B. Trindade

Influence of Ti addition on the properties of W–Ti–C/N sputtered films

Thin films of W–Ti–CyN were deposited by d.c. reactive magnetron sputtering from W–Ti targets with 0, 10, 20 and 30 wt.%Ti. The influence of titanium and interstitial element (carbon and nitrogen) contents on the structure, hardness and adhesion of the coatings was evaluated by X-ray diffraction analysis, ultramicroindentation and scratch-testing, respectively. The results show different compositional dependencies of the structure and grain size of the films. Hardness was related with the structure of the films, including lattice distortion and grain size. The higher hardness values (f50 GPa) were obtained for W–Ti–N films with 40–45 at.%N deposited from the W–20 wt.%Ti target in a reactive N atmosphere. However, these films present relatively 2 low adhesion to the substrates with critical loads of 30 N. The best compromise between hardness and adhesion was reached for W–Ti–N films with low nitrogen and titanium contents. 2003 Elsevier Science B.V. All rights reserved.

Amorphous phase forming ability in(W–C)-based sputtered films

Abstract The effect of adding transition metals, Me, to the structure of (W–C)-based films obtained by sputtering has been studied by the means of electron probe microanalysis (EPMA), secondary ion mass spectrometry (SIMS), low angle X-ray diffraction (XRD), hot stage transmission electron microscopy (TEM), Mossbauer spectroscopy, extended X-ray absorption fine structure (EXAFS), magnetic measurements and differential thermal analysis (DTA). The results obtained for the films in the as-deposited conditions show two types of structures with different degrees of structural order. Films with Ti, Cr or Au are crystalline with a metastable structure of β -(W,Me)C 1- x with 1- x extending from near unity down to about 0.6. In opposition to these, films with Me=Group VIIIA transition metal, show crystalline→amorphous state transitions for Me percentages in the range 5–10 at.%. The structure of these films consists of small β -MC 1- x crystallites with a size of a few unity cells, surrounded by a disordered phase rich in element Me. Concerning the results obtained at increasing temperatures, the chemical and structural behaviour of the W–Me–C films depend on the affinity of carbon for the element Me. Strong or moderate carbide-forming elements (Ti or Cr) improve the stability of the crystalline phase at high temperatures; the films formed by W, C and a weak or non carbide-forming metal (Fe, Co, Ni, Pd or Au) change structurally in the temperature range studied.

The Influence of the Addition of a Third Element on the Structure and Mechanical Properties of Transition-Metal-Based Nanostructured Hard Films: Part I—Nitrides

Transition metal (TM) carbides and nitrides have been the most studied and investigated compounds since the beginning of the use of hard coatings to improve the performance of mechanical components. Since the pioneering study on the deposition and characterization of TiC and TiN, many different approaches have been followed in order to make these coatings perform better and better. In fact, the enthusiasm among researchers grew quite rapidly because the final results reached with coated components were so much better than with uncoated bulk materials. As a result, the application of hard coatings as a universal panacea for all the wear problems occurring in the mechanical industry was immediately installed. Nonetheless, it is obvious that whenever new situations were envisaged for the application of a hard coating, there were new demands that could not be satisfied with the existing Ti-based compounds. In most of the studies performed to develop “new” hard coatings, the supporting ideas were naturally based on the acquired knowledge of researchers

Modification of the structural order of transition metal–carbon systems by the addition of a Group VIII element

Abstract ATransition-metal carbides M–C from different groups of the periodic table (IVA–VIA), doped with iron, were produced by sputtering, and their chemical composition and crystal structure were evaluated. The M–C binary thin films have different ranges of structural order depending on their heat of formation and tendency to crystallize to a structure of the NaCl type. Iron provokes a significant decrease of the range of structural order of these carbides. The iron content required for the appearing of structures with intermediate-range order is a function of the constituent transition metal of the carbide, and is higher for stronger carbide formers.

Structure and properties of sputtered TiAl-M (M = Ag, Cr) thin films

Abstract The aim of this work was to study the influence of two additional elements — silver and chromium — on the structure and mechanical properties of TiAl–M (M=Ag, Cr) thin films synthesised by sputtering. The films were studied in the as-deposited condition (metastable state) and after successive annealings performed in order to obtain the stable (γ-TiAl)-based intermetallic phase. The experimental techniques used in this work for chemical and structural characterisation were electron probe microanalysis, transmission electron microscopy/electron diffraction, X-ray diffraction and differential scanning calorimetry. The mechanical analysis consisted of the determination of hardness and ductility. To do this, a new tensile test procedure able to evaluate the ductility of thin films was developed. The results showed that, contrary to the as-deposited state, the addition of silver or chromium does not lead to a significant improvement in the mechanical properties, hardness and ductility of the heat-treated films (γ-TiAl structure). However, they did contribute to a better understanding of the role of silver and chromium on the structure of these titanium aluminides.

Structural stability and crystallization studies of metastable sputtered WNiC films

Abstract The as-deposited state and the annealing behaviour of metastable WNiC films, synthesised by non-reactive r.f. magnetron sputtering, have been studied by means of electron probe microanalysis, secondary ion mass spectrometry, X-ray diffraction, differential thermal analysis and in-situ high temperature transmission electron microscopy. The results are presented and correlated with previous studies on W(Fe,Co)C films. As will be shown, the as-deposited structure of the films is dependent on chemical composition and varies from crystalline to amorphous with increasing nickel content. The transformation structures produced during annealing of the films are consistent with those anticipated from the WNiC equilibrium phase diagram.

Deposition and characterization of fine-grained W–Ni–C/N ternary films

W-Ni-C/N ternary films with 3 <at.% Ni<14 and 0<at.% C, N<30 were synthesized by reactive sputtering from a W-10 wt.% Ni target with increasing partial pressures of methane or nitrogen and substrate bias. The films have been characterized by electron probe microanalysis, X-ray diffraction, ultramicrohardness and scratch testing. The results show that the degree of structural order of the films decreases with increasing nickel and metalloid element contents. The hardness values obtained vary between 25 and 55 GPa, with a maximum for films with low nitrogen and carbon contents (6-8 at.%), deposited with a substrate bias of -70 V. The Young modulus follows the same trend as hardness, with a maximum modulus value of 550 GPa. The crystalline coatings present higher critical loads than the amorphous coatings. The more adherent coatings have critical loads higher than 70 N.

Synthesis and characterisation of new sputtered metastable carbides

Abstract This paper describes part of a work carried out to develop new ternary M–M1–C systems (M=metal of the Groups IV–VI and M1=Group VIII element) by sputtering. The results obtained in this study on Ti–Fe–(C) and Mo–Fe–(C) systems showed that, depending on the type and content of iron, the obtained materials are structurally metastable, formed either by structures with enlarged solubility domains or amorphous structures. The amorfisation was verified in the Ti–Fe and Mo–Fe-C systems, as a result of the introduction of iron. The Ti–Fe–C system shows better resistance to amorphisation than the Mo–Fe–C system.

Mechanical characterisation of γ-TiAl thin films obtained by two different sputtering routes

Abstract In this study (TiAl)-based films were magnetron sputtered using two different methods: two targets (Ti+Al) and a γ-TiAl target. In both cases, the as-deposited films had to be heat treated in order to obtain the intermetallic γ-TiAl. The effect of the addition of chromium on the structure and mechanical properties was studied. The films were submitted to ageing treatments and the resulting structures and mechanical properties were also studied. To get more insight into the films, the residual stresses were also evaluated. After heat treatment (HT), the films sputtered from two targets are constituted by a single γ-TiAl phase while in the films produced with one target it is possible to observe the presence of the α2-Ti3Al phase. Under annealing, the as-deposited compressive stresses give rise to low tensile stresses. The 18 h HT leads to a pronounced increase in hardness in the films obtained by using two targets. The hardness of the films produced using one target increases gradually with the HT holding time. In all cases, ductility and hardness exhibit inverse trends.

The effects of a third element on structure and properties of W–C/N

Abstract We have studied the effect of adding different metallic (Fe, Co, Pd, Cr, Ti, Ni,…) and non-metallic (Si) elements to the structure of W–C/N-based films deposited by sputtering. The influence of a Group VIII element on interstitial carbides has also been studied in order to clarify its role in structure amorphization. The results obtained for films in the as-deposited condition show different types of structures with various degrees of structural order, depending on the type and content of the element added. The new coatings can be structurally stable or metastable, formed either by structures with enlarged solubility domains or amorphous structures, with or without nanophases inside. The transformation kinetics of the metastable phases with temperature for different types and contents of a third element added have been investigated. From the results obtained at high temperatures, we conclude that the chemical and structural behavior mainly depends on the position of the third element in the Periodic Table, and on its affinity to carbon and nitrogen. Strong and moderate carbide/nitride-forming elements improve the phase stability at high temperatures; the other elements lead to structural changes in the operating temperature range of the coating during the technological application.