Study of the effect of the embedment of Invar36 in Ni60 coating

Abstract

Powder metallurgy (PM) is a rapidly evolving technique that is widely used for manufacturing novel materials. PM dies are exposed to harsh working conditions and are prone to damage. In this work, 45 steel was coated with Ni60 through high-frequency induction cladding to develop inexpensive PM mandrels with long service lives. The thermal expansion coefficient of the Ni60 coating reduced on embedment with Invar36 sticks. The temperature field was simulated through the finite-element method and experimentally verified. The microstructure and elemental composition of the coating were observed by using an electron probe microanalyzer, an energy-dispersive spectrometer and an X-ray diffractometer. A thermal mechanical analyzer and a Vickers microhardness tester were used to measure thermal expansion coefficients and microhardness, respectively. Results showed that current density and heating duration were the main factors that affected temperature distribution and the addition of Invar36 decreased coating temperature by 3–4°C. Energy-dispersive spectrometry revealed that metallurgical bonds formed among Ni60, Invar36 and 45 steel. The addition of Invar36 reduced the thermal expansion coefficient of the coating by 17·8% at 800°C. The microhardness of the coating surface reached as high as 800 Vickers hardness and was unaffected by the embedded Invar36.