Electroless Ni-B-W coatings for improving hardness, wear and corrosion resistance: Nanašanje Ni-B-W s cementacijskim galvaniziranjem za izboljšavo trdote, obrabe in odpornosti proti koroziji

In this study the formation of a Ni-B-W coating on steel using an electroless plating process and evaluation of the hardness, wear and corrosion resistance was analyzed. The Ni-B-W coating was prepared using an alkaline borohydride-reduced electroless nickel bath. Scanning electron microscopy (SEM) of the cross-sectional view of the Ni-B-W coating was analyzed and the layer characteristics were investigated. The Ni-B-W coating was characterized using XRD. The study reveals that the Ni-B-W coating is amorphous in the as-plated condition and after heat treatment at 450 °C for 1 h the Ni-B-W coatings crystallize and produce nickel and nickel borides. The hardness of the as-plated and heat-treated Ni-B-W coatings were compared with Ni-B coatings. In both coatings the hardness increased with heat treatment. The wear resistance of Ni-B-W coatings annealed at different temperatures was analyzed using a ball-on-flat test. The wear resistance of the coating increased with heat treatment and reached a maximum value at 400 °C. An optical microscope and EDS analysis were applied on the wear tracks to determine the wear mechanism. Ductile failure and an abrasive wear mechanism were dominant for the coating heat treated up to 400 °C. Network cracks and shearing marks were detected for the coatings annealed at 450 °C and above, indicating brittle failure. For investigating the corrosion characteristics of the coatings, immersion tests in 5 % H2SO4 and 10 % HCl acidic solutions for seven days were applied. According to the corrosion test results, the Ni-B-W coatings showed good corrosion resistance in the H2SO4 solutions. V tej študiji je bil analiziran postopek cementacijskega galvaniziranja za nanašanje Ni-B-W na jeklo in analizirana je bila trdota, obraba in korozijska odpornost. Nanos Ni-B-W je bil pripravljen z uporabo alkalne z borhidridom reducirane cementacijske galvanske kopeli niklja. Z vrstičnim elektronskim mikroskopom (SEM) je bil analiziran prečni prerez nanosa Ni-B-W in preiskane so bile značilnosti plasti. Nanos Ni-B-W je bil karakteriziran z XRD. Študija je odkrila, da je nanos Ni-B-W amorfen v nanesenem stanju, po toplotni obdelavi pri 450 °C, 1 h je bil nanos Ni-B-W kristaliziran in nastali so nikelj in nikljevi boridi. Primerjani sta bili trdota nanesenega in toplotno obdelanega nanosa Ni-B-W. V obeh primerih je trdota narastla s toplotno obdelavo. S preizkusom s kroglico na ploskvi je bila preizkušena obrabna odpornost nanosa Ni-B-W, žarjenega pri različnih temperaturah. Odpornost proti obrabi se je povečevala s toplotno obdelavo in je dosegla najvišjo vrednost pri 400 °C. Svetlobni mikroskop in EDS-analiza sta bila uporabljena na obrabljeni tečini, da bi ugotovili mehanizem obrabe. Žilav prelom in mehanizem abrazijske obrabe sta prevladovala pri nanosu, segretem do 400 °C. Pri nanosu, segretem na 450 °C in višje, se je pojavila mreža razpok in znaki striženja, kar kaže na krhek prelom. Za ugotavljanje korozijskih lastnosti so bili uporabljeni preizkusi s potapljanjem sedem dni v raztopino 5 % H2SO4 in 10 % HCl. Pri korozijskem preizkusu je nanos Ni-B-W pokazal dobro korozijsko odpornost v raztopini H2SO4.