This work investigated the failure analysis of the boiler tube secondary superheats in a power plant utility. The tube was composed of low carbon steel with 2.25Cr-1Mo addition, which was ruptured after a 26 h working test. The investigation of the tube’s failure was performed through several analysis, such as microstructure, elemental analysis, and mechanical test. It was found the abrupt increase in the operating temperature as the primary factor of the material degradation of the tube. The microstructure analysis shows the existence of elongated grain with the formation of microcracks on the grain boundaries, indicating the exceeded stress applied in the material. The hoop stress in the ruptured tube was 42.47 MPa, which is higher than the allowable stress of 23.5 MPa at 605 °C. Furthermore, the equiaxed grain was observed in the unruptured tube, implying the microstructural change after exposure at high temperatures.
The effect of different process parameters on the formation of lack of fusion (LOF) in Ti-6Al-4V alloy fabricated using DED was studied. The specific energy was calculated to evaluate the minimal amount of required energy to avoid LOF. The results showed that a specific energy smaller than 2700 J.g-1 led to the formation of LOF; however, a higher specific energy was able to successfully prevent the defect. A smaller amount of specific energy resulted in inadequate heat, which was too low to completely melt the metal powder, and resulted in insufficient penetration depth. Subsequently, LOF was observed between the interface of the deposited layers. Furthermore, a higher powder feed rate had a more significant effect on the formation of LOF than higher laser power.
This study investigated the effect of microstructural decomposition on the mechanical properties of additively manufactured Ti-6Al-4V by directed energy deposition. The formation of ' martensite and massive phase ( m ) was observed in the deposited layers. The ' and m in the lastly deposited layer appeared as a needle-shaped and a sub-lamellar structure, respectively. However, the morphology of ' and m was decomposed in the lower layers due to the intrinsic heat treatment. Moreover, The heat conduction rate calculation showed that the lower powder feed rate generates more heat conduction. Therefore, the microstructure was further decomposed for the specimen with a lower powder feed rate. These phenomena consequently affected the mechanical properties and fracture behavior of the Ti-6Al-4V alloy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.