The Influence of Heat-treatment on Hardness and Structural Characteristics of Electroless Ni-B Deposited Ferrous Powder Metal Compacts

The Ni-B alloy deposited on ferrous powder metal compacts by electroless coating method and its morphology, structure and microhardness were investigated. Some of the coated specimens were heat treated at different temperatures (300, 400 and 500 °C) as isothermal for 1 h. The phases and morphology of coatings were examined by x-ray diffraction (XRD) and scanning electron microscope (SEM). Phase transformation behavior was studied by differential scanning calorimetry (DSC). Microhardness of Ni-B coatings and PM compacts were evaluated using a Qness Q10 micro Vickers tester. The results showed that, Ni-B coating had an amorphous structure in the coated state but after heat treatment, it turned into a crystalline structure. It was found that nickel borides (Ni2B, Ni3B) precipitated in the nickel matrix. It was determined that precipitation has caused the increase of hardness. The maximum hardness was provided in the heat treated Ni-B coating at 400 °C