Carbon segregation and inclusions effects on surface fracture morphology of a 12% chromium stainless steel

Martensitic 12% chromium stainless steel is generally used for the manufacture of water vapour turbine blades. This material, under these environmental conditions, develops fatigue corrosion with failure as a result of the segregation of certain constituent elements such as phosphorus (P) and sulphur (S),^[1–3] or the presence of some types of inclusions.^[2–4] To be able to understand and explain these phenomena, in situ characterization of the fractured surfaces were performed for two types of samples: steel 1 as manufactured turbine material whose fracture mode is intergranular and steel 2 issued from last stage turbine blades after 100 000 h service at 40 °C whose fracture mode is transgranular. The techniques used for characterization were scanning electron microscopy (SEM) coupled with the x-ray analysis by energy dispersive spectroscopy (EDS), and auger electron spectroscopy (AES). The Auger results enabled the understanding of the brittle to ductile transition for the material by showing the simultaneous diffusion of carbon from grain boundaries (GB) to grains (G) and chromium from G to GB. Furthermore, the heavy segregation of phosphorus at the GBs could explain the intergranular crack rupture traces observed in steel 2. SEM observations coupled with EDS analysis showed the presence of different types of non-metallic inclusions such as silicon-based complex inclusions and manganese sulfides (MnS). The presence of silicon-based complex inclusions at GB could explain the intergranular fracture mode previously reported. The characterization of the fracture appearance suggests also that MnS inclusions can act as nucleation sites for secondary microcracks at the GB level that were observed after service.     

Behavior Study of the Nanostructured Zn1-xCdxO (0 ≤ x ≤ 0.1) Semiconductor Thin Films Deposited onto Silicon Substrate by Dip-Coating Method

Silicon - The specimens of nanostructured semiconductor of Zn1-xCdxO (0 ≤ x ≤ 0.1) thin films were grown on silicon substrate using a dip-coating method. The...     

Influence of Low Cd-Doping Concentration (0.5 and 3 wt.%) and Different Substrate Types (Glass and Silicon) on the Properties of Dip-Coated Nanostructured ZnO Semiconductors Thin Films

Journal of Inorganic and Organometallic Polymers and Materials - The investigation of semiconductor films of undoped ZnO and doped with two weight percentages of Cadmium (0.5 and 3) were grown on...     

X-Ray Diffraction, Microstructure, and M?ssbauer Studies of Fe72Al28 Alloy Elaborated by Mechanical Milling

Nanocrystalline Fe₇₂Al₂₈ alloy samples were prepared by mechanical alloying process using planetary high-energy ball mill. The alloy formation and different physical properties were investigated as a function of milling time, t, (in the 0-24?h range) by means of X-ray diffraction technique, scanning electron microscopy (SEM), energy dispersive X-ray, and M?ssbauer spectroscopy. The complete formation of bcc-FeAl solid solution was observed after 4?h of milling. The lattice parameter quickly increased to a maximum value of 0.291?nm within the first hours of 12?h of milling, then decreased to a value of 0.2885?nm after 24?h. The grain size decreased from 55 to 10?nm, while the strain increased from 0.18 to 0.88%. Grain morphologies at different formation stages were observed by SEM. The M?ssbauer spectrum showed the presence of a singlet and sextet after 4?h of milling. The singlet indicated the presence of paramagnetic phase characteristic of A₂ disordered structure and the sextet with a mean hyperfine field, ??H _hf??, of 21?T was indicative of ordered DO₃ structure. After 8?h of milling, the paramagnetic phase disappeared allowing the appearance of a sextet. For the higher milling time, i.e., 24?h, the M?ssbauer spectrum was analyzed with two components. The first with ??H _hf?? equal to 29.9 T and the second with a ??H _hf?? value of 10.25 T.     

Microstructure and Corrosion Aspects of Dissimilar Joints of Zircaloy-4 and 304L Stainless Steel

In this study, diffusion bonding is used to join rods of Zircaloy-4 with stainless steel 304L. The microstructure of the interface of the dissimilar joints was characterized by SEM-EDS and x-ray diffraction (XRD). It consists of three distinct layers, each separately localized in the modified stainless steel and Zircaloy-4 (Zy-4) matrix. The XRD patterns indicate the presence of intermetallics in the diffusion-bonded joints. Joint corrosion was evaluated by potentiodynamic polarization and some aspects were discussed according to the mixed potential theory. The corrosion results indicate the presence of a local galvanic effect. SEM examination of the corroded joints indicates preferential corrosion around the Zy-4/SS304L interface, probably due to residual stresses and the intermetallic compounds generated during diffusion bonding process at high temperature.