查看更多>>摘要：In order to understand the microstructure evolution characteristics of AlCoCrFeNi high entropy alloy (HEA) coating at high environmental temperatures, a laser cladded AlCoCrFeNi HEA coating is heated to 700 ℃, 900 ℃ and 1100 ℃ respectively, holding for 30 min and cooled in air. Microstructure and micro-hardness of the treated coatings are investigated, in both interface and coating areas. In interface area, FCC blocks exist on the boundary of interface and coating in untreated specimen, besides the BCC single phase in coating. The primary FCC blocks remain in 700 ℃ treated coating, while they disappear in 900 ℃ and 1100 ℃ treated coatings. However, new FCC particles are formed instead near interface. In coating area, BCC single phase is acquired in untreated and 700 ℃ treated coatings. In 900 ℃ and 1100 ℃ treated coatings, lots of FCC and σ (Cr-rich carbide) particles are distributed mainly on grain boundaries of BCC phase matrix and spinodal decomposition occurs to BCC phase. Micro-hardness of 700 ℃ treated coating is slightly higher than that of untreated coating due to the age hardening effect, while the micro-hardness of 900 ℃ and 1100 ℃ treated coatings are much lower than that in untreated and 700 ℃ treated coatings due to the formation of soft FCC phase. Micro-hardness of 1100 ℃ treated coating is slightly lower than that of 900 ℃ treated coating due to the coarsening of σ particles and spinodal decomposed structures.
查看更多>>摘要：Internal oxidation, carburization, and nitridation are three forms of internal corrosion commonly experienced by high-temperature alloy components in industrial plants. They are characterized by ingress of an oxidizing species (oxygen, carbon or nitrogen) into the sub-surface region of the affected material, often accompanied by formation of precipitate phases. These microstructural changes can have a signifcant impact on mechanical performance. Management of such threats to equipment integrity therefore requires a comprehensive understanding of microstructural evolution, including rate information. In this work, we use optical, scanning electron, transmission electron, and atomic force microscopy to study precipitate phases and quantify internal corrosion rates in the austenitic stainless steel Alloy 800H subjected to nitriding in a 95% N2 + 5% H2 atmosphere at service-relevant temperatures (800-1000 ℃). We identify and characterize carbide and carbonitride precipitates formed alongside the expected nitrides, and use the thermodynamic software Thermo-Calc to show that formation of carbides during nitridation is thermodynamically possible in this alloy. This work ultimately demonstrates that a wide-ranging analytical approach may be crucial to gaining a full picture of the effects of internal corrosion in complex industrial alloys.
查看更多>>摘要：Hybrid reinforced (TiB_(2p) + TiB_w)/Cu composites were prepared via the double-beam mixed casting method. In order to improve the tensile strength of the composites, 0.04 wt% rare earths (La, Ce and Y) were separately added to the composites. The size, distribution and morphology of the reinforcements and the tensile strength of composites were studied, and the strengthening mechanism and failure behavior of the composites were discussed. Results indicate that the TiB2 particles with rare earths are refned and rounded, the average size are refned from 654 nm (without) to 515 nm (Ce), 567 nm (Y), 596 nm (La), respectively. TiB whiskers with rare earths also show different refnement effects in length and diameter directions. The effect of rare earths on the size and morphology of the reinforcements are mainly due to the promotion of the nucleation stage and the inhibition of segregation in the growth stage. After heat treatment and rolling, the tensile strength of the samples increased from 524 MPa without rare earth to 624 MPa (Ce), 606 MPa (La), and 595 MPa (Y). In particular, a remarkable change in the tensile strength appeared with 0.04 wt% Ce. The microcracks initiate at the interface between the reinforcements and the matrix, then propagate along the interface, and fnally the reinforcements debond from the matrix.
T. Martinez OstormujofR.R.P. Purushottam Raj PurohitS. Breumier
11页
查看更多>>摘要：Electron Backscattering Diffraction (EBSD) provides important information to discriminate phase transformation products in steels. This task is conventionally performed by an expert, who carries a high degree of subjectivity and requires time and effort. In this paper, we question if Convolutional Neural Networks (CNNs) are able to extract meaningful features from EBSD-based data in order to automatically classify the present phases within a steel microstructure. The selected case of study is ferrite-martensite discrimination and U-Net has been selected as the network architecture to work with. Pixel-wise accuracies around ~95% have been obtained when inputting raw orientation data, while ~98% has been reached with orientation-derived parameters such as Kernel Average Misorientation (KAM) or pattern quality. Compared to other available approaches in the literature for phase discrimination, the models presented here provided higher accuracies in shorter times. These promising results open a possibility to work on more complex steel microstructures.
查看更多>>摘要：In the paper, mechanical properties and microstructure of pure Mg hat-shaped samples after dynamic impact and quasi-static compression were studied. Results showed that the maximum peak strength 241.46 MPa and yield strength 51.65 MPa at 1.8 x 10~4 s~(-1)were obtained, and strain rate sensitivity and hardening rate under dynamic impact were much higher than those under quasi-static compression. Grains in matrix region kept the size of the original grains, and the (0001) direction was parallel to the loading direction. A strong texture appeared within the shear bands, and the maximum intensity between 15 and 21 increases as increasing strain rate. The <0001> direction of most grains with the sizes between 3 and 4.5 μm, in general, was perpendicular to shear band direction or shear direction. {1012} (1011) tension twins played an absolute leading role in twins, while the fraction of other types of twins was negligible. The temperature within adiabatic shear band (ASB) reached the maximum value of 376 K at 1.8 x 10~4 s~(-1), and the maximum absorbed energy density (ΔE) of 226.37 MJ-m~(-3) also was obtained. The average ASB widths between 87 and 135 μm decreased with increasing strain rate, and the trend was the same with that predicted by Bai-Dodd model. Dynamic recrystallization (DRX) grains slip and rotate under the action of normal stress Fn, and form ASB together. Fracture occurred along shear band, and brittle fracture characterized by cleavage surface and ductile fracture characterized by dimples both existed during the fracture progress.
查看更多>>摘要：An evolution law of δ phase of IN718 superalloy in temperature/stress coupled feld is studied in the present research. The results show that the δ phases accelerate precipitates on the grain boundaries with applied stress. In the temperature/stress coupled feld, both the nucleation and growth rate of a δ phase will be signifcantly accelerated with stress. The increasing driving force of nucleation depends on the increase of the strain energy and reduction of the system free energy, promoting nucleation of the δ phase. The high growth rate is caused by increasing the joint phenomenon of the adjacent same-oriented δ rods with the coupled action of the temperature and stress.
NSTL
Elsevier