Materialwissenschaft und Werkstofftechnik最新文献

Nickel–based super alloys such as Rene 142 are widely used in turbine vanes due to their exceptional high–temperature performance, yet long–term service in extreme environments leads to complex degradation mechanisms that threaten component integrity. This study investigates the microstructural evolution and failure mechanisms of a Rene 142 brazed turbine vane after more than 40,000 operational hours. Through a combination of scanning electron microscopy (scanning electron microscopy), energy–dispersive x–ray spectroscopy (energy dispersive spectroscopy), and thermodynamic simulations (JMatPro), this work elucidates the interplay between phase transformations, elemental segregation, and crack initiation in vane and brazed regions. Key findings reveal that the Rene 142 brazing alloy exhibits reduced γ′ phase stability (30 wt.-% at 600 °C vs. 70 wt.-% in Rene 142), preferential segregation of Cr and Ti, and the formation of brittle intermetallic phases and carbides at grain boundaries. These microstructural changes, compounded by oxidation–driven Al depletion and thermal stresses, promote crack nucleation and propagation within the vane. The study further demonstrates that crack growth is accelerated by rafting of γ′ phases, porous oxide–layer formation, and stress concentration at carbide–rich interfaces. These insights advance the understanding of long–term degradation in brazed superalloys and provide actionable recommendations for improving the design and maintenance of turbine components to mitigate premature failure.

With this approach, it is for the first time possible to map all for the direct calibration relevant influences on the impact energy that are to be tested according the standard and to determine complete the respective deviation and measurement uncertainty component. Therefore it is necessary to transfer the tested parameters in influences on the indicated absorbed energy. Based on the numerical example of a presented specific calibration, it has been shown that many influences that have not yet been considered must also be considered, whereas some components can be neglected.

Stress corrosion cracking is a significant failure mechanism affecting carbon steels in seawater environments. This study aims to evaluate the effect of controlled plastic pre-strain on the stress corrosion cracking behavior of ASTM A36 steel immersed in a 3.5 % sodium chloride solution. Four pre-strain levels (2.5 %, 5 %, 7.5 %, and 10 %) were applied before testing using the slow strain rate testing method. Tensile tests were conducted to assess mechanical properties, and scanning electron microscopy was used to examine fracture surface morphology and crack propagation features.

The experimental results revealed a progressive reduction in elongation from 20.0 % to 11.57 % and an increase in tensile strength from 418.02 MPa to 473.70 MPa with increasing pre-strain, indicating strain hardening. stress corrosion cracking susceptibility, quantified by the ratio of area reduction in the corrosive environment to that in air, peaked at 12.5 for the 2.5 % pre-strained specimen, while remaining constant at about 10 at higher pre-strain levels. These findings highlight the complex influence of plastic deformation on stress corrosion cracking behavior and provide insights into crack initiation mechanisms in low-carbon steels under simulated seawater exposure.

This study investigates the mechanical behavior and machinability of a novel hybrid metal matrix composite comprising aluminum–copper alloy reinforced with 5 weight-% silicon carbide and 5 weight-% graphene nanoplatelets. The composite was fabricated using the stir casting technique and subjected to mechanical testing, which revealed significant improvements in tensile strength, compressive strength, and hardness compared to the unreinforced aluminum–copper matrix. Abrasive water jet machining was employed to evaluate the machinability of the composite under varying process parameters jet pressure (1500 bar – 3000 bar), standoff distance (1 mm – 3 mm), and traverse speed (50 mm/min – 200 mm/min) using a taguchi L27 orthogonal array. Key output responses such as kerf width, material removal rate, and surface roughness were analyzed through analysis of variance, which identified jet pressure as the most significant factor affecting kerf formation. Machine learning models including artificial neural networks, random forest regression, and decision trees were developed to predict machining performance. Among these, the artificial neural networks model achieved the highest prediction accuracy (coefficient of determination (R²) > 0.98), effectively captu^ring nonlinear dependencies. Multi-objective optimization using a desirability function identified the optimal abrasive water jet machining parameters to be 2700 bar jet pressure, 2 mm standoff distance, and 50 mm/min traverse speed. The study demonstrates that the integration of ceramic and nano-reinforcements significantly enhances both mechanical and machinability performance, while machine learning models provide reliable real-time predictive capabilities. The findings support the adoption of intelligent, high-precision machining strategies for advanced hybrid composites in aerospace and structural applications.

Testing the rheological properties of magnetorheological fluids often faces challenges in measurement accuracy and magnetic field uniformity. To address these, this study proposes a novel cone-recess interlocking shear fixture for measuring magnetic flux density and shear yield stress. Finite element analysis simulated the device's magnetic circuit and flux distribution. Comparative experiments confirmed its uniform magnetic field, direct flux density measurement, and high accuracy and repeatability in shear yield stress testing.