Abstract: Nickel-chromium based precise resistance alloys, including primarily Ni-Cr-Al-Fe and Ni-Cr-Al-Cu alloys, are developed from the electrothermal alloy Ni80Cr20 by adding some other alloy elements. Because of their excellent electrical properties, such as high resistivity, low temperature coefficient of resistivity (TCR) and copper thermoelectric potential, these alloys are the key of high-performance resistance elements and attract much attention. However, fundamental researches on the precise resistance alloys are seldom reported, restricting the development of the manufacturing technology of these alloys. In this paper, a series of alloys with different compositions were designed and manufactured so as to investigate the effects of the concentration of Al and Fe, which were the main alloying elements in Ni-Cr-Al-Fe precise resistance alloy on the mechanical and electrical properties. Also, solid solution and aging treatment processes were conducted in order to explore the influence of heat treatment on the properties because the preci-sion resistance alloys were usually used after aging treatment. Grain sizes, hardness and tensile properties of different alloys were measured. The electrical properties of alloy were tested by using resistance tester, TCR tester and thermocouple calibration furnace respectively. It was found that the grain size decreased with the increase of Al but it was not sensitive to the content of Fe, in the concentration range of this work. As for the mechanical properties, the strength and hardness of the alloy increased with the increase of Al and Fe content, and the plasticity decreased correspondingly. But the effect of Fe was much less than Al. After aging treatment, the strength and hardness increased simultaneously, but the plasticity almost had no change. In terms of electrical properties, as the Al and Fe content increased, the resistivity increased too. These two elements affected the TCR conversely, i. e., the TCR declined with the increase of Al but rose with the increase of Fe. Furthermore, negative TCR values were attained under some conditions. Hence, it was expectable to get TCR values close to zero by adjusting the ratio of Al and Fe properly. With the increase of Al content, the copper thermoelectric potential decreased first and then increased, and the minimum appeared at 3.2wt%—3.7wt% Al. However, it was not sensitive to Fe content. Aging treatment affected the electric properties favorably, that is, it increased the resistivity but decreased TCR and copper thermoelectric potential. Generally, the content of Al affected the electrical and mechanical properties obviously, while the primary effect of Fe content was on TCR. In this paper, the mechanism of the evolution of mechanical and electrical properties of precise resistance alloys with composition and heat treatment was discussed from the aspect of grain size, microstructure variation during heat treatment and extranuclear electron distribution of different elements. These results was hopeful to provide some practical references for the optimization of the composition, process and performance of Ni-Cr-Al-Fe precise resistance alloy.
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2019, Vol. 33 
