Electrodeposited nickel(3) aluminide base intermetallic coatings and their resistance to high temperature degradation in hydrocarbon cracking environments.

摘要

This research was aimed at developing novel Ni-A1 base intermetallic coatings to protect commercial Fe-Ni-Cr tube alloys from severe corrosive degradation at high temperatures. These alloys are widely used in petrochemical, chemical, and energy conversion industries. The coating process and coating evaluation were the two main aspects of this investigation.; A two-step coating processing has been successfully developed to in situ apply pure and CeO2-modified Ni3Al intermetallic coatings onto Fe-Ni-Cr substrates. The process consists of the electrodeposition of Ni-Al and Ni-Al-CeO2 composite coatings from a Watt's nickel bath containing Al and CeO2 particles via a cost-effective electroplating technique and an annealing treatment of the as-plated coatings. It was found that the deposition of Al particles obeyed a Guglielmi model, and that REO particles interfered significantly with the deposition of Al particles.; The long-term resistance of pure and CeO2-modified Ni 3A1 coatings to cyclic oxidation, carburization, coke formation, and metal dusting was evaluated in flowing dry air, 2 % CH4-H 2, and CO-H2-H2O respectively. Due to the high porosity, pure and CeO2-dispersed Ni3Al coatings exhibited poor resistance to cyclic oxidation at 850°C. CeO2 improved the spallation resistance of the Ni3Al base coatings during cyclic oxidation at 1050°C. CeO2-dispersed Ni3Al coatings showed better carburization resistance, particularly at 1050°C. Ni 3A1-based coatings. Those CeO2-dispersed were susceptible to coke formation and metal dusting at 650°C. Pre-oxidation improved the resistance of Ni3Al-based coatings to coke formation and metal dusting at 650°C, but the effectiveness depended on the integrity of the induced alumina scale. Special attention was paid to several aspects of coating degradation. These aspects included microstructure changes, degradation mechanisms, coating/substrate interdiffusion, effect of corrosive atmosphere, and effect of CeO2 on coating performance. Advanced analytic technologies---including SEM, EDS, EPMA, XRD, XPS, and AES---were adopted in this investigation.