钼的晶界内耗峰及少量间隙杂质影响晶界脆性的机制

用扭摆法测出钼的晶界内耗峯,频率约为1周/秒,峯温在1020℃附近,渗氧或渗碳可使晶界峯消失,但在较低温度出现合金晶界峯:氧峯在890℃附近;碳峯在925℃附近。由于钼单晶的内耗曲线上没有出现这些峯,故可认为都是晶界弛豫引起,如果试样中同时有氧和碳,又在960℃和985℃附近出现两个合金晶界峯,用改变频率方法求得各峯激活能,其相对大小与各峯的峯温次序相同,即氧晶界峯的激活能最小(80千卡/克分子);碳晶界峯次之(98千卡/克分子);纯钼晶界峯最大(119千卡/克分子);其他两个峯激活能略小于纯钼晶界峯。配合了断口金相试验,观察到当有氧峯出现时断口晶界面上有黑色氧化物沉淀粒子;当有碳峯出现时,晶界面上有羽毛状碳化物;当试样中同时有氧和碳存在时,也即当内耗曲线上出现960℃和985℃交互作用峯时,晶界面上有大量的有黑圈的白色沉淀物。从以上结果我们对少量间隙杂质在钼的晶界脆性中所起作用,特别是氧和碳同时存在时能起改善脆性的作用提出了一种看法。

GRAIN BOUNDARY RELAXATION OF MOLYBDENUM AND THE MECHANISM OF THE EMBRITTLING EFFECT OF INTERSTITIAL IMPURITY ADDITIONS

The grain boundary peak in molybdenum was measured by a torsion pendenlum, when the frequency of vibration is 1 cps, the peak occurs around 1020℃. This G. B. peak is reduced by oxygen or carbon additions, but an "alloy grain boundary peak" appears at the lower temperatures on the same damping curve. Using frequency of 1 cps, "Oxygen peak" occurs around 890℃; and "carbon peak" occurs around 925℃. Since no peak is evident on the damping vs temperature curve of molybdenum single crystals, it may be concluded that these peaks are all associated with the stress relaxation across grain boundaries. If some carbon is also present in the sample containing oxygen, the other two "alloy grain boundary peaks" appear around 960℃ and 985℃. The activation energys of all the peaks were determined. The higher is the peak temperature, the larger is the value of activation energy, i.e. the activation energy of "oxygen peak" is the smallest one (80 kcal/mol); that of "carbon peak" is somewhat larger (98 kcal/mol); that of "pure grain boundary peak" is the largest (119 kcal/mol); and the activation energies of the other two "interaction peaks" are somewhat less than that of "pure grain boundary peak".Fractographic work was made after the damping measurements had been taken. Many black oxide spots were observed on the intergranular facets of the specimen, by which the "oxygen peak" had been measured; the feathery carbides were observed on the intergranular facets of the same specimen as we had measured the "carbon peak". When both oxygen and carbon are present in the specimen, which gives the "interaction peaks" around 960℃ and 985℃, many white precipitations embeded by black rings were observed on intergranular fracture facets.Based on the results presented above, the mechanism of the embrittlement of molybdenum by a small amount of interstitial solute elements was discussed, especially the fact that carbon counteracts the severe embrittling effect of oxygen was also explained.