Fundamental Research On Rapid Prototyping Nanocrystalline Copper Oriented By Jet Electroforming

Rapid prototyping and nanometer-structure materials are important contents of current manufacture and material research fields. Rapid manufacturing of metal parts has become the research hot spots in the field of rapid prototyping, and it is also the one of extreme goals of rapid prototyping. The method of fabricating dimensional bulk nanocrystalline materials with high quality is one of the key technologies. Electroforming is a precision manufacturing technology in which a part is produced by the deposition of metal ions onto a pre-shaped cathode mandrel. The cathode limit current density and the deposition speed can be greatly increased, and the deposit grain sizes can be greatly refined in jet electroforming. In this paper, a new method, in which jet electroforming and rapid prototyping are integrated, is developed to fabricate metal parts directly. The fundamental experimental researches of preparing bulk nanocystalline coppers and copper parts are carried out. The major conclusions got in this dissertation are presented as follows: (1) The main factors that effect on electroforming speed are analyzed basing on the electro-deposition theory, the methods which can increase electroforming speed and refine deposit grain sizes are concluded. Based on the flow-field and electro-field of jet electroforming, the probability of rapid prototyping oriented by jet electroforming is analyzed. (2) A new technology, namely rapid prototyping oriented by jet electroforming, is brought forward, with which metal parts can be formed directly and rapidly. The device system and a pulse power are developed successfully. (3) The effects of direct current, pulse current, thiourea and nano-Al2O3 particles on the surface morphology of the copper deposits are researched systematically. The results show that fine grains and level surface of the deposits can be got by increasing electrolyte flow velocity and scanning speed of nozzle at the same current density. Using pulse current, and adding thiourea and nano-Al2O3 grains into the electrolyte are benefit for getting level deposit surfaces, and among them, the role of thiourea is the best one. (4) Nanocrystalline coppers with grain sizes in 30~80nm regime have been made in a wide rang of current density by different methods. The scanning speed of nozzle has a great effect on the pore structure of copper deposits. Using pulse current, and adding thiourea and nano-Al2O3 grains into the electrolyte can play a role in refining the grain sizes and improving the density of the copper deposits, and the role of thiourea is the best one among them, thiourea can also restrain the formation of dendrite at high current density in the course of deposition. (5) Mechanical properties of the nanocrystalline coppers fabricated by different methods are measured. The results show that the processing ways of preparing nanocrystalline coppers have great effects on the properties of the copper deposits. The coppers fabricated by direct current and composite methods have good ductilities, the elongation of the best one reaching to 17%, and no strain hardening occurs in the ductility deformation stage, the copper deposits made by using pulse current and thiourea have higher strength and micro-hardness, the maximum tensile strength of the nanocrystalline copper is about twice the one of the cold-rolled copper. The relative weight loss of nanocrystalline copper as a electode is smaller than the one of coarse-crystalline copper. (6) Electroforming speed, spot precision, thickness contribution in the deposit spots and their effects on the parts' precision are studied. A group of nanocrystalline copper parts with good shapes and size precision, and bulk nanocrystalline coppers with the thickness in 1.1~2.0mm regime are manufactured by the rapid prototyping device.