HVOF Coatings of MoB/CoCr against Erosion by Molten Al-Zn Alloy

摘要

MoB/CoCr with excellent durability against molten metal hasbeen developed to be applied to aluminum die casting parts inautomobile and to hot continuous dipping rolls in Zn and Al-Zn plating lines for steel industries. Our previous study hasrevealed that the MoB/CoCr coating prepared by high velocityoxy-fuel (HVOF) spraying has much higher resistance againstattack of the molten Al-45wt%Zn alloys compared toconventional WC/12wt%Co coating from evaluation bylaboratory scaled molten metal immersion test. However,performance with no damage is only limited when applyingonto the substrate with smaller thermal expansion similar tothe MoB/CoCr coatings.This paper describes the solution to prepare the MoB/CoCrcoating without damage onto austenitic stainless steel ofAISI316L with larger thermal expansion, whose material iscommonly utilized for the hot continuous dipping rolls. It hasbeen found that use of undercoat is effective to reduce thenegative influence of large difference in thermal expansionbetween the MoB/CoCr coating and substrate of AISI316L.Optimized thickness of topcoat and undercoat and itscombination showed intrinsic performance of low reactiveMoB/CoCr without any mechanical damage such as crackand/or peeling.