Effect of Granulated Powder on Joint Strength of Permalloy-Stainless Steel Composites by Sinter Joining
Kunio Okimoto, Kazuhisa Iwamoto and Yoshiyuki Kato
Abstract:Granulated powder produced from fine powder for the MIM ( metal powder injection molding ) process was used to fabricate a composite part consisting of Fe-47Ni permalloy and SUS410L ferritic stainless steel. Green compacts of disk and ring shapes were separately fabricated and assembled into a unit. The unit was sintered at 985`1255 for 1h in vacuum. The use of the granulated powder increased the joint strength. In case of fine powder, cracking was observed frequently in the outer ring after sintering, but the generation of cracks did not occur in the granulated powder. The joint strength was discussed in terms of the inner disk and outer ring materials and the clearance between them. The joint strength of the composite prepared with a combination of an inner disk of SUS410L stainless steel and an outer ring of Fe-47Ni permalloy (B type) was superior to that of the composite fabricated with the opposite combination (A type). This is reverse to the result in using the fine powder for the MIM. It is due to the fact that difference (Ã) in the change in diameter between the outer ring and the inner disk of the granulated powder compacts by sintering is smaller than that of the fine powder compact. It can be concluded that, in the granulated powder, the effect of diffusion during sintering shrinkage on the joint strength is relatively lowered compared to the fine powder for MIM and the effect of thermal expansion of the inner disk is enlarged on the contrary. Key Words:Sinter joining, Joint strength, Composite material, Powder forming, Stainless steel, Permalloy, Diffusion, Bonding