Development of High-strength Nanocrystalline Ni-W Electrodeposited Alloys and Their Plastic Deformation

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Electrodeposition is a superior technique for producing nanocrystalline materials having grain sizes anywhere from the essentially amorphous to nanocrystalline materials for the grain sizes of about 5-50 nm in bulk form or as coatings with no post-processing requirements. In this paper, we show the nanocrystalline Ni-W alloys having both high hardness and high ductility can be produced by electrodeposition. Especially, the high-strength nanocrystalline Ni-W alloys containing about 12.3 at.% W and 20.7 at.% W with average grain sizes of about 5 nm have been obtained : their tensile strengths were attained to about 1400 MPa and 2300 MPa, respectively.On the other band, the nanocrystalline Ni-W alloys were severely embrittled during annealing treatments. After annealing at 200 ℃, the ductile-brittle transition temperature(DBTT) increased rapidly up to about 100 ℃ at the initial period of annealing and then increased gradually with increasing the annealing time. After annealing at 180 ℃ and below, the DBTT saturated below the room temperature. By using the mold clamping techniques, the forming behaviour of the alloys with their slight grain growth during annealing at the temperature of 180 ℃ and below has been observed So, we propose 3-dimensional high precision forming processing in micrometer-size range of the nanocrystalline Ni-W alloys by combining the UV-lithographic technologies and the mold clamping ones. Formation of microduplex structures consisting of the nanocrystalline Ni-W alloy and ductile metallic phase can be possible by using the UV-lithographic techniques. Tensile strength at fracture was increased up to about 20% with forming the microduplex structures.