Internal stresses are measured in CVD diamond coatings deposited on a variety of substrate materials by low incident beam angle X-ray diffraction and by micro-Raman spectroscopy. The X-ray diffraction technique gives an integral stress value over a comparably large coating area whereas the Raman technique results in localized stress information with a lateral resolution of down to 1 µm. The stress values obtained from both methods compare well for diamond coatings of 6 μm thickness whereas a difference is observed for thicker coatings.

The experimental fact that measured elastic and structural properties of superlattices are strongly correlated can be understood on the basis of a simple model based on the packing of hard spheres. The model is consistent with features of many models that have been proposed to explain the supermodulus effect, but contrary to previous explanations, it allows predictions for a given pair of constituents to be made. For an arbitrary pair of elements, it predicts the existence or non-existence of an elastic anomaly, and a rough estimate of its magnitude.

Films of Al, Al2O3 and Al/Al2O3 microlaminates were formed by ion beam assisted deposition (IBAD) at R ratios from 0.0025 to 0.5 and film thicknesses between 150 and 2600 nm. Oxide films were amorphous while metal layers were crystalline with small grains and texture for both PVD and IBAD conditions. The average stress in the oxide film is tensile at R=0 and becomes compressive, saturating at approximately 15 eV/atom. The residual stress in the Al films is tensile over all R ratios and the stress in the microlaminate roughly follows a rule of mixtures. Deformation of ductile substrates on which films had been deposited revealed that the critical strain to fracture was strongly dependent on residual stress. Large compressive stresses in monolithic films produced by ion beam assisted deposition delayed the onset of crack initiation while the presence of multiple layers, in general, lowered the crack density at saturation, suggesting a possible ductilizing effect.

The elastic and anelastic properties of AgNi multilayers prepared by sputtering were investigated during the course of anneal cycles. The respective temperature variations of some of the elastic constants and moduli were followed by Brillouin scattering and dynamical methods based on use of a torsion pendulum and a vibrating-reed system. The last two enabled to investigate the internal damping associated with the presence of two-dimensional defects. It appears that the motion of interfaces and grain boundaries is inhibited by the high defect density. In contrast, substantial effects associated with the motion of the magnetic domain walls were evidenced. Concurrently, internal stresses were studied by in situ deflection measurements. Flow stress values on the order of 1 GPa were observed. Dilatometry experiments showed that a large part of the non-recoverable modifications in the state of stress induced by thermal cycling originates in the densification of the material.

The structure, composition and strain in Ni/Ti multilayers are analyzed using x-ray diffraction theories. The repeat period of the multilayers used in this study ranges from 1.3 to 12.8 nm. The composition modulation is obtained by using a kinematical theory of x-ray diffraction. A sine wave for the shorter repeat period and a rectangular wave for the longer repeat period are predicted for the composition modulation. The strain within each atomic layer is found by iteratively fitting the experimental x-ray diffraction pattern with the simulated one from a dynamical theory of x-ray diffraction. The strain at the interface is tensile in Ni and compressive in Ti with a complete relaxation of the strain at a distance away from the interface.

We have determined residual stresses and the layer microstructure in as-prepared Cu/W multilayers of different periods ranging from 5.2 to 20 nm by both X-ray diffraction and the curvature radius method. The magnitude of the principal in-plane stress is large in the W layers (around - 6 GPa) and small in the Cu layers (-0.5 - + 0.5 GPa). The stress state is independent of the multilayer period. Under the compressive stress, the W cubic unit cell becomes monoclinic-like. The stress-free lattice parameter is found higher than the bulk one.

We also studied the stress relaxation and the layer microstructure modification in W layers induced by Kr ion irradiation., the relaxation is almost achieved after only low fluence irradiations and the decrease of the stress-free lattice parameter in W layers observed for higher fluences is attributed to the formation of a sursaturated solid solution W(Cu).

Al/SiC multilayer microlaminates grown by sequential deposition of sputtered Al and SiC layers were used as a model system to study stress and mechanical properties of metal-matrix composites. The average stress in as-deposited and annealed microlaminates was determined as a function of laminate geometry. Film stress tends to approach constant values for increasing Al layer thickness, large numbers of bilayers, and high layer densities. Microlaminates with thin Al and SiC layers showed purely elastic deformation in σ -T tests to 400ºC. Even though the total measured film stress in a microlaminate geometry exhibited deviations from a simple rule of mixtures, the rate of change of stress with temperature in a microlaminate in the elastic region equals the sum of the slopes obtained separately from each of the individual layers.

In the lamellar form of the ordered intermetallic TiAl, mismatches at the lamellar interfaces, of order 1%, give rise to internal stresses and lo interracial dislocations. The geometry of the microstructure ensures extreme plastic anisotropy. Three main trends are evident in the plastic tensile properties: Both the yield and fracture stresses are low when deformation occurs in the plane of the lamellae and they are high when deformation occurs across the lamellae, the ductility is high when the tensile axis lies close to the lamellar plane and low when the tensile axis is nearly normal to the lamellar plane. The variations of the yield stress and the fracture stress are explained principally by the effects of Schmid factors and anisotropies in the Hall-Petch (or Stroh) stresses resulting from the lamellar shapes. The variation in ductility may be understood in terms of a competition between the ductile propagation of dislocations across interfaces and the creation of Stroh cracks at the heads of dislocation pile-ups.

Using elastic fields of dislocations in a layered material, a simple form of a periodic potential is proposed to account for the fluctuation in dislocation line energy with position in a multilayer. This potential is incorporated into a fracture analysis which uses a Rice-Thomson criterion for dislocation emission [1] and a corresponding local stress intensity factor condition for cleavage extension. The analysis is rate-dependent, in that the velocity of a nucleated dislocation is proportional to the energetic force on that dislocation. Predictions of dislocation patterns in the vicinity of a crack parallel to the interface, as well as initial R-curve behavior, are discussed as a function of loading rate, layer thickness, and elastic properties of a two-component multilayer.

"Symmetric" and "asymmetric" x-ray diffraction measurements are proposed as a tool for quantitative and complete determination of the superlattice structure. A general procedure which takes into account the atomic structure of the sublayers as well as structural disorder are presented. The "asymmetric" geometry using the "sin2psi" method is particularly emphasized.

Constant-stress molecular dynamics simulations are used to study the mechanical properties of equal concentration Cu-Ni (111) metallic multilayers of repeat lengths 0.4–5.0 nm. Uniaxial stress is applied along the close-packed [110] and perpendicular to the close-packed [112] directions within the (111) plane. The observed elastic modulus does not display a super-modulus effect as observed in experimental bulge tests for the biaxial modulus. However, both the average interlayer spacing and the out-of-plane Poisson ratio display anomalous effects for multilayer repeat lengths below about two nanometers.

Multilayers of Ru-Cu and Ru-Ti have been prepared by electron beam evaporation technique. One set of composites has Ru thickness varying from 250 to 2500Å alternating with Cu or Ti of 15Å. The other set has 250Å of Ru and the Cu or Ti layer varies between 15 and 200Å. Nanoindentation measurements show that there is no significant change in hardness as either Ru or Cu/Ti thickness varies. However, the Ru-Cu multilayer has twice the hardness of the Ru-Ti system. High resolution transmission electron microscopy discloses that there is an epitaxial orientation relationship between Ru and Ti in Ru-Ti while no such relationship exists in Ru-Cu.

The strengthening mechanism proposed by Koehler [1] predicts that Ru-Ti composites should have a higher strength than Ru-Cu due to the larger modulus difference between Ru and Ti. The discrepancy between the prediction and the experimental results suggests that other strengthening mechanism(s) may be operating. We have proposed two models based on a "shear" mechanism to explain the differences observed between these two systems. The effects of these mechanisms in controlling the deformation process in nanolayer composites are discussed.

Cu/Cu-Zr multilayer foils were fabricated and indented to determine the degree to which multilayer hardness is enhanced by increasing the volume fraction of the harder phase. Using sputter deposition and thermal processing a series of foils was fabricated in which the thicknesses of the Cu layers remained fixed while the thicknesses of the alternate Cu-Zr layers varied. These samples were then indented both parallel and normal to their layering. In general, hardness increased as the volume fraction of the harder Cu-Zr phase rose. When the films were loaded parallel to their layering, the measured hardnesses were higher and the dependencies on volume fraction of the Cu-Zr phase were stronger than when the films were loaded normal to their layering. These results agree with predictions based on isostress and isostrain theories. The relationships between hardness and volume fraction are used to compare the hardnesses of the Cu-Zr phases: amorphous Cu-Zr, Cu51Zr14 and Cu9Zr2, and to show that the hardness of the textured, as-deposited Zr layers is highly anisotropic .

A multiscalar approach is used to demonstrate the ability to control strength and toughness in microlaminates composed of molybdenum and tungsten. Here, two different thickness scales are utilized; an alternating stack of molybdenum and tungsten layers having thicknesses on the nanometer scale are combined with a layer of molybdenum having a thickness on the micron scale. The stack of thin layers acts as a strong phase and the thick layer acts as a tough phase. Multilayers of two configurations were fabricated which had total thicknesses of 31μm and 50μm. The tough phase thickness was 5μm for the 31μm multilayer and 1μm for the other. The strong phase contained a stack of 29 alternating 4nm thick layers of molybdenum and tungsten. Uniaxial tensile testing was performed using a standard Instron tensile testing machine, followed by optical analysis of specimen fracture surfaces. Fracture toughness ranged from 2.4 to 9.5MPa(m)1/2, and tensile strengths were observed from 126MPa to 883MPa. Control of mechanical properties was demonstrated by an increase in the upper bound fracture toughness from 2.7 to 9.5MPa(m)1/2 when the tough layer thickness was increased from 1μm to 5μm.

We have detected magnetic transitions in Ni/Cu (100) films as a function of Ni thickness through in situ measurements of the magneto-optic Kerr effect (MOKE). Crystalline quality was monitored using in situ RHEED and Auger electron spectroscopy. Films were deposited by molecular beam epitaxy on silicon wafers and cleaved sodium chloride with varying epitaxial Ni layer thicknesses between 10 and 200 A. High-resolution TEM images of these films indicate decreasing misfit dislocation spacing and decreasing strain as measured by moiré fringe analysis with increasing Ni thickness. These observations have been correlated with changes in magnetic anisotropy as measured by MOKE. MOKE, therefore, may provide a tool for in situ monitoring of the kinetics of misfit accommodation in magnetic thin films.