J. Kitamura, Fujimi incorporated, Kakamigahara, Japan; S. Osawa, H. Ibe, H. Mizuno, S. Tawada, Fujimi Incorporated, Kakamigahara, Gifu, Japan
The aim of this study is to improve impact resistance of WC-Cr3C2-Ni based coatings by means of modification of powder properties and use of undercoat. The poor impact resistance of conventional WC cermet coatings of WC-20%Cr3C2-7%Ni has become higher by increase of Ni metal content and addition of blended metal powders with retention of abrasive and erosive wear resistances. Influence of hardness of undercoat or substrate also has been studied for further improvement on impact resistance. The study has revealed that undercoat is better to improve impact resistance compared to base metal substrate at similar hardness around 200-300 in Vickers hardness. Undercoats with Vickers hardness ranging from 400-600Hv are also found to be effective drastic increase of impact resistance. However, impact resistance of the coatings on hard undercoats of more than 700Hv has decreased contrary. Influence of ball weight used in falling ball test for evaluation of impact resistance has been also mentioned that optimal undercoat hardness shifts from around 600 to 400Hv when decreasing the ball weight.
Summary: This paper describes two methods are applied in order to improve impact resistance of WC cermet HVOF coatings. One is changing powder content increasing metal contents and its mixing way with retention of wear resistance. The other is use of undercoat and its hardness. Finally we have found that middle hardness of undercoat aroung 400-600 drastically improve the impact resistance that will offer new opprtunity to expand the machininery applications.
