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本文对镍铬-镍硅热电偶合金进行高温长期和循环加热的热稳定性试验及氧化动力学试验,结果表明：在NiCr10合金中加入0．05-0．2％的钇(Y),在NiSi25合金中加入0．05-0．15％的Mg,它的热电势稳定性有明显提高,抗氧化性能增强,使热电偶的最高使用温度和高温使用寿命有较大幅度的提高。直径为1．2mm的偶丝在1200℃,408小时长期热稳定性试验结果：NiCr10Y和NiCr10两种合金的热电势变化分别为-245μV和-1113μV,相差约为4．5倍。NiSi2．5Mg和NiSi2．5两种合金的热电势变化分别为+88μV和+867μV,相差近10倍。直径为3．2mm的裸线热电偶在1300℃连续加热,NiCr10-NiSi2．5热电偶与NiCr10Y-NiSi2．5Mg热电偶比较,使用寿命由100多小时提高到800小时以上。本文还用金相、X射线分析和电子探针微区分析等方法对热电偶合金的高温氧化机理进行了一定的研究。在NiCr10、NiSi2．5合金中加入少量的Y、Mg后,减少了合金的氧化烧损,促进了组织结构的稳定。同时使合金氧化膜的形态与结构也发生了较大的变化。在NiCr10合金中加入少量的Y后,加速了合金中Cr、Si离子的扩散,较快地形成了薄而致密的Cr2O3氧化膜。同时在氧化膜与基体交界处,Y、Si的氧化物像树枝状伸向基体。这样就大大改善了氧化膜对基体的保护性与粘附性,使合金的抗氧化性能有较大的提高。在NiSi2．5合金中加入少量Mg使合金的氧化膜中Si的氧化物分布均匀,改善了氧化膜对基体的保护性,同时减少了合金基体的内氧化。这使镍硅合金的抗氧化性能提高。
In this paper, the thermal stability and oxidation kinetics of NiCr-NiSi thermocouple alloys under long-term and cyclic heating at high temperature were studied. The results show that the addition of 0.05-0.2% yttrium (Y) NiSi25 alloy by adding 0.05-0.15% of Mg, its thermoelectric power stability has improved significantly, enhanced oxidation resistance, the maximum temperature of the thermocouple and high temperature service life has greatly improved. The long-term thermal stability test results of 1,200 mm diameter and 1,200 mm long couples at 1200 ° C for 408 hours showed that the thermoelectric coefficients of NiCr10Y and NiCr10 alloys were -245μV and -1113μV, respectively, with a difference of about 4.5 times. The thermoelectric potentials of NiSi2.5Mg and NiSi2.5 alloys are + 88μV and + 867μV, respectively, a difference of nearly 10 times. 3.2mm diameter bare wire thermocouple at 1300 ℃ continuous heating, NiCr10-NiSi2.5 thermocouple and NiCr10Y-NiSi2.5Mg thermocouple comparison, the service life of more than 100 hours to 800 hours or more. In this paper, metallographic, X-ray analysis and electron probe microanalysis methods were also used to study the mechanism of high temperature oxidation of thermocouple alloys. In NiCr10, NiSi2.5 alloy by adding a small amount of Y, Mg, reducing the oxidation of the alloy burning, and promote the stability of the organizational structure. At the same time, the morphology and structure of the alloy oxide film also changed greatly. Adding a small amount of Y into the NiCr10 alloy accelerated the diffusion of Cr and Si ions in the alloy and formed a thin and dense Cr2O3 oxide film faster. At the same time in the oxide film and the substrate junction, Y, Si oxide like dendrite extending to the substrate. This greatly improves the oxide film on the substrate of the protective and adhesion, the oxidation resistance of the alloy have greatly improved. Adding a small amount of Mg into the NiSi2.5 alloy makes the Si oxides in the oxide film of the alloy evenly distributed, improving the protection of the oxide film to the substrate and reducing the internal oxidation of the alloy substrate. This improves the oxidation resistance of the nickel-silicon alloy.