Electrodeposition of boron and boron compounds onto metal and metal alloys

ELECTRODEPOSITION OF BORON AND BORON COMPOUNDS ONTOMETAL AND METAL ALLOYS(Ph.D. Thesis)Hüseyin ÇELİKKANGAZİ UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYJanuary 2007ABSTRACTMetal and metal alloys are covered with boron and boron compounds inorder to give them superior corrosion resistance, mechanicalproperties and catalytic features. Although electrochemical boridingmethods are less popular than physical and chemical methods theyhave certain advantages such as better control over the stoichiometryand crystal structure of the coverage and simpler instrumentation.Electrochemical boriding processes are carried out with molten boronsalts at elevated temperatures such as 900-1200 oC. However the use ofelevated temperatures involves high cost and carries the risk ofdistorting the structure of the metal and metal alloy to be borided.In this study the electrochemical reduction mechanism of BBr3 waselucidated by the use of cyclic voltammetry, chronoamperometry,chronocoulometry, ultramicro disc electrodes and rotating discelectrodes with a Pt electrode. Then Pt, Ti6Al4V alloy and St37 nonalloyed soft steel were borided in solution by the use of electrochemicalmethod at room temperature. The structure of the coverage wasinvestigated with SEM micrographs. The borided Ti6Al4V and St37surfaces were subjected to a tempering process under argonatmosphere. The composition, crystal structure and morphology of thefinal boride coverage were examined with XRD and SEM techniques.It was observed that it was possible to form compact metal boridecoverage upon metal surfaces at much lower temperatures than thosereported in literature such as 500 and 700 oC. Temperature was found tocontrol the diffusion process towards the substrate. In boriding studiescarried out on Ti6Al4V the temperature was found to have a linearrelationship with the amount of boride deposited upon the surface.However there was no such relation observed for St37 steel. This wasattributed to the higher affinity of the titanium to boron than iron.