Analysis of thermodynamic response for materials characterization using tensile and nanoindentation testing

Materials characterization using materials testing technique of the tensile test evolved from engineering practice to design for specific properties or ad hoc applications. With the advent of single crystal test specimens, this technique was widely used to validate dislocation mechanics predictions of plastic flow. From this vast data base, a sound basis for thermally activated flow of crystalline material has evolved and is reviewed in this study. The current challenge is to apply the predictions of this integrated theory to behaviour in polycrystalline engineering materials such that the thermodynamic response signature can be correlated to specific mechanisms. A good opportunity exists since this signature can now be precisely determined by precision strain rate sensitivity (PSRS) method developed at Queen's University.;This study endeavours to summarize the theoretical predictions for solid solution hardening, inverse Portevin-LeChatelier effect and creep and critically evaluate the data under tensile test conditions in order to validate the predictions. This examination takes the form of not only experimental testing and analysis but also modelling. The results show that an unique signature for each of these cases can be delineated.;The analytical and experimental study is extended to nanoindentation testing. To carry out this major work, the apparatus was redesigned and assembled and the software NanoRama written in assembly language. The issues of surface damage caused by specimen preparation on hardness measurements, the recovery process during unloading and the role of the substrate on hardness measurements of thin films are thoroughly discussed. The displacement rate change implemented with step ramp technique to compensate for the elastic response of the total load system proved successful in determining PSRS. To illustrate its application to metallographic specimens, the PSRS at an embrittled grain boundary in rephosphorized interstitial free steel is compared to that which is non-embrittled. The differentiation between the two cases is clearly detectable but due to the large scatter in PSRS values determined at various points in the grain interiors, kinetic studies of phosphorous segregation to the grain boundary appear to be difficult.