Showing papers on "Stress relaxation published in 1992"

Creep resistance of CMSX-3 nickel base superalloy single crystals

Abstract: Creep deformation in 〈001〉 oriented nickel base superalloy single crystals has been studied in an effort to assess the factors which contribute to the overall creep resistance of superalloys with high volume fractions of γ′ phase. Detailed observations of three dimensional dislocation arrangements produced by creep have been made with the use of stereo electron microscopy. In the temperature range of 800–900°C at stresses of 552 MPa or lower, the dislocation-free γ′ precipitates are resistant to shearing by dislocations. As a result, creep deformation occurs by forced bowing of dislocations through the narrow γ matrix channels on {111} planes. At moderate levels of temperature and stress there are incubation periods in virgin crystals prior to the onset of primary creep. The incubations arise because of the difficult process of filling the initially dislocation starved material with creep dislocations from widely spaced sources. When the newly generated dislocations percolate through the cross section, incubation comes to an end and primary creep begins. In primary creep neither work hardening nor any type of recovery plays an important role. The creep rate decelerates because the favorable initial thermal misfit stresses between γ and γ′ phases are relieved by creep flow. Continued creep leads to a build-up of a three-dimensional nodal network of dislocations. This three-dimensional network fills the γ matrix channels during steady state creep and achieves a quasi-stationary structure in time. In situ annealing experiments show that static recovery is ineffective at causing rearrangements in the three-dimensional network at temperatures of 850°C or lower. The kinematical dislocation replacement processes which maintain the quasi-stationary dislocation network structures during apparent steady state creep are not understood and require further study. Because of the impenetrability of the γ′ precipitates, dislocations move through the γ matrix by forced Orowan bowing, and this accounts for a major component of the creep resistance. In addition, the frictional constraint of the coherent or semi-coherent precipitates leads to the build-up of pressure gradients in the microstructure, and this provides load carrying capacity. There is also a smaller component of solid solution strengthening. Work hardening is comparatively unimportant. Finite element analysis shows that the non-deforming precipitates are increasingly stressed as creep deformation accumulates in the matrix. In the later stages of steady state creep and during tertiary creep the stresses in the precipitates rise to high enough levels to cause shearing of the γ′ particles by dislocations entering from the γ matrix. The recovery resistance of the material is in part due to a very low effective diffusion constant and in another part due to the fact that the three-dimensional dislocation networks formed in the γ matrix serve to neutralize the misfit between the γ and γ′ phases.

Stress relaxation in living polymers: Results from a Poisson renewal model

Abstract: The problem of stress relaxation in entangled, reversibly breakable polymers (e.g., wormlike micelles) is considered. In the case where the dominant diffusive mode for the polymers is reptation, this problem has been treated in earlier numerical work by coupling the full reaction kinetics of scissions and recombinations to the dynamics of reptation (represented by a one‐dimensional stochastic process). Here we study a simplified renewal model, which replaces the exact reaction kinetics by a Poisson jump process that neglects temporal correlations in the chain length experienced by a particular monomer or tube segment. Between jumps in chain length, the stress relaxation is presumed to follow that of an equivalent unbreakable chain. We apply the solution to the case of reptating flexible polymers and compare the resulting complex modulus with the earlier numerical treatments. It is found that agreement is very good. The renewal model is then used to analyze in detail, for the first time, the crossover to a rapid‐scission regime in which chain diffusion between scission events is dominated by breathing modes. A third regime, in which the motion between scission events is Rouse‐like, remains unsuitable for study with this model, for reasons that we explain. Various implications of the renewal model for the interpretation of experimental results are discussed. We also provide explicit estimates for chain lengths in CTAC/NaSal/NaCl systems using experimental Cole–Cole plots.

Relaxation Process of the Thermal Strain in the GaN/α-Al2O3 Heterostructure and Determination of the Intrinsic Lattice Constants of GaN Free from the Strain

Abstract: The relaxation process of the thermal strain in a GaN film due to the thermal expansion coefficient difference in the GaN(0001)/α-Al2O3(0001) heterostructure is studied by varying the film thickness of GaN in a wide range from 1 to 1200 µm. The lattice constant c has a large value of 5.191 A at a film thickness less than a few microns, while it decreases to about 150 µm, and becomes constant above 150 µm, indicating that the strain is almost completely relaxed. The intrinsic lattice constants of wurtzite GaN free from the strain, a0 and c0, are determined to be 3.1892±0.0009 and 5.1850±0.0005 A, respectively.

Internal stress reduction by nitrogen incorporation in hard amorphous carbon thin films

Abstract: Results of a study on internal stress, hardness, and structure of nitrogen‐doped amorphous hydrogenated hard carbon films deposited by rf glow discharge from methane‐nitrogen mixtures onto silicon substrate are presented. Films obtained for different N2 partial pressures (bias voltage Vb=−370 V and total pressure P=8 Pa) were characterized by infrared spectroscopy, Raman scattering, and nuclear techniques. The elemental composition, density, and structure are correlated with Vickers hardness and internal stress values, obtained from the substrate bending method. It has been observed that internal stress considerably decreases with increasing nitrogen content, in contrast to hardness, structure, and hydrogen concentration, which remain unchanged.

Creep behavior of discontinuous SiCAl composites

Abstract: A review of creep data of discontinuous SiCAl composites (whisker and particulate) shows that the creep behavior of these composites exhibits two main characteristics: (a) the stress dependence of the steady state (or minimum) creep rate, as described by the value of the stress exponent, is high and variable and (b) the temperature dependence of the steady state (or minimum) creep rate, which is measured by the creep activation energy, is much larger than that for self-diffusion in aluminum. These two characteristics are examined in the light of theoretical treatments describing the origin of high temperature strengthening in discontinuous metal matrix composites and dislocation models proposed for dispersion-strengthened alloys.

The relationship between deposition conditions, the beta to alpha phase transformation, and stress relaxation in tantalum thin films

Abstract: We demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes a large decrease in the resistance of thin films and a complete stress relaxation in films that were intrinsically compressively stressed. 100 nm beta tantalum thin films with intrinsic stresses of 2.0×1010 dynes/cm2 (tensile) to −2.3×1010 dynes/cm2 (compressive) were deposited onto thermally oxidized (100) silicon wafers by evaporation or dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured at 10 °C/min up to 850 °C in purified helium. Upon heating, the main stress mechanisms were elastic deformation at low temperature, plastic deformation at moderate temperatures and stress relief because of the beta‐to‐alpha phase transition at high temperatures. The temperature ranges over which the elastic and plastic deformation and the beta‐to‐alpha phase transition occurred varied with deposition pressure and substrate biasing. Incomplete compressive stress relaxation at high temperatures was observed if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800 °C due to substrate biasing during the deposition. We conclude that the main stress relief mechanism for tantalum films with intrinsic compressive stresses to completely relax their stress is the beta‐to‐alpha phase transition, while for intrinsically tensile films, this transformation has a much smaller effect on the stress.

Lamellae orientation in dynamically sheared diblock copolymer melts

Abstract: Two distinct lamellae orientations have been identified by small-angle neutron scattering (SANS) in dynamically sheared poly(ethylene-propylene)-poly(ethylethylene) (PEP-pEE) diblock copolymer melts. Near the order-disorder transition temperature, T→T ODT , and at low shear frequencies, the lamellae arrange with unit normal perpendicular to the flow direction and parallel to the velocity gradient direction (parallel orientation). Higher frequency processing leads to lamellae with unit normal perpendicular to both the flow and velocity gradient directions (perpendicular orientation). The crossover from low to high frequency behavior occurs at ω≃τ -1 where τ is the relaxation time for local doamin deformations. At temperatures further from the ODT, T<

Strain relaxation by domain formation in epitaxial ferroelectric thin films.

Abstract: The origin of strain-induced, modulated domain structures observed in epitaxial ferroelectric lead titanate thin films is discussed using a phenomenological total-energy calculation Linear elasticity is used to account for the substrate contribution while a free-energy functional of the Landau-Ginzburg-Devonshire type is used to calculate the domain-wall and the polarization contributions from the film Good agreement between the predictions of this model and the experimental results is found for thickness-dependent properties such as the relative domain population and spontaneous strain

Component Relaxation Dynamics in a Miscible Polymer Blend: Poly(ethylene oxide)/Poly(methyl methacrylate)

Abstract: Relaxation dynamics in miscible blends of PEO and PMMA ranging in composition from 20 to 60 wt% of PMMA are studied subsequent to a linear step strain using the simultaneous measurement of infrared dichroism and birefringence. From the temperature and composition dependences of component relaxation times it is clear that each component of the blend retains a separate rheological identity. Component relaxation dynamics shows a dramatic and complex sensitivity to blend composition. In PMMA-rich blends each component adopts a separate friction factor with a unique temperature dependence

Delayed relaxation by surfactant action in highly strained iii-v semiconductor epitaxial layers

Abstract: It is demonstrated that the concept of surfactant applies to the epitaxial growth of highly strained III-V semiconductors. The pseudomorphic growth regime of InAs on GaAs(001) is extended from 1.5 to 6 monolayers by the use of Te as surfactant. This delayed plastic relaxation of the strain is correlated with the modification of the growth mode via surface energy minimization.

Viscoelastic properties of physically crosslinked networks: Part 3. Time-dependent phenomena

Abstract: The initial value problem is solved for the transient network model of physically crosslinked gels Stress relaxation following a sudden macrodeformation is calculated for several realistic models of the chain breakage rate β(r) It is shown that, on large time scales, stress decay obeys a power law when β(r) has significant r-dependence, the precise value of the power being dependent on the high stretching behaviour of β(r) For instance, the shear stress decays as ≈t −5 n if β(r) is proportional to rn at high stretching Although the Lodge-Meissner relation still holds, time-strain separability loses its physical background Overshoot phenomena in shear and normal stress, which appear after steady flows are started at the initial equilibrium state, are also analyzed It is found that the shear stress first shows a transient maximum, and then maxima of the first and second normal stress differences follow Larger overshoot is expected for larger values of the shear rate γ, but the time at which the stress reaches its maximum is almost independent of γ The elongational stress is also obtained as a function of time

The analysis of internal strains measured by neutron diffraction in Al/SiC metal matrix composites

Abstract: Neutron diffraction measurements of internal strain development during tensile loading are analysed so as to deduce the extent and mechanisms of load transfer taking place between matrix and reinforcement. It is demonstrated that the observed lattice strains in Al/20 vol.% SiC whisker and particulate composites can be understood largely in terms of an elastic transfer of load arising from the higher stiffness of the reinforcing phase, however at loads approaching a conventional 0.2% yield stress, plastically induced stresses also become important. Furthermore, in the particulate composite there is clear evidence that stress relaxation mechanisms are also important.

Evaluation of the Strength and Creep–Fatigue Behavior of Hot Isostatically Pressed Silicon Nitride

Abstract: The strength of a commericially available hot isostatically pressed silicon nitride was measured as a function of temperature. To evaluate long-term mechanical reliability of this material, the tensile creep and fatigue behavior was measured at 1150°, 1260°, and 1370°C. The stress and temperature sensitivities of the secondary (or minimum) creep strain rate were used to estimate the stress exponent and activation energy associated with the dominant creep mechanism. The fatigue characteristics were evaluated by allowing individual creep tests to continue until specimen failure. The applicability of the four-point load geometry to the study of strength and creep behavior was also determined by conducting a limited number of flexural creep tests. The tensile fatigue data revealed two distinct failure mechanisms. At 1150°C, failure was controlled by a slow crack growth mechanism. At 1260° and 1370°C, the accumulation of creep damage in the form of grain boundary cavities and cracks dominated the fatigue behavior. In this temperature regime, the fatigue life was controlled by the secondary (or minimum) creep strain rate in accordance with the Monkman–Grant relation.

Strain-induced crystallization of poly(ethylene terephthalate)

Abstract: The fabrication of poly(ethylene terephthalate), PET, into fibers, films, and containers usually involves molecular orientation caused by molecular strain, which may lead to stress- or strain-induced crystallization (SIC). The SIC of PET was studied by the methods of birefringence, density, thermal analysis, light scattering, and wide-angle X-ray. The development of crystallinity is discussed in relation to the rate of crystallization, the residual degree of orientation, and stress relaxation. The experimental procedure involves stretching samples at temperatures above the glass transition temperature, Tg, to a given extension ratio and at a specific strain rate of an Instron machine. At the end of stretching, the sample is annealed in the stretched state and at the stretching temperature for various periods of time, after which the sample is quickly quenched to room temperature for subsequent measurements. During stretching, the stress strain and the stress relaxation curves are recorded. The results indicate that the SIC of annealed, stretched PET can proceed in three different paths depending on the residual degree of orientation. At a low degree of residual orientation, as indicated by the birefringence value, annealing of stretched PET leads only to molecular relaxation, resulting in a decrease of birefringence. At intermediate orientation levels, annealing causes an initial decrease in birefringence followed by a gradual increase and finally a leveling off of birefringence after a fairly long period of time. At higher orientation levels, annealing causes a rapid increase in birefringence before leveling off. The interpretation of the above results is made using the measurements of light scattering, differential scanning calorimetry, and wide-angle X-ray. The rate of the SIC of PET is also discussed in terms of specific data analysis.

Shear Thickening Creep in Superplastic Silicon Nitride

Abstract: A novel shear-thickening phenomenon has been observed in superplastic silicon nitrides compression tested between 1500" and 1600°C. Liquid-enhanced creep of SiAlONs undergoes a transition from Newtonian behavior to shear-thickening behavior at a characteristic stress, with the strain rate sensitivity increasing from unity to around 2. The transition stress is always around 20 MPa, even though the Newtonian flow stress is very sensitive to temperature, grain size, and phase composition. Rheopexic hysteresis, manifested as a slow stress relaxation to a steady-state value after a strain rate decrease, was also observed in the shear-thickening regime. We attribute the cause for shear thickening to a repulsive force between initially wetted SiAlON grains, which form a "dry" and "rigid" bridge in between when pressed above a characteristic stress, possibly due to the contact of the residue Stern layers on the opposing grain/liquid interfaces. A micromechanical model, which takes into account the stress variation among differently oriented grain boundaries, has been formulated to assess the effect of "rigid" grain boundaries. A continual stochastic rearrangement of grain configurations and a relatively thick Stern layer are suggested as the necessary prerequisites for shear thickening in liquid-enhanced creep. [Key words: sialons, superplastic, shear, creep, models.]

A Simple Test for Thermomechanical Evaluation of Ceramic Fibers

Abstract: A simple bend stress relaxation (BSR) test was developed to measure the creep related properties of ceramic fibers and whiskers. The test was applied to a variety of commercial and developmental Si based fibers to demonstrate capabilities and to evaluate the relative creep resistance of the fibers at 1200 to 1400 C. The implications of these results and the advantages of the BSR test over typical tensile creep tests are discussed.

Surface patterns on single-crystal films under uniaxial stress: Experimental evidence for the Grinfeld instability.

Abstract: We study the stress relaxation in single-crystal films of polymerized polydiacetylene, in epitaxy with their monomer substrate. Polymerization induces a uniaxial stress. Two types of surface patterns are observed and studied by atomic force microscopy: films thicker than 175 nm exhibit quasiperiodic cracks perpendicular to the polymer chains; thinner ones exhibit regular wrinkles with the same orientation. The wrinkle surface deformation is stress relaxing and plastic. We show that all experimental results, in particular, the order of magnitude of the pattern spacings, are compatible with the following interpretation: as polymerization proceeds, the uniaxial stress generates a Grinfeld instability (Dok. Akad. Nauk SSSR 290, 1358 (1986) [Sov. Phys. Dokl. 31, 831 (1986)]) fed by surface diffusion. The crack pattern is a secondary instability, initiated at the sites of stress concentration provided by the wrinkles.

Crystal and molecular deformation in strained high‐performance polyethylene fibers studied by wide‐angle x‐ray scattering and Raman spectroscopy

Abstract: Wide-angle x-ray scattering (WAXS) and Raman spectroscopic data show that on both the crystal and molecular levels, a bimodal stress distribution exists in strained high-performance polyethylene fibers. In part of the crystalline PE the microscopic strain level is high (ca. 70% of macroscopic strain); in the remainder, the microscopic strain level is low (independent of macroscopic strain, ca. 0.4%). During stress relaxation the fraction of highly strained PE decreases with time. WAXS revealed no indication of a change in the a and b unit-cell dimensions. Furthermore, no indications for stress-induced formation of monoclinic and/or hexagonal PE and for crystal breaking were found. From the latter it can be deduced that all chains within one crystal are equally strained. The WAXS results are used to calibrate the stress-induced frequency shifts of Raman bands.

Creep of soils and related phenomena

Abstract: 1. Introduction. Macro- and microapproach. Aim of rheological investigations. Creep and the accuracy of its prediction. Limitations of rheological theories. Conception of this book. 2. Examples of the rheological behaviour of geomaterials. Settlement of structures. Dam displacements. Slope displacements. Conclusion. 3. Structure and texture of soils. Introduction. Mathematical and physical modelling of constitutive relations. Structural units. Fabric. Bonding. Internal stress. Structure of some tested soils: Zbraslav sand, Landstejn sand, Loess, Kyjice clay, Sedlec kaolin, ablice claystone, Strahov claystone, Conclusion. Changes of soil structure. 4. State parameters of soils. Porosity. Water content. Stress and stress path. Strain. Time. Temperature. Conclusion. 5. Elasticity, viscosity and plasticity. Introduction. Elasticity. Viscosity. Plasticity: Introduction, Rigid-plastic approach, Modelling of constitutive behaviour, Plastic potential approach, Other physically motivated concepts, Rate-type relations. Concluding remarks. 6. Experimental rheology. Introduction. Water content and temperature fluctuations. Choice of the apparatus. Evaluation of the experimental results. 7. Macrorheology. Introduction. Method of rheological models. Method of integral representation. Empirical relations. 8. Microrheology. Introduction. Micromechanical approach. Particle-based conception: Fabric as the principal constitutive factor, Mixed analysis. 9. Primary and secondary consolidation. Introduction. Primary consolidation. Secondary consolidation. Conclusion. 10. Long-term strength of soils. Introduction. Stress - long-term strain diagrams. Long-term strength. Creep failure (rupture). Conclusion. 11. Creep and stress relaxation. Creep. Stress relaxation. Conclusion. 12. Numerical solution of rheological problems. Introduction. Numerical methods: Numerical methods in geomechanics, Finite-element method, Nonlinear techniques, Path-dependent constitutive model. Numerical modelling of creep: Review, Algorithms for computing creep by FEM. Applications: Dams, Tunnels. Conclusions. 13. Concluding comments. Appendix 1. Appendix 2. Bibliography. Author index. Subject index.

Elastic and viscoelastic analysis of stress in thin films

Abstract: The occurrence of stress in thin films has led to serious considerations of stability problems in the semiconductor industry. It may cause mechanical failure of films, such as adhesion reduction or contact peel‐off, or variations in electrical properties. The existence of stress will also alter electromigration behavior for thin metal lines. The elastic stress in a multilayered structure due to thermal processing is calculated by use of the principle of mechanics balance. It is found that the variation of thickness in one film will not affect the magnitude of stress in another film. The shearing and peeling stress at the edge of a patterned structure, which is responsible for the peeling of a film at the edge, is then modeled and discussed in detail. Finally, the relaxation of stress by viscous motion of SiO2 is analyzed based on Maxwell’s viscoelastic model.

On the state of stress in the near-surface of the earth's crust

Abstract: Five models for near-surface crustal stresses induced by gravity and horizontal deformation and the influence of rock property contrasts, rock strength, and stress relaxation on these stresses are presented. Three of the models—the lateral constraint model, the model for crustal stresses caused by horizontal deformation, and the model for the effects of anisotropy—are linearly elastic. The other two models assume that crustal rocks are brittle or viscoelastic in order to account for the effects of rock strength and time on near-surface stresses. It is shown that the lateral constraint model is simply a special case of the combined gravity-and deformation-induced stress field when horizontal strains vanish and that the inclusion of the effect of rock anisotropy in the solution for crustal stresses caused by gravity and horizontal deformation broadens the range for predicted stresses. It is also shown that when stress levels in the crust reach the limits of brittle rock strength, these stresses become independent of strain rates and that stress relaxation in ductile crustal rocks subject to constant horizontal strain rates causes horizontal stresses to become independent of time in the long term.

Linear viscoelastic behavior of commercial and model mayonnaise

Abstract: Oscillatory shear experiments in the linear viscoelastic domain were carried out on four commercial brands of mayonnaise and three samples of model mayonnaise with different oil contents (75, 77.5, and 80% w/w), at temperatures between 10 and 40 °C. A power‐law relationship between complex viscosity and frequency was found for all the samples. The power‐law indexes were compared with those obtained from stress relaxation tests carried out on commercial mayonnaise. No significant differences between them were found. Shear strain in the nonlinear viscoelastic region, above a certain threshold value, produced an irreversible structural breakdown of the emulsion. This was dependent not only on the magnitude of the strain but also on the elapsed time since the deformation started.

The effect of strain rate on the deformation and relaxation behavior of 6/6 nylon at room temperature

Abstract: The influence of strain rate changes in the range from 10−3 to 10−6 1/s on the zero-to-tension loading and unloading behavior as well as short term relaxation properties is investigated using cylindrical specimens of circular cross section. A clip-on extensometer measures and controls the axial strain in an MTS servohydraulic, computer-controlled mechanical testing machine. Strains do not exceed twenty percent and all deformation is macroscopically homogeneous. An increase in strain rate causes an increase in stress level. Surprisingly, the total stress drop in a 20 min relaxation period increases with prior strain rate. When the relaxation test is started in the inelastic region with low tangent modulus the total stress drop is nearly independent of the stress and strain at which relaxation commences. Unloading to zero load is not linear but curved and the strain recovery at zero stress is significant. It occurs at an ever decreasing rate and does not exceed three percent in a 12 h period. Like the relaxation behavior the recovery rate increases with prior strain rate. Repeated relaxation periods during zero-to-tension cycling can show a stress magnitude decrease during loading but a stress magnitude increase during unloading. The results suggest that a unified model with an overstress dependence of the inelastic rate of deformation could be useful in modeling.

Finite element modelling of creep deformation in fibre-reinforced ceramic composites

Abstract: The tensile creep and creep-recovery behaviour of a unidirectional SiC fibre-Si3N4 matrix composite was analysed using finite element techniques. The analysis, based on the elastic and creep properties of each constituent, considered the influence of fibre-matrix bonding and processing-related residual stresses on creep and creep-recovery behaviour. Both two- and three-dimensional finite element models were used. Although both analyses predicted similar overall creep rates, three-dimensional stress analysis was required to obtain detailed information about the stress state in the vicinity of the fibre-matrix interface. The results of the analysis indicate that the tensile radial stress, which develops in the vicinity of the fibre-matrix interface after processing, rapidly decreases during the initial stages of creep. Both the predicted and experimental results for the composite show that 50% of the total creep strain which accumulated after 200 h at a stress of 200 MPa and temperature of 1200°C is recovered within 25 h of unloading.

A spinning drop tensioextensometer

Abstract: We examine some theoretical and experimental aspects of the measurement of interfacial tension, stress relaxation in elongational flow, and yield stresses in organic liquids, blends of polymer melts, and liquid crystal polymers. This study is based on an instrument which is an improved version of the spinning drop apparatus that is commonly used to measure interfacial tension between melted polymers. Problems of vibrations at high speed, heating of the bearings, high temperatures required to melt the polymers, outgassing at the reduced pressures generated by rotation, and other problems have been eliminated in the improved apparatus. This same instrument can be used to generate curves of volume expansion versus temperature for blended systems and to detect and interpret yield stresses which occur in some polymers and strongly influence the properties of blends. The instrument has been enhanced for accurate measurements of drop diameter, length and shape as a function of time and initial conditions. A theory of upper and lower bounds for interfacial tension and a theoretically based method of exponential fitting has been developed to help to overcome the problems of slow approach to equilibrium between highly viscous melts. We have developed and propose to develop further a theory of relaxation in which transient measurements of drop diameter can be used to obtain rheological properties like elongational and yield stresses and interfacial tension and more generally to interpret the curves of relaxation generated in the experiments.

Thermal stability of Si1−xCx/Si strained layer superlattices

Abstract: The thermal stability of epitaxial silicon‐carbon alloys grown by molecular beam epitaxy on (001) silicon was investigated using high resolution x‐ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy measurements. Different superlattices, with alloy compositions of Si0.997C0.003, Si0.992C0.008, and Si0.985C0.015, all nominally 6 nm thick, with 24 nm Si spacer layers were employed. Annealing studies determined that there are different pathways to strain relaxation in this material system. At annealing temperatures of 900 °C and below, the structures relax only by interdiffusion, indicating that these layers are stable during typical device processing steps. At temperatures of 1000 °C and above, SiC precipitation dominates with enhanced precipitation in the Si1−xCx layers with the highest initial carbon content.