To obtain stronger metal foams, a heat treatment was done to strengthen the matrix of the foams. A powder of SUS440C stainless steel, the strongest of all stainless steels, was used as the starting material.The green foams of the SUS440C steel powders with various porosities made by vacuum process using slurry were debound at 450°C and sintered at 1200°C in H 2 into SUS440C steel foams. Some of the foams were heat treated under a specified condition. The compressive test was done on both the heat treated and non heat treated specimens.Non heat treated SUS440C steel foams, even at a porosity as low as 53, showed plateau regions with a stress of 168 MPa and a strain of 60. These results suggest that these foams have potential for use as a good shock absorber. On the other hand, the plateau stress of the heat treated SUS440C steel foams were twice as high as the non heat treated foams. The two heat treated SUS440C steel foams, having densities of 2.7 and 4.5 g/cm 3 , showed almost the same yield stress as the wrought Al and Ti alloys, respectively. This demonstrates that the SUS440C steel foams could be inexpensive alternatives for those alloys. The maximum weight lightening achieved with the SUS440C steel by making porosity inside was one third of the guideline of the minimum weight design.

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In order to fabricate the NiTi foams with greater than 80% porosity, a vacuum process applied to a slurry was developed. A mixture of elemental Ni and Ti powders was dipped into a solution of 7.5 mass% polyvinyl alcohol, and stirred to make the slurry. The lightly compacted lumps of slurry were then subjected to reduced atmospheric pressure to make foamed compacts. The green foams were debound and sintered under vacuum into NiTi sintered foams with 85% porosity. X-ray analysis showed alloying of NiTi was completed by the sintering at =1100 C. X-ray diffraction analysis and DSC measurement also indicated that the NiTi foams consisted of B2 austenite and B19 0 martensite phases. Measurement of shape recovery strain showed the NiTi foams obtained by this process had the far excellent shape recovery characteristics compared with those of wrought NiTi alloys. Furthermore, repeated compressive deformation and heating greatly increased the shape recovery strains of these high-porosity NiTi foams.

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