Method of surface hardening sintered bodies by using vibrations

The present invention relates to a method of surface hardening a plurality of sintered bodies comprising a hard phase such as WC and a binder phase such as cobalt or nickel. The method comprises the steps of placing the bodies in a container, and thereby forming a system comprising the container and the bodies therein, and causing the bodies to move and collide with each other and with inside walls of the container. The container is vibrating utilizing a mechanical resonance frequency of the system, the vibrations being preferably unixial and acoustic with a frequency of 20 - 80 Hertz and an acceleraionof 30 - 100 G.