Novel Approach for Using Ductile Iron as Substrate in Bimetallic Materials for Higher Interfacial Bonding Bearings

The Sn-based Babbitt and ductile iron bimetallic composites were fabricated by liquid–solid compound casting process. The Sn-based Babbitt alloy was melted in an electrical furnace and then poured into a mould containing ductile iron solid substrate. Different pre-treatment conditions for ductile iron surface using grinding, polishing and normalizing heat treatment were applied before tinning process for the aim of surface graphite decarburization. Such kind of approach can be considered as a promising way allowing using ductile iron as a substrate in the manufacturing of bimetallic materials. The results of the experiments show that only 40% of interfacial bonding area was achieved by the grinding and polishing (for 10 min) of ductile iron substrate, whereas, by the normalizing heat treatment of ductile iron substrate at 850 °C for 25 min (along with grinding and polishing), an increasing of the interfacial bonding area of 85% was achieved. All these variations can be attributed to the relatively higher percentage of surface graphite decarburization under controlled conditions of heat treatment and substrate preparation. The test of shear stress value of the bimetal with normalized ductile iron substrate is significantly higher (9.5 ± 0.48 MPa) than that of bimetal with grinded–polished ductile iron substrate (5.5 ± 0.28). Furthermore, Babbitt/ductile iron bimetallic specimens fabricated under these certain conditions of grinding and normalizing demonstrates a relatively higher interfacial hardness level (42 ± 2.1 HV). It can be reported that the lower value of free carbon in bimetal interface of normalized ductile iron substrate improves the interfacial bonding area and the elements diffusion and consequently, leads to increasing the microhardness.