JOM最新文献

Austenitic stainless steels are used in power generation components subjected to elevated temperatures over long service lives. Replacing these components can involve lengthy lead times and deteriorate the robustness of the energy infrastructure. Wire arc directed energy deposition (WA-DED) has the potential to enable rapid manufacturing of replacement parts, but the long-term stability of microstructures and mechanical properties produced by WA-DED is not well understood. In this work, we explore the influence of aging at 650°C for 1000 h on the formation of embrittling phases, such as sigma (σ), in the commercially available austenitic stainless steel wire feedstocks 316L, 316LSi, 316H and 16-8-2. All WA-DED samples formed secondary phases at grain boundaries (likely σ, possibly other phases as well), but these phases caused negligible changes in tensile properties in 316L, 316LSi and 316H. Samples of 16-8-2 formed significant amounts of ferrite and/or martensite after aging, which increased tensile strength but reduced ductility when tested at room temperature. This work demonstrates the need to design feedstock compositions that are stable with respect to ferrite and/or martensite formation, in addition to phases typically associated with embrittlement, to ensure microstructure and mechanical property stability for high-temperature applications with long service lives.

The effects of Mg and Si contents on the microstructure and solidification behavior of dilute Al-Mg-Si alloys with about 0.1 wt.% Fe impurities were investigated using optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDS), differential scanning calorimeter (DSC) and thermodynamic simulation. The results show that the grain size and secondary dendrite arm spacing of as-cast dilute Al-Mg-Si-Fe alloys decrease with the increase in Mg and Si content, and the grain size can be predicted using growth restriction factor Q. The increase in Mg content suppresses the transformation from α-AlFeSi to β-AlFeSi. However, the increase in Si content promotes α-AlFeSi converted to β-AlFeSi. In addition, the increase in either Mg or Si content decreases the melting point. The Mg/Si ratio can influence the formation of the eutectic structure as well as the type of Fe-bearing phase in it. The Fe-bearing phases in the eutectic structures of excess Mg and excess Si alloys are α-AlFeSi and β-AlFeSi, respectively. The results of thermodynamic simulation of solidification behavior are in good agreement with experiments.

In this article, the crack passivation phenomenon associated with grain size mismatch in nanocrystalline (NC) materials with bimodal structure is extracted theoretically. By description, a portion of the dislocation emanating from the crack tip penetrates the grain boundary (GB). The calculated effective stress intensity factor indicates that the crack growth is inhibited. The suppression is related to the varying structures caused by grain size mismatch. Our results support the experimental results and provide a reasonable explanation that microcracks tend to grow and form in the nanocrystal matrix of bimodal Al. In addition, we extract GB misorientation effect on the crack blunting in bimodal materials. The study found that increasing the GB misorientation leads to the blunting of cracks in bimodal materials.

The hot deformation behavior and microstructure evolution of superalloys may occur in the special service environment, which directly affects their performance. To explore the response of GH3536 alloy prepared by selective laser melting (SLM) at high temperature, hot compression tests were carried out to investigate the mechanical properties of SLM-GH3536 alloy at different conditions. The deformation temperature ranges from 900°C to 1050°C, and the strain rate ranges from 0.01 s⁻¹ to 10 s⁻¹. The results show that the flow stress and deformation mechanism are significantly influenced by the deformation conditions. The relationship between deformation conditions and flow stress is established by applying an Arrhenius-type constitutive equation. The flow stress was further predicted by using the strain compensation constitutive equation with high accuracy (AARE = 7.10%). The microstructure observation revealed that temperature has a greater influence on the degree of dynamic recrystallization (DRX). Two DRX mechanisms are analyzed. Discontinuous DRX is the primary deformation mechanism, which is accelerated with increasing temperature and strain rate, whereas continuous DRX is a cooperative deformation auxiliary mechanism, which is facilitated as temperature increases and strain rate decreases.

The present investigation highlights the development of a suitable and novel deep neural network-based learning model for accurately predicting the weld quality and mechanical properties of difficult-to-join dissimilar materials. Optimized experimental welding parameters in the available literature were taken as input in the deep neural network (DNN). A feed-forward and back-propagated DNN was developed to apprehend the high non-complexity present in friction stir welding of dissimilar materials. Unlike most neural networks, activation functions were altered between layers, effectively capturing non-linearity. The developed model was used to design an experimental condition for dissimilar friction stir welding of aluminum and titanium. Microstructural characterization of the weld was performed to comprehend the influence of parameters on the quality of the joint produced. A close correlation between the machine-learning model and the experimental results was established. The coefficient of determination (R^2) between the predicted strength and the actual strength was 0.95 on the training dataset and 0.9 on the testing dataset. Similarly, (R^2) between the predicted strength and the actual strength for the experimental dataset was 0.91, thus making the model suitable for predicting experimental conditions and corresponding mechanical properties with the highest accuracy for any unknown dissimilar friction stir welds.