化学成分及时效处理对镍铬铝铁精密电阻合金性能的影响

Effect of Chemical Composition and Aging Treatment on Properties of Ni-Cr-Al-Fe Precise Resistance Alloy

镍铬改良型精密电阻合金是在Ni80Cr20电热合金基础上经过成分优化发展而来,目前常用的有Ni-Cr-Al-Fe和Ni-Cr-Al-Cu两个系列。该类合金具有高电阻率(ρ)、低电阻温度系数(TCR)和低对铜热电势等优异的电学性能,是制作高性能电阻元件的关键材料,受到了我国研究者的高度重视,但关于其基础研究的报道很少,制约了相关生产技术的进步。Al和Fe是Ni-Cr-Al-Fe系精密电阻合金中两种主要的合金元素,本研究通过合理的成分设计,研究了这两种元素对合金力学和电学性能的影响规律;同时该合金通常是在固溶和时效处理状态下使用,因此也设计了相应的热处理工艺,以考察时效处理对合金性能的作用规律。本工作分析了不同合金的晶粒尺寸,测试了合金的硬度和拉伸性能,并利用电阻测试仪、电阻温度系数测试仪和热电偶检定炉等检测了合金的电学性能。结果表明,在本研究设计的成分范围内,合金的晶粒尺寸随Al含量的增加而减小,但其对Fe含量的变化不敏感。在力学性能方面,合金的硬度和强度随Al和Fe含量的增加而提高,塑性相应下降,但Fe的作用较Al弱;经时效处理后,合金的强度和硬度上升,但塑性无明显变化。在电学性能方面,Al和Fe含量的增加均使合金电阻率升高,但二者对电阻温度系数的影响规律相反,TCR随Al含量的增加而减小、随Fe含量的增加而增大,并且在一定条件下会出现负值,因此通过合理调整Al和Fe含量的比例,有望得到接近于0的TCR;合金的对铜热电势随Al含量的增加而先降后增,在Al含量为3.2%~3.7%(质量分数)范围内出现最小值,但其对Fe含量不敏感;经时效处理后,合金的电学性能得到明显改善,即电阻率升高、TCR下降、对铜热电势下降。总体而言,Al含量对该精密电阻合金力学和电学性能均有显著影响,而Fe的作用主要体现在对电阻温度系数的调控方面。本研究结合晶粒尺寸、微观结构在热处理过程中的变化以及元素的核外电子分布等特点,讨论了成分和热处理导致合金力学和电学性能改变的内在机理,该研究结果对于Ni-Cr-Al-Fe精密电阻合金的成分、工艺和性能的优化具有重要的实用价值。

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.