Processing Study On Microelectroforming Of Metallic Microparts

Microelectroforming provides a set of high-precision and low-cost methods for fabricating complex-shaped and nanocrystalline metallic microparts.However,there are several disadvantages for traditional molds.The preparation of traditional molds is complicated and expensive,furthermore,these molds are available for only one-time use,which seriously limit the wide applications of microelectroforming.One of the key issues in the development of microelectroforming is the preparation of new microelectroforming molds.In this thesis,two different types of conductive polydimethylsiloxane?PDMS?molds are developed for microelectroforming.One is PDMS molds coated with Au;the other is Ag-PDMS composite molds.All the molds are replicated from microstructured masters by soft lithography.Finally,microparts of Ni,Ni-Fe alloy,and Ni Fe-Al₂O₃ composite are prepared by microelectroforming.The structural integrity,growth of layers,phase compositions and mechanical properties of the microparts are investigated.The main fingdings are listed as follows:?1?Ni micro gears of a diameter of 3.60 mm and a thickness of 0.18 mm are prepared using two different molds:one is composed of a PDMS mold wh ich is adhered onto a graphite substrate,the other one is a PDMS mold coated with Au.The results show that Ni micro gears can not be prepared completely in the former mold,however,this mold can produce freestanding Ni microparts.The PDMS mold which is adhered onto a graphite substrate is suitable for microelectroforming of micro-patterns.Micro gears of high integrity can be fabricated by using the Au-coated PDMS mold,but it requires subsequent polishing to remove the residual PDMS and gold coatings adhering to the surface of the Ni micro gear.The Au-coated PDMS mold is suitable for microelectroforming of three-dimensional microparts.Both the micro gears have similar grain sizes,howerver,the micro gear prepared in the Au-coated PDMS mold has smaller residual stress.?2?Micro Ag particles are uniformly dispersed as the conductive filler in the PDMS matrix,and then Ag-PDMS composite molds with lateral feature sizes?160?m?are fabricated by soft lithography.Freestanding Ni microchannel parts with high density and microhardness can be prepared using the Ag-PDMS composite molds.The Ag-PDMS composite molds have good elasticity and mechanical properties,which make demolding easy.The Ag-PDMS composite molds can be reused many times,however,the conductivity of the surface of them gradually deteriorates as the micro Ag particles are pulled out during the demolding process,resulting in unsuccessful microelectroforming.?3?Ni-Fe alloy and Ni Fe-Al₂O₃ composite microchannel parts with high density and microhardness are prepared using Ag-PDMS composite molds by adjusting the formula of electroforming solution s.Compared with Ni microchannel parts,the solid solution strengthening of Fe atom can improve the microhardness of the Ni-Fe alloy microchannel parts.The addition of Al ₂O₃ particles to the Ni-Fe alloy can improve the density and microhardness of the Ni Fe-Al₂O₃ composite microchannel parts.