**4. Effect of bonding variables on microstructural evolution**

This section investigates the effects of bonding variables on the chemical and microstructural homogeneity across the joint region. Factors affecting TLP bonding are; bonding temperature, bonding time, contact pressure and interlayer thickness and composition. Contact pressure can also affect the strength of the bond produced and this has been reported extensive in the scientific literature. However in this work, when bonding pressure increased beyond 0.1 MPa the result is rapid creep failure during the bonding process. Therefore the bonding pressure was held constant at 0.01MPa. The effects of these parameters were evaluated using WDS and XRD to study the change in chemical composition across the joint region as a function of bonding variable.
