Details on the Formation of Ti2Cu3 in the Ag-Cu-Ti System in the Temperature Range 790 to 860 °C

Abstract

Silver-copper-titanium (Ag-Cu-Ti) ternary alloys are often used as active braze alloys for joining ceramics to metals at temperatures ranging from 780°C (the melting point of the Ag-Cu eutectic) up to 900°C. When Ti/Ag-Cu joints are brazed at low temperature (near 800°C), the intermetallic compound Ti 2 Cu 3 (tetragonal, P4/nmm, a = 0.313 nm, c = 1.395 nm) is systematically missing from the interface reaction layer sequence. An experimental investigation based on isothermal diffusion experiments in the Ag-Cu-Ti ternary system has then been undertaken to clarify the issues of thermal stability and formation kinetics of this compound. Evidence has been found for the stability of Ti 2 Cu 3 at temperatures ranging from 790 to at least 860°C. By heat treating Ag-Cu-Ti powder mixtures at 790°C for increasing times, it has moreover been shown that Ti 2 Cu 3 forms at a much slower rate than the two adjacent Ti-Cu compounds: TiCu 4 , the first phase to form, and Ti 3 Cu 4 . This explains why although thermodynamically stable, Ti 2 Cu 3 is not obtained when temperature is too low or reaction time too short.

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

“…After corrections for atomic number, absorption and fluorescence, the atomic contents of Ag, Cu and Ti were obtained with an accuracy better than ± 0.5 at%. It had been previously verified by X-ray powder diffraction [7] that the crystalline phases for which each interface reaction layer or crystal analysed were effectively obtained under the same heat-treatment conditions.…”

“…For these reasons, it was decided to further investigate the chemical interaction between titanium and the eutectic Ag-Cu alloy at temperatures down to 780 °C, the temperature of the eutectic transformation. In the first approach at investigating the kinetics of compound formation in the Ag-Cu-Ti system, cold-pressed mixtures of Ag, Cu and Ti powders were heated at 700-860 °C and characterized [7]. In the present work, additional experiments have been carried out at 780-800 °C on Ti/Ag-Cu semi infinite couples and Ti/Ag-Cu/Ti sandwiches in order to determine the extent and constitution of the interface reaction zone formed between solid Ti and liquid Ag-Cu eutectic alloy.…”

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

“…[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). The presence of Cu-Ti-based amorphous phase in the BZ, as shown earlier, signifies that the entire melt did not transform into crystalline phases upon solidification.…”

Influence of Micron-Ti and Nano-Cu Additions on the Microstructure and Mechanical Properties of Pure Magnesium

“…In Mg-(Ti + Cu) BM , in addition to Mg, Ti, Cu and Mg 2 Cu phases, low intensity peaks corresponding to Ti-Cu intermetallic phase can be seen; in contrast, in the un-ball milled, directly added Mg-Ti-Cu these peaks are not prominent. Considering that the formation enthalpies of various Ti-Cu intermetallics phases such as TiCu, TiCu 4 , TiCu 2 , Ti 2 Cu 3 , Ti 3 Cu 4 , Ti 2 Cu, Ti 3 Cu and TiCu 3 are close to each other, the reaction between Ti and Cu can result in any of these intermetallics phases [24][25][26][27][28]. On comparing the experimental diffraction peaks with the standard powder diffraction data, it can be associated to either Ti 2 Cu 3 or Ti 3 Cu phase.…”

“…On comparing the experimental diffraction peaks with the standard powder diffraction data, it can be associated to either Ti 2 Cu 3 or Ti 3 Cu phase. However, as the Ti 2 Cu 3 intermetallic phase formation occurs only at ~780 °C to 860 °C and also at a much slower cooling rate, the observed Ti-Cu intermetallics peaks can hence be identified as Ti 3 Cu [25]. …”