tailieunhanh - The Materials Science of Coatings and Substrates Part 6

Tham khảo tài liệu 'the materials science of coatings and substrates part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 126 Electrodeposition to produce a variety of electrodeposited alloys. The burgeoning field of elecưodeposition of multilayer coatings by cyclic modulation of the cathodic current or potential during deposition 40 also offers promise for production of new superplastic alloys. Composition-modulated alloys CMA which have been produced by this process include Cu-Ni Ag-Pd Ni-NiP Cu-Zn and Cu-Co. At present no data on superplasticity of these alloys have been obtained however the room temperature tensile Sữength of CMA Ni-Cu alloys has been shown to exhibit values around three times that of nickel itself 41 . INFLUENCE OF IMPURITIES Elecưodeposited films contain various types of inclusions which typically originate from the following sources 1-deliberately added impurities . organic or organometallic additives addition agents 2-metallic or nonmetallic particles for composite coatings 3-intermediate cathodic products of complex metal ions 4-hydroxides or hydroxides of a depositing metal and 5-gas bubbles for example containing hydrogen 42 . Figure 10 provides a pictorial illusưation of these various types of inclusions. Much has been written on the influence of small amounts of inclusions on the appearance of deposits. However very little information is available on their influence on properties of deposits. The purpose of this section is to provide examples showing how small amounts of impurities can noticeably affect properties. With nickel low current density deposits have higher impurity contents and this can affect sữess and other properties. For example Table 4 shows that for nickel sulfamate solution hydrogen and sulfur contents are much higher for low cuưent density deposits 54 A m2 than for those produced at higher current densities 43 . Electrical resistance of electroformed nickel films shows a unique dependence on plating current density Figure 11 . Films deposited at a low cuưent density of 120 A m2 show considerably lower residual resistance than high .