Inclusion of W in electroless Ni-B coating developed from a stabilizer free bath and investigation of its tribological behaviour

In the present study, tribological and corrosion behaviour of electroless Ni-B-W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 degrees C, 90 degrees C, and 95 degrees C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 degrees C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV100 at bath temperatures of 85 degrees C, 90 degrees C, and 95 degrees C respectively. The inclusion of W to Ni-B coating enhanced the hardness by similar to 150 HV100. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 degrees C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 degrees C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.