Transient Liquid Phase (TLP) Bonding of TiAl-Alloys: Wettability, Microstructure, Mechanical Properties and Potential for Automation

摘要

This paper presents an investigation of the joining of Ti-48 at. percent Al-2 at, percent Cr-2 at. percent Nb ("48-2-2") substrates by transient liquid phase (TLP) bonding. In view of the low solubility, in the 48-2-2 alloy, of potential melting-point depressants, the work discussed in the paper focuses on the use of 48-2-2 + copper composite interlayers. The composite interlayer approach was originally developed specifically for wide joint gaps, but in the case of TLP bonding of TiAl-alloys, this technique is highly beneficial, even with relatively narrow-gap bonds. Following detailed hot-stage light microscopy, the process by which copper wets the 48-2-2 substrate is identified. The paper proposes that the wetting mechanism involved is significantly different from those observed conventionally in brazing or TLP bonding processes. Microstructural development is examined in detail with cross-sectional (edge-on) transmission electron microscopy studies and microstructure - mechanical property relationships are determined. The paper also considers a simple automated deposition process for the composite interlayers, which shows the potential for producing bonds with parent-metal-like microstructures (and hence parent-metal properties) with relative ease.