Wetting, spreading and joining in the alumina–zirconia–Inconel 738 system

doi:10.1016/j.scriptamat.2003.10.015

Scripta Materialia

Volume 50, Issue 3, February 2004, Pages 325-330

https://doi.org/10.1016/j.scriptamat.2003.10.015 Get rights and content

Abstract

A study is presented on the wetting and spreading behaviour of Ag–Cu–Ti on zirconia and alumina–zirconia ceramics and on the Inconel 738. The results are discussed in terms of thermodynamic and kinetics of spreading, and on the basis of the morphological analysis, including microhardness tests, of the interfacial layers, both in the wetting couples and in the different joints.

Introduction

The optimisation of the joining techniques in metal-ceramic systems requires a good knowledge of the physico-chemical properties of all constituents and in particular of the wetting characteristics of both the metallic support and the ceramic constituent [1], [2], [3], [4], [5]. In particular, low values of the contact angles are necessary to assure good penetration of the brazing alloy whereas a reduced extent of interfacial reactions is necessary to avoid the formation of weak phases.

This paper is related to a larger study of the role the additions of reactive elements (e.g. Zr, Ti, Hf) have on the behaviour of brazing alloys for the production of metal-ceramic and ceramic–ceramic joints [6]. Here the effects of Ti when added to the eutectic Ag–Cu alloy are described when in contact with the refractory alloy Inconel 738 (IN738), largely used for turbines components (blades, high temperature parts etc.) and the ceramic phases Y-stabilised ZrO₂ and Al₂O₃–20%ZrO₂. This last “composite” material is of the greatest interest for its low production cost and its excellent physico-chemical and mechanical properties [7], [8]. In the past years the metal-zirconia system has been analysed in a temperature range between 600 and 1500 °C: the most interesting results [9] seem to converge on the choice of a filler Ag–Cu–Ti alloy, or on Zr–Ni or Ni–Ti mainly because they seem to make possible the application of the ‘transient liquid phase bonding” technique [10], [11], [12], [13]. Experiments are reported here on the wetting and spreading of the base materials and on the morphology of the ceramic–ceramic and metal-ceramic joints.

Section snippets

Experimental part

Wetting experiments have been conducted using the sessile-drop technique in conjunction with the specially designed ASTRA^© image analysis software which allows real time surface tension and contact angle data to be obtained during each experimental run [14], [15]. Two specially designed furnaces have been used: the first one, which can reach 1600 °C, is made of two concentric, horizontal, alumina tubes connected to a high vacuum line. Between the two tubes a constant flux of argon guarantees

Contact angles and kinetics of spreading

The wetting behaviour has been analysed in terms of equilibrium contact angle and of kinetics of spreading under the conditions already described. All the experiments have been made introducing the ceramic (or metallic) substrate, with a small cylinder of the filler alloy on top of it, inside the hot part of the furnace when all the physico-chemical parameters were in a steady state. Thus, the alloy reached the pre-set temperature in a certain time lapse. Specific measurements have shown that a

Ag–Cu–Ti/IN738

The SEM analysis on a perpendicular section of the solid–liquid interface (Fig. 4) shows, in the bulk brazing alloy, two coexisting phases: one composed by Ag88%–Cu12% and a second one composed by Ag10% and Cu87% with Ti3%. A complex transition zone is found between the bulk Inconel and filler metals phases. This zone, some 40 μm thick, is rich in Ti, Cu and Ni; precipitates can be seen, deriving from segregation during the rapid solidification process, formed by a dark Ti-rich phase

Joints

The different joints have been realised at 950 °C, as already described. No additional mechanical pressure has been applied on the specimens.

The joints have been prepared by interposing, between the two pieces, a thin (100 μm) layer of the Ag–Cu–Ti alloy. This thickness, after the treatment, reduced to nearly 50 μm in the case of metal-ceramic joints and to 70 μm with ceramic–ceramic joints. A dark-grey zone always appeared at the interface in the ceramic body, 2–3 mm thick which, as discussed,

Discussion and final considerations

The wettability and interfacial reactivity tests have shown that the Ag–Cu–Ti can be successfully used to join the ZrO₂/IN738, Al₂O₃–ZrO₂/IN738, Al₂O₃–ZrO₂/ZrO₂ and Al₂O₃–ZrO₂/Al₂O₃–ZrO₂ couples. The low contact angle values, below 22°, and a good value of the solid–liquid work of adhesion warrant a proper formation of the joints. Interfacial analyses have shown reaction and interdiffusion phenomena at the solid–liquid interfaces with the formation of new phases both in the ceramic and in

Acknowledgments

This work was partially supported by the Progetto Finalizzato MSTA II and by ASI through the contract I/R/27/00. The Authors wish to thank Alida Bellosi and Frederic Monteverde (ISTEC-CNR) for supplying the alumina–zirconia ceramics and Carlo Bottino for SEM-EDS analyses.

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Muolo ML, Passerone A, Delsante A, Bottino C, Bellosi A. In: Daolio S, et al., editors. Syntheses and methods in...

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Wetting, spreading and joining in the alumina–zirconia–Inconel 738 system

Abstract

Introduction

Section snippets

Experimental part

Contact angles and kinetics of spreading

Ag–Cu–Ti/IN738

Joints

Discussion and final considerations

Acknowledgments

Scripta Mater.

J. Eur. Ceram. Soc.

J. Colloid. Interf. Sci.

Scripta Mater.

Acta Mater.

Acta Mater.

Acta Mater.

Scripta Metall. Mater.

Mater. Sci. Eng.

Joining processes

Mater. Manuf. Process.

Wettability at high temperature

Trans. JWRI