Microstructure, mechanical properties and chemical degradation of brazed AISI 316 stainless steel/alumina systems

Abstract

The main aims of the present study are simultaneously to relate the brazing parameters with: (i) the correspondent interfacial microstructure, (ii) the resultant mechanical properties and (iii) the electrochemical degradation behaviour of AISI 316 stainless steel/alumina brazed joints. Filler metals on such as Ag-26.5Cu-3Ti and Ag-34.5Cu-1.5Ti were used to produce the joints. Three different brazing temperatures (850, 900 and 950 • C), keeping a constant holding time of 20 min, were tested. The objective was to understand the influence of the brazing temperature on the final microstructure and properties of the joints. The mechanical properties of the metal/ceramic (M/C) joints were assessed from bond strength tests carried out using a shear solicitation loading scheme. The fracture surfaces were studied both morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The degradation behaviour of the M/C joints was assessed by means of electrochemical techniques.It was found that using a Ag-26.5Cu-3Ti brazing alloy and a brazing temperature of 850 • C, produces the best results in terms of bond strength, 234 ± 18 MPa. The mechanical properties obtained could be explained on the basis of the different compounds identified on the fracture surfaces by XRD. On the other hand, the use of the Ag-34.5Cu-1.5Ti brazing alloy and a brazing temperature of 850 • C produces the best results in terms of corrosion rates (lower corrosion current density), 0.76 ± 0.21 Acm −2 . Nevertheless, the joints produced at 850 • C using a Ag-26.5Cu-3Ti brazing alloy present the best compromise between mechanical properties and degradation behaviour, 234 ± 18 MPa and 1.26 ± 0.58 Acm −2 , respectively. The role of Ti diffusion is fundamental in terms of the final value achieved for the M/C bond strength. On the contrary, the Ag and Cu distribution along the brazed interface seem to play the most relevant role in the metal/ceramic joints electrochemical performance.

Influence of the brazing parameters on microstructure, residual stresses and shear strength of diamond–metal joints

“…[47]. An influence of the microstructure on the mechanical performance could also be found for steelalumina joints brazed with Ag-Cu-Ti filler alloy [7]. Compared to the reported shear strength of 130 MPa of a 110 lm thick CVD diamond film brazed (Ag-Cu-Ti filler alloy) on a hard metal substrate [48], our results are quite high.…”

“…The formation of different interlayers is often found when brazing metal-ceramic joints with an active silver-copper based filler alloy and titanium as the reactive element [7,38,39]. Here, two interlayers, namely (Fe,Cr,Ni) 2 Ti and (Fe,Ni,Cu)Ti, on top of the steel substrate are formed, whose thicknesses are influenced by the brazing parameters.…”

“…The effect of this TiC layer on the residual stresses and the mechanical properties of the joint is still unclear. It is known that the filler alloy microstructure has a significant influence on the mechanical properties of metal-ceramic joints [7]. Due to the non-equilibrium conditions the formation of brittle phases in the filler alloy as well as at the interfaces can occur, which is possibly related to the interfacial strength.…”

Diffusion Bonding and Transient Liquid Phase (TLP) Bonding of Type 304 and 316 Austenitic Stainless Steel—A Review of Similar and Dissimilar Material Joints

“…If the sample geometry allows it, parts can also be press-fitted and put under pressure into a vacuum furnace where they are then diffusion bonded when the temperature is increased [68][69][70]. If no relevant pressure was applied [67,[71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87], the experiments were not reported here since we considered them brazing rather than diffusion bonding using the definitions introduced earlier. In brazing some pressure is often applied to fix the parts so that a definition between brazing and TLP bonding that only relates to applied pressure is not sufficient.…”

Joining of Al2O3 to 316SS Using Braze-infiltrated Ni Net

“…However, the joint needs to be applied in small dimension, such as the high vacuum feedthrough or at slow heating and cooling rates to avoid thermally induced cracking. [14][15][16][17][18] The brazed joint is not reliable with large scattering in bond strength due to the brittle nature of the interfacial reaction layer(s).…”