation condition between white cast iron and gray cast iron, respectively. (8分)

2.(a) Brie?y describe the microstructural difference between spheroidite and tempered martensite. (b) Explain why tempered martensite is much harder and stronger.（10分）

四、计算题（每题10分，共40分）

1. Calculate the radius of an iridium atom given that Ir has an FCC crystal structure, a density of 2

2.4 g/cm3, and an atomic weight of 192.2 g/mol.

2. Two previously undeformed specimens of the same metal are to be plastically deformed by reducing their cross-sectional areas. One has a circular cross section, the other is rectangurlar; during deformation the circular cross section is to remain circular, and the rectangurlar is to remain as such. Their original and deformed dimensions are as

3.At approximately what temperature would a specimen of γ-iron have to be carburized for 3h to produce the same diffusion result as at 900℃ for 15h? Assume the preexponential D0 and activation energy Q d for carbon inγ-iron are 2.3×10 - 5 m2/s and

148KJ/mol, respectively. The diffusion coefficient D of carbon inγ-iron at 900℃ is 5.9×10-12 m2/s, and the activation energy Q d for carbon inγ-iron does not change with temperature.

4. Suppose that a wing component on an aircraft is fabricated from an aluminum alloy that has a plane strain fracture toughness of 40m

MPa. It has been determined that fracture results at a stress of 365 MPa when the maximum internal crack length is 2.5 mm . For this same component and alloy, compute the stress level at which fracture will occur for a critical internal crack length of 4.0 mm.