Volume 92, Issue 10

The applicability of combinatorial methods in developing advanced materials is illustrated presenting four examples for the deposition and characterization of one- and two-dimensionally laterally graded coatings, which were deposited by means of (reactive) magnetron sputtering and plasma- enhanced chemical vapor deposition. To emphasize the advantages of combinatorial approaches, metastable hard coatings like (Ti,Al)N and (Ti,Al,Hf)N respectively, as well as Ge–Sb–Te based films for rewritable optical data storage were investigated with respect to the relations between structure, composition, and the desired materials properties.

Es werden systematische Untersuchungen zur Abscheidung von Siliziumcarbid und Siliziumcarbid mit koabgeschiedenem Silizium auf Kohlenstoffsubstraten vorgestellt. Die Abscheidung erfolgt mittels thermischer CVD (chemical vapor deposition) in einer CH 3 SiCl 3 –H 2 –Ar-Atmosphäre. Dabei können neue Zusammenhänge zwischen den Schichteigenschaften, wie chemische Zusammensetzung und Struktur, und den Beschichtungsparametern abgeleitet werden. In einem zweiten Schritt wird das koabgeschiedene Silizium durch eine thermische Nitridierung in Siliziumnitrid umgewandelt. Dabei reagiert auch die Siliziumcarbidschicht zu Siliziumnitrid. Über den Umweg des Titan-Ein-baus in das SiC(Si)-System – bei Beschichtungstemperatur bilden sich Titaniumsilizide – wird eine Mischschicht angeboten, die das koabgeschiedene Silizium selektiv in Siliziumnitrid umwandelt.

LaNi 5 films were deposited on a nickel substrate using a La 2 Ni 7 alloy target with a sputtering power, W S , of 50– 400 W at substrate temperature, T S , of 323–573 K by a radio frequency magnetron sputtering apparatus. The nickel content of the films decreased with increasing W S and increased with increasing T S . At low W S and low T S , amorphous films were deposited. In other conditions, the films were polycrystalline. The films deposited at high W S and low T S exhibited only a ( hk · 0) peak in the X-ray diffraction profiles. This indicates that the c-axis of crystalline films was oriented parallel to the substrate plane. At high W S and high T S , the films with columnar structure were obtained. The hydrogen absorption capacity of the films increased with increasing W S . On the other hand, the equilibrium pressure of the films decreased with increasing W S . The films deposited at 400 W represented a pressure plateau on the pressure –composition isotherms.

Chemical vapor deposition (CVD) is an important method to produce thin films on various substrate materials. Most work concentrates on the quality of the resulting materials and on the surface chemistry, while gas phase chemistry is often overlooked. The present article discusses the role of gas phase chemistry for CVD processes at high growth rates by analysing two deposition systems. In silicon CVD, the gas phase reactions reduce the growth rate, while diamond CVD is impossible without gas phase activation prior to deposition. In both cases, a fundamental knowledge of these gas phase processes assists in obtaining high growth rates and in optimizing the CVD process.

The application of thermodynamic calculation methods to the prediction of ranges of composition of metastable coating structures formed in PVD processes is described. Particular attention is given to available methods for obtaining the stable-to-metastable structural transformation energies necessary to carry out the calculations. Using these methods in combination with experimental calorimetric data, calculations have been carried out with respect to (Ti, Al) N coatings with the hexagonal wurtzite and cubic NaCl structures. Comparison of the predicted ranges of these two structures is also made for a number of other (Me, Al) N systems, where Me is a transition metal.

Based on some original thoughts by J.W. Gibbs, a refined method for the introduction of kinetic controls into complex equilibrium calculations has been devised. The new method avoids problems affecting the entropy of mixing in solution phases that originate from the use of simple image components which have been applied earlier. The method is explained in detail and successful applications are discussed.

Two approaches are presented by which the thermochemical properties of multicomponent oxide melts can be modeled and estimated at an accuracy well sufficient for the treatment of industrial processes. Both approaches exploit information on the number, chemical composition, and constitutional relations of compounds in the crystalline reference system of a given melt. Both models use data on individual components and compounds only and do not require any additional information on thermodynamic excess data.

The subsolidus phase relationships in the Nd 2 O 3 -Al 2 O 3 –SiO 2 system and in the Si 6–z Al z O z N 8– z (0 ≤ z ≤ 4)–“Al 2 O 3 : AlN”-Al 2 O 3 -Nd 2 O 3 -SiO 2 -range of the Nd–Si–Al–O–N system have been determined. 50 three- and four-phase equilibria were established in this phase region. The phase equlibria define the regions of stable coexistence between β-sialon Si 6– z Al z O z N 8– z (0 ≤ z ≤ 4) and oxide or oxynitride compounds, which are potential grain boundary phases for silicon nitride ceramics. α-Si 3 N 4 coexists with N-melilite (Nd 2 Si 3– x Al x N 4– x (0 ≤ x ≤ 1)), N-α-wollastonite NdSi 2 ON, a nitrogen-rich (Al, N)-apatite solid solution and Nd 2 Si 2 O 7 . Between 0 ≤ z ≤ 0.8 ß-sialon (Si 6– z Al z O z N 8– z ) is compatible with N-melilite (Nd 2 Si 3– x Al x N 4– x ( x = 1)), an (Al,N)-apatite of intermediate composition and Nd 2 Si 2 O 7 . The equilibrium phases between z = 0.8 to z = 4 are NdAlO 3 and the U-phase (Nd 3 Si 3– x Al 3+ x O 12+ x N 2– x ) as well as NdAl 11+ x O 18 N x ( x = 1) and corundum at the Al-rich terminal composition ( z = 4).

Interface structure and chemical stability in composites of NiAl reinforced with alumina silica fibers (Sumitomo) were investigated by means of TEM, XEDS, EELS and electron diffraction. The composite specimens were fabricated by diffusion bonding in vacuum at 1300 ~ 1450 °C/ 5 ~ 15MPa/2h. The experimental results showed no Ni diffusion from the NiAl matrix into the fiber to occur during diffusion bonding. However, the fiber underwent complex thermodynamic processes depending on hot-pressing temperatures. They involved intrinsic chemical reactions between the fiber components to produce mullite and reduce silica, as well as extrinsic reactions between free oxygen and NiAl at the interface to generate α-Al 2 O 3 . The experimental results are discussed.

Anhand des Schichtsystems SiC auf Graphit, hergestellt durch ein Chemical-vapour-deposition (CVD) Verfahren, wurde die Anwendung der Fourier-Transform-Infrarot (FTIR)-Reflexionsspektroskopie als zerstörungsfreie Methode zur Probencharakterisierung demonstriert. Dabei zeigte sich, dass neben den in der Probe enthaltenen Materialien die Topologie des Schichtsystems maßgeblich die Reflexionsspektren beeinflusst und eine herkömmliche Spektreninterpretation sogar unmöglich macht. Spektrensimulationen auf Basis eines die Probe adäquat beschreibenden optischenModells ermöglichen es, aus den gemessenen Reflexionsspektren Informationen über Schichtzusammensetzung und Probenaufbau zu gewinnen. Dabei wurde die Interface-Rauheit im optischen Modell durch Effektiv-Medien-Modelle beschrieben.

The coating impact test, in combination with finite elements method (FEM) simulation, is successfully used to characterize the fatigue performance of coatings. Critical values for stress components, responsible for distinctive fatigue failure modes of the coating, are obtained and the fatigue limits of various coatings are illustrated in form of generally applicable Smith and Woehler diagrams, determined through a developed evaluation software. This software takes into account the impact test experimental data, as well as coating and substrate constitutive laws. Herewith coating adhesive and cohesive failure modes are elucidated and a cutting performance prediction of coated tools can be carried out. On the other hand, creep phenomena of plasma sprayed coatings are quantitavely interpreted.

By using differential scanning microcalorimetry, X-ray phase analysis, electron microscopy and secondary ionmass spectrometry, the phase formation was studied in Al –Co powder, prepared by mechanical alloying, and also in Al –Co thin films of Al 13 Co 4 composition. It was shown that solid-phase reaction between Al and Co starts from Al 9 Co 2 formation. The heat of Al 9 Co 2 formation was estimated, approximately the same in both types of materials. In mechanically alloyed powders the Al 9 Co 2 phase formed at lower temperatures than in thin films. The growth of the Al 9 Co 2 phase is a two-stage process. It is supposed that the first stage is controlled by Co diffusion in Al, and the second stage is controlled by Co diffusion through the intermetallic phase Al 9 Co 2 .