Low-Cycle Fatigue of Ultra-Fine-Grained Cryomilled 5083 Aluminum Alloy

The cyclic deformation behavior of cryomilled (CM) AA5083 alloys was compared to that of conventional AA5083-H131. The materials studied were a 100 pct CM alloy with a Gaussian grain size average of 315 nm and an alloy created by mixing 85 pct CM powder with 15 pct unmilled powder before consolidation to fabricate a plate with a bimodal grain size distribution with peak averages at 240 nm and 1.8 μm. Although the ultra-fine-grain (UFG) alloys exhibited considerably higher tensile strengths than those of the conventional material, the results from plastic-strain-controlled low-cycle fatigue tests demonstrate that all three materials exhibit identical fatigue lives across a range of plastic strain amplitudes. The CM materials exhibited softening during the first cycle, similar to other alloys produced by conventional powder metallurgy, followed by continual hardening to saturation before failure. The results reported in this study show that fatigue deformation in the CM material is accompanied by slight grain growth, pinning of dislocations at the grain boundaries, and grain rotation to produce macroscopic slip bands that localize strain, creating a single dominant fatigue crack. In contrast, the conventional alloy exhibits a cell structure and more diffuse fatigue damage accumulation

Ultrafine grained plates of Al-Mg-Si alloy obtained by Incremental Equal Channel Angular Pressing : microstructure and mechanical properties

In this study, an Al-Mg-Si alloy was processed using via Incremental Equal Channel Angular Pressing (I-ECAP) in order to obtain homogenous, ultrafine grained plates with low anisotropy of the mechanical properties. This was the first attempt to process an Al-Mg-Si alloy using this technique. Samples in the form of 3 mm-thick square plates were subjected to I-ECAP with the 90˚ rotation around the axis normal to the surface of the plate between passes. Samples were investigated first in their initial state, then after a single pass of I-ECAP and finally after four such passes. Analyses of the microstructure and mechanical properties demonstrated that the I-ECAP method can be successfully applied in Al-Mg-Si alloys. The average grain size decreased from 15 - 19 µm in the initial state to below 1 µm after four I-ECAP passes. The fraction of high angle grain boundaries in the sample subjected to four I-ECAP passes lay within 53-57 % depending on the examined plane. The mechanism of grain refinement in Al-Mg-Si alloy was found to be distinctly different from that in pure aluminium with the grain rotation being more prominent than the grain subdivision, which was attributed to lower stacking fault energy and the reduced mobility of dislocations in the alloy. The ultimate tensile strength increased more than twice, whereas the yield strength - more than threefold. Additionally, the plates processed by I-ECAP exhibited low anisotropy of mechanical properties (in plane and across the thickness) in comparison to other SPD processing methods, which makes them attractive for further processing and applications

Verschleissfeste PVD-/CVD-Trockenschmierstoffschichten fuer die umweltschonende und innovative Fertigung. Teilprojekt 3: Kohlenstoffbasierte Trockenschmierstoffschichten (TSS-C) Abschlussbericht

The partners Bosch, Metaplas Ionon and Roth and Rau developed dry lubricant coatings on a carbon coating base. The cutting tools used for the testing were developed in former dry cutting projects especially for cutting with minimum quantity lubrication (MQL). The coatings were tested in cutting and metal forming. After tribological testing at the coating companies the deposited coatings were evaluated by machining tests in drilling, thread forming and metal forming at the universities of Darmstadt and Kassel. The best coatings were tested in production field tests (laboratory) or, if possible, in the production at company Bosch and at other end users of the joint project. It was possible to show that carbon coatings are very good at punching and sheet bending. Also at drilling and thread forming in cast iron and low alloyed steels the results are good enough for production. The results at drilling and thread forming in aluminium alloys and high alloyed steels (X90CrMoV18) were not good enough for production under dry conditions. But testing with a reduced amount of MQL (6ml/h) showed better cutting parameters than commercial coatings. Also cutting length and quality of the parts are better. Even with the best coatings it was not possible to make dry massive forming with reduced temperature. At these high temperatures and high surface pressures it was not possible to work without lubricants. (orig.)Im Projekt wurden von den Partnern Bosch, Metaplas Ionon und Roth and Rau Trockenschmierstoffschichten auf Kohlenstoffbasis entwickelt. Diese wurden auf Werkzeuge abgeschieden, deren Geometrien in bereits abgeschlossenen Projekten fuer die Trockenzerspannung mit Minimalmengenschmierung optimiert wurden. Die Schichten sind fuer die Zerspannung und Umformtechnik vorgesehen. An tribologische Tests bei den Beschichtern schlossen sich Filtertests an den Hochschulen Darmstadt und Kassel an, bei denen die Schichten in Bohr-, Gewindeform- und Umformtests untersucht wurden. Geeignete Schichten kamen in fertigungsnahe Feldtests bzw. in die Fertigung beim Endanwender Bosch und projektuebergreifend bei anderen Endanwendern des Gesamtprojektes. Es zeigte sich, dass die Kohlenstoffschichten bei Stanz- und Blechumformungsoperationen hervorragende Ergebnisse liefern. Auch beim Bohren und Gewindeformen in Gusswerkstoffen und niedrig legierten Staehlen konnten trocken fertigungsrelevante Ergebnisse erzielt werden. Bohren und Gewindeformen in Aluminiumlegierungen und hochlegierten Staehlen war trocken mit fertigungsrelevanten Schnittwerten nicht moeglich. Vergleichsversuche mit Minimalmengenschmierung haben jedoch aufgezeigt, dass trotz Reduzierung der Minimalmenge auf 6 ml/Std. deutlich hoehere Schnittwerte gefahren werden konnten, als mit bisher am Markt erhaeltlichen Beschichtungen. Auch die Standmenge und die Qualitaet der Bearbeitungen konnte verbessert werden. Der Versuch, besonders gute Beschichtungen auch in der Halbwarm-Massivumformung einzusetzen, ist leider gescheitert. Bei den hohen Temperaturen und Flaechenpressungen war ein Arbeiten ohne Schmiermittel grundsaetzlich nicht moeglich. Die Arbeiten wurden deshalb zur Mitte des Projektes abgebrochen. (orig.)SIGLEAvailable from TIB Hannover: F03B70 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Using the SMiLE Monitoring Infrastructure to Detect and Lower the Inefficiency of Parallel Applications

. The efficiency of a parallel execution is always underlined. Many parallel programs, however, don't run efficiently upon Networks of Workstations for a variety of reasons such as frequent accesses of remote memories. In this article we present a hardware-based monitoring system which uses a hardware monitor to keep watch of all of the underlying transactions on the network and allows tools to utilize the observed information about the memory behavior of parallel programs to manipulate their execution in run-time. This makes the parallel applications execute more efficiently upon clusters. Keywords: Performance monitor, Distributed shared memory, Load balancing, Thread migration, Performance optimization, SCI 1 Introduction Parallel processing is a key technology both for commercial applications and for research. Besides multiprocessor and multicomputer systems, COWs and NOWs play also an important role. Due to the synchronization and communication between processes as well..