高校问答三宝词道教十方韵:300分工科材料类英文论文求好翻译.5
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mechanisms of phase transformation, and the phase
transformation rate of different mechanisms can be
evaluated according to the value of parameter n.
Under the condition of linear growth, if the nuclea-
tion rate increases with time, the value of parameter
n is more than 4; if the nucleation rate decreases
with time,there is4>n>3; if the nucleation rate
decreases to zero after initial nucleation, the value of
parameter n is equal to 3 [13].
JMA equation was discussed by Cahn under the
condition of nucleation at the surfaces of grain
boundaries and grain edges [13]. According to their
calculation, if the grains were large enough, the nu-
cleus at the surface of grain boundaries or grain
edges were rapidly saturated so that the new nucleus
would not form any more. Therefore, the new
phases could grow only by the parallel advancing
into parent grains of the new phases on the surfaces
of grain boundaries or by the coarsening in the radial
direction of the new phases embracing the grain
edges. At this time, the Avrami coefficients are 1 and
2, respectively.
The experimental results of DC at temperatures
of 200 and 250℃ were fitted to obtain the Avrami
index. Except that the Avrami exponent of
AIZn-2Cu at 250℃ was about 0.4, others were
slightly less than 1. This was because that DC cells
only nucleated at original boundaries and DP cellu-
lar boundaries.
The size of DP cells formed in the AlZn-2Cu al-
loy aged at 250℃ was large, and the lamellae inside
the cells were coarse. Therefore, the driving force of
DC was small, and there were only a few nucleation
sites. Moreover, the growth of DC cells was blocked
by the Cu-rich phase, and the growth velocity was
reduced, which led to the small Avrami exponent.
(1) The coarsening of DP in AlZn and AlZn-2Cu
alloys is different as aging temperature varies. At
150℃,the fine lamellar microstructure of DP is
dissolved and spheroidized; with the aging tempera-
ture increasing up to 200 or 2500C, the DP micro-
structure mainly changes into coarser lamellar mor-
phology by DC. Coarsening cells nucleate at original
boundaries and DP cellular boundaries.
(2) The DC growth velocity of DP in the AlZn
and AlZn-2Cu alloys rapidly reaches the maximum
at the beginning of transformation, and decreases
with the extension of aging time. Moreover, the
growth velocity of coarsening cells at 250℃ is lar-
ger than that at 200℃. However, the speed of trans-
formation from DP to DC at 250℃ is slower than
that at 200℃.
(3) The addition of Cu reduces the coarsening
speed of DP microstructure.
参量n 的价值反射阶段变革不同的机制, 并且不同的机制的阶段变革率可能被评估根据参量n 的价值。在线性成长的情况下, 如果nuclea- tion 率增加以时间, 参量n 的价值是超过4; 如果生核率减少以时间, 那里is4 n 3; 如果生核率减少到零在最初的生核以后, 参量n 的价值是相等的到3 [ 13 ] 。JMA 等式由Cahn 谈论了在生核的情况下在表面晶界和五谷边缘[ 13 ] 。根据他们的演算, 如果五谷是足够大的, nu- cleus 在晶界表面或五谷边缘迅速地饱和了以便新中坚力量不会形成。所以, 新阶段能增长只由平行推进入新阶段的父母五谷在晶界表面或由coarsening 在新阶段的辐形方向接受五谷边缘。此时, Avrami 系数是1 和2, 各自地。DC 的实验性结果在温度200 和250? 适合获得Avrami 索引。除了AIZn-2Cu Avrami 方次数在250? 1 是大约0.4, 其他人轻微地是少于。这是因为那DC 细胞只有核在原始的界限和DP cellu- lar 界限。DP 细胞的大小形成了在AlZn-2Cu al- loy 变老在250? 是大的, 并且鳞片在细胞里面是粗糙的。所以, DC 驱动力小, 并且有唯一几个生核站点。而且, DC 细胞成长在富有Cu 的阶段以前阻拦了, 并且成长速度被减少了, 导致小Avrami 方次数。(1) coarsening DP 在AlZn 和AlZn-2Cu 合金里是不同的因为变老的温度变化。在150?, DP 美好的薄片状微结构被溶化和spheroidized; 用老化tempera- ture 增加200 或2500C, DP 微结构主要改变到更加粗糙的薄片状平均观测距离phology 由DC 。Coarsening 细胞nucleate 在原始的界限和DP 多孔的界限。(2) DC 成长速度DP 在AlZn 和AlZn-2Cu 熔合迅速地到达最大值在变革开始, 和减少以老化时间引伸。而且, 成长速度coarsening 细胞在250? 比那是lar- ger 在200? 。但是, trans- 形成的速度从DP 到DC 在250? 比那慢的在200? 。(3) Cu 的加法减少DP 微结构的coarsening 速度。