biermann@ww.tu-freiberg.de Abstract. A novel steel-based composite material, composed of metastable austenitic stainless steel as matrix and up to 15 % zirconia as reinforcement, is processed by two powder metallurgy routes. The matrix exhibits the so-called TRIP-effect (TRIP: TRansformationInduced Plasticity) and shows a deformation-induced formation of martensite. Compression tests of rod samples processed by cold isostatic pressing show increased strength compared to the non-reinforced steel matrix up to 20 % strain. Three-point bending tests show, however, reduced ductility for high zirconia contents. Filigree honeycomb structures were produced by a novel extrusion technique with extraordinary high values of specific energy absorption. IntroductionMost Metal-Matrix-Composites (MMCs) have a light-metal matrix such as aluminum or magnesium. MMCs with a steel matrix, however, have not been examined very much up to now, although they may be possible candidates for use as high strength and wear resistant materials [1,2].The combination of a steel matrix which shows the TRIP effect (TRIP: Transformation-Induced Plasticity) with a metastable ZrO 2 -reinforcement also exhibiting a martensitic phase transformation was until now only investigated by the group of Guo et al. with regard to the mechanical properties. The studied composite was produced by the conventional powder metallurgical route and hot pressing [3][4][5]. Guo et al. thus created TRIP-steel matrix composites with reinforcements made of yttriapartially stabilized zirconia-particles (2Y-PSZ) and obtained an extraordinary high strength in high deformation rate compression experiments.In the present work results of a new collaborative research center with the title "TRIP-MatrixComposites -design of tough, transformation reinforced composite materials and structures on FeZrO 2 -basis" are presented. Samples of the steel-matrix composite materials were produced by coldisostatic pressing and a novel extrusion technique which is used conventionally in ceramic technology. First results of a variant of the family of composite materials to be developed were already presented in very recent papers [6][7][8].

Powder metallurgy is a widely used technology to produce metal and composite components, respectively. This technology has a high efficiency in terms of material and offers the possibility to produce materials which cannot be formed by conventional techniques. In the field of metal matrix composites, hard metals are well-known examples. Other metal matrix composite materials offer high strength, wear resistance, and/or stiffness values combined with significant ductility or toughness, respectively.Most composite materials are based on light metal matrices as aluminum or titanium. However, iron-based composites have drawn only limited attention until now. Nevertheless, some examples of steel-based composite materials are presented in literature with high wear resistance or strength, respectively. [1][2][3][4][5] In the last decade several scientists have investigated different composite materials and micro-and macrostructure designs according to their ''crashworthiness.'' [6,7] Crashworthiness is the absorption of mechanical energy through controlled failure mechanisms and modes that enable a defined load profile during energy absorption. The specific energy absorption (SEA) per unit mass, the SEA per unit volume as well as the interlaminar fracture toughness as a ratio of the fracture toughness parameter to the Young's modulus are expressions in terms of the crashworthiness.In the present study, a novel composite material is suggested, composed of a metastable austenitic stainless steel as matrix which shows the so-called transformation-induced plasticity (TRIP) effect. This TRIP effect yields high strain hardening and high ductility due to the deformation-induced formation of martensite. [8][9][10][11][12] As reinforcing phase, we suggest MgO partially stabilized zirconia (Mg-PSZ), which also shows a martensitic phase transformation from the tetragonal to the monoclinic crystal structure during deformation and/or temperature changes. [13][14][15] The transformation of Mg-PSZ provides a high shear and volume expansion, thus increasing the TRIP-effect of the steel.In terms of this work the ceramic extrusion technology, i.e., a plastic forming process at room temperature has been applied in order to produce cellular honeycomb structures based on MgO partially stabilized zirconia (Mg-PSZ) reinforced austenitic TRIP-steel matrix composites. [16,17] Compact COMMUNICATION Novel composites on basis of austenitic stainless TRIP-steel as matrix with reinforcements of Mg-PSZ are presented. Compact rods were produced by cold isostatic pressing and sintering, square honeycomb samples by the ceramic extrusion technique. The samples are characterized by optical and scanning electron microscopy before and after deformation, showing the microstructure and the deformationinduced martensite formation. The mechanical properties of samples with 5 vol% zirconia are superior compared to zirconia-free samples and composites with higher zirconia contents in terms of bending and compression tests. The honeycomb samples exhibit extraordin...