On the capability of in-situ exposure in an environmental scanning electron microscope for investigating the atmospheric corrosion of magnesium

The feasibility of environmental scanning electron microscope (BEM) in studying the atmospheric corrosion behavior of 99.97% Mg was investigated. For reference, ex-situ exposure was performed. A model system was designed by spraying few salt particles on the metal surface and further promoting the corrosion process using platinum (Pt) deposition in the form of 1 x 1 x 1 pm(3) dots around the salt particles to create strong artificial cathodic sites. The results showed that the electron beam play a significant role in the corrosion process of scanned regions. This was attributed to the irradiation damage occurring on the metal surface during the BEM in-situ experiment. After achieving to a reliable process route, in a successful attempt, the morphology and composition of the corrosion products formed in-situ in the ESEM were in agreement with those of the sample exposed ex-situ

On the early stages of localised atmospheric corrosion of magnesium–aluminium alloys

The surface film on pure magnesium and two aluminium-containing magnesium alloys was characterised after 96\ua0h at 95% RH and 22\ua0\ub0C. The concentration of CO2 was carefully controlled to be either 0 or 400\ua0ppm. The exposed samples were investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and electron microscopy. The results showed that when the alloys were exposed to the CO2-containing environment, aluminium cations (Al3+) was incorporated into a layered surface film comprising a partially “hydrated” MgO layer followed by Mg(OH)2, and magnesium hydroxy carbonates. The results indicated that aluminium-containing magnesium alloys exhibited considerably less localised corrosion in humid air than pure magnesium. Localised corrosion in the materials under investigation was attributed to film thinning by a dissolution/precipitation mechanism

Surface preparation of powder metallurgical tool steels by means of wire electrical discharge machining

The surface of two types of powder metallurgical (PM) tool steels (i.e., with and without nitrogen) was prepared using wire electrical discharge machining (WEDM). From each grade of tool steel, seven surfaces corresponding to one to seven passes of WEDM were prepared. The WEDM process was carried out using a brass wire as electrode and deionized water as dielectric. After eachWEDM pass the surface of the tool steels was thoroughly examined. Surface residual stresses were measured by the X-ray diffraction (XRD) technique. The measured stresses were found to be of tensile nature. The surface roughness of the WEDM specimens was measured using interference microscopy. The surface roughness as well as the residual stress measurements indicated an insignificant improvement of these parameters after four passes of WEDM. In addition, the formed recast layer was characterized by means of scanning electron microscopy (SEM), XRD, and X-ray photoelectron spectroscopy (XPS). The characterization investigation clearly shows diffusion of copper and zinc from the wire electrode into the work material, even after the final WEDM step. Finally, the importance of eliminating excessive WEDM steps is thoroughly discussed

Burden of tracheal, bronchus, and lung cancer in North Africa and Middle East countries, 1990 to 2019: Results from the GBD study 2019

ObjectiveTo provide estimates on the regional and national burden of tracheal, bronchus, and lung (TBL) cancer and its attributable risk factors from 1990 to 2019 in the North Africa and Middle East (NAME) region.Methods and materialsThe Global Burden of Disease (GBD) 2019 data were used. Disability-adjusted life years (DALYs), death, incidence, and prevalence rates were categorized by sex and age groups in the NAME region, in 21 countries, from 1990 to 2019. Decomposition analysis was performed to calculate the proportion of responsible factors in the emergence of new cases. Data are presented as point estimates with their 95% uncertainty intervals (UIs).ResultsIn the NAME region, TBL cancer caused 15,396 and 57,114 deaths in women and men, respectively, in 2019. The age-standardized incidence rate (ASIR) increased by 0.7% (95% UI -20.6 to 24.1) and reached 16.8 per 100,000 (14.9 to 19.0) in 2019. All the age-standardized indices had a decreasing trend in men and an increasing trend in women from 1990 to 2019. Turkey (34.9 per 100,000 [27.6 to 43.5]) and Sudan (8.0 per 100,000 [5.2 to 12.5]) had the highest and lowest age-standardized prevalence rates (ASPRs) in 2019, respectively. The highest and lowest absolute slopes of change in ASPR, from 1990 to 2019, were seen in Bahrain (-50.0% (-63.6 to -31.7)) and the United Arab Emirates (-1.2% (-34.1 to 53.8)), respectively. The number of deaths attributable to risk factors was 58,816 (51,709 to 67,323) in 2019 and increased by 136.5%. Decomposition analysis showed that population growth and age structure change positively contributed to new incident cases. More than 80% of DALYs could be decreased by controlling risk factors, particularly tobacco use.ConclusionThe incidence, prevalence, and DALY rates of TBL cancer increased, and the death rate remained unchanged from 1990 to 2019. All the indices and contribution of risk factors decreased in men but increased in women. Tobacco is still the leading risk factor. Early diagnosis and tobacco cessation policies should be improved

Atmospheric corrosion of Mg and MgAl alloys – characterization and mechanisms

The atmospheric corrosion of Mg and MgAl alloys was investigated. Corrosion tests were performed in the laboratory under controlled environment. CP Mg, AM50 and AZ91 samples were exposed at 95% RH and 22\ub0C in the presence and in the absence of 400 ppm CO2 for 24 h to 672 h. The passive film was characterized by means of XPS, FTIR, AES and XRD. It was shown that the film consisted MgO/Mg(OH)2 with carbonate on top of the film in the presence of CO2. In addition, Al3+ was present in the film formed on the alloys. Thickening of the surface film was described in terms of a hydration mechanism. Also, a dissolution-precipitation mechanism was proposed for the break-down of the passive film in humid air. FIB cross-section revealed that in the presence of CO2 dissolution of the metal substrate increased compared to CO2-free exposures. The NaCl–induced atmospheric corrosion of Mg and MgAl alloys was studied in the same environment. Brucite was the main corrosion product in the absence of CO2. In the case of the alloys, meixnerite was also detected. Magnesium hydroxy carbonates were the dominating corrosion products in the presence of 400 ppm CO2. All tested materials exhibited higher corrosion rates in the absence of CO2 compared to exposures with CO2. The electrochemical corrosion cells were more extensive in the absence of CO2 compared to when 400 ppm CO2 was present. EDX analysis revealed that η-phase particles were more efficient cathodes compared to the β-phase and the interdendritic areas. Using the FIB and BIB techniques combined with SEM-EDX it was shown that Cl accumulated at the bottom of the pits.The localized corrosion in the presence of NaCl (aq) and in the presence and absence of CO2 was investigated in 2D and 3D. Plan view characterization was performed by means of SE and BSE imaging in SEM. Interference microscopy was employed in order to study the distribution of the pits after corrosion product removal. SEM-3D imaging was performed using a FIB-SEM system investigating pitted regions. It was showed that the β-phase acted as a barrier against corrosion, especially in the case of alloy AZ91. In the absence of CO2 the corrosion pits tended to interconnect below the metal surface forming severely pitted regions. In the presence of CO2 the pits were isolated and shallower. The beneficial effect of CO2 on corrosion is attributed to its acidity that caused neutralization of the catholyte

Atmospheric corrosion of Mg and MgAl alloys – characterization and mechanisms

The atmospheric corrosion of Mg and MgAl alloys was investigated. Corrosion tests were performed in the laboratory under controlled environment. CP Mg, AM50 and AZ91 samples were exposed at 95% RH and 22\ub0C in the presence and in the absence of 400 ppm CO2 for 24 h to 672 h. The passive film was characterized by means of XPS, FTIR, AES and XRD. It was shown that the film consisted MgO/Mg(OH)2 with carbonate on top of the film in the presence of CO2. In addition, Al3+ was present in the film formed on the alloys. Thickening of the surface film was described in terms of a hydration mechanism. Also, a dissolution-precipitation mechanism was proposed for the break-down of the passive film in humid air. FIB cross-section revealed that in the presence of CO2 dissolution of the metal substrate increased compared to CO2-free exposures. The NaCl–induced atmospheric corrosion of Mg and MgAl alloys was studied in the same environment. Brucite was the main corrosion product in the absence of CO2. In the case of the alloys, meixnerite was also detected. Magnesium hydroxy carbonates were the dominating corrosion products in the presence of 400 ppm CO2. All tested materials exhibited higher corrosion rates in the absence of CO2 compared to exposures with CO2. The electrochemical corrosion cells were more extensive in the absence of CO2 compared to when 400 ppm CO2 was present. EDX analysis revealed that η-phase particles were more efficient cathodes compared to the β-phase and the interdendritic areas. Using the FIB and BIB techniques combined with SEM-EDX it was shown that Cl accumulated at the bottom of the pits.The localized corrosion in the presence of NaCl (aq) and in the presence and absence of CO2 was investigated in 2D and 3D. Plan view characterization was performed by means of SE and BSE imaging in SEM. Interference microscopy was employed in order to study the distribution of the pits after corrosion product removal. SEM-3D imaging was performed using a FIB-SEM system investigating pitted regions. It was showed that the β-phase acted as a barrier against corrosion, especially in the case of alloy AZ91. In the absence of CO2 the corrosion pits tended to interconnect below the metal surface forming severely pitted regions. In the presence of CO2 the pits were isolated and shallower. The beneficial effect of CO2 on corrosion is attributed to its acidity that caused neutralization of the catholyte

Atmospheric corrosion of the MgAl alloy AM50 in rheocast and high pressure diecast conditions - Influence of Microstructure, CO2 and NaCl

The NaCl-induced atmospheric corrosion of the high pressure diecast (HPDC) MgAl alloy AM50 was investigated. Commercially pure (CP) Mg was used as the reference. Two levels of salt; i.e. 14 and 70\ub5g/cm\ub2 NaCl were added to the polished samples before exposure. Specimens without salt were used as references. The exposures were carried out in air with 0 or 400ppm CO2 to investigate the influence of carbon dioxide on corrosion. Gravimetric data was collected after the exposures. Alloy AM50 corroded less severely compared to CP Mg. The passive film and the corrosion products were analyzed qualitatively by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Brucite was the main corrosion product in the absence of CO2. Three magnesium hydroxy carbonates were the major corrosion products in the presence of CO2. The microstructure of the as-cast material and the morphology of the corroded samples were studied by scanning electron microscopy (SEM) and the elemental composition of the different alloy constituents was investigated by energy dispersive X-ray spectroscopy (EDX).The corrosion behavior of HPDC AM50 was compared to that of the alloy manufactured by rheocasting (RC). The average corrosion rate was lower for the RC alloy compared to the HPDC form in the presence of CO2. Larger primary α-Mg grains were observed in the RC alloy. Also, the RC alloy had a larger area fraction of β particles compared to the HPDC alloy

Texture of Electrodeposited Nanocrystalline Ni-Fe with banded structure

Optical microscopy on the etched cross-section of a nanocrystalline Ni-18 wt.% Feelectrodeposit revealed the existence of a banded structure perpendicular to the growth direction. Toevaluate if the banded structure is affecting grain growth and texture development, EBSDorientation maps were obtained after annealing for 30 min at 300, 350, and 400\ub0C. Grown grainswere found to be random in shape and no preferential sites for grain growth were observed. Thetexture of the grown grains is changing upon annealing and the final fibre texture parallel togrowth direction of the electrodeposit can be obtained from texture components found at lowerannealing temperatures when performing one or two consecutive twinning operations

Texture of Electrodeposited Nanocrystalline Ni-Fe with banded structure

Optical microscopy on the etched cross-section of a nanocrystalline Ni-18 wt.% Feelectrodeposit revealed the existence of a banded structure perpendicular to the growth direction. Toevaluate if the banded structure is affecting grain growth and texture development, EBSDorientation maps were obtained after annealing for 30 min at 300, 350, and 400\ub0C. Grown grainswere found to be random in shape and no preferential sites for grain growth were observed. Thetexture of the grown grains is changing upon annealing and the final fibre texture parallel togrowth direction of the electrodeposit can be obtained from texture components found at lowerannealing temperatures when performing one or two consecutive twinning operations

Electrodeposited nanocrystalline Ni-Fe with banded structure

The microstructure of a Ni–18 wt.% Fe electrodeposits having a banded structure is described in detail. The aim is to investigate the influence of the banded structure on grain growth behaviour and texture and to elucidate if there are other mechanisms operative in the stabilization of nanocrystalline electrodeposits. Spectroscopy techniques have been used to characterize the variations in alloy/impurity concentration perpendicular to the growth direction. The influence of these chemical variations on the microstructural evolution has been monitored by in-situ annealing treatments in the TEM. Local texture of the annealed material has been determined by use of the electron backscatter diffraction (EBSD) technique. SEM and TEM investigations have shown that the banded structure is not related to phase changes and that grain growth is not affected by the banded structure, i.e. there is no preferred growth along bands. The first grown grains have <100>, <112> and <111> orientations with the growth direction and upon further grain growth a <111> fibre texture with respect to the growth direction of the electrodeposits is formed. The banded structure seems not to affect the general behaviour of nanocrystalline electrodeposits