Syntactic metal foams -a special foam type consisting of a metal matrix with integrated hollow elements like micro glass bubbles -offer an interesting spectrum of properties, like low densities, high capacity for crash energy absorption, vibration dampening capacity, and pressure-tightness. [1,2] For low melting matrix alloys infiltration techniques can be used for production, whereas for higher melting alloys other techniques are needed. Iron-based (e.g., pure Fe, FeNi2, FeCu3) micro-porous syntactic foam components were produced by means of metal injection moulding (MIM) showing very good deformation energy absorption capabilities in compression but quite low fracture elongations in quasi-static tensile tests (<1%)). [3,4] Several reasons for this brittle behavior can be assumed: micro-cracks formed during cooling from sintering temperature due to the different thermal shrinkage behavior of matrix and glass spheres, insufficient bonding at the interface between iron matrix and hollow glass spheres or stress and strain concentrations in soft matrices near the hard glass spheres in the early stages of deformation which can cause premature failure of the test component.Therefore, experiments with Invar (FeNi36) alloy and S60HS micro hollow glass spheres were recently done in order to address two of the above-mentioned three points: Invar shows a considerably reduced thermal expansion reducing the risk of crack formation during cooling down from sintering temperature and has a higher strength in comparison to pure iron which might lead to a better adapted deformation of matrix and hollow spheres. Indeed, an enormous increase of tensile elongation could be observed, corroborating the initial assumptions. [5] Density values, deformation behavior, and metallographic sections of FeNi36-foams indicated a complex interplay of matrix powder particles and hollow glass spheres during sintering. Glass hollow spheres like 3M-S60HS are very soft at the sintering temperatures employed, they shrink and preserve their shape only because of the mechanical support of the adjacent metal powder particles. [5] Considering this interplay the present work's objective was to investigate the influence of the metal powder particle size on the resulting foam structure and mechanical behavior. The use of coarse powder is economically and ecologically advantageous especially for Ni. On the other hand fine powders improve sintering behavior and sphere shape stability.

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Metal hollow spheres (MHS) and metal hollow sphere structures are special types of cellular metals with an enormous application potential in structural and functional applications. A lot of effort has been made during the last two decades in order to develop the manufacturing process and to investigate the properties of this type of structure. Additional functionalizing of MHS is possible by filling the spheres with ceramic powders or phase change materials. Furthermore, by coating the spheres with different ceramic layers new properties and functions are added. Thus, the structures show excellent mechanical damping properties as well as high heat capacity for thermal storage and fast heat loading and unloading. Grinding or ceramic coating bring more functions to the surface of the spheres. The manufacture and properties of different types of functionalized MHS and their possible applications are highlighted here.

The ability to determine in situ mechanical properties of components would be of great value in monitoring the effect of processing condition excursions on service performance and for quality control. An approach to this problem based on testing small rectangular bars prepared directly from a component by water-jet cutting and subsequent grinding is presented. Impact resistance, tensile strength and transverse rupture strength values obtained from a PM synchroniser hub are consistent with those obtained for conventional tensile specimens, within the limits of experimental error. The specimen types are shown to have similar compositions and microstructures when processed under the same conditions. The new method has been applied to assess the effects of processing variations on the mechanical properties of a synchroniser hub.