Novel Nanostructural Biomaterial Composites

2002 ◽  
Author(s):  
R. J. Narayan
Keyword(s):  
Heart Valves ◽  
Antimicrobial Properties ◽  
Internal Stresses ◽  
Dlc Coatings ◽  
Compressive Stresses ◽  
Diamondlike Carbon ◽  
Nanotube Composites ◽  
Novel Processing ◽  
Hardness Values ◽  
Poor Adhesion

Hydrogen-free diamondlike carbon (DLC), with hardness values close to that of diamond, possess many desirable biocompatible properties for a variety of biomedical applications. The DLC coatings can be applied to joints prostheses, heart valves, and other medical devices. Unfortunately, hydrogen-free DLC coatings have a large compressive stresses which result in poor adhesion and wear characteristics. In this paper, we present results on silver doping of DLC to alleviate internal stresses as well as create DLC-Ag nanocomposites where Ag is in the form of nanoparticles. The Ag nanoparticles are expected to impart antimicrobial properties by providing sources of electrons. In the second part of the paper, we have created DLC and nanotube composites where nanotubes grow normal to the surface. This novel architecture not only alleviates internal stresses, but DLC + Nanotube composites have enhanced hardness and unique antimicrobial properties. Finally, we discuss novel multilayer DLC and hydroxyapatite (HA) composite where HA and DLC films are deposited sequentially at room temperature. The HA films with composites close to that of bone is considered very desirable for biocompatibility and integration with base structures. We discuss novel processing, characterization, hardness and bioeompatible properties of all these composites in detail.

Theoretical study of the prestressing strand's stress by computer modeling methods

2020 ◽  
Vol 76 (11) ◽  
pp. 1139-1148
Author(s):  
A. G. Korchunov ◽  
E. M. Medvedeva ◽  
E. M. Golubchik
Keyword(s):  
Residual Stresses ◽  
High Strength ◽  
Pearlitic Steel ◽  
Internal Stresses ◽  
Steel Microstructure ◽  
Compressive Stresses ◽  
Wide Range ◽  
Prestressing Strands ◽  
Increasing Temperature ◽  
Wire Strand

The modern construction industry widely uses reinforced concrete structures, where high-strength prestressing strands are used. Key parameters determining strength and relaxation resistance are a steel microstructure and internal stresses. The aim of the work was a computer research of a stage-by-stage formation of internal stresses during production of prestressing strands of structure 1х7(1+6), 12.5 mm diameter, 1770 MPa strength grade, made of pearlitic steel, as well as study of various modes of mechanical and thermal treatment (MTT) influence on their distribution. To study the effect of every strand manufacturing operation on internal stresses of its wires, the authors developed three models: stranding and reducing a 7-wire strand; straightening of a laid strand, stranding and MTT of a 7-wire strand. It was shown that absolute values of residual stresses and their distribution in a wire used for strands of a specified structure significantly influence performance properties of strands. The use of MTT makes it possible to control in a wide range a redistribution of residual stresses in steel resulting from drawing and strand laying processes. It was established that during drawing of up to 80% degree, compressive stresses of 1100-1200 MPa degree are generated in the central layers of wire. The residual stresses on the wire surface accounted for 450-500 MPa and were tension in nature. The tension within a range of 70 kN to 82 kN combined with a temperature range of 360-380°С contributes to a two-fold decrease in residual stresses both in the central and surface layers of wire. When increasing temperature up to 400°С and maintaining the tension, it is possible to achieve maximum balance of residual stresses. Stranding stresses, whose high values entail failure of lay length and geometry of the studied strand may be fully eliminated only at tension of 82 kN and temperature of 400°С. Otherwise, stranding stresses result in opening of strands.

Evaluation of DLC Coatings for High-Temperature Foil Bearing Applications

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Said Jahanmir ◽  
Hooshang Heshmat ◽  
Crystal Heshmat
Keyword(s):  
Carbon Film ◽  
Dlc Coatings ◽  
Foil Bearings ◽  
Dlc Coating ◽  
Foil Bearing ◽  
Flat Disk ◽  
Wide Range ◽  
Diamondlike Carbon ◽  
Powder Lubrication ◽  
Foil Thrust Bearing

Diamondlike carbon (DLC) coatings, particularly in the hydrogenated form, provide extremely low coefficients of friction in concentrated contacts. The objective of this investigation was to evaluate the performance of DLC coatings for potential application in foil bearings. Since in some applications the bearings experience a wide range of temperatures, tribological tests were performed using a single foil thrust bearing in contact with a rotating flat disk up to 500°C. The coatings deposited on the disks consisted of a hydrogenated diamondlike carbon film (H-DLC), a nonhydrogenated DLC, and a thin dense chrome deposited by the Electrolyzing™ process. The top foil pads were coated with a tungsten disulfide based solid lubricant (Korolon™ 900). All three disk coatings provided excellent performance at room temperature. However, the H-DLC coating proved to be unacceptable at 300°C due to lack of hydrodynamic lift, albeit the very low coefficient of friction when the foil pad and the disk were in contact during stop-start cycles. This phenomenon is explained by considering the effect of atmospheric moisture on the tribological behavior of H-DLC and using the quasihydrodynamic theory of powder lubrication.

Fracture toughness of diamondlike carbon coatings

1999 ◽  
Vol 14 (5) ◽  
pp. 2173-2180 ◽  
Author(s):  
M. Nastasi ◽  
P. Kodali ◽  
K. C. Walter ◽  
J. D. Embury ◽  
R. Raj ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Length ◽  
Total Work ◽  
Carbon Coatings ◽  
Dlc Coatings ◽  
Si Substrates ◽  
Dlc Coating ◽  
Diamondlike Carbon ◽  
Radial Cracks ◽  
Work Of Fracture

The fracture behavior of diamondlike carbon (DLC) coatings on Si substrates has been examined using microindentation. The presence of DLC coatings reduces the radial crack length to less than one-half the crack length observed in uncoated Si at the same indenter load. A total work of fracture analysis of the radial cracks formed in the DLC-coating/Si-substrate system gives 10.1 MPa m1/2 as the average fracture toughness for DLC alone. A bond-breaking calculation for DLC suggests that the elastic limit fracture toughness should be 1.5 MPa (m)1/2. The higher value obtained from experiment and total work analysis suggests that plastic work and/or a tortuous path crack evolution occurred during DLC fracture process.

Buckling instabilities of thin cap layers deposited onto low-k dielectric films

2002 ◽  
Vol 734 ◽  
Author(s):  
F. Iacopi ◽  
S.H. Brongersma ◽  
T.J. Abell ◽  
K. Maex
Keyword(s):  
Dielectric Films ◽  
Dielectric Substrates ◽  
Low Dielectric ◽  
Film Adhesive ◽  
Compressive Stresses ◽  
Film Adhesion ◽  
Low Elastic Modulus ◽  
Adhesive Energy ◽  
Low K ◽  
Poor Adhesion

ABSTRACTCompressive stresses in thin capping films deposited onto low-k dielectric substrates are particularly prone to relaxation through buckling. This is due to insufficient cap/low-k film adhesion energy and to the compliance of low dielectric constant films. Low-k dielectric films, especially when porous, have low elastic modulus and demonstrate poor adhesion to other layers.When adhesion is poor the cap film can locally buckle as if unconstrained. The buckle front can propagate like a crack and lead to complete delamination of the cap layer. If the cap/low-k film adhesive energy is high, wrinkling instabilities can take place under specific conditions determined by the geometry and the mechanical properties of the stack. In this case the dielectric also deforms due to stress relaxation. A theoretical and experimental evaluation of the parameters influencing the occurrence of these instabilities is presented. This study was carried out to explore the application and reliability of low-k materials as dielectrics for advanced interconnects.

Diamondlike Carbon Materials as Low-k Dielectrics for Multilevel Interconnects in Ulsi

1996 ◽  
Vol 443 ◽  
Author(s):  
A. Grill ◽  
V. Patel ◽  
K.L. Saenger ◽  
C. Jahnes ◽  
S.A. Cohen ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Dielectric Constant ◽  
Dielectric Constants ◽  
Internal Stresses ◽  
Diamondlike Carbon ◽  
Potential Applications ◽  
Etch Stop ◽  
Si Content ◽  
Low K ◽  
Thermal Stability Of

AbstractA variety of diamondlike carbon (DLC) materials were investigated for their potential applications as low-k dielectrics for the back end of the line (BEOL) interconnect structures in ULSI circuits. Hydrogenated DLC and fluorine containing DLC (FDLC) were studied as a low-k interlevel and intralevel dielectrics (ILD), while silicon containing DLC (SiDLC) was studied as a potential low-k etch stop material between adjacent DLC based ILD layers, which can be patterned by oxygen-based plasma etchingIt was found that the dielectric constant (k) of the DLC films can be varied between >3.3 and 2.7 by changing the deposition conditions. The thermal stability of these DLC films was found to be correlated to the values of the dielectric constant, decreasing with decreasing k. While DLC films having dielectric constants k>3.3 appeared to be stable to anneals of 4 hours at 400 °C in He, a film having a dielectric constant of 2.7 was not, losing more than half of its thickness upon exposure to the same anneal. The stresses in the DLC films were found to decrease with decreasing dielectric constant, from 700 MPa to about 250 MPa. FDLC films characterized by a dielectric constant of about 2.8 were found to have similar thermal stability as DLC films with k >3.3. The thermally stable FDLC films have internal stresses <300 MPa and are thus promising candidates as a low-k ILD.For the range of Si contents examined (0-9% C replacement by Si), SiDLC films with a Si content of around 5% appear to provide an effective etch-stop for oxygen RIE of DLC or FDLC films, while retaining desirable electrical characteristics. These films showed a steady state DLC/SiDLC etch rate ratio of about 17, and a dielectric constant only about 30% higher than the 3.3 of DLC.

Improved adhesion of diamondlike coatings using shallow carbon implantation

2000 ◽  
Vol 15 (3) ◽  
pp. 590-592 ◽  
Author(s):  
Gerard W. Malaczynski ◽  
Alaa A. Elmoursi ◽  
Chi H. Leung ◽  
Aboud H. Hamdi ◽  
Albert B. Campbell
Keyword(s):  
Silicon Content ◽  
Carbon Matrix ◽  
Metal Carbides ◽  
Cohesion Strength ◽  
Subsequent Growth ◽  
Dlc Coatings ◽  
Dlc Coating ◽  
Diamondlike Carbon ◽  
Plasma Immersion Ion Implantation ◽  
Implantation Profile

A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamondlike carbon (DLC) coating. A plasma immersion ion implantation (PIII)-based procedure is described, which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. A shallow implantation profile, followed by argon sputter cleaning and continued until a saturated carbon matrix is brought to the surface, provides an excellent interface for subsequent growth of DLC. At a carbon retained dose above 1018 atoms/cm2 the DLC adhesion exceeds the coating's cohesion strength. Regardless of the silicon content in the aluminum, the coating produced by this method required tensile strengths typically exceeding 140 MPa to separate an epoxy-coated stud from the coating in a standard pull test. Improved DLC adhesion was also observed on chromium and titanium. The reported tensile strength is believed to substantially exceed performance of DLC coatings produced by any other method.

scholarly journals In vivo biocompatibility of diamond-like carbon films containing TiO2 nanoparticles for biomedical applications

2021 ◽  
Vol 32 (9) ◽  
Author(s):  
C. C. Wachesk ◽  
S. H. Seabra ◽  
T. A. T. Dos Santos ◽  
V. J. Trava-Airoldi ◽  
A. O. Lobo ◽  
...  
Keyword(s):  
Inflammatory Process ◽  
Antimicrobial Properties ◽  
Chemical Vapor ◽  
High Hardness ◽  
Carbon Films ◽  
High Wear Resistance ◽  
Diamond Like Carbon ◽  
Dlc Coatings ◽  
Inflammatory Reactions

AbstractHybrid diamond-like carbon (DLC) with incorporated titanium dioxide (TiO2) nanoparticle coatings have low friction coefficient, high wear resistance, high hardness, biocompatibility, and high chemical stability. They could be employed to modify biomedical alloys surfaces for numerous applications in biomedical engineering. Here we investigate for the first time the in vivo inflammatory process of DLC coatings with incorporated TiO2 nanoparticles. TiO2-DLC films were grown on AISI 316 stainless-steel substrates using plasma-enhanced chemical vapor deposition. The coated substrates were implanted in CF1 mice peritoneum. The in vivo cytotoxicity and biocompatibility of the samples were analyzed from macrophage lavage. Analysis in the first weeks after implantation could be helpful to evaluate the acute cytotoxicity generated after a possible inflammatory process. The in vivo results showed no inflammatory process. A significant increase in nitric oxide production on the uncoated substrates was confirmed through cytometry, and the coated substrates demonstrated biocompatibility. The presence of TiO2 nanoparticles enhanced the wound healing activity, due to their astringent and antimicrobial properties. DLC and TiO2-DLC coatings were considered biocompatible, and the presence of TiO2 nanoparticles reduced the inflammatory reactions, increasing DLC biocompatibility.

scholarly journals DLC Films Deposited by the DC PACVD Method

10.14311/398 ◽  
2003 ◽  
Vol 43 (1) ◽  
Author(s):  
D. Palamarchuk ◽  
M. Zoriy ◽  
J. Gurovič ◽  
F. Černý ◽  
S. Konvičková ◽  
...  
Keyword(s):  
Vapour Deposition ◽  
Chemical Vapour ◽  
Diamond Like Carbon ◽  
Deposition Method ◽  
Surface Layers ◽  
Carbon Coatings ◽  
Dlc Coatings ◽  
Steel Substrates ◽  
Poor Adhesion ◽  
Chemical Vapour Deposition Method

DLC (Diamond-Like Carbon) coatings have been suggested as protective surface layers against wear. However hard DLC coatings, especially those of greater thickness, have poor adhesion to substrates. We have used several ways to increase the adhesion of DLC coatings prepared by the PACVD (Plasma Assisted Chemical Vapour Deposition) method on steel substrates. One of these is the DC PACVD method for preparing DLC films.

Internal Stresses in Plasma Coatings with an Amorphous Structure

1998 ◽  
Author(s):  
Y. Borisov ◽  
V. Korzhyk
Keyword(s):  
Stress State ◽  
Boron Content ◽  
Amorphous Structure ◽  
Internal Stresses ◽  
Compressive Stresses ◽  
Stress Formation ◽  
Coating Layers ◽  
Plasma Sprayed ◽  
Amorphous Coatings ◽  
Material Temperature

Abstract The stress state of plasma sprayed amorphous coatings of the Fe-B based alloys with the boron content of 15-35 %, as well as of the above type alloys but with additions of Ni, Cr, Mo, was studied. Internal stresses depend on the type of a plasma gas, thickness and composition of the coatings, material, temperature and conditions of additional cooling of the substrate. Additional cooling of the substrate was found to be the most efficient method of decreasing the internal stress. Formation of compressive stresses in the coating layers adjoining the substrate is shown to lead to 25-30 % increase in its fatigue strength under alternating loads.

Micro- And Nano-Mechanical Behavior of Diamondlike Carbon Containing Foreign Atoms Prepared by Pulsed Laser Deposition

1998 ◽  
Vol 555 ◽  
Author(s):  
Q. Wei ◽  
R. J. Narayan ◽  
A. K. Sharma ◽  
J. Sankar ◽  
S. Oktyabrsky ◽  
...  
Keyword(s):  
Short Range ◽  
Random Network ◽  
Pulsed Laser ◽  
Laser Deposition ◽  
Internal Stresses ◽  
Spectroscopy Analysis ◽  
Stress Changes ◽  
Diamondlike Carbon ◽  
Target Design ◽  
Continuous Random Network

AbstractWe have prepared diamondlike carbon (DLC) films using KrF excimer pulsed laser (248 nm). The DLC films were deposited on Si (100) substrates and Cu and Ti were incorporated into the films through adopting a new target design. Visible Raman spectroscopy analysis of G-peak was correlated to internal stress changes in the DLC films due to incorporation of foreign atoms. Reduction of internal stresses in the presence of foreign atoms was established. This is consistent with adhesion studies that showed significant improvement in adhesion of DLC films containing dopants. Nanohardness and Young's modulus of DLC films containing Ti and Cu showed some decrease as compared to pure DLC. The experimental results are discussed in terms of the effect of dopants on the short range environment of the continuous random network (CRN) of DLC.

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