Patent GB-1463937-A (GB)
Title: Method of joining by diffusion welding a hollow part of non ferrous metal onto the inner surface of a hollow part of ferrous metal
IPC: B23K35/00
Filed: 1975-04-04
Abstract: 1463937 Diffusion bonding EBARA MFG CO Ltd 4 April 1975 [7 May 1974 5 July 1974 13 Aug 1974] 13813/75 Heading B3R A method of joining a hollow part 12 of non- ferrous metal to the inner surface of a bore in a hollow part 11 of ferrous metal by diffusion welding, the non-ferrous metal having a larger coefficient of thermal expansion than the ferrous metal, comprises inserting the hollow part 12 into and in those contact with the bore of the hollow part 11, inserting a core 13 of material having a higher strength and a higher melting point than the non-ferrous metal into and in close contact with a bore of the hollow part 12, and subsequently heating the resulting composite part to a diffusion welding temperature at reduced pressure or in a non-oxidizing atmosphere at atmospheric pressure. The hollow parts are thus brought into contact under pressure generated by the difference in thermal expansion while the core prevents deformation inwardly of the hollow part 12. Liquid metal 15 having a lower melting point than the material of the parts 11, 12 and core is caused to penetrate the gaps between the parts 11, 12 and the part 12 and core, the heating to diffusion welding temperature effecting solidphase-liquid phase diffusion between the ferrous metal and non-ferrous metal in solid phase, and the low melting metal in liquid phase, and, subsequently, effecting solid phase-solid phase diffusion between the ferrous metal and non- ferrous metal in solid phase. The hollow part 11 may be of steel and comprise the cylinder block of an axial piston pump, and the part 12 may be in the form of a bush of copper or copper alloy, such as bronze, so as to improve the sliding property, wear or corrosion resistance of the part 11. The bores may be cylindrical, elliptical or polygonal. The core may be solid or tubular and be metallic material, such as high manganese steel having a larger coefficient of expansion than the part 11, or non-metallic; such as graphite, ceramic or cermet. The low melting point metal 15 may be tin. The part 12 is inserted in part 11 and the core 13 is inserted in part 12 and the low melting point metal 15 is inserted in an annular groove 14. The metal 15 may be lumpy or granular or in the form of an annular wire. To prevent brittleness caused by alloying, the metal 15 may comprise tin and copper provided in the form of separate wires or in the form of a wire having a core of copper and a sheath of tin. The composite assembly 11<SP>1</SP>, Fig. 3, is placed in a furnace having heating means 17, and vacuum means 18 where the part 11, is heated to above the creep temperature of the part 12 under a vacuum of about 5 Torr or in a non-oxidizing atmosphere under atmospheric pressure. Filling of the gaps between the parts 11, 12 and core 13 and part 12 is promoted by using gases such as N 2  and Ar. When the temperature is raised, the low melting point metal fills the gaps in liquid phase until the parts 11, 12, by expansion, are brought into close contact with one another and the metal 15 in liquid phase is diffused into the parts or is discharged from the gaps into the groove and solid phase-solid phase diffusion occurs between the parts 11, 12 in solid phase. After welding, the core is removed by withdrawing, cutting or other method.