High strain rate compression testing of hot-pressed TRIP/TWIP-Matrix-CompositesDonnerstag (06.07.2017) 14:00 - 14:20 Uhr Bestandteil von:
Metal matrix composites with ceramic reinforcements such as particles or fibers have come into focus during the past decades due to rising requirements on engineering materials. In this work, composite materials out of high-alloy CrMnNi-steel matrices with varying Ni-contents (3 wt.% and 9 wt.%) and 10 vol.% Mg-PSZ were processed by hot-pressing. The variation in Ni-content resulted in a change in stacking fault energy (SFE) which significantly influenced the deformation mechanisms. Due to the metastable austenitic matrix the materials can show either a martensitic transformation (TRIP) or twinning (TWIP) in addition to dislocation gliding under mechanical loading. Therefore, high strength, ductility and toughness properties can be achieved. Additionally, the Mg-PSZ particles can undergo a stress-induced martensitic phase transformation from the tetragonal to the monoclinic structure during deformation. If those metastable zirconia particles are embedded into the TRIP/TWIP-steel, composites with high energy absorption and damage tolerance can be designed.
The mechanical behavior of the developed composites was investigated in a wide strain rate range between 0.001 s-1 and 2300 s-1 under compressive loading. This was done by a servohydraulic testing system, a drop weight tower, and a Split-Hopkinson pressure bar for the high strain rates. To study the influence on the deformation mechanisms such as martensitic transformations and/or twinning, interrupted tests were also carried out at 25 % compressive strain. Subsequent microstructural examination was done by a magnetic balance to measure the quantity of α’-martensite as well as light-optical-microscopy, SEM and XRD-measurements. The results show an increase of strength and strain hardening with decreasing SFE of the matrix due to increased α’-martensite formation. The addition of the Mg-PSZ particles resulted in further strengthening over almost the entire deformation range for all investigated composites. At high strain rates adiabatic heating suppressed the martensite transformation and reduced the strain hardening capacity of the matrix. Nonetheless the particle reinforcement retains its strengthening effect.