Session BB4.4

2:15 PM BB4.4
EFFECT OF B4C ADDITION ON CAVITATION RESISTANCE OF THE HVOF SPRAYED NiCrBSi ALLOY. Y.T. Wu, T.S. Chin, National Tsing Hua University, Hsinchu, TAIWAN.

Cavitation resistance of metals is critically required in applications such as hydraulic turbine, ship, propeller, and so on. The effect of adding 6 to 18 wt% B4C into the HVOF sprayed NiCrBSi self-fluxing alloy on its cavitation resistance was studied. It was found that porosity of the as-sprayed layers increased linearly, while the hardness and adhesion lowered, with the B4C contents. These led to lower cavitation resistance. After heat treatment at 1050 C, the cavitation resistance was increased 9%, while the hardness of the coating was greatly ehanced 29% to Hv 1035 of the 12 wt% B4C added layer. The reasons of such variation were studied by DTA, SEM and OM. The increase in porosity is due mainly to the release of CO gas from the reaction of B4C with oxides in the alloy melt. While the increase in hardness and cavitation resistance after heat treatment are arisen from the formation of borides, carbides and borocarbides at around 890 980 C during heat treatment.