Metal injection molding of shape memory alloys using prealloyed NiTi powders

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Metal injection molding (MIM) was applied for the production of shape memory parts using prealloyed NiTi powders with different Ni contents as starting materials. The MIM process allows the production of near-net-shape components without the occurrence of rapid tool wear as found in the case of conventional machining operations. With optimized manufacturing conditions, including feedstock preparation, injection parameters and sintering conditions, densities of more than 98% of the theoretical value could be achieved. Determination of the phase transformation behavior, as a basic requirement for the shape memory effect, was done by differential scanning calorimetry (DSC). In a first approach, tensile tests in the austenitic state showed pseudoelastic behavior. An elongation at failure of 3.8% was found. For martensite, up to 5% was obtained. Reasons for the lower strain compared to melted NiTi alloys are discussed. For martensitic samples the one-way shape memory effect (1WE) was demonstrated.

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