Laser Thermomechanical Evaluation of Bonding Integrity

Thermal imaging for the nondestructive evaluation (NDE) of materials appears to be of ever increasing importance for industrial applications. The development of new materials. both metallic and ceramic. as thermal and oxide barrier coatings present new challenges to inspection techniques. Thermal imaging methods seem ideally suited for such applications. being particularly sensitive to surface and near surface material thermal inhomogeneities that may be defect-related. However, these same sophisticated materials can pose rather sever requirements upon the efficacy of any particular type of thermal imaging. Typical problems encountered include rough. optically scattering surfaces. surfaces ranging from highly reflective to absorptive, complex surface geometry and microscopic to very macroscopic (practical components) imaging requirements.</p

Comprehensive Analysis of the Effect of Ausforming on the Martensite Start Temperature in a Fe-C-Mn-Si Medium-Carbon High-Strength Bainite Steel

The comprehensive effect of strain and ausforming temperature on the martensite start temperature (MS) of a medium-carbon bainite steel was investigated by thermal simulation, optical microscope, scanning electron microscope, etc. It is already known that small strain increases the MS, while larger strain decreases the MS. However, the effect of ausforming temperature on the MS has not been reported and clarified. In this study, the concepts of critical strain (εc) and saturated strain (εs) are proposed. The MS at the critical strain is equal to the MS of the nondeformed specimen. The saturation strain, which is first observed, is the strain value, and the MS does not further decrease with the increasing strain. The results show that the MS depends on the strain amount of ausforming but is not affected by the ausforming temperature. Moreover, with the increase of strain amount and ausforming temperature, the length of the martensite laths decreases. In addition, the hardness of the specimen increases with the increase of the ausforming strain amount, whereas the ausforming temperature has little effect on the hardness

Martensite Formation in Partially and Fully Austenitic Plain Carbon Steels

The progress of martensite formation in plain carbon steels Fe-0.46C, Fe-0.66C, and Fe-0.80C has been investigated by dilatometry. It is demonstrated that carbon enrichment of the remaining austenite due to intercritical annealing of Fe-0.46C and Fe-0.66C does not only depress the start temperature for martensite, but also slows the progress of the transformation with temperature compared to full austenitization. In contrast, such a change of kinetics is not observed when the remaining austenite of lean-Si steel Fe-0.80C is stabilized due to a partial transformation to bainite, which suggests that the stabilization is not of a chemical but of a mechanical nature. The growth of bainite and martensite is accompanied by a shape change at the microstructural scale, which leads to plastic deformation and thus strengthening of the surrounding austenite. Based on this stabilizing mechanism, the athermal transformation kinetics is rationalized by balancing the increase in driving force corresponding to a temperature decrease with the increase in strain energy required for the formation of martensite in the strengthened remaining austenite.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin