Preparation And Characterization Of Foamed Steel Used By Sacrificial Template Method

As a new type of materials with excellent performance and unique structure, metal foam is widely used in so many high-and-new technology field, such as aviation,aerospace, energy, machinery and chemical engineering. Porous material and its performance were attached great importance to the manufacture. Foamed steel with various densities provides us new opportunity in structural engineering.In this paper, iron powder as matrix material, choosing different contents of urea:cellulose acetate, dextrin and starch(including lotus root starch, wheat, potatoes, etc.)were used as a pore-forming agent additive. With the use of sacrificial template method and argon vacuum sintering, foamed steels of different porosities were obtained. After that, mercury intrusion method, differential thermal analysis, scanning electron microscopy, X-ray diffraction techniques and methods Archimedes' method of test samples were applied in analyzing to study whether mixing process is oxidation or not,as well as the phenomenon in sintering process. So preparation processes could be optimized, such as adjusting the temperature curve, choosing the best pore-forming agent, obtaining foamed steel which has uniform pore structure, excellent mechanical properties. Moreover, the compressive strength, flexural properties and hardness of formed steel samples prepared by different pore-forming agent can also were studied.Through the above analysis, the conclusions can be seen as follows:(1) By using sacrificial template method, comparing foamed steels with different pore-forming agent under the condition of 900~1200oC were prepared. It shows that the formed steels obtained at 1100oC and holding time 2h has the optimal performance by the observation of the apparent sample, phase composition and mechanical properties analysis.(2) Under the optimal condition and the same pore-forming agent content of 40% by volume, the samples with certain strength using by cellulose acetate and dextrin as pore-forming agent were obtained. Furthermore, the mechanical properties of samples using dextrin as pore-forming agent were better than the samples using cellulose acetate. The reason was that the sample prepared using dextrin as pore former had lower porosity. To be more detail, dextrin had spherical particle morphology and a lower volatilization temperature which made the volume shrinkage of the sample stronger than the sample use cellulose acetate as pore-forming agent in the sintering process.(3) Under the optimal condition, foamed steel samples were prepared by dextrin as pore former of 20%~40%, respectively. Samples prepared by pore-foaming agent content of 40% volume had the best compressive strength, flexural properties and hardness. And the sample had uniform pore structure,lower porosity and thicker pore walls under scanning electron microscope. When the pore-foaming agent content was high,the contact between Fe granule was insufficient and the granules had to diffuse the volume to sinter with each other,the volume of sample shrank more during this process, which resulted in a lower porosity sample.