Interface structure and mechanical properties of the brazed joint of TiC cermet and steel

doi:10.1016/j.jeurceramsoc.2005.01.043

Journal of the European Ceramic Society

Volume 26, Issue 7, 2006, Pages 1287-1292

https://doi.org/10.1016/j.jeurceramsoc.2005.01.043 Get rights and content

Abstract

A commercially available Ag–Cu braze alloy foil with Zn was used to join TiC cermet and steel. According to the experimental observations, the interface structure is (Cu, Ni)/Ag (s.s.) + Cu (s.s.)/(Cu, Ni)/(Cu, Ni) + (Fe, Ni) from TiC cermet to steel side. With increased brazing temperature or time, the amounts of (Cu, Ni) near the base metals/Ag–31Cu–23Zn interface and (Cu, Ni) + (Fe, Ni) near the Ag–31Cu–23Zn/steel interface increase, while the amount of Ag (s.s.) + Cu (s.s.) in the middle of the braze alloy decreases. The whole joining process consists of diffusion and solution among atoms of the braze alloy foil and base metals. The maximum shear strength is 120.7 MPa for the joint brazed at 850 °C for 10 min.

Introduction

In the last few years, materials formed by ceramics and metallic phases (“cermets”) have received increasing attention because of their singular mechanical, electrical and magnetic properties.¹ These cermets have been proposed as excellent candidates for structural and high added-value functional applications related to aerospace industry, energy conversion, sensors and transductors.² Most metal-matrix cermets, especially those reinforced by ceramics, can be produced economically by a combustion synthesis process, sometimes called self-propagating high-temperature synthesis (SHS), which provides an attractive affordable alternative to the conventional methods of producing advanced materials.3, 4, 5, 6

As a new type of material, TiC cermet synthesized by SHS has great potential to become an important candidate for advanced application owing to its high hardness, excellent wear resistance and high elevated-temperature strength.⁷ The major constituents of TiC cermet consist of TiC particles, which are hard and brittle, and the minor constituent binder metal Ni, which is relatively soft and ductile.

To expand the practical applications of the cermets, it is necessary to bond them to metals. Now, the research on the bonding technologies of ceramics to metals is well documented, such as brazing,8, 9, 10, 11, 12, 13 diffusion bonding,14, 15 microwave welding¹⁶ and ultrasonic welding.¹⁷ Of them, brazing has become one of the main methods of bonding ceramics to metals. However, to braze ceramics to metals successfully, it has to face two challenges. Most of the metals have poor wettability with ceramics. The most convenient method to resolve this is to use active filler metal for brazing ceramics and metals. Previous studies and comprehensive reviews have been published in this area.18, 19, 20, 21, 22, 23 The other challenge of brazing ceramic to metal rests with accommodating the thermal expansion mismatch between ceramics and metals, and minimizing the resulting residual stresses.

It is well-known that Ag-based braze alloys are widely used to braze most ceramics. Especially, the utilization of a Ag-base braze alloy with Zn can improve the wetting and spreading on the surface of ceramics, and the disadvantageous effects of Zn on corrosion resistance of the joint can be reduced by the evaporation of Zn after the braze alloy melts in the vacuum circumstances. The current investigation concentrates on the joining of TiC cermet and steel using Ag–31Cu–23Zn braze alloy. The interface structure, interface evolution mechanism, and shear strength are comprehensively studied to access the relation between the microstructure and the joint performance.

Section snippets

Experiment procedures

The cermet material used in the experiments was TiC cermet, the content of which was 60 wt.% TiC and 40 wt.% Ni. Commercially obtained Ag–31Cu–23Zn (wt.%) braze alloy (thickness 120 μm) and steel were used in the test. The chemical content of the steel is shown in Table 1. The microstructure of TiC cermet and steel are shown in Fig. 1.

The size of the brazed specimens was 40 mm × 10 mm × 5 mm. TiC cermet and steel were overlapped for 8 mm along the length of the specimens (see Fig. 2a). All joined surfaces

Interface structure of the brazed TiC cermet/Ag–31Cu–23Zn/steel joint

Fig. 3 shows the back-scattered electron image and major element content distributions (along the line indicated in the electron image) of TiC cermet/steel joint brazed with Ag–31Cu–23Zn braze alloy foil at 850 °C for 15 min. It can be seen from the image that there are three zones between the TiC cermet and the steel. For the sake of convenience, the irregular dark blocks adjacent to the TiC cermet and the steel are, respectively, called A and C zones, and the zone between the A and C zones is

Conclusions

According to the experimental observation, there exist (Cu, Ni), Ag (s.s.) + Cu (s.s.), (Cu, Ni), (Cu, Ni) + (Fe, Ni) zones on TiC cermet/Ag–31Cu–23Zn/steel joint. The whole interface evolution process can be divided into three stages. The diffusion of atoms exists in the first stage and solid solution of atoms appears in the second and third stages. With the increased brazing temperature or time, the amount of (Cu, Ni) + (Fe, Ni) increases, while the amount of Ag (s.s.) + Cu (s.s.) decreases. The

Acknowledgement

This work was supported by the National Natural Foundation of Science (No. 50325517), People's Republic of China.

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Interface structure and mechanical properties of the brazed joint of TiC cermet and steel

Abstract

Introduction

Section snippets

Experiment procedures

Interface structure of the brazed TiC cermet/Ag–31Cu–23Zn/steel joint

Conclusions

Acknowledgement

Mater. Sci. Eng. A

J. Mater. Process. Technol.

Mater. Lett.

Mater. Lett.

J. Eur. Ceram. Soc.

Mater. Sci. Eng. A

J. Eur. Ceram. Soc.

Mater. Charact.

Mater. Sci. Eng. A

J. Mater. Process. Technol.

J. Mater. Process. Technol.