Preparation And Thermal Stability Of Ni(-Mo)-P/Cu Alternate Multilayers

Amorphous alloys, especially amorphous nickel-base alloys, have very excellent physical and chemical properties as the anti-corrosion and non-magnetism. Multilayers also have many excellent properties such as anti-corrosion and magnetic reluctance.In this thesis, Ni-P/Cu and Ni-Mo-P/Cu alternate multilayers were electrodeposited using twin bath technique. Ni-P and Ni-Mo-P alloys were electrodeposited in ammoniac citrate electrolyte and copper layer in acidic sulphate electrolyte, respectively.UV-Visible spectrum and infrared spectrum techniques were used to investigate the mechanism of the pre-electrolysis in the electrodeposition of Ni-Mo alloy. UV-Visible and infrared spectrum of the Ni-Mo alloy bath were detected to elucidate the variations in the pre-electrolysis. This change in the spectroscopy of Ni-Mo alloy bath was caused by the pre-electrolysis, in which new substances Mo(JV) from the reduction of Mo(VI) were formed. It may be the reason that the quality of Ni-Mo alloy was improved in the electrodeposition. So we can speculate that the molybdenum was electrodeposited in the multisteps, i.e., firstly Mo(VI) in the baths was electrochemically reduced to low valence molybdenum, which was reduced to molybdenum in the alloy successively. Just the low valence molybdenum from the pre-electrolysis promotes the electrodeposition of Ni-Mo alloy.The structures of Ni-P/Cu and Ni-Mo-P/Cu were investigated before and after the heat treatment by X-Ray Diffaclion (XRD). The structure of the Ni-P and Ni-Mo-P single films in the multilayers can be controlled to be amorphous. These amorphous alloys can be crystallized to Ni3P and Ni in the heat treatment process when up to a certain temperature.Also the textile of the copper films electrodeposited was investigated in acidic sulphate electrolyte. The copper electroplating filmes prefer to deposit to (220) crystal face when the current is in the moderate current density based on the stainless-steel substrates.Differential Scanning Calorimeter (DSC) was used to study the crystalization process of the amorphous alloys. The DSC experimental results showed that amorphous Ni-Mo-P/Cu and Ni-P/Cu alloys can be translated into the crystal under the temperature between 200癈 and 420 癈. The crystallization process of Ni-P and Ni-Mo-P films maybe take place in two steps. And Ni-Mo-P/Cu alternate multilayers have higher crystallization temperature, therefore have better thermostability than Ni-P films and Ni-P/Cu alternate multilayers. The crystallization activating energy, which was calculated using Kissinger method, was obviously influenced by phosphorus and molybdenum contents in the multilayers. The higher phosphorus or molybdenum contents in the multilayers, the higher crystallization temperature.The cross section and surface morphologies of the Ni-P/Cu and Ni-Mo-P/Cu multilayers were studied by Scanning Electron Microscopy (SEM). The conditions of electrodeposition affected the granularity of the alloys obviously. The surface fabric of the multilayers are depended mainly on molybdenum and not on phosphorus contents in the electrolyte. High molybdenum content in Ni-Mo-P film will result in high internal stress and more irregular microcracks on the surface of the Ni-Mo-P films.