Durchgangswiderstand von partikulären Systemen

The electrical properties of particles especially the volume resistance of bulk particles have decisive implication on a multitude of processes in the process engineering such as, product qualification or fire and explosion protection. Since the charge transport in a disperse system and a homogeneously solid is different, the product properties of the particles and the fluid are crucial for the volume resistance. In this work the dependence of the volume resistance on the internal structure of the bed, the relative humidity, the conditioning time at different climates and the average particle size was investigated. All measurements were carried out in a concentric measuring cell.     

Mechanical Properties and Corrosion Resistance of Nitrided or Oxinitrided,and Powder Painted Regular and Interstitial Free (IF) Drawing Steel Sheet

Specimens of 0.8 mm thick regular and interstitial free (IF) drawing steel sheet have been nitrided in fluidised bed for 2 hours at 620 °C and 560 °C with and without a post‐oxidation, and slow and accelerated cooling. As a result, surface hardness, yield and tensile strength of the sheets increased considerably without a critical loss of ductility. Resistance welds between the sheets did not lose their original strength after nitriding‐oxinitriding. Nitrided‐oxinitrided at 620 °C and then powder painted sheets, as compared with powder painted raw sheets, were more corrosion resistant in neutral salt spray and climatic tests. Some mechanical and anticorrosion properties of the IF steel sheet that had undergone the nitriding‐oxinitriding processes were definitely better than those of equally processed regular steel sheet.     

Microstructure and mechanical properties of Mg–6Sn and Mg–6Zn alloys prepared by different processing techniques: a comparative study

The microstructure and mechanical properties of Mg–6Sn and Mg–6Zn are investigated and compared in cast/heat treated, rolled and extruded conditions. Compared to the heat treated alloys, the grain size of both alloys decreases while the volume fraction of precipitates increases by rolling and extrusion in Mg–6Sn alloy at 350 ºC due to dynamic recrystallization and dynamic precipitation of intermetallic phases. Zinc has a stronger grain refining effect than tin in the heat treated alloys while the opposite effect is found in the rolled and extruded alloys. For the heat treated alloys the Mg–6Sn the strength reached 158.7 MPa with elongation 5.2% while Mg–6Zn exhibited a higher strength of 183.7 MPa and 8.4% elongation. In rolled condition the strength of Mg–6Sn reached 224 MPa with 1.6% elongation while Mg–6Zn exhibited a lower strength of 124 MPa and a lower ductility of 0.5% elongation due to susceptibility to hot shortness. Extrusion of Mg–6Sn alloy resulted in the maximum attained strength of 281 MPa and an elongation of 6.1% while Mg–6Zn cracked during extrusion due to hot shortness. The results obtained are discussed with respect to microstructure evolution in both alloys.     

Austempered ductile iron heat treatment for machine hammer peening of milled tool surfaces

Austempered ductile iron (ADI) has become a competitive material to conventional steels. In addition to its favorable price the main reasons are its mechanical properties can be adjusted over a wide range via heat treatment. Austempered ductile iron consists of ferrite, graphite and metastable austenite. Tailoring its microstructure (phase fractions, stability) with regard to the application is an important challenge. A cast iron used for forming dies is EN‐JS2070. In earlier studies it could be shown that EN‐JS2070 can be transformed into austempered ductile iron [1]. Machine hammer peening, causes martensitic transformation of the metastable austenite and leads to hard and smooth surfaces. Focus of this study is to optimize the microstructure with regard to machine hammer peening process. Before and after machine hammer peening the sample surfaces were characterized using optical and laser microscopy, X‐ray diffraction and hardness measurement. It could be shown that a combination of high amount of metastable austenite with a high carbon content leads to the best results in surface roughness and hardness.     

Adhesion and interfacial reactions on metal/oxide interface during plastic deformation at room temperature

Properties of interfaces in solid state metal/oxide joints (Al/SiO₂, Al/MgO, Al/glass, Mg/MgO, Mg/SiO₂, In/glass etc.) are reported. The interfaces were formed at plastic deformation of metal on the oxide surface at room temperature. Their structure, chemical composition, and micromechanical properties were studied by the AFM, XRD, SIMS, optical microscopy, and precision microindentation techniques. A noticeable adhesion was observed for metals with high affinity for oxygen and only in the regions of the maximum shear stress. Formation of an interfacial reaction zone with an oxygen concentration gradient is detected. In this zone metals are nanostructured and noticeably hardened. The effect of mechanoactivation is considered as a result of physical and chemical interaction and formation of nanostructures in deformed metal/oxide systems.     

Texture effect on serrated flow in 2090 Al‐Li alloy

Tensile specimens of 1×6×25 mm in gauge dimension were cut from the surface and centre of 12.7 mm thick 2090 Al‐Li alloy plate, which were solution treated at 550 °C for 30 min, peak‐aged at 190 °C for 18 h, or reversion‐treated at 275 °C for 2 min. The flow stress of the centre layer was higher than that of the surface layer, regardless of the heat treatments. The textures of the surface and centre layers were approximated by the {001}<110> and {011}<211> orientations, respectively. The solution‐treated specimens gave rise to extensive serrations in their flow curves at a strain rate of 2×10^‐4 s^‐1. The serration amplitude was drastically reduced after the specimens were peak‐aged or reversion‐treated. However, for the peak‐aged alloy, the surface‐layer specimens underwent complex, serrated flows, whereas the flow curve of the centre‐layer specimen was almost devoid of serration. The serration, especially fine‐type serration in the peak‐aged and reversion‐treated specimens tended to disappear with increasing strain rate. The tensile behavior was explained in terms of the texture and strain rate.     

Effect of surface oxidation treatment on the tribological performance of carbon fiber reinforced polyimide composites

The effect of ozone surface treatment of carbon fibers (CF) on the tensile strength and tribological properties of carbon fiber reinforced polyimide (CF/PI) composite was investigated. Experimental results revealed that the tensile strength of ozone and air oxidation treated CF reinforced PI composite was improved compared with that of untreated composite. Compared with the untreated and air‐oxidated CF/PI composite, the ozone treated composite had the lowest friction coefficient and specific wear rate under given applied load and reciprocating sliding frequency. Ozone treatment effectively improved the interfacial adhesion between CF and PI. The strong interfacial adhesion of the composite made CF not easy to detach from the PI matrix, and prevented the rubbing‐off of PI, accordingly improved the friction and wear properties of the composite.     

Simulation based microstructural optimization of thermo‐mechanically treated steel components

A simplified approach for the simulation based estimation of the phase distribution in a thermo‐mechanically treated steel component is presented. A key aspect of the approach is the time‐temperature relation for each volume element. Based on a forming simulation with a commercial tool the numerically calculated temperature evolution in the component is analyzed with an in‐house code. The code allows estimating the local phase distribution after the forming process with the help of the continuous‐cooling‐diagram of the material used. A first validation fits well with the existing phase distribution in the component, even though the phase transition in the component is critical in terms of time, deformation and local chemical composition of the material used.     

Mikromechanische Eigenschaften von Weizenkörnern

The investigation of deformation and breakage behavior of wheat grains by compression test was carried out. The force‐displacement curve was obtained at stressing rate 0.02 mm s^–1. The elliptical wheat grains show quasi‐elastic and elastic‐plastic deformation behavior depending on applied force. The simple transformation procedure was applied to adapt the contact model for spherical particles to elliptic wheat grains. The breakage force, energy, strength and displacement distributions were fitted with normal distribution function.     

Texture Formation and Anisotropy of Mechanical Properties of Retaining Rings made of austenitic CrMnN Steel

The formation of texture and its influence on some mechanical properties of retaining rings manufactured from stainless austenitic CrMnN steel were studied. It was found that different crystallite orientations prevail in tangential, radial and axial direction of the retaining ring as a result of plastic deformation by cold expansion. The change of texture from the inner to the outer diameter of the ring occurs because of a decreasing deformation. The formation of texture causes an anisotropy of mechanical properties.