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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.

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.

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.

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.

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.

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.

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.