Some Evaluations on the Technical State of Metal Products and Determination of their Safe Operation Period on the Basis of Criterial Control

Over a long period of operation, under the influence of corrosion and stresses from the acting forces, metal structures lose their strength. There is a need for their periodic non-destructive testing. The development of new methods is relevant in the field of control of building metal structures, such as bridge structures, structures of building cranes and other mechanical engineering products. The applied methods should be reliable and should not require huge material and labor costs. In this work, informational relationships between acoustic characteristics and parameters of metal microstructure are established. The proposed method can be useful for specialists and experts in the field of monitoring the technical condition of metal products requiring non-destructive testing. The safety of the operated objects depends on the accuracy of the applied criteria, as well as the degree of resource saving due to the full use of the product resource.

Enhancing SERS Intensity by Coupling PSPR and LSPR in a Crater Structure with Ag Nanowires

The sensitive characteristics of surface-enhanced Raman scattering (SERS) can be applied to various fields, and this has been of interest to many researchers. Propagating surface plasmon resonance (PSPR) was initially utilized but, recently, it has been studied coupled with localized surface plasmon resonance that occurs in metal nanostructures. In this study, a new type of metal microstructure, named crater, was used for generating PSPR and Ag nanowires (AgNWs) for the generation of LSPR. A crater structure was fabricated on a GaAs (100) wafer using the wet chemical etching method. Then, a metal film was deposited inside the crater, and AgNWs were uniformly coated inside using the spray coating method. Metal films were used to enhance the electromagnetic field when coupled with AgNWs to obtain a high SERS intensity. The SERS intensity measured inside the crater structure with deposited AgNWs was up to 17.4 times higher than that of the flat structure with a deposited Ag film. These results suggest a new method for enhancing the SERS phenomenon, and it is expected that a larger SERS intensity can be obtained by fine-tuning the crater size and diameter and the length of the AgNWs.

EFFECTS OF INJECTION SPEED ON MECHANICAL PROPERTIES IN HIGH-PRESSURE DIE CASTING OF MG-RE ALLOY

In this study, in order to clarify the unknown physical properties of the Mg-Al-Th-RE alloy, the relationship between the injection conditions and the internal porosities and the mechanical properties exerted by the solidification microstructure were investigated. The obtained cast samples were investigated using X-ray CT internal measurements, tensile tests, Vickers hardness tests and solidification microstructure observations. The flow simulation and the X-ray CT analysis results showed that the porosity volume increased as the injection speed increases. The higher injection speed also affected the metal microstructure to become denser, which leads to a higher material strength and hardness. The eutectic phases quickly formed because of the shorter filled and cooled time. Therefore, the growth of the primary phase α-Mg was suppressed. On the other hand, it was considered that the material strength and hardness were greatly reduced by the coarse primary phase.

Steam Generator Grade P91 Steel Components Creep-Assessment By Test After Extended Service

Previous study carried out creep analysis for steam generator high-temperature-section two components, outflow tubing and manifold of the superheater harp: they may have been critical because of the long continued service (109,000 hours or twelve years) and loading conditions, including maximum operation temperature (565°C) and applied stress (65 MPa). Metallographic methods by replica had showed no evidence of the creep cavitation in all the positions considered for both tubing and manifold. In particular, they had not found any cavitation or phases affecting creep strength of the material in the base, HAZ and weld metal microstructure. Now, present study carries out investigation for the two components based on the next plant outage outcome, after further 20,000-hours service. Both metallographic methods and hardness measurements’ results would compare with previous ones providing microstructure evolution in the period.

Microstructural and corrosion study of aluminum foams obtained by space holder process using low-cost removable preforms

The space holder process (SHP) is a useful and common technique to obtain metal foams. However, an important question remains unsolved: Would the quality of the salt affect the properties of the aluminum foam obtained? In this paper, removable preforms of two types of salt (refined and unrefined) were infiltrated with A356 aluminum alloy to obtain metal foams with different pore sizes. The interaction preform-metal was studied from analyzing the morphological structure of the foams, the metal microstructure, and the corrosion resistance of the Al356 alloy. It was observed that, although the two types of salt exhibited some differences, they did not show variations in relation to the porous structure and metal microstructure in the aluminum foams obtained. Additionally, the electrochemical analyses did not show significant effects on the corrosion behavior of aluminum foams caused by the interaction with the salt preforms.

Hydrogen Sulfide Stress Cracking in a Q345R Welded Joint

In this paper the failure reason of Q345R Welded Joint was studied through macroscopic observation, chemical properties, metallurgical analysis, scanning electron microscope (SEM) and EDS test method. The results showed that there were a large number of micro-cracks in the fracture surface. The reason of cracking is severe banded structure in base metal microstructure, which provided opportunity for hydrogen atoms to enter into the internal of steel when contact with wet hydrogen sulfide environment. The existence of tensile stress promotes the entry of hydrogen atoms and the propagation of cracks. The welding products of this procedure are not suitable for use under sour conditions.

Influence of the Structure of Iron Coatings on their Physical and Mechanical Properties

The influence of electrolysis parameters on the structure and properties of iron coatings is shown. The dependencies of hardness of iron coatings upon the parameters of metal microstructure characterized by dilatation are established. It is shown that dilatation can be used as a checkup parameter for iron strength properties. The influence of some factors on the properties of iron deposits obtained under non-stationary deposition regimes is analyzed.

Weld Metal Microstructure Prediction in Laser Beam Welding of Austenitic Stainless Steel

In the present work an approach to weld metal microstructure prediction is proposed, based on an analytical method that allows the evaluation of the thermal fields generated during the laser beam travel on thick plates. Reference is made to AISI 304L austenitic steel as a base material, with the aim to predict the molten zone microstructure and verify the best condition to avoid hot cracking formation, which is a typical issue in austenitic steel welding. The “keyhole” full penetration welding mode, characteristic of high-power laser beam, was simulated considering the phenomenological laws of conduction by the superimposition of a line thermal source along the whole thickness and two point sources located, respectively, on the surface and at the position of the beam focus inside the joint. This model was fitted on the basis of the fusion zone profile, which was experimentally detected on a weld seam obtained by means of a CO2 laser beam, in a single pass on two squared edged AISI 304L plates, that were butt-positioned. Then the model was applied to evaluate the thermal fields and cooling rates, the fusion zone composition and the solidification mode.