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Increasing requirements on coating properties results in trends to develop new system, the most important of which is a multilayer coating. Multilayer coating can solve simultaneously very different requirements that the coating can meet at both the substrate/coating interface and the upper functional layer of the coating. Ti/TiN multilayer coatings were deposited on a silicon (100) by rf magnetron sputtering, using multi S-guns. Under the condition in which the total thickness kept 150 nm, the numbers of layers were changed from 4 to 40. Mechanical properties of a film were improved by straining and preferable crystalline orientation. Energy evolved in the coating during its growth can dissipate, and this may decrease internal stresses in the coating, improve its resistance to mechanical loadings, and prevent breaking of the coating. A mechanism of improving mechanical properties with increase of a layer number was discussed based on various analyses and measurements-that is, auger electron spectroscopy, x ray diffraction, nano-indenting test, scratch test and atomic force microscopy. Suppose that the overall energy Whkl of multilayer film with constant overall thickness is the sum of the surface or interface energy Shkl and strain energy Uhkl (Whkl=Shkl+nUhkl where n is layer number), the preferred orientation of the film grown by physical vapor deposition is decided by the lowest conditions Whkl resulting from a critical competition between Shkl and Uhkl. Therefore a film should exhibit preferred orientation of the lowest Uhkl at small n but exhibit that of the lowest Shkl at large n. The preferred orientation is predicted to change from (111) to (100) with increase of layer number because S (100) U (111). XRD gives expected result. Relative strengths σ/τ along 100 and 111 can be estimated for the slip system of TiN, 100 by using Schmid's law.
Mori et al. (Sat,) studied this question.