Reduction Of Internal Stress Research Articles

Microstructure And Wear Resistance Of Doped Diamondlike Carbon Prepared By Pulsed Laser Deposition

ABSTRACTWe have investigated the microstructure and tribological properties (wear resistance) of diamondlike carbon (DLC), DLC doped with Cu and DLC doped with Ti deposited by a sequential pulsed laser ablation of two targets onto Si(100) substrates. The composition of these films was determined by Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy(XPS). Raman spectroscopy and detailed analysis of the electron diffraction pattern of the films showed typical features of DLC with a structure dominated by sp3 bonded carbon. Wear resistance measurements made on these samples by means of the “crater grinding method” showed that DLC + 2.75%Ti has the highest wear resistance, while that of undoped DLC has the lowest among the samples. The improvement of wear behavior of the doped films was attributed to the reduction of internal compressive stress due to the presence of more compliant atoms, as indicated by the G-peak position shift to smaller Raman shift. The XPS studies showed the evidence for the formation of Ti- C bonding in the Ti doped films. Thus we expect metal-doped DLC coatings can have better tribological properties than the undoped, highly stressed DLC coatings.

Doping Induced Internal Stress Reduction in Diamondlike Carbon Films Deposited by Pulsed Laser Ablation

ABSTRACTWe have investigated the effect of dopants on the reduction of internal compressive stress in diamond-like carbon (DLC) films prepared by pulsed laser deposition on Si(100) substrates. A novel target configuration was used to incorporate dopants into DLC films by sequential pulsed laser ablation of two targets. These dopants include copper, titanium and silicon. The thickness of the DLC films deposited was measured in the range 400nm - 600nm using a profilometer. Raman spectroscopy was employed to analyze the chemistry of the films. The shifts of the G-peak position in the Raman spectrum, due to different concentrations of dopant, were used to estimate the internal stress changes. All of the films showed a Raman spectrum typical of DLC films containing a high fraction of sp3 species, with the G-peak centered at around 1510–1560cm−1. The shift of the G-peak due to the presence of dopants was observed for all the DLC films as compared to the undoped one. It was found that Ti has the strongest tendency to reduce the compressive stress of DLC films. This effect increases with increasing concentration of dopants. Silicon was also observed to have this effect, but the G-peak position did not appear to shift with different Si concentrations. Buckling occurred in the as-deposited, undoped DLC film because of the relief of the large compressive stress accumulated in the film, while all the doped DLC films showed good adhesion to the substrate. The results are discussed combining the atomic structure of DLC and the structure and properties of the dopants.

A structural study of chemical stability of (Y1?x Ca x)(Ba2?x La x )Cu3O7??(x= 0.0, 0.2, and 0.4)

Neutron structural studies are made on (Y1−xCax)(Ba2−xLa x )Cu3O7−δ for compositions corresponding to x=0.0, 0.2, and 0.4 in order to evaluate any correlation between the remarkably high chemical stability of the cosubstituted samples (x=0.2 and 0.4) and the structural parameters. It is suggested that the increased chemical stability is caused by a decrease in the puckering of the Cu-O planes with increase inx, causing them to flatten, which leads to a reduction in the internal stresses existing in the perovskite lattice of this technologically important material.

Reduction of internal stress in sputter-deposited films by energetic ion bombardment

Considerable relaxation of the high internal stresses which arise in HfN thin films during their deposition by a sputtering method has been accomplished through bombarding the films with energetic silicon ions. The internal stresses have been estimated from the measurements of the surface curvature. Our results indicate a relaxation of the internal compressive stresses in the films, which occurs via a transport of the interstitial defects within the thermal spikes created by a post-deposition energetic ion bombardment. The mechanical properties of HfN films before and after the treatment have been studied by depth-sensing indentation technique while the structural analysis has been made using x-ray diffraction, Rutherford backscattering, and Auger electron spectroscopy. Ion bombardment did not affect resistivity of the thin films while improving their plastic properties.

Ar/H 2 sputtering deposition of 350 μm thick Si:H/SiO 2- x:H multilayers having flat interfaces for optical applications

Thick Si/SiO 2 multilayered films with flat interfaces are needed to achieve optical devices with low optical propagation losses, such as a laminated polarization splitter operating at a 1 550 nm wavelength. Such films can be realized by a sputtering method using an Ar/H 2 gas mixture because of the successful reduction of internal stress and surface roughness of films compared with those of conventional ones. We fabricate 350 μm thick Si:H/SiO 2-x:H multilayered films having flat interfaces by such a hydrogénation technique. The absorption losses at 1 550 nm wavelengths of both films measured separately are negligibly small.

Asymmetric DC-magnetron sputtered carbon-nitrogen thin-film overcoat for rigid-disk applications

An asymmetric DC-magnetron sputtering technique was evaluated to deposit carbon-nitrogen (C:N) overcoats for rigid-disk applications. The tribological characteristics of very thin C:N overcoats (/spl sim/100 /spl Aring/) were investigated by using thin-film flying inductive heads, Tripad-proximity recording heads, and carbon-coated magneto-resistive (MR)-heads in different test environments. Comparison of >20 K contact start-stop (CSS) test cycles showed superior stiction and durability performance for the asymmetric DC-magnetron sputtered (asym-C:N) films compared to standard symmetric DC-magnetron sputtered (sym-C:N) films. After CSS testing, no visible wear marks and/or head-build up were observed. Comparison of stress and hardness data showed a reduction of internal stress without noticeable change in hardness for asym-C:N films. Also, elemental analysis showed higher nitrogen content in asym-C:N films. In addition, Raman spectroscopy data suggest that the asym-C:N films have higher sp/sup 3/ content than that of sym-C:N films, which can contribute to greater durability.

Reduction of Internal Stress in Nickel Deposits Using Periodic Reverse Current Electrolysis.

In the present work, th influence of the PR plating conditions, especially the anodic current density, on the residual stresses in the nickel film plated from the Watt-type bath of pH 3.00 was investigated

Peculiarities in strengthening of Nb and Ta due to super-imposed ultrasonic and plastic deformation

Relaxation of disordered dislocation structures under ultrasonic influence in a two-dimensional square-shaped grain is investigated using the discrete-dislocation approach. The model grain contains three non-parallel glide systems inclined at an angle of 60° to each other. Non-equilibrium grain boundary state is modeled by means of a mesodefect located at the corners of the square-shaped grain. The stress fields of this mesodefect are described by those of a wedge junction disclination quadrupole. Oscillating stresses result in a rearrangement of lattice dislocations and their gliding towards the grain boundaries. This process is accompanied by a reduction of internal stress fields and cancellation of the wedge disclination quadrupole. The presence of non-parallel glide systems leads to a formation of Lomer–Cottrell locks, when two or more dislocations belonging to different systems meet at one point. Influence of the amplitude of ultrasonic treatment on the relaxation of dislocation structures is studied. Ultrasound of low amplitudes results in a formation of dislocation walls in the grain interior, while at higher amplitudes the dislocation substructure is destroyed and majority of the lattice dislocations are absorbed by the grain boundaries. The model predicts an existence of optimal values of the ultrasound amplitudes, at which the maximum reduction of internal stresses can be achieved. Dependence of the relaxation of disordered dislocation structures on the grain size is explored. The results obtained are consistent with those of previous theoretical and experimental studies.

The use of mica flakes for reducing internal stress in cured epoxy resin

AbstractMica, in the form of flakes of different sizes and size distributions, was mixed with a difunctional epoxy resin to the extent of 10 to 50 parts by weight of the resin. To this resin–filler mixture, a stoichiometric amount of a tetrafunctional curing agent was added. First, a thin a aluminium strip was coated with the mica–resin–amine mixture and was subjected to two curing cycles. Second, sheets were cast from the mixture by subjecting them to the same two cure cycles. The internal stresses that developed in the coated samples, and their relaxation with time, were studied. The dynamic torsional spectra of rectangular bars cut from the sheet were also mapped. The debonding and microcracking, resulting from internal stress, have been shown to result in a significant reduction in internal stress in the mica‐filled samples, particularly in samples containing large mica flakes in which delamination of the mica layers in the flake has also been shown to occur. However, despite this phenomenon, the filled samples were found to have adequate mechanical and electrical properties. © 1994 John Wiley & Sons, Inc.

Influence of Silicon Incorporation on the Properties of Hard a-C:H Films

ABSTRACT- Results on the properties of silicon incorporated hard a-C:H films deposited on the cathode of a glow discharge decomposition system using methane and silane gaseous mixtures are reported. Obtained samples showed an increased deposition rate, high hardness comparable to that of a-C:H, and a large decrease of the internal stress upon silicon incorporation. The structure of the samples seems to be similar to diamond-like a-C:H, as revealed by the total hydrogen content, infrared absorption and hydrogen effusion experiments. Our results indicate that the observed reduction of residual internal stress may be attributed to a less compact material and/or to a smaller density of voids containing hydrogen in comparison to pure a-C:H.

Improved SiO2-coatings against high temperature sulphidation by internal stress reduction

Alloys such as AIS1 304 and AIS1 321 stainless steels and Incoloy 800H can be protected against high temperature corrosion by means of amorphous SiO2-coatings deposited by metal organic chemical vapor deposition (MOCVD). The coated alloys are only attacked locally after exposure to a 19% H2, 1% H2S, 1.5% H2O, Ar bal. environment at 823 K (pS2 = 1.2 x 10-9bar and pO2 = 9.3 x 10-29 bar). The crack density observed after sulphidation is identical for silica deposited onto all metallic substrates. Decohesion of amorphous silica coatings from AISI 304 is observed, when the coating thickness exceeds 1.7 µm, while coatings on Incoloy 800H are adherent up to 4 µm. These phenomena can be explained by the fact that the adhesion is a function of the chemical interactions between the metal and the coating, whereas crack formation is only a function of the internal stresses in the coating. Two methods are studied to reduce the coating failure by means of a reduction of internal stresses in the coating, the first is changing the deposition process and the second is reducing the thermal mismatch between the coating and the metal.

Question of the mechanism of formation of the damping condition of high-chromium ferritic steels

Damping in high-chromium ferritic steels is formed primarily as the result of magnetoelastic dispersion of energy, the level of which is determined by the character of interaction of the magnetic domain boundaries moving in the field of applied cyclic stresses with some subsystems of stoppers, defects of the crystalline structure. The maximum in damping capacity of Kh16, Kh16M4, and Kh25 steels is observed after annealing at 900–1000°C and is the result of superposition of individual oppositely acting on the magnetic constituent of damping contributions during evolution of structural defects under different temperature-time actions. An analysis of the contribution of different crystalline lattice defects makes it possible to predict the path of formation of the controlled level of vibration absorbing properties of high-chromium steels. The high-damping condition is characterized by a low level of internal stresses, moderate values of coercive force, and non-linearity of the elastic properties under the action of external stresses. The damping capacity after annealing in the temperature area of stratification of high-chromium ferrite and appearance of 475°-brittleness is determined by the action of two primary tendencies, the reduction of internal stresses as the result of ecomposition of the supersaturated solid solution of interstitial impurities and the subsequent increase in them as the result of stratification of high-chromium ferrite and formation of zones enriched with chromium.

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

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.

Reduction of Internal Stress of a-Si:H Films by in Situ Measurements of Optical Emission Intensity from SiH4 Plasma

ABSTRACTA parameter which determine internal stress of hydrogenated amorphous silicon (a-Si:H) prepared by plasma CVD method has been investigated to prevent a peeling off or crack forming problem. It is clarified that the internal stress changes from tension to compression as a function of supplied rf power density during deposition process. Supplied rf power density is closely connected to H o and SiH* optical emission intensity ratio (H α /SiH* ) of CVD plasma. Ve find that the internal stress can be reduced remarkably by controlling this ratio to 0.3. This H α/SiH* parameter has a superiority that the internal stress can be in situ controlled.

New Profile of Ultra Low Stress Resin Encapsulants for Large Chip Semiconductor Devices

lnternal stress, as a result of temperature cycle testing (TCT), causes package cracking, passivation film cracking, aluminum pattern deformation, etc. This is particularly evident in IC's and LSI devices with large-size chips and larger memory capacity. Greater reduction of internal stress imparted by resin encapsulants is required to address these problems. To reduce the internal stress, it was previously determined that it is effective to introduce very small sized silicone domains into the epoxy matrix and to create a strong interaction layer between the domain/matrix interface in a heterogeneous structure where soft polymer particles are dispersed as domains in the epoxy matrix as a continuous phase. To date, research efforts have yielded epoxy resins having about 0.1-µm domains with a strong interaction layer at the domain/matrix interface using special silicone modifiers. Comparisons were. made between silicone-modified epoxy resins having 2-5-µm domains and smooth domain/matrix interfaces with versions having 0.1'µm domains. From these comparisons we have drawn the following conclusion: as the silicone domain size decreases within the epoxy matrix, the internal stress imparted by the encapsulant decreases as measured by temperature cycle testing.

DOCUMENTATION OF HIGH SUMMER FLOWS ON THE POTOMAC RIVER FROM THE WOOD ANATOMY OF ASH TREES1

ABSTRACT: Ash trees (Fraxinus americana L. and F. Pennsylvanica Marsh.) collected from the flood plain of the Potomac River near Washington, D.C., were studied for evidence of associations between known periods of above‐average summer flows and changes in wood‐growth anatomy. Concentric bands of latewood fibers with atypically large lumens and thin walls commonly developed in trees growing near the low‐water channel. Discharge records indicate that roots of most trees with these “white rings” were flooded temporarily during the latewood‐growth interval. Trees apparently were not damaged and a concomitant reduction of internal water stresses seems to have accelerated the rate of radial growth. The intra‐ring position of anomalous fibers generally corresponded to the time of increased discharge within the estimated interval of latewood growth. Anomalous fibers occasionally formed in unflooded trees, but their position also coincided with episodes of increased discharge. The results of these studies may have applications for streamflow‐reconstruction techniques where hydrologic data are incomplete or lacking.

Designing of extrusion lines

AbstractThe design of extrusion lines deals with the extruder and the die as well as with the down stream equipment, especially the cooling section. This paper aids in the design of these three units, regarding different aspects. The scale‐up of extruders by means of the model theory is demonstrated in its practical use with examples. Emphasis is laid on the design of series of single screw extruders with mixing‐pins and of twin‐screw extruders (scale‐up). There the adequate selection of the necessary restrictions for the compilation of model laws is discussed in detail. This is an approach to the safe machine design on the basis of model theory.The present standard of the calculation of threedimensional flow patterns in extrusion dies by means of the finite‐element‐method (FEM) is shown in order to point out how design‐aids for the die‐designer are derived from these calculations. After a discussion of application‐criteria for the FEM, examples will show possible ways of using FEM‐results.For the shaping of Y‐branches in twin‐screw machines the FEM‐results point to possible plate‐out areas and to their avoidance by geometrical modifications. The calculation of a die for a T‐profile helps to design the passages between entry and exit sections. Finally, flow coefficients for the calculation of pressure losses in different cross sections are given.The design and optimization of cooling sections, as it can be done with the aid of the actual cooling models, is shown for some important extrusion processes. Heat transfer coefficients for practical cases (film‐sheet‐, pipe‐ and parison extrusion) are presented. Examples show, how diagrams for the design and optimization of cooling sections (for example the reduction of internal stresses and warping) can be made, using a microcomputer.

ジメチルアミンボランを用いた無電解メッキ法によるNi-B非晶質状メッキ膜

The structure of the deposited alloy film by the electroless plating method changes continuously from crystalline, which is the aggregation of very fine crystals, to amorphous with increasing boron or phosphorous contents in the deposited film. In this investigation, the deposit condition to make the amorphous alloy in the electroless plating bath using dimethylamine borane (DMAB) as a reducing agent was studied. The increase of reducing agent concentration in the plating bath increases the boron content in the deposited film and contributed to make an amorphous film. Furthermore, the decrease of pH and the increase of temperature of the plating bath also had the same effect. The added other agent for reduction of internal stress in the deposited film and to stabilize the pH of the plating bath did not show any pronounced effect on the concentration of boron in the deposited film. Finally, the Ni-B alloy film prepared in this investigation contained a maximum amount of 16.2 at%B and showed an amorphous-like structure with a small amount of fine nickel crystals.

Effect of modifying substances on internal stress variation in gelatin films

The effect was shown of modifying additives on the reduction of internal stress in gelatin films formed during isometric heating. The higher the concentration of the modifying substance in gelatin, the more considerable this reduction. The modifying effect is determined by the chemical nature of modifiers, the introduction of which into gelatin results either in plasticization, or in the formation of a heterophase system. An explanation is given to this effect.

Weldable heat-resistant nickel alloys and principles of alloying them

1. The resistance to welding cracks during welding and heating of weldments depends mainly on the stresses in the material. 2. Reduction of internal stresses by use of a hardening phase with crystallographic parameters near those of the solid solution and ensuring slow precipitation of the hardening phase make it possible to increase the resistance of weldments. 3. The nickel alloys hardened with intermetallic phase Ni3(Nb, Al) have high heat resistance, good workability, and are recommended for welded parts operating at temperatures up to 800°.