REDUCTION EXPANSION SYNTHESIS OF SINTERED METAL
Rydalch, Wilson L.
Luhrs, Claudia C.
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In this work we demonstrate that the unique Reduction Expansion Synthesis-Sintered Metal (RES-SM) technique can be employed to create sintered nickel and iron bodies at hundreds of degrees below their melting temperature. The first process step is “activating” the metal powder in a bath of hydrogen peroxide. In the second step activated metal powder is mixed with the corresponding metal oxide powder. The mixed powder is used to fill a 3D-printed plastic mold. Next, the oxidized metal powder and the metal oxide powder are reduced through the chemical process that takes place with the exposure of the decomposition of urea. The thermal decomposition of urea produces radical species that reduce the metal particles. Optimal results were achieved by heating the powder shapes to 900 degrees Celsius for 1200 seconds in an inert atmosphere with nitrogen gas flowing. Inspection using scanning electron microscopy revealed that the metals samples were held together by necking in between the metal particles. X-ray powder diffraction confirmed that the RES-SM technique produced a completely reduced metal sample. The samples produced in the study are completely self-supporting, but they are similar to metal parts that require post-processing to fully densify, also known as “green” metal parts. Green metal parts are generally understood to not be as hard, dense, or ductile as metal parts. However, the post-processing procedures for green metal parts are widely understood, and can be applied.
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