be created then a selected additive is diffused into the insert in areas not protected by the refractory material diffusion barrier one of ordinary skill in the art would appreciate that a suitable diffusion barrier refractory material will depend on the selected additive that is to be used in the diffusion step in accordance with some embodiments of the invention materials that can withstand the high temperatures required for additive diffusion e g sintering temperature for the additive material can be used as refractory materials for example group vi group v and most group vi transition metal carbides nitrides or carbonitrides may be used as refractory materials to coat the inserts and create localized gradients of material properties in accordance with one embodiment of the invention titanium nitride tin is used as a refractory material particularly when boron is selected as the additive to illustrate a method in accordance with one embodiment of the invention rectangular bars of wc u2014 co 1 5 inch u00d7 1 inch u00d7 0 25 inch in size about 10 wt co were coated with a refractory material e g tin using a suitable method such as physical vapor deposition pvd to a proper thickness e g about 2 u03bcm on all sides except one one of ordinary skill in the art would appreciate.