TWI Industrial Member Report Summary 530/1995
M B D Ellis and T G Gooch
Background
One of the structural materials of interest in future aerospace programmes is likely to be SiC fibre (SICf) reinforced titanium metal matrix composite (MMC). This material has high specific modulus and strength and excellent high temperature properties, and thus is of potential use on hypersonic aircraft and advanced propulsion systems in situations where other light alloys are unsuitable. However, as with the vast majority of other materials, at some stage it will have to be joined to itself or other titanium alloys to produce components.
Fusion welding of Ti/SiCf composites leads to the matrix reacting with the SiC fibres, thus seriously degrading the material properties. Solid phase joints occur at lower temperatures, in principle allowing bonding without significant interfacial reaction. In this work, a novel solid state joining method was studied for Ti/SiC f, material, based on resistance (spot) welding. Normally, resistance welding involves high currents applied over a short period of time giving fusion of the parent materials. For the present purpose, the welding currents were relatively low and applied over longer welding times, to avoid fusion but promote solid phase bonding.
Trials were carried out, varying i) welding parameters (i.e welding current, hold time and electrode force) and ii) the surface condition of the MMC (i.e degreased, etched and employing a Ti-6A1-4V interlayer). Mechanical properties were assessed using the lap tensile shear test. Fractographic analysis and metallography were carried out.
Objective
- To develop a solid state joining technique for Ti/SiCf MMCs.