Braze alloys used for brazing PCD cannot be used to braze single crystals of diamond as they do not 'wet' diamond. A reactive or 'active' braze alloy is needed. 

These alloys contain a small percentage of titanium metal.  When heated, the carrier alloy melts and bonds to the tool substrate which should be molybdenum or cemented carbide. 

The free titanium reacts with the diamond surface forming titanium carbide (TiC).  It is this reaction layer which gives the bond to the diamond.