Abstract
This paper reviews the researches in powder forming which were carried out by the author. In the compaction and forming of metal powders, first a compaction criterion in a stress state such that σ2=σ3 was obtained; this gives a relation between principal stresses and density of the green compact. Next, by using the results obtained from the cold forgeability of sintered iron, a ductile fracture criterion for porous metals was proposed. The formation process of joint strength
in the infiltration joining was made clear. Furthermore, rapidly solidifying superplastic powder was prepared by centrifugal atomization method.
In the forming processing of magnetic powders, meantime, a new type of composite magnetic material was fabricated by combination with electro-magnetic properties of ferrite powder and the superplastic properties of Zn-22Al alloyed powder. To improve the magnetic characteristics of the permanent magnets, orientation forming of magnetic powders mixed with a MIM binder was attempted and a new orientation forming process was proposed. Moreover, for the purpose of producing ferrite part with a complicate shape which has different alignment of the ferrite crystallites, the feasibility of combined sinter joining method was carried out. As another application of combined sinter joining, a stainless steel-permalloy composite was fabricated and the forming conditions to give sufficiently high joint strength to it were found.
