Abstract
The authors investigated the mechanical properties of Ni-58mass%Fe alloy electrodeposits, which are expected to be used as low thermal expansion materials, before and after heat treatment for one hour at 400 to 600°C.
For the Ni-58mass%Fe alloy electrodeposits without heat treatment, ultimate tensile strength (UTS) was 1610MPa, elongation (&delta) was 7%, and hardness was 430HV. After heat treatment for one hour at 400, 500, and 600°C to stabilize the liner expansion coefficient of the Ni-58mass%Fe alloy electrodeposits, the alloy electrodeposits had a UTS of 830MPa, a &delta of 9%, and a hardness of 270HV at 400°C ; a UTS of 720MPa , a &delta of 17%, and a hardness of 240HV at 500°C ; and a UTS of 640MPa, a &delta of 22%, and a hardness of 220HV at 600°C. After heat treatment for one hour at 400 to 600°C, the mechanical properties of the Ni-58mass%Fe alloy electrodeposits were comparable to those of melted Ni-58mass%Fe alloys for IC leadframes.
Though a reduction in the ductility of the Ni-58mass%Fe alloy electrodeposits after heat treatment for one hour at 400 to 600°C by grain boundary segregation of sulfur was expected because the alloy electrodeposits contained 0.04mass% sulfur, ductility of the alloy electrodeposits was not reduced after heat treatment in this temperature range. It was considered that since sulfur dispersed as granular Fe-Ni-S compounds in the Ni-58mass%Fe alloy electrodeposits after heat treatment for one hour at 400 to 600°C, embrittlement originating from sulfur segregation to grain boundaries of the alloy electrodeposits was able to be prevented.
