EFFECT OF COLD WORK ON OXIDATION OF NICKEL AT HIGH-TEMPERATURE
EFFECT OF COLD WORK ON OXIDATION OF NICKEL AT HIGH-TEMPERATURE
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DOI：
10.1149/1.2404444
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发表时间：
1972-01-01
影响因子：
3.9
通讯作者：
COHEN, M
中科院分区：
文献类型：
--
作者：
CAPLAN, D;GRAHAM, MJ;COHEN, M
本文研究了冷加工和退火纯镍在1atm O_2中从700到1270 ℃、从1 min到20 h的连续称重氧化实验，并用衍射、电子光学技术和金相截面对氧化试样进行了检验。发现冷加工的Ni比退火的Ni氧化得更快，并形成更细粒度的氧化物。图的表观抛物线速率常数，Kp，冷加工镍显示了一个初始的高值，随着氧化物随时间的推移而变粗迅速下降。对于退火Ni，Kp较低，晶粒尺寸较大，两者随时间变化不大。相应地，在每个温度下获得Kp值的范围，并且在Ni氧化的Arrhenius图上，存在表观活化能EA的相应变化。这些结果可以合理地解释的基础上的氧化物晶界作为Ni通过NiO层的容易的扩散路径：对于细晶粒的氧化物，Kp较高，EA较低。氧化物在形成单晶过度生长的Ni晶粒上最薄（并且衍生的EA最高）。在1000 ~附近的阿克里尼乌斯图中的中断是低于1000的传输主要通过泄漏路径的结果，而在较高温度下体积传输更重要。氧化层生长的活化能为54 + 2kcal/mol（晶格扩散输运），比晶界扩散输运的活化能小得多.在以前对Fe（1，2）氧化的研究中发现，冷加工Fe的氧化速度比退火Fe快得多.所提出的解释是冷加工抑制了在Fe 3 O 4-Fe界面处形成扩散空腔（否则会阻碍阳离子转移的空腔），并且此外，通过在冷加工的Fe上形成的Fe 3 O 4，通过Fe 3 O 4的阳离子扩散更快。在高于600 ° C的温度下，其中在Fe 304和Fe之间形成FeO层，该效应消失：冷加工和退火的Fe以相同的速率氧化，在任一情况下都没有扩散腔。本工作的目的是通过研究冷加工对Ni氧化的影响，获得关于氧化层生长机理的进一步信息。选择Ni是因为仅形成一个氧化物相，这是预期简化内部氧化物的因素。
The oxidation of cold-worked and annealed pure Ni in 1 atm O2 was investigated from 700 to 1270~ in continuous weighing experiments for periods from 1 rain to 20 hr and the oxidized specimens examined by diffraction, electron-optical techniques, and metatlographic cross sections. Cold-worked Ni was found to oxidize faster than annealed Ni and form finer-grained oxide. Plots of the apparent parabolic rate constant, Kp, for cold-worked Ni show an initial high value that decreases rapidly as the oxide coarsens with time. For annealed Ni, Kp is lower, grain size larger, and both change little with time. Accordingly, a range of Kp values is obtained at each temperature and, on an Arrhenius plot of Ni oxidation, there is a corresponding variation in apparent activation energy, EA. These results can be plausibly interpreted on the basis of oxide grain boundaries acting as easy diffusion paths for Ni through the NiO layer: for fine-grained oxide, Kp is higher and EA lower. The oxide is thinnest (and the derived EA highest) on Ni grains which form a single crystal overgrowth. A break in the Arrhenius plot around I000~ is the result of transport below 1000 being largely by leakage paths while at higher temperatures volume transport is more important. The estimated activation energy for growth of the oxide layer is 54 __+ 2 kcal/mol for transport by lattice diffusion and appreciably less for transport by grain boundary diffusion.In previous studies of the oxidation of Fe (1, 2) it had been found that cold-worked Fe oxidized considerably faster than annealed Fe. The explanation proposed was that cold work suppressed the formation of diffusion cavities at the Fe304-Fe interface (cavities which otherwise would block cation transfer) and, in addition, that cation diffusion through Fe304 was faster through Fe304 formed on cold-worked Fe. At temperatures above 600~ ie, where a layer of FeO developed between the Fe304 and Fe, the effect disappeared: cold-worked and annealed Fe oxidized at the same rate with no diffusion cavities in either case. The purpose of the present work was to obtain further information on the growth mechanism of oxide layers by studying the effect of cold work on the oxidation of Ni. Ni was chosen because only one oxide phase is formed, a factor expected to simplify inter-