Christian Weigelt

Cellular Energy Absorbing TRIP-Steel/Mg-PSZ Composite: Honeycomb Structures Fabricated by a New Extrusion Powder Technology

Lightweight linear cellular composite materials on basis of austenite stainless TRIP- (TRansformation Induced Plasticity-) steel as matrix with reinforcements of MgO partially stabilized zirconia (Mg-PSZ) are described. Two-dimensional cellular materials for structural applications are conventionally produced by sheet expansion or corrugation processes. The presented composites are fabricated by a modified ceramic extrusion powder technology. Characterization of the microstructure in as-received and deformed conditions was carried out by optical and scanning electron microscopy. Magnetic balance measurements and electron backscatter diffraction (EBSD) were used to identify the deformation-induced martensite evolution in the cell wall material. The honeycomb composite samples exhibit an increased strain hardening up to a certain engineering compressive strain and an extraordinary high specific energy absorption per unit mass and unit volume, respectively. Based on improved property-to-weight ratio such linear cellular structures will be of interest as crash absorbers or stiffened core materials for aerospace, railway, or automotive applications.

Effect of zirconia and aluminium titanate on the mechanical properties of transformation-induced plasticity-matrix composite materials

Metal-matrix composite materials composed of an austenitic stainless steel with different ceramic particle reinforcements were investigated in this study. The test specimens were prepared via a powder metallurgical processing route with extrusion at room temperature. As reinforcement phase, either magnesia partially stabilized zirconia or aluminium titanate with a volume content of 5% or 10% was used. The mechanical properties were determined by quasi-static compressive and tensile loading tests at ambient temperature. The microstructure characteristics and failure mechanisms during deformation contributing to significant changes in strength and ductility were characterized by scanning electron microscopy including energy dispersive X-ray spectroscopy and electron back-scatter diffraction, and by X-ray diffraction. The composite materials showed higher stress over a wide range of strain. Essentially, the deformation-induced formation of α′-martensite in the steel matrices is responsible for the pronounced strain hardening. At higher degrees of deformation, the material behavior of the composites was controlled by arising damage evolution initiated by particle/matrix interface debonding and particle fracture. The particle reinforcement effects of zirconia and aluminium titanate were mainly controlled by their influences on martensitic phase transformations and the metal/ceramic interfacial reactions, respectively. Thereby, the intergranular bonding strength and the toughness of the steel/ceramic interfaces were apparently higher in composite variants with aluminium titanate than in composites with magnesia partially stabilized zirconia particles.

Investigations on the sintering response of steel-ceramic composites

Purpose of this article is the evaluation of the influence of sintering parameters on the microstructure evolution and mechanical properties of pressureless sintered metal matrix composites consisting of metastable 16Cr7Mn7Ni-steel with 0 or 5 vol.% magnesia partially stabilized zirconia (Mg-PSZ) particles. The materials were prepared from powder raw materials via extrusion at ambient temperature. Three different temperatures between 1280 °C and 1380 °C and two varying dwell times of 40 min and 120 min at maximum temperature were applied. Both, tensile and compression tests are conducted at quasi-static strain rates for comparison of strength level, deformability and energy absorption capability. The results are discussed with regard to the porosity of the specimens, the interface between steel and ceramic, the TRansformation Induced Plasticity (TRIP)-effect occurrence and the failure behavior.

Joining of Zirconia Reinforced Metal-Matrix Composites

Metal-matrix composite materials, based on a metastable austenitic stainless steel reinforced with a magnesia partially stabilised zirconia have been prepared by a ceramics-derived extrusion technology. Using this powder metallurgical method enables the shaping of lightweight cellular structures as well as bulk specimens with a variety of steel/ceramic ratios at room temperature. However, the extrusion of composite structures is limited by the uniform cross section throughout its entire length. Joining of these metal-matrix composite preforms after sintering by conventional welding techniques is a challenging task. The presence of ceramic fractions may lead to several complications and the subsequent heat exposure during joining may initiate phase transformations in both metastable components resulting in a deterioration of the mechanical properties of the composite material. An adapted ceramics-derived joining technology allows the combination of varying TRIP-steel/zirconia composite materials. The main features are the machining and joining of the parts in their dry green state at room temperature before their thermal treatment. Thus, the material’s consolidation and the formation of the joint take place simultaneously. The ability of joining different parts offers the possibility to create structures for complex applications and testing conditions. The key to advanced properties of the joining zone are the base materials, the surface treatment of the parts, and the paste used for joining. The joining process of different base materials, the mechanical properties, and the microstructure of sinter-joint samples are presented.

Microstructure And Mechanical Properties Of Cold Extruded, Cellular TRIP-matrix Composite Structures Under Quasi-static And Dynamic Compression

Novel composites based on austenitic stainless TRIP steel AISI 304 as a matrix with reinforcements of MgO partially stabilized zirconia (Mg-PSZ) were developed. The presented honeycomb materials were produced by a modified ceramic extrusion technology that is composed of mixing precursor powders with binders, paste preparation and plastic molding, finally debinding and sintering. After processing, sintered products have a global density in the range of 2.7 to 3.0 g cm –3 and a wall thickness of 260 µm. These square-celled honeycomb samples are characterized by optical and scanning electron microscopy before and after quasi-static or dynamic compressive deformation, indicating a noticeable deformation-induced martensite formation. The mechanical properties of samples with up to 10% Mg-PSZ are compared with zirconia-free samples in terms of compression tests at strain rates in the range of 10 –3 to 10 2 s –1 . The honeycomb composite materials exhibit an increased work hardening and also extraordinary high specific energy absorption per unit mass and unit volume, respectively. According to improved property-weight-ratio and excellent crashworthiness, such filigree cellular structures can be beneficial as crash absorbers or stiffened core materials in aerospace, railway or automotive applications.

Verbundwerkstoffe aus Stahl und Keramik — Hochbelastbare Materialien mit Leichtbaupotential

KurzfassungMetall-Matrix-Verbundwerkstoffe (MMCs) aus Stahl mit keramischen Partikelzusätzen bieten aufgrund ihrer mechanischen Eigenschaften ein großes Potential für verschiedenste Anwendungsgebiete, wie z. B. Crash-Absorber, Maschinenbauelemente und Konstruktionsbauteile. Das Zusammenspiel von duktiler Matrix und keramischen Teilchenverstärkung ermöglicht eine Werkstofffamilie mit ausgezeichneten Festigkeits-, Verformungs- und Energieabsorptionseigenschaften. Durch Kombination der keramischen Extrusionsroute bei Raumtemperatur und pulvermetallurgischer Methoden können Verbundwerkstoffe mit nahezu beliebiger Werkstoffkombination und Geometrie erzeugt werden. Die Halbzeuge sind im Grünzustand leicht bearbeitbar und können nach dem Prinzip des keramischen Fügens kombiniert und somit die Geometrie- und Werkstoffvielfalt zusätzlich erweitert werden. Während der abschließenden konventionellen Sinterung entsteht ein hochbelastbarer und schadenstoleranter Verbundwerkstoff.AbstractMetal-matrix composites (MMCs) based on a steel with ceramic particles offer a wide range of high mechanical load applications such as crash-absorber, mechanical engineering, and structural components. The combination of a ductile matrix material with reinforcing ceramic particles such as zirconia enable the formation of composite materials with outstanding ductility, high strength, and reasonably high energy absorption capacity. By combining the ceramics-derived extrusion route with powder metallurgical processing allows the generation of materials with various metal/ceramic-ratios and geometries at ambient temperature. The dried specimens are machinable and can be joined in multiple manners. The consolidation by pressureless sintering generates a highly stressable and failure tolerant composite material.