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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.

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 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.

Patients suffering from high-risk myelodysplastic syndrome (MDS) or acute myelogenous leukemia (AML) secondary to MDS (sAML) are characterized by poor response to conventional cytotoxic chemotherapy. The purpose of our prospective single-center study was to examine the safety and efficacy of an allogeneic hematopoietic stem cell transplantation (HSCT) following a sequential conditioning regimen as first-line therapy for previously untreated patients with high-risk MDS or sAML. Between November 2003 and June 2010, 30 patients (20 high-risk MDS, 10 sAML) received fludarabine (4 × 30 mg/m(2)), amsacrine (4 × 100 mg/m(2)), and Ara-C (4 × 2 g/m(2), FLAMSA). After 2 to 3 days of rest, patients received high-dose melphalan alone (200 mg/m(2) for patients with an age50 years, 150 mg/m(2) for patients with an age between 50 and 60 years, and 100 mg/m(2) for patients with an age60 years; n = 24) or melphalan and thiotepa (10 mg/kg, Mel/Thio, n = 6). Following these high-dose conditioning regimens, a median number of 7.7 × 10(6) CD34(+) cells/kg body weight (range: 2.9 × 10(6)-17.2 × 10(6)) were transplanted from 13 related or 17 unrelated donors. Antithymocyte globulin (Fresenius 30-60 mg/kg) as well as tacrolimus and mycophenolate mofetil were used for graft-versus-host disease (GVHD) prophylaxis. All patients except 1 with primary graft failure achieved complete remission after HSCT. After a median follow-up time of 28 months (range: 7-81), 21 patients (70%) were alive and free of disease. Overall, 4 patients relapsed. At 2 years, overall survival, event-free survival, and treatment-related mortality were 70%, 63%, and 30%, respectively. Because of undue toxicity, thiotepa is no longer part of the conditioning regimen. Our results add to the body of evidence that a FLAMSA-based sequential conditioning therapy is effective for previously untreated patients with high-risk MDS or sAML.