The properties of Fe-Ni-Mo-Cu-B materials produced via liquid phase sintering

Abstract

Sintered materials base on pre-alloyed powders (Fe-Ni-Mo-Cu) are expansively applied in the automotive industry. However, their applications are limited by the particular porosity values of those materials. To reduce the porosity and, simultaneously, to increase the consolidation of sintered alloys, miscellaneous methods within powder metallurgy technologies are utilised, as well as an activated sintering process; for example some boron is added. The boron and iron built a system that is not soluble in any of the three allotropie forms of iron. While sintering at a temperature higher than 1433 K, a permanent liquid phase was generated as a result of a eutectic reaction between iron and Fe2B. Owing to the limited boron solubility in iron, a liquid phase was continuously present during the sintering process, influence changes in the morphology of the porosity and the increase in density, also mechanical properties. In addition, boron showed a strong chemical affinity to oxygen; in sintering process it reacted with a chemically bound oxygen on the surface of powder particles and it simultaneously activated the sintering process. The paper presents the production of sintered materials based on Höganäs Distaloy SA (Fe-1.75% Ni-0.5% Mo-1.5% Cu) powder modified by boron powder in amounts of 0%, 0.2%, 0.4% and 0.6%. Alloys were manufactured using powder metallurgy technology through mixing of powders, compacting at 600 MPa pressure and sintering at 1473 K, during 30 minutes in hydrogen atmosphere. One of the phenomenon, which exists on the surface of sinters made from boron modified pre-alloyed powders (Fe-Ni-Mo-Cu) type Distaloy SA is creating a thickened layer. The similar thickened layer was observed also on the surface of another samples base on pre-alloyed powders with boron addition. As well as the properties: density, hardness, tensile strength were examined and microstructure investigations were performed. Experimental results showed that if boron was added, while sintering, the shrinkage phenomena increased and properties were improved.