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The paper shows an adaptation of thermoanalytical techniques such as Differential Scanning Calorimetry (DSC) for the investigation of interfacial phase formation during corrosion of stainless steel 316L (FeCr18Ni10Mo3)- and 16-7-3 (FeCr16Mn7Ni3)-based composites with TiO2 and ZrO2 in molten aluminium alloy (AlSi7Mg0.3). The DSC was able to detect the formation of corrosion phases on cooling after two hours of retention at 850 °C. The method allows the recognition of the solidification temperature of new corrosion phases (binary η-AlFe and ternary τ3, τ5, τ5, τ11-AlFeSi) as well as the assessment of the conversion rate of both materials. Scanning Electron Microscopy (SEM) was used for the analysis of the corrosion products.

Metal-Matrix-Composites (MMCs) based on steel with certain ceramic additions offer a wide range of applications in automotive, construction, and mechanical engineering. These MMCs combine the specific properties of steels such as their room temperature deformation behavior with the advantageous hard but brittle ceramic reinforcements which makes them favorable in crash-absorbing or strengthening components. However, common technologies such as casting or infiltration of ceramic preforms by metal melts suffer from the differences between metal and ceramic material characteristics involved during material processing and from geometrical restrictions. The adaption of the ceramics-derived extrusion technology at ambient temperature on materials established in the powder metallurgy (PM) enables an efficient manufacturing process of advanced fine-grained materials with particularly cellular (lightweight) structures as well as bulk specimens. Using powder raw materials enables a wide range of material combinations between TRIP/TWIP steels and various ceramic components considering the pronounced material characteristics of the composite. Knowing the influence of the raw materials, the processing parameters for shaping and the indispensable thermal processing transforming the formed powders into a solid material is crucial for proper manufacturing of MMCs with tailored characteristics. The joining process for these components extends the applicability of the investigated PM-MMCs.

This study investigates the preparation of samples with equimolar parts of silica and silicon nitride and the subsequent reaction synthesis of silicon oxynitride. The influence of the raw material and the processing parameters on the conversion yield was analyzed. In detail, the effects of the silica crystallinity and of the grain size of the silicon nitride were investigated. Furthermore, the reaction synthesis was activated by magnesium hydroxide or calcium hydroxide. The samples were prepared by slip casting in plaster molds. Firstly, the optimal dispersant type, a synthetic polyelectrolyte, was determined. For the batches with the finer silicon nitride the measured optimal amount was 0.6 wt%. For the batches with the coarser silicon nitride it was 0.18 wt%. From the cast and demolded samples, broken pieces were fired at 1550 °C for 1, 8 or 15 h in nitrogen atmosphere. The conversion yield of silicon oxynitride was analyzed by quantitative X-ray diffraction. The fraction of silicon oxynitride increased with extended holding time at the sintering temperature, by the use of fine silicon nitride, and by the addition of magnesium hydroxide as sintering additive. The silica crystallinity had no statistically significant effect. The obtained maximum conversion yield was 92 wt%.

Metallic cellular materials are characterized by a low specific weight and a high energy absorption capability, which make them promising for application in devices of the transportation industry in order to meet the requirements of a reduced fuel consumption and carbon dioxide output. This intention necessitates the evaluation of material performance under several load conditions. Investigations have shown that the out-of-plane properties with regard to specific energy absorption (SEA) capability of high-density steel honeycomb structures with square-celled profile are outstanding while the potential under in-plane conditions is distinctly lower. Therefore, FEM-based numerical analyses are conducted by the use of ABAQUS-software to investigate the influence of cell geometry. The results reveal an enhancement of absorbable energy in in-plane direction by applying an ordered sequence of hexagons and triangles, the so-called Kagome geometry. Comparative quasi-static compression tests serve to verify the FE-analysis. The obtained results are discussed with respect to strength level and achieved SEA capability in dependence of the cell geometry and load condition.

The mechanical properties and the related microstructure of metal-matrix composites (MMC) based on a high-alloyed CrMnNi steel with varying particle reinforcements (5% or 10 vol%) of magnesia partially stabilized zirconia and/or aluminium titanate were investigated. The powder metallurgical processing comprised the cold extrusion and conventional solid-state sintering at 1350 °C. The mechanical properties were examined by quasi-static compressive and tensile loading tests at ambient temperature. The microstructure characteristics contributing to significant changes in strength and ductility and affecting the failure mechanisms during deformation were characterised by scanning electron microscopy including energy-dispersive X-ray spectroscopy and electron backscatter diffraction, and by X-ray diffraction. For all compositions the stress-strain and the deformation behaviour were mainly controlled by dislocation hardening and α ’-martensite formation in the steel matrix, but it was further improved by the particle strengthening of the ceramic reinforcement. Thus, the composite materials showed higher strength and work hardening than unreinforced steel specimens over a wide strain range. The pressureless sintering triggers several reactions at the metal/ceramic interface, which leads to pronounced destabilisation of the initial metastable zirconia particles with a lack of transformation toughening capability, and the formation of invalid olivine. These MMC suffer from early particle/matrix displacement and particle fracture under loading. A more positive effect of interfacial reactions was observed in the composites with addition of aluminium titanate. Here, the formation of a dense spinel structure and the reliable matrix/particle interface bonding during firing provides a significant particle strengthening effect. The combination of zirconia and aluminium titanate provides mechanical and microstructural benefits as well. Thus, aluminium titanate facilitates the consolidation of powder metallurgical processed steel-matrix MMCs via the conventional sintering for advanced load applications. The results of the study help to understand essential hardening mechanisms in composite materials and provide potential for future cellular MMC structures.

The mechanical behavior of a high density square celled composite honeycomb structure is examined with respect to the influence of different matrix materials and ceramic particle additions. For this purpose two high alloyed metastable austenitic CrMnNi-steels with varying Ni contents and reinforcements of 0, 5 and 10 vol.% magnesia partially stabilized zirconia (Mg-PSZ) were chosen as cell wall material to evaluate the contribution of the TRansformation Induced Plasticity (TRIP)- and TWinning Induced Plasticity (TWIP)-effect on the strength, deformation and damage characteristics of the honeycombs. Out-of-plane compression tests were conducted in the strain rate range of 0.001–180 s−1 and at temperatures of −60 °C and 20 °C having a great effect on the driving force and extent of both material effects. The results reveal a considerably higher strength level for the TRIP-assisted structures which can be improved by the addition of Mg-PSZ at certain deformation degrees whereas the TWIP-matrices are more damage-tolerant.

In this study, a novel metal matrix composite based on 60 vol% 316L stainless steel and 40 vol% MgO manufactured by powder metallurgy technology was developed. The corrosion resistance of the developed steel&ndash, MgO composite material against molten aluminum alloy AlSi7Mg0.3 was investigated by means of wettability tests and long-term crucible corrosion tests. The wettability tests were carried out using the sessile drop method with the capillary purification technique in a hot-stage microscope (HSM). Static corrosion tests were performed in molten aluminum alloy at 850 &deg, C for 168 h to evaluate the impact of pre-oxidation of the composite surface on the corrosion resistance. The pre-oxidation of steel&ndash, MgO composites was carried out at 850 and 1000 &deg, C for 24 h, based on preliminary investigations using thermogravimetry (TG) and dilatometry. The influence of the pre-oxidation on the composite structure, the corrosion resistance, and the phase formation at the interface between the steel&ndash, MgO composite and aluminum alloy was analyzed using SEM/EDS and XRD. The impact of the steel&ndash, MgO composite material on the composition of the aluminum alloy regarding the type, size, and quantity of the formed precipitations was investigated with the aid of ASPEX PSEM/AFA and SEM/EBSD. It was revealed that the pre-oxidation of the steel&ndash, MgO composite at 1000 &deg, C induced the formation of stable MgO-FeO solid solutions on its surface, leading to a significant increase of long-term corrosion resistance against the liquid aluminum alloy.

As the mechanical properties of honeycomb structures are influenced by several parameters, detailed analysis is necessary before their potential application in transportation industry components. Previous Finite Element Model (FEM)-based numerical analysis demonstrated that variation in cell geometry affects the achievable strength level and, thus, the energy absorption capability. According to this FEM study, the Kagome geometry – an ordered sequence of hexagons and triangles – exhibits properties that are particularly promising when compared to the square-celled structures investigated to date. When the load is applied parallel to the channel axis (the out-of-plane direction), the increment of strength is comparatively low, whereas in the in-plane direction (loading orthogonal to the channel axis), the dissipated specific energy can reach almost double that of the square-celled structure. In this study, the results of static and dynamic compression tests – performed in the out-of-plane and in-plane modes – are presented to examine the influence of strain rate and loading direction on the characteristic deformation stages of squarecelled and Kagome structures. Particular attention is paid to deformation induced martensite formation in the cell wall material, indicating the TRansformation Induced Plasticity (TRIP) effect as a function of applied cell geometry, strain rate and loading direction.

The mechanical and structural responses of high-density TRIP steel and TRIP-steel/zirconia composite honeycomb structures were studied under uniaxial compression in the out-of-plane loading direction over a wide range of strain rates. Their mechanical response, buckling, and failure mechanisms differ considerably from those of conventional thin-walled, low-density cellular structures. Following the linear-elastic regime and the yield limit of the bulk material, the high-density square honeycombs exhibited a uniform increase in compression stress over an extended range of (stable) plastic deformation. This plastic pre-buckling stage with axial crushing of cell walls correlates with the uniaxial compressive response of the bulk specimens tested. The dominating material effects were the pronounced strain hardening of the austenitic steel matrix accompanied by a strain-induced α’-martensite nucleation (TRIP effect) and the strengthening effect due to the zirconia particle reinforcement. The onset of critical plastic bifurcation was initiated at high compressive loads governed by local or global cell wall deflections. After exceeding the compressive peak stress (maximum loading limit), the honeycombs underwent either a continuous post-buckling mode with a folding collapse (lower relative density) or a symmetric extensional collapse mode of the entire frame (high relative density). The densification strain and the post-buckling or plateau stress were determined by the energy efficiency method. Apart from relative density, the crush resistance and deformability of the honeycombs were highly influenced by the microstructure and damage evolution in the cell walls as well as the bulk material’s strain-rate sensitivity. A significant increase in strain rate against quasi-static loading resulted in a measured enhancement of deformation temperature associated with material softening. As a consequence, the compressive peak stress and the plastic failure strain at the beginning of post-buckling showed an anomaly with respect to strain rate indicated by minimum values under medium loading-rate conditions. The development of the temperature gradient in the stable pre-buckling stage could be predicted well by a known constitutive model for quasi-adiabatic heating.

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.

Metal–matrix composites composed of an austenitic stainless steel and magnesia partially stabilized zirconia were prepared via a powder metallurgical processing route with the ceramics-derived extrusion at room temperature. Various combinations of the base materials with zirconia volume fractions of 0, 5, and 10% were joined by applying an aqueous paste which forms the joint during thermal processing. The materials were tested under tensile loading at room temperature. The addition of zirconia particles led to a considerable decrease of the plasticity and ultimate tensile strength of the basic compositions. However, the strength of joint specimens was not limited by the bonding strength of the joining zone. Among all material combinations tested, failure occurred in the joining partner with the higher zirconia volume fraction and not at the joint interface. Thus, the strength of sinter-joined materials based on MMC with 0–10 vol% was limited by the strength of the base materials. The advance of the present sinter-joining method is the single thermal operation of the composite materials. The formation of a homogeneous bonding zone and the absence of a heat-affected zone lead to negligible interference with the microstructure and the mechanical properties of the base materials.

Metal–matrix composites composed of an austenitic stainless steel and magnesia partially stabilized zirconia were investigated. Both components undergo a martensitic phase transformation on mechanical load leading to enhanced mechanical properties. In the present work composite materials with a volume fraction of 10% ceramic particles were prepared by using a powder metallurgical processing route. The composite materials showed improved strength during quasi-static compressive deformation at room temperature. The reinforcing mechanism based on the tetragonal to monoclinic phase transformation is affected by the amount of metastable zirconia and the metal/ceramic interface boundary. As a result of thermal treatment the steel/zirconia interface shows destabilization due to the diffusion of Mg out of the particles and the formation of precipitations. These particles with high amounts of non-transformable monoclinic zirconia are loosely embedded in the metal matrix. The addition of 1–3 vol% titanium leads to a significant decrease of zirconia destabilisation during sintering and the formation of an improved steel/zirconia interface. The material is characterised by quasi-static compressive load tests and microstructural analysis using SEM/EBSD. Both the relation of martensitic phase transformation in metal and ceramic as a function of the titanium content is shown.

Using X-ray diffraction and scanning electron microscopy two commercial Mg-PSZ ceramics were studied regarding their thermal stability at 1350 °C. The Mg-PSZ material was investigated in as-received, sintered, and powdered states. Drastic increasing of the m-ZrO2 content was observed for the as-received powders. Whereas the Mg-PSZ ceramics sintered at 1600 °C exhibit certainly better thermal stability. Two mechanisms of thermal destabilization were defined using observations of the sintered Mg-PSZ material. Influence of the particle size of Mg-PSZ on its thermal stability is defined.

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.

The interactions between microstructure evolution and mechanical properties of square-celled TRIP steel and particle-reinforced TRIP steel/zirconia honeycombs are investigated over a wide range of test temperatures. Based on a powder metallurgical route of a ceramic extrusion technology, two-dimensional channeled structures are made of an austenitic AISI 304 CrNi-steel or a TRIP steel matrix composite with up to 10 vol.% of a MgO partially stabilized zirconia (Mg-PSZ) ceramic. Honeycomb specimens with a cell frame of 196 cpsi and a relative density of 0.37 (viz. 2.9 g cm−3) are tested under quasi-static compression in out-of-plane loading direction at temperatures between -196 °C and 150 °C. During compression, the cellular materials deform in a strain-dominated buckling mode initiating a plastic hinge formation in the cell walls at higher strain levels. Their crush resistance is intensively controlled by the material design including the plastic yield and strengthening mechanisms of the TRIP steel matrix and the constraint or particle reinforcement effects of the embedded zirconia ceramic. Since the thermodynamic driving force for the α′-martensite nucleation and the intrinsic stacking fault energy are strongly influenced by temperature, different material strengthening and softening processes and a varied microstructure evolution are detected. A sigmoidal initial stress-strain response as well as the highest compression stress are measured at test temperatures below room temperature due to a pronounced α′-martensite volume fraction. However, at higher test temperatures, mechanical twinning and dislocation glide are the dominant deformation mechanisms. In summary, strength, ductility and energy absorption which identify the crashworthiness of the honeycombs, are significantly affected by the temperature-sensitive macro- and microstructure phenomena.

Particle reinforced metal matrix composites (MMCs) based on high-alloyed CrMnNi steels and partially stabilized zirconia (Mg-PSZ) are produced using the hot pressing technique. The resulting materials differ in the chemical composition of the high-alloyed steel matrix and volume fraction of Mg-PSZ. The change of chemical composition has a substantial influence on the austenite stability and stacking fault energy, triggering different deformation mechanisms in terms of the deformation-induced transformation of austenite into ϵ- and/or α′-martensite and/or deformation-induced twinning. MMCs with 5 and 10 vol% Mg-PSZ as well as unreinforced steels are investigated in total strain controlled fatigue tests. The focus of this work is to clarify the effect of the matrix strength and Mg-PSZ volume fraction on the cyclic deformation behavior. This includes the discussion of cyclic hardening and/or softening during fatigue tests, consequences on the fatigue life times and deformation-induced microstructures.

In this study, the low-cycle fatigue (LCF) behavior of powder metallurgy stainless steel/MgO partially stabilized zirconia (Mg-PSZ) composite materials is presented. The steel matrix based on conventional AISI 304 steel (1.4301) is reinforced with Mg-PSZ. The investigated composite materials were manufactured using the spark plasma sintering (SPS) technique. Total strain-controlled LCF tests were performed on materials containing 0, 5, and 10 vol% Mg-PSZ, respectively, in order to evaluate the influence of the ceramic reinforcement. Electron backscatter diffraction (EBSD) measurements were applied to identify the locations where the martensitic phase transformations in the steel matrix and stress-assisted as well as athermal martensitic phase transformations of the Mg-PSZ ceramic reinforcement take place. The resulting cyclic deformation behavior is correlated with the microstructural features of the composite material.

The mechanical and structural response of powder metallurgical square-celled honeycomb structures to quasi-static and dynamic impact loads are described. By constructing the cellular lattice with a novel metal matrix composite material based on a metastable high-alloyed austenitic TRIP-steel particle-reinforced by magnesia partially stabilized zirconia (Mg-PSZ), high specific yield and ultimate collapse strengths as well as a high ductility and an enhanced specific energy absorption were gained. In order to prove the temperature sensitivity of the honeycomb structures, a selected low-reinforced composite condition was investigated in a pre-series of quasi-static compression tests at temperatures in the range between −190 and 150°C. The present study shows that the deformation mechanisms of the TRIP-matrix composite honeycomb structures can be classified with respect to strain rate and deformation temperature, including the failure characteristics and the strain-induced α′-martensite transformation in the austenitic steel matrices ensuring the TRIP effect. The evolution of the α′-martensite phase content in the central crush zone of the TRIP steel and TRIP-Matrix Composite honeycombs is demonstrated based on the results of magnetic balance measurements.

A metal matrix composite (MMC) consisting of AISI 304 austenitic stainless steel with up to 10 vol.-% MgO-PSZ was produced by a powder metallurgic process through sintering at 1300 °C and 1390 °C. The hot working of sintered samples was conducted between 900 °C and 1100 °C. The behaviour of softening kinetics was investigated using flow curve recording methods (dynamic softening) and the double-hit method (static softening). The influence of the deformation parameters such as temperature, strain rate, inter-pass time and relative density of the samples was determined. The microstructure development of the sintered composite after hot forming was determined by optical microscopy and SEM and was interpreted with the help of qualitative microstructure analysis. The results show a general acceleration of softening processes with increasing temperature and strain rate, with the addition of ZrO2 particles and a decrease in the density of composite materials. A mathematical-physical model was developed to predict the softening behaviour and optimize the forming processes of the composite in the light of these results.

Composite materials have been in focus of scientific studies since decades. Metal-matrix composites have received extensive attention in the last years. The combination of a metastable austenitic TRIP-steel with magnesia partially stabilized zirconia is presented in this study. The stress induced martensitic phase transformation in both components leads to advantageous mechanical behavior. Raised compression strength as well as increased specific energy absorption on plastic deformation offers a range of structural and crash-absorption applications. Samples with zirconia additions are reinforced by volume increase during tetragonal-monoclinic phase transformation at compressive strains below 35%. The microstructure and phase evolution of partially stabilized zirconia as well as steel has been investigated by EBSD with purpose to correlate mechanical properties with phase evolution.

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.

A pure TRIP-steel alloy and a novel zirconia reinforced TRIP-steel matrix composite were implemented in a 2D square-celled honeycomb structure fabricated by a paste extrusion method, respectively. In terms of a series of compression tests in out-of-plane loading direction the buckling and the pronounced strain hardening behavior of the honeycomb structures are described with regard to different material compositions and varied nominal strain rates. Both the compressive flow behavior and the microstructure evolution in the crushed zones are controlled by the rate of formation of strain-induced martensite and the ceramic particle/steel matrix interactions. The insertion of magnesia partially-stabilized zirconia (Mg-PSZ) particles in the austenitic steel matrix cause an increased yield strength and higher compression stresses up to certain deformations degrees. The limited ductility of the composite materials is a consequence of the rearrangement and fracture of zirconia particles initiating cracks and shear bands during deformation. Consistently, the visible strain rate effects on the mechanical responses of the honeycomb structures are similar to AISI 304L austenitic stainless steel specimens in the form of compact rods. However, at high local strain rates generated in drop weight impact tests a micro-inertia factor support the failure behavior of the cellular structures.

Composite materials are up-to-date products in a growing range of applications and markets. Due to the advantageous combination of two or more materials new generations of materials can be generated. Closely linked to expanding variations of material combinations are increasing numbers of manufacturing techniques. The combination of ductile metals with hard and brittle ceramics offers a range of applications in the field of crash-absorber and structural products with high mechanical load. This paper deals with the challenges of powder metallurgical processing of TRIP-steel/Mg-PSZ composite materials. The presented results are a contribution to improvements in plastic processing especially for lightweight honeycomb structures.

Ceramic-steel compound materials are used in a wide range of applications up to date. Major advantages are the mechanical properties due to the combination of brittle ceramic with tough steel. This study deals with effects of the sintering process on austenitic TRIP-steel/Mg-PSZ composite materials for mechanical load applications. Both, the Fe-Cr-Ni-steel and partially stabilized zirconia offer their special mechanical behavior only in a metastable state. The ability of phase transformation depends mainly on the chemical composition. Mutual interactions of the alloying metals (Cr, Ni, Mn, and Fe) and the ceramic stabilizer (MgO) during sintering may prevent the martensitic phase transformation. This may cause disadvantageous mechanical behavior on mechanical load in use.

This research work presents the fatigue behaviour of a high-alloyed austenitic TWIP steel as well as metal matrix composites based on this steel grade as matrix material and MgO partially stabilized zirconia (Mg-PSZ) as reinforcing phase. The specimens were produced using the hot pressing technique. The unreinforced steel and MMCs containing 5 and 10 vol.% Mg-PSZ were investigated under total strain control in order to clarify the influence of the ceramic reinforcement. The cyclic deformation behaviour in terms of cyclic softening and/or cyclic hardening as well as fatigue lives of the different materials are discussed. Microstructures were examined to study the deformation and dislocation structures as well as phase transformations using electron channelling contrast imaging (ECCI) and electron backscatter diffraction (EBSD), respectively.

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.

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.

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.

Two designs of square-celled metallic honeycomb structures fabricated by a modified extrusion technology based on a powder feedstock were investigated. The strength and ductility of these cellular materials are achieved by an austenitic CrNi (AISI 304) steel matrix particle reinforced by an MgO partially-stabilized zirconia building up their cell wall microstructure. Similar to the mechanical behaviour of the bulk materials, the strengthening mechanism and the martensitic phase transformations in the cell walls are affected by the deformation temperature and the nominal strain rate. The microstructure evolution during quasi-static and dynamic impact compression up to high strain rates of 10 3 1/s influences the buckling and failure behaviour of the honeycomb structures. In contrast to bending-dominated quasi-isotropic networks like open-celled metal foams, axial compressive loading to the honeycomb’s channels causes membrane stretching as well as crushing of the vertical cell node elements and cell walls. The presented honeycomb materials differ geometrically in their cell wall thickness-to-cell size-ratio. Therefore, the failure behaviour is predominantly controlled by global buckling and torsional-flexural buckling, respectively, accompanied by plastic matrix flow and strengthening of the cell wall microstructure.