Influence of Powder Size on Production Parameters and Properties of Syntactic Invar Foams Produced by Means of Metal Powder Injection Moulding

Abstract

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.

Production and Properties of 316L Stainless Steel Cellular Materials and Syntactic Foams

“…For the latter, liquid metal processes have recently been reported, but usually powder metallurgy (PM) techniques are employed to limit processing temperatures. As porosity‐inducing particles, glass microspheres or ceramic macro‐ and microspheres are used . A special variant are all‐steel syntactic foams based on metallic hollow spheres and produced powder metallurgically, too.…”

“…Experimental procedures closely follow the approach previously laid down by Weise et al, though with adapted process parameters reflecting the requirements of the new matrix. 5 µm 316L‐powder acquired from Sandvik Osprey was mixed with 50 vol% binder in a 400 mL Brabender mixer at 120°C.…”

Compressive behaviour of aluminium matrix syntactic foams reinforced by iron hollow spheres

“…In particular, the strain-rate sensitivity response at three different strain rate levels was studied by taking into account the influence of type and volume fraction of glass spheres. The materials' behaviour was found to be very similar to that of the metal matrix [2,[6][7][8]. Castro and Nutt produced steel based MMSFs, filled with ceramic hollow spheres by gravity fed and mechanical pressure infiltration.…”

“…MMSFs were developed for lightweight structures, requiring high strength and energy absorbing capacity [1]. The matrix material is usually an aluminium alloy (light and low cost), but nowadays high strength iron based matrices are also investigated [2][3][4][5][6][7][8][9][10][11]. As filler material, commercially available mixed-oxide ceramic [12][13][14][15], metallic [12] or SiC [16,17] hollow spheres are frequently applied, however Taherishargh et al have been made efforts for the application of low cost perlite filler as well [18][19][20].…”

Metallic Foams

“…11) [64,65]. It was found that the compression stress-strain curve has a pronounced plateau regime; the plateau stress and plateau length depend on the added amount of glass hollow spheres.…”