Low-Temperature Interface Reaction Between Titanium and the Eutectic Silver-Copper Brazing Alloy

Abstract

Reaction zones formed at 790 °C between solid titanium and liquid Ag-Cu eutectic alloys (pure and Ti-saturated) have been characterized. When pure Ag-Cu eutectic alloy with 40 at.% Cu is used, the interface reaction layer sequence is: αTi / Ti 2 Cu / TiCu / Ti 3 Cu 4 / TiCu 4 / L. Because of the fast dissolution rate of Ti in the alloy, the reaction zone remains very thin (3-6 µm) whatever the reaction time. When the Ag-Cu eutectic alloy is saturated in titanium, dissolution no longer proceeds and a thicker reaction zone with a more complex layer sequence grows as the reaction time increases. Four elementary chemical interaction processes have been identified in addition to Ti dissolution in the liquid alloy. These are growth of reaction layers on Ti by solid state diffusion, nucleation and growth from the liquid of TiCu 4 , isothermal solidification of silver and, finally, chemical conversion of the Cu-Ti compounds by reaction-diffusion in the solid state. A mechanism combining these processes is proposed to account for the constitution of Ti/ Ag-Cu/ Ti joints brazed at 780-800 °C.

Microstructure and Interfacial Reactions During Vacuum Brazing of Stainless Steel to Titanium Using Ag-28 pct Cu Alloy

“…The formation of the Cu 4 Ti 3 phase (layer 5) in the SS/Ti BZ was also reported in other investigations. [12,13,20,[34][35][36] However, contrary to the present observations, Shiue et al [19] and Shafiei et al [20] reported the formation of the Cu 4 Ti phase in the BZ, whereas they did not report the formation of Cu 3 Ti 2 phase which formed conspicuously in the present study. Andrieux et al [40] in an experimental investigation on the phase stability study on the Cu-Ti system showed that the Cu 3 Ti 2 phase is stable and can form by solid state reaction in a temperature range of 1063 K to 1133 K (790 C to 860 C).…”

“…[12,13,20,34,35] This phase also formed in the interaction zone during the solid-liquid reaction between Ti and Ag-Cu alloys [19,36] and solid-solid reactive diffusion between Ti and Cu. [29] Laik et al [29] demonstrated that during the reactive diffusion of Cu and Ti, CuTi is the first one to form in the diffusion zone, using the ''effective heat of formation model.''…”

“…[53] The formation of a narrow CuTi 2 phase layer during brazing in similar systems has been demonstrated in a number of earlier studies. [12,13,19,20,36] The formation of the CuTi 2 phase between CuTi and Ti can be considered to be a solid state reaction between these two adjacent phases, caused by interdiffusion of Cu and Ti atoms.…”

Wettability of Ti3SiC2 by Ag–Cu and Ag–Cu–Ti melts

“…Indeed, during temperature rise to 900°C the kinetics of dissolution of Ti in Ag-40at.%Cu eutectic is significantly reduced by the formation at solid Ti/liquid AgCu interface of different Cu x Ti y compounds such as Cu 4 Ti, Cu 3 Ti 4 or CuTi [31]. As a consequence the effective activity of Ti in the drop is lower than the nominal one.…”

Brazing of zirconia to titanium using Ag-Cu and Au-Ni filler alloys

“…It was suggested that copper has a strong tendency to rapid formation of intermetallics with titanium, and Ag is the less active element of Ag-Cu filler alloys with low diffusivity through the CuTi layer; however, the presence of Ag can remarkably increase the activity of filler alloys to promote interfacial reactions with technically stable ceramics [9,22,23]. Other elements such as V, Cr, Zr, V, Nb, Ta and Hf can also be considered chemically active in braze alloys composition -especially Ti, which can make chemical interactions (dissolution, interdifusion and/or product formation reaction) at the ceramic/metal interfaces to enhance wetting on the ceramic surface [5,6,24].…”