Authors : Abdul Raheem K.AbidAli, Farzad Mahoubi and Alaa Mohammed Hussein Wais
Abstract: The present work aims to study the hardness and wear resistance of as-plated and plasma-nitrided electroless Ni-B-CNT coatings. electroless Ni-B coatings. Ni-B-CNT composite was deposited on AISI 4340 steel using different concentration of CNTs ranging, 0, 0.35 and 0.7 g L–1 in an electroless bath. After the plating process, all samples were plasma nitrided in an atmosphere comprising of 50%N2-50% H2, at 400°C, for 4 h. The friction and wear behavior of the composite coatings were evaluated using a pin on disk method at an applied load of 10 N. An alkaline bath having nickel chloride as the source of nickel, borohydride as the reducing agent and Multi walled carbon nanotubes (MWCNT)was used to prepare the electroless Ni-B-CNT coatings. The samples were then characterized by means of XRD, FESEM, microhardness and surface roughness measurements. Worn surfaces were further analyzed by FESEM and EDS spectroscopy. Microhardness results revealed that the maximum hardness of 1250 HV was obtained for Ni-B 0.35 g L–1 CNT plasma-nitrided sample. According to the results, increasing the CNTs concentration caused the as-plated Ni-B amorphous structure to change to crystalline. Presence of CNTs not only decreased the grain size in the plasma-nitrided samples but also prevented excessive heat generation during the wear test and thus the friction coefficient was declined during the test. Moreover, image of the worn surface of Ni-B 0.35 g L–1 CNT plasma-nitrided sample indicated the smoothest wear trace with no apparent cracks and the highest wear resistance among all the samples was achieved. While, in Ni-B-0.7 g L–1 CNT sample, agglomeration created asperities as well as large particles weakly bonded to the Ni matrix which ultimately led to an increase in the specific wear rate.
Abdul Raheem K.AbidAli, Farzad Mahoubi and Alaa Mohammed Hussein Wais, 2019. Effect of Plasma Nitriding on Wear Behavior of Ni-B-CNT Electroless Coating of AISI 4340. Journal of Engineering and Applied Sciences, 14: 8978-8990.