The aim of this work is to evaluate the effect of a deep cryogenic treatment (DCT) on the wear behavior and on the microstructure of an aluminum alloy. In order to compare the level of improvement on the wear resistance provided by the DCT with a more traditional technique, a test matrix which included DCT, CrN coated specimens, and combinations of both modification methods was conducted. The wear behavior was investigated using microabrasive wear tests. The cryogenic treated specimens proved to have similar low wear rates as the specimens coated with CrN. The most distinct improvement was reached with a combination of both techniques. In the case of the DCT, the performed microstructural analysis identified the generation of additional GP-zones as the reason for the improved wear resistance.
The development of new high strength ADI (Austempered Ductile Iron) materials and their evaluation for light weight design purposes are parts of the German research project LEA. [1] The Fraunhofer IWM is investigating the capabilities of ADI materials under crash loading situations by conducting high rate tensile tests which quantify the material's strain rate sensitivity. These investigations result in a reduction of the austenitic phase content of initially about 35%, decreasing to 5-10% after fracture (as characterized by X-ray diffraction), indicating a phase transformation comparable to a TRIP effect. Several ADI 1000 and ADI 1200 samples show an increase in strength of about 100 MPa up to crashrelevant strain rates of 100 s À1 , and the elongation at fracture is constant or increasing, in some cases up to more than 20%. Thus, the newly developed high strength ADI materials exhibit good potential for crash loaded automotive components.
We studied three series of Z-phase strengthened steels using scanning electron microscopy, transmission electron microscopy, and atom probe tomography to reveal the detailed microstructure of these steels. In particular, the phase transformation from M(C,N) to Z-phase (CrMN) was studied. Carbon content in the steels is the governing factor in this transformation. The impact toughness of some test alloys was rather low. This is attributed to the formation of a continuous W-rich film along prior austenite grain boundaries. Cu and C addition to the test alloys changed Laves phase morphology to discrete precipitates and improved toughness dramatically. BN particles were found in some steels. Formation of BN is directly linked to the B concentration in the steels.
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