Volume 48, Issue 12

Intermetallic TiAl alloys are light-weight high-temperature materials and intended to partly replace Ni based alloys in jet engines. Due to difficult forming operations, component prices are high and limit the possible field of application. During hot-working, recovery and recrystallization effects determine the microstructural evolution and thereby the mechanical properties of the finished part as well as its behavior during deformation. To study the occurring phenomena, in-situ diffraction experiments with high-energy X-rays were conducted. By means of this method, the dominating processes were identified. The results were validated through electron back scatter diffraction experiments.

The use of automated measurement methods which combine scanning electron microscopy and energy dispersive X-ray analysis in order to carry out quantitative particle analyses allows for an exact characterization of the level of purity in steel in the context of aiming at ensuring a high-quality final product as well as deepening the knowledge of different steps of production in the field of metallurgy. As there is still a lack of standardization when it comes to the examination method, deviations in measurement results are possible. These can lead to reproducibility problems and limited comparability. Within the subcommittee for metallography of the ASMET a working group has been established in order to carry out a round robin test to clearly identify problems of these measurement methods and to propose and/or implement possible solutions. Four different laboratories participated in the round robin test, all of them using different measurement systems to characterize inclusions. These examinations resulted in the definition of measures to possibly standardize measurements (setting of equivalent measurement parameters, using a calibration standard for the setting of gray values). This led to reaching a good agreement of results when comparing the registered morphological and chemical values of all participants and it emphasized the great potential of the method to reach reproducible and generally usable data.

In this work, the results of the examinations of morphology and chemical composition of the primary AlTMSi intermetallic phases precipitates observed in the Al–Si cast alloys microstructure have been presented. A procedure for the treatment of EDS X-ray microanalysis results (selection and classification) using fuzzy logic concept has been developed and then tested in application for AlTMSi phase identification. Statistically significant differences in the chemical composition have been revealed between the analyzed groups of precipitates of both α- and β-AlTMSi phases formed in hypo- and eutectic Al-Si alloys with the same content of transition metals. The range of the measured Mn solubility in the precipitates of different crystal lattices has been statistically estimated.

A thermally upset screw head had numerous cracks at the intersection screw head / screw shaft. The screw consisted of steel that usually does not tend to hot crack. The screw failed when tightening it by applying a torque lower than the nominal torque. The screw head was simply sheared off. A hot crack has clearly been identified as damage-causing mechanism of the material, or, more precisely, liquation cracks. Other damage hypotheses such as liquid metal induced stress corrosion cracking have reliably been excluded in the course of examinations. The material used was 1.7711, 40CrMoV4–6, a material especially used for creep resistant fasteners such as screws and nuts for operating temperatures up to 540°C. This material belongs to the group of low alloy chromium molybdenum vanadium steels. It is typically used in the tempered condition. In Europe, it corresponds to standard EN 10269. In the USA, this steel is known as ASTM A193 GR B16.