Dense TRIP-matrix composites containing 5 vol.% Mg-PSZ as reinforcing phase were produced by employing the spark plasma sintering technique. A continuous and seamless interface between the ceramic particles and the steel matrix was achieved. Compression tests revealed better mechanical properties of the 5 vol.% Mg-PSZ-TRIP steel composites in comparison with both, pure and Al2O3 reinforced TRIP steel. The underlying deformation mechanism within the austenitic matrix entailed a pronounced martensite formation. An additional phase transformation was observed within the ZrO2 particles. The enhanced mechanical properties of the 5 vol.% Mg-PSZ composite are dedicated to the transformation strengthening of the ceramic particles. Finally a model of the reinforcing mechanism is proposed.

Reinforcing Mechanism of Mg‐PSZ Particles in Highly‐Alloyed TRIP Steel

Metal matrix composites (MMC) containing TRIP-steel/Mg-PSZ were processed by cold pressing and conventional sintering in different atmospheres. The MMC was based on austenitic steel in the system Fe-Cr-Mn-Ni showing transformation induced plasticity (TRIP). Depending on the sintering temperature, the sintering atmosphere and the steel composition the phase compositions of MgO partially stabilized zirconia (Mg-PSZ) were analysed by scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDX) as well as electron backscatter diffraction (EBSD). The interactions between the alloying elements of austenitic stainless steel and the ceramic stabilizer (MgO) as well as the technological parameters lead to a significant change in the phase composition of the Mg-PSZ. The changes can be analysed by EBSD due to the high spatial resolution.

Determination of the Phase Distribution in Sintered TRIP‐Matrix / Mg‐PSZ Composites using EBSD

In-situ characterization of the microstructure evolution during cyclic deformation of novel cast TRIP steel

The temperature dependence of surface tension and density for Fe–Cr–Mo (AISI 4142), Fe–Cr–Ni (AISI 304), and Fe–Cr–Mn–Ni TRIP/TWIP high-manganese (16 wt% Cr, 7 wt% Mn, and 3–9 wt% Ni) liquid alloys are investigated using the conventional maximum bubble pressure (MBP) and sessile drop (SD) methods. In addition, the surface tension of liquid steel is measured using the oscillating droplet method on electromagnetically levitated (EML) liquid droplets at the German Aerospace Centre (DLR, Cologne). The data of thermophysical properties for Fe–Cr–Mn–Ni is of major importance for modeling of infiltration and gas atomization processes in the prototyping of a “TRIP-Matrix-Composite.” The surface tension of TRIP/TWIP steel increased with an increase in temperature in MBP as well as in SD measurement. The manganese evaporation with the conventional measurement methods is not significantly high within the experiments (∆Mn < 0.5 %). The temperature coefficient of surface tension (dσ/dT) is positive for liquid steel samples, which can be explained by the concentration of surface active elements. A slight influence of nickel on the surface tension of Fe–Cr–Mn–Ni steel was experimentally observed where σ is decreased with increasing nickel content. EML measurement of high-manganese steel, however, is limited to the undercooling state of the liquid steel. The manganese evaporation strongly increased in excess of the liquidus temperature in levitation measurements and a mass loss of droplet of 5 % was observed.

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Surface tension and density data for Fe–Cr–Mo, Fe–Cr–Ni, and Fe–Cr–Mn–Ni steels

Porous materials have received extensive attention for energy absorption in the last years. In terms of this study austenitic TRIP-steel/Mg-PSZ composite–open cell foam structures are formed based on replicas using open-celled polyurethane foam as a skeleton with and without a supporting dense face (jacket) coating. Their compression strength as well as their specific energy absorption SEA has been registered as a function of the compressive strain. The zirconia addition has reinforced the composite material with the face coating up to a compressive strain of 50%. The stress-induced martensitic transformation of partially stabilized zirconia phases has been investigated as a function of the compressive strain by EBSD. The zirconia phase transformation is triggered already at low compressive strains below 2%.

Novel TRIP-Steel/Mg-PSZ Composite-Open Cell Foam Structures for Energy Absorption

Porous materials have received extensive attention for energy absorption in the last few years. In terms of this study, austenitic TRIP-steel/Mg-PSZ-composite honeycomb structures are formed with different mixing proportions due to ceramic extrusion at room temperature. Their specific energy absorption SEA as well as their compression strength have been registered as a function of the compressive strain. X-ray diffractometry (XRD), electron backscatter diffraction (EBSD) as well as electron dispersive X-ray (EDX) analysis support the microstructure characterization. The zirconia addition has mainly contributed as a hard phase in a ductile TRIP steel matrix and has reinforced the composite material up to a compressive strain of about 24%.

Ullrich Martin

Papers

Energy-Absorbing TRIP-Steel/Mg-PSZ Composite Honeycomb Structures Based on Ceramic Extrusion at Room Temperature