3、论述题(30 分)
3.1 Consider one such alloy that initially has a uniform carbon concentration of 0.25wt% and is to be treated at 950℃. If the concentration of carbon at the surface is suddenly brought to and maintained at 1.20wt%, how long will it take to achieve a carbon content of 0.80wt% at a position 0.5mm below the surface? The diffusion coefficient for carbon in iron at this temperature is 1.6×10-11 m2/s; assume that the steel piece is semi-infinite.
3.2 在同一坐标系中画出金属晶体和半晶态聚合物的应力应变曲线。两曲线分别可以分为几个阶段?各个阶段发生了哪些变化?并说明两种材料强化和软化的机理。