. . "For example, as the layer is predominantly iron, as set fonth in the heretofore mentioned application, Serial No. 540,842, sintering is preferably carried out for about forty minutes at 2050 F. If the material of layer 30 is predominantly copper, for example, if said layer is a copper-tin-leadgraphite material as disclosed in Wellman Patent 2,178,527. 1550 F. to l700 F. is preferred for a period o" . .