Joining of stainless steel (AISI 304L) to hot isostatically pressed alumina (HIP-Al 2 O 3 ) using the brazing alloy 72Ag-28Cu was investigated. The microstructural characterization at various stages of joining, including metallization, annealing of overlaid Ni coating, and brazing, was comprehensively evaluated. The interface structure and the growth of phases were analyzed with optical microscope, scanning electron microscope, and electron probe microanalyzer (EPMA). Additionally, the leak tightness of these joints was assessed using a He-leak detector. Experimental results indicated the development of the manganese aluminate spinel (MnAl 2 O 4 ) layer at the metallizing stage, which penetrated into HIP-Al 2 O 3 . The Ni overlaid coating further resulted in the formation of the Ni(Mo) solid solution layer followed by the Mo-rich phase. During the solid-state reaction and subsequent brazing cycle, the growth of the spinel layer close to HIP-Al 2 O 3 was not adversely affected. The microstructure of the brazed joint was complex. It showed a eutectic structure within the brazed zone and a thin layer of Mo-rich, Ni-rich phases close to HIP-Al 2 O 3 . Increasing the brazing time resulted in the excessive growth of the thin layer that seriously affected the leak tightness of the joint.

Joining of aluminium and aluminium alloys to stainless steel is frequently required in many low temperature and nuclear applications. The present study describes a relatively new method of bonding these materials by suitably combining the deformation bonding and solid state bonding techniques for joining tubular assemblies. The stainless steel and aluminium specimens have been machined to form cylindrical tube specimens and special grooves have been machined on the inner diameter (ID) side of the stainless steel specimens. The polished stainless steel specimens have been coated with Ni, Cu and Ag in sequence on these grooves and Zn, Cu and Ag in sequence on the outer diameter side (OD) of the aluminium. The specimens have been bonded in hot vacuum press using argon as a pressurising medium and allowing the aluminium to plastically flow into the stainless steel grooves. Metallurgical investigation of the diffusion bonded specimen carried out at 315uC for 4 h indicated excellent bonding and total absence of the intermetallic compounds in the reaction zone. The joints bonded at this temperature indicated that the bond strength was superior to that of the base material of aluminium and the bending angle was .40u. The paper presents the details of this technique and also methodology adopted for optimising the bonding parameters.

Diffusion bonding of stainless steel (SS) has been attempted in temperature range of 623 -773 K using multiple inter-layers of nickel, copper and silver. The intermediate layers were electro-deposited taking care to avoid oxidation at the interfaces. The bonded area was examined for the formation of any intermetallic compound through electron probe micro-analyzer (EPMA) and nano-indentation technique. Results indicate the absence of brittle intermetallics at the interfaces and the strength of the bonding was found to be satisfactory. The bond strength was found to be 130 ± 10 MPa and the bond was found to be leak tight with negligible leak rate.

Laser surface alloying is a new and promising technique for generating surface alloys having a wide range of favourable properties. The process involves altering the surfaces of inexpensive substrates by adding small quantities of alloying elements to a pool of molten metal produced by local melting using the intense heat of a laser. Certain defects such as cracks, porosity, surface roughness, compositional inhomogeneity, and excessive dilution have been observed during laser alloying (pulsed Nd : YAG laser) with chromium on mild steel, and with molybdenum and Ni–Mo on stain less steel. Specific deterioration in surface properties has been observed and discussed and the techniques utilised to control such defects have been outlined.

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