An x-ray tube cathode assembly (28) includes a support arm (36) comprising a first metal. A ceramic insulator (70, 82) has a first metalized surface (72, 86) wherein the metalized surfaces comprise a desired amount of the first metal. A first member of filler material (90) is in contact with the support arm (36) and the first metalized surface (72, 86) of the ceramic insulator (70, 82), the first member of filler material comprising at least a second metal (96a, 96b) wherein a first alloy system (FIG. 5) comprising the first and second metals includes an alloy minimum point percentage composition (P) of the first and second metals having a first alloy system minimum melting point (M) for the alloy minimum point percentage composition that is lower than both of the melting point of the first metal and second metal. A bonding region resulting from heating the cathode assembly causing diffusion bonding to proceed, the bonding region has a layer of alloy comprising the minimum point percentage composition (P) and the heating of the cathode assembly continues to a bonding temperature of at least the first alloy system minimum melting point (M) and holding at that temperature for a desired period of time.