An investigation on quench cracking behavior of superalloy udimet 720LI using a fracture mechanics approach

Quench cracking can be a serious problem in the heat treatment of high strength superalloys. A new fracture mechanics approach, quench cracking toughness (K _Q ), was introduced to evaluate the on-cooling quench cracking resistance of superalloy Udimet 720LI. A fully automatic computer controlled data acquisition and processing system was set up to track the on-cooling quenching process and to simulate the quench cracking. The influences of grain size, cooling rate, solution temperature, and alloy processing routes on quench cracking resistance were investigated. Research results indicate that quench cracking revealed a typical brittle and intergranular failure at high temperatures, which causes a lower quench cracking toughness in comparison to fracture toughness at room temperature. Fine grain structures show the higher quench cracking resistance and lower failure temperatures than intermediate grain structures at the same cooling rates. Moreover, higher cooling rate results in lower cracking toughness under the same grain size structures. In comparison of processing routes, powder metallurgy (PM) alloys show higher cracking resistance than cast and wrought (CW) alloys for fine grain structures at the same cooling rates. However, for intermediate grain structure, there is no obvious difference of K _Q between the two processing routes in this study.     

Anisotropy in the Spatial Distribution of Roller-Measured Soil Stiffness

The geostatistical analysis of roller-measured soil properties (from continuous compaction control and intelligent compaction) is required for advanced quality control/quality assurance of earthwork and asphalt compaction. This paper explores the existence of anisotropy in the spatial distribution of roller-measured soil stiffness and the effect of anisotropy on kriging. Field testing was conducted to collect roller measurement value (MV) data over typical roadway embankment evaluation areas and on a large square area to enable a robust investigation of anisotropy. The semivariogram analysis of the field data clearly indicates that range anisotropy exists. The spatial distributions of roller MV data are different in the longitudinal x-direction than in the transverse y-direction. Magnitudes of range anisotropy (x-range/y-range) varied from 2.4 to over 5. The observed range anisotropy is not due to the roller measurement system; rather, it is likely due to the directional nature of earthwork construction activities and to alignment geometry. The influence of anisotropy on kriging was found to be significant when considering the use of kriged data in earthwork specifications. The error introduced by not accounting for anisotropy in kriging varied from 5 to 17% when considering pass to pass or layer to layer map analysis. The anisotropy in the spatial distribution of roller MV data should be factored into kriging and other geostatistical analyses. For typical earthwork area geometries, the roller mapping procedure requires a slight modification to determine the y-range and anisotropy ratio.     

The effect of temperature on coalescence of liquid drops at liquid/liquid interfaces

Drop/interface coalescence times measured at 293–343K are reported for three oil/water systems (benzene, paraffin oil and 1,1,2,2-tetrabromoethane) with different interface ages. The anomalous coalescence behavior of water droplets is explained by considering the static electrical double-layer residing at the interface which influences the film thinning and the film rupture processes. Analyses using simplified coalescence models reveal that the incorporation of temperature dependence on the physical properties such as density difference between phases, viscosity of the continuous medium and interfacial tension, does not produce satisfactory agreement with the measured coalescence times. The effect of mutual saturation in contrast to unsaturated systems on coalescence times is illustrated. The reproducibility of the drop/interface coalescence times is examined and explanations are offered, relating the method and the conditions of the experimentation. Finally the importance of both the coalescence time and the film thickness to drop stability analysis is demonstrated.     

Vermeidung von Korrosionsproblemen bei Aluminiumwerkstoffen

Corrosion protection of Aluminium sheet alloys Aluminium is considered to be the optimum corrosion resistant material for light weight constructions. The present paper provides a summary on the reasons for the corrosion of aluminium in inappropriate applications, the different types of corrosion and the relevant mechanisms. As an example, aluminium car body sheets are considered. Proper surface treatment of the sheets by coil coating is an interesting possibility to guarantee the high quality requirements allowing at the same time an improved and cost-effective processing of the material by the car producers. The established surface treatment techniques are described and new environmental friendly developments are indicated. Future success of these surface pretreatments depends on an improved understanding of the complex system of the interface aluminium/aluminium oxide/conversion layer/lacquer. This requires close cooperation between metallurgists, surface specialists, chemists and users of the material.     

Umformbare Al-Werkstoffe – für jede Anwendung

Highly Formable Multi-Purpose Al Alloys Microstructural control through appropriate alloy design and definition of processing schedule, as well as a critical view on the interaction of alloy and forming process, has enabled successful application of aluminium alloy sheet in areas where a good formability is a requirement together with an elevated strength level. Further developments along these lines will promote the introduction of aluminium alloys in new markets where, despite its advantages in terms of weight and corrosion resistance, their penetration has been hindered by only moderate formability.     

Polyaluminum chloride with high Al30 content as removal agent for arsenic-contaminated well water

Polyaluminum chloride (PACl) is a well-established coagulant in water treatment with high removal efficiency for arsenic. A high content of Al₃₀ nanoclusters in PACl improves the removal efficiency over broader dosage and pH range. In this study we tested PACl with 75% Al₃₀ nanoclusters (PACl_Al30) for the treatment of arsenic-contaminated well water by laboratory batch experiments and field application in the geothermal area of Chalkidiki, Greece, and in the Pannonian Basin, Romania. The treatment efficiency was studied as a function of dosage and the nanoclusters’ protonation degree. Acid-base titration revealed increasing deprotonation of PACl_Al30 from pH 4.7 to the point of zero charge at pH 6.7. The most efficient removal of As(III) and As(V) coincided with optimal aggregation of the Al nanoclusters at pH 7-8, a common pH range for groundwater. The application of PACl_Al30 with an Al_tot concentration of 1-5 mM in laboratory batch experiments successfully lowered dissolved As(V) concentrations from 20 to 230 μg/L to less than 5 μg/L. Field tests confirmed laboratory results, and showed that the WHO threshold value of 10 μg/L was only slightly exceeded (10.8 μg/L) at initial concentrations as high as 2300 μg/L As(V). However, As(III) removal was less efficient (<40%), therefore oxidation will be crucial before coagulation with PACl_Al30. The presence of silica in the well water improved As(III) removal by typically 10%. This study revealed that the Al₃₀ nanoclusters are most efficient for the removal of As(V) from water resources at near-neutral pH.     

Surgical aspects of mycobacterioses. Evolution during the last 20 years

INTRODUCTION: Tuberculosis remains one of the major infectious diseases. Its incidence has grown in immigrants and in immunosuppressed patients, and, moreover, cases of drug resistance are on the increase. The goal of this study was to analyze the implications of these new developments and surgical experience in our patients. METHODS: The cases of 104 patients with tuberculosis hospitalized between 1975 and 1995 were reviewed retrospectively. RESULTS: 22% of the patients (23/104) were immigrants. No HIV-positive patients were described but association with debilitating diseases was frequent. Diagnosis was chiefly by histology. The culture was positive in only 30/104 patients (29%). Drug resistance was seen in only one patient (1%). 72/104 patients (69.2%) presented with an infection of the pulmonary parenchyma, 21/104 (20.2%) with pleural tuberculosis including tuberculous empyema, 3/104 (2.9%) with tuberculosis of the chest wall and 8/104 (7.7%) with mediastinal tuberculosis. Surgery was performed in 84/104 patients (80.8%). The chief indications were suspected carcinoma in 39/84 cases (46.4%), destroyed lung in 11/84 (13.1%), empyema combined with bronchopleural fistula in 10/84 (11.9%), enlarged mediastinal lymph-nodes of unknown dignity in 7/84 (8.3%), recurrent pleural effusion in 5/84 (5.9%) and bronchial stenosis in 4/84 (4.8%). CONCLUSION: The number of surgical patients with tuberculosis has remained fairly stable over the last 20 years, but the proportion of immigrants has grown since 1990. Thoracoscopy is playing an increasingly important role in the diagnosis and surgical treatment of tuberculosis (recurrent pleural effusion, resection of peripheral pulmonary nodules turning out to be tuberculoma).