EFFECT OF ALLOYING ELEMENTS ON PRODUCTION OF DUPLEX PREFORMS WITH COMPOSITE PROPERTIES

An experimental investigation was conducted to produce cylindecical powder preforms with high hardness at rim and enough toughness at core to suite the requirements in gearing systems. The difference in properties was achieved only by the different alloying additives. A special composite die was designed to perform the partial compaction of either rim or core beside. the final compaction of the specimen as a whole. Preforms were produced by 600 MPa compaction pressure and 2 hours sintering under H2 atmosphere at 1200°C. A series of experiments were carried out using different compositions to achieve the required difference in properties between the core and the rim and secure enough bond and adhesion between them. A mixture consisting of Fe + 5% Cu in the core and Fe + 2% C + 5% Cu+ 6% Ni in the rim yielded a compact allowing a shear strength value of 225 N/mm2 at the interface, hardness value of 412 HV in the rim, hardness value of 125 HV, in the core, and an overall sintered density of 7.26 gm/cm3. Another series of experiments were carried out using manganese as alloying additive beside copper and nickel to improve the properties at the interface.
A mixture consisting Fe + 5% Cu in the core and Fe + 2% C + 2% Cu+ 6% Ni + 2% Mn in the rim yielded a compact allowing a shear strength value of 250 N/mm2 at the interface, hardness value of 232 HV in the rim, hardness value of 112 HV, in the core and an overall sintered density of 7.28 gm/cm3.