Development of Technology of Nicrosil and Nisil Thermocouple Materials Using Extrusion of Metal Powders

Abstract

Nicrosil-nisil (NiCrSi-NiSi) thermocouples (Type N) have a high thermal EMF stability, radiation resistance, resistance to oxidation of the thermocouple wires and can be used as a universal means of measuring temperatures up to 1300 °C. However, when the traditional metallurgical method is used for the production of rod and wire materials of nicrosil and nisil from ingots of metals, it is difficult to ensure the homogeneity of the ingots and materials of the thermocouple. It is known that powder metallurgy methods can provide a greater homogeneity of the material compared to casting technology. The aim of this work was to study the possibility of using powder technology for the fabrication of rods of nicrosil and nisil thermocouple materials by extrusion and sintering of powders of source metals. Reduction in size and mixing of the raw powder components in a planetary ball mill was investigated. The regularities of pressing the prepared mixtures and microstructure of materials sintered from them were determined. Samples of nicrosil and nisil thermocouple materials in the form of cylindrical rods with a diameter of about 5 mm and a length of 200 mm with an uniform microstructure were also fabricated by extrusion of prepared mixtures followed by sintering. Experimentally determined specific differential thermal EMF of the thermocouple made from the sintered rods coincided with the theoretical value.