Dresden 2017 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 3: Topical Session: Interface-Controlled Microstructures: Mechanical Properties and Mechano-Chemical Coupling - Segregation and Embrittlement I
MM 3.2: Vortrag
Montag, 20. März 2017, 10:45–11:00, BAR 205
Engineering the chemistry of grain boundaries in Mo-Hf alloys — •Daniel Scheiber1, Katharina Leitner2, Reinhard Pippan3, Peter Puschnig4, and Lorenz Romaner1 — 1Materials Center Leoben, Austria — 2Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Austria — 3University of Graz, Institute of Physics, Austria — 4Erich Schmid Institut of Materials Science, Austrian Academy of Sciences, Leoben, Austria
Molybdenum alloys are known for their outstanding material properties like low thermal expansion coefficients and high strength at elevated temperatures. However, many Mo alloys are prone to brittle intergranular fracture at room temperature, which is attributed to low grain boundary (GB) cohesion. GB engineering searches for ways to counteract the low GB cohesion, e.g. by alloying with elements that segregate to the GB and enhance GB cohesion. In this study, Mo samples with different Hf contents are investigated, which exhibit a change from intergranular fracture to transgranular fracture with increasing Hf content. To reveal the underlying effects of this change in fracture mode, different experimental and theoretical methods are applied. A detailed atom probe tomography (APT) study shows the change in GB chemistry for the alloys and clarifies that not Hf, but rather segregated B and C atoms lead to the increase in GB cohesion. Subsequent ab-initio simulations of a GB observed in APT allows for comparison of the GB chemistry with experiment. With the agreement at hand, the simulations explain the change in GB chemistry and provide recommendations for Mo alloys with reduced intergranular fracture.