Mechanical and chemical consequences of the residual stresses in plasma sprayed hydroxyapatite coatings

PURPOSE: To describe a preliminary investigation of a model of naltrexone therapy and counselling for use by primary care providers and evaluate its impact on drinking behaviors in a cohort of alcohol-dependent subjects. PATIENTS AND METHODS: The subjects enrolled in this study were 29 alcohol-dependent individuals. They were managed within a primary care treatment model located at a university-affiliated substance research program in New Haven, Connecticut. Subjects were assigned to a primary care provider for treatment of their alcohol dependence and were placed on naltrexone at a dose of 50 mg per day. They were seen for an initial "new patient" visit and 7 "brief" follow-up visits during the 10-week study. The primary outcomes for this study were completion of treatment, change in drinking behaviors from baseline, change in liver enzymes from baseline, provider ratings of improvement, and patient ratings of improvement and satisfaction with treatment. RESULTS: Of the 29 subjects: 21 (72%) completed treatment, and 10 (35%) relapsed to heavy drinking. All drinking behaviors improved significantly from baseline: percent of days abstinent increased from 36.6% to 88.8% (P < 0.0001), percent days abstinent from heavy drinking increased from 48.7% to 97.3% (P < 0.0001), and mean number of drinks per occasion decreased from 9.5 to 2.5 (P < 0.0001). The mean serum gamma glutamyl transferase (GGT) for the group decreased from 67.1 U/L to 45.3 U/L (P < 0.0001). CONCLUSIONS: In this preliminary investigation, treatment of alcohol dependence with our model of naltrexone and counselling by primary care providers appeared to be both feasible and effective.     

Mechanical and histological evaluation of amorphous calcium phosphate and poorly crystallized hydroxyapatite coatings on titanium implants

The effect of amorphous calcium phosphate (Ca/P) and poorly crystallized (60% crystalline) hydroxyapatite (HA) coatings on bone fixation to "smooth" and "rough" (Ti-6A1-4V powder sprayed) titanium-6Al-4V (Ti) implants was investigated. Implants were evaluated histologically, mechanically, and by scanning electron microscopy (SEM) after 4 and 12 weeks of implantation in a rabbit transcortical femoral model. Histological evaluation of amorphous vs. poorly crystallized HA coatings showed significant differences in bone apposition (for rough-coated implants only) and coating resorption (for smooth- and rough-coated implants) that were increased within cortical compared to cancellous bone. The poorly crystallized HA coatings showed most degradation and least bone apposition. Mechanical evaluation, however, showed no significant differences in push-out shear strengths between the two types of coatings evaluated. Differences between 4 and 12 weeks were significant for coating resorption and push-out shear strength but not for bone apposition. Significant enhancement in interfacial shear strengths for bioceramic coated as compared to uncoated implants were seen for smooth-surfaced implants (3.5-5 times greater) but not for rough-surfaced implants at 4 and 12 weeks. Rough implants showed greater mean interfacial strengths than uncoated smooth implants at 4 and 12 weeks (seven times greater) and to coated smooth implants at 12 weeks only (two times greater). Mechanical failure of the bone/coating/implant interface consistently occurred within the bone, even in the case of the poorly crystallized HA coatings, which had almost completely resorbed on rough implants. These results suggest that once early osteointegration is achieved biodegradation of a bioactive coating should not be detrimental to the bone/coating/implant fixation.     

Mechanical and microstructural properties of titanium/hydroxyapatite functionally graded material fabricated by spark plasma sintering

ABSTRACT

In this article, different functionally graded material specimens were made from titanium powder and hydroxyapatite (HA) submicron particles. The spark plasma sintering method was applied to fabricate the specimens. Two kinds of starting powder mixture were used: mixed powder and ball-milled powder. Percentage of HA was changed from 0 vol.-% to 40 vol.-% in the different number of layers (2, 3 and 5-layer). The effects of the number of the layers and ball-mill process were investigated on microstructure, microhardness, compressive strength and fracture surface. The results show that the grain size has been enhanced by increasing the amount of HA in the layers. In addition, the Vickers microhardness has been first increased by enhancing the percentage of HA, while it has been decreased in the layers with a higher amount of it. Furthermore, the highest compressive strength could be achieved in the five-layer samples. Moreover, specimens with ball-milled powder have higher microhardness and less compressive strength.     

Tribological properties of detonation coatings based on titanium aluminides and aluminum titanate

Operation of coatings based on tialite, γ-TiAl, titanium aluminides with discrete inclusions of TiN and also alloys based on cobalt, nickel, and titanium in friction pairs with polyethylene grade “Chirulen” and stainless steel 12Kh18N10T is studied. It is established that tialite coatings formed from nanostructure powders of Ti-Al by detonation deposition are the best for operation under dry friction conditions in a pair with stainless steel 12Kh18N10T (minimum friction coefficient and minimum wear of the contact surfaces). It is shown that in the sliding rate range selected effective operation of material in friction pairs with polymer is provided due to transfer it to the contact surface and formation between rubbing surfaces of a thin film fulfilling the function of a solid lubricant. It is established that stable operation with the minimum wear in a friction pair with polyethylene grade “ Chirulen” is provided by a coating of γ-TiAl and Al₂TiO₅, and also coatings based on titanium aluminide with fine TiN inclusions.     

Structure and properties of rapidly solidified dispersion strengthened titanium alloys: Part II. tensile and creep properties

The effects of incoherent dispersoids on tensile and creep properties were determined in rapidly solidified Ti-Er and Ti-Nd alloys. Uniform distributions of. fine incoherent dispersoids in Ti matrix were produced by rapid solidification at cooling rates > 10³ °C per second and subsequent annealing at 700 to 800°C of Ti-1.0Er, Ti-2.0Er, Ti-1.5Nd, and Ti-3.0Nd alloys. The rapidly solidified particulates consolidated by vacuum hot pressing were isothermally forged, rolled, and annealed to produce fully recrystallized microstructures. The incoherent dispersoids in Ti-Er and Ti-Nd alloys increase by 40 to 110 pct the yield strength and ultimate tensile strength of Ti with no significant loss in ductility. The strength increments were analyzed in terms of the superposition of dispersion-, solid solution-, and fine grain-strengthening. Dispersion strengthening is offset to some extent by the reduction in interstitial oxygen solid solution strengthening caused by the scavenging of oxygen by Er and Nd. The dispersoids decrease the creep rates and increase the stress rupture lifetimes of Ti at 482 to 700 °C.     

Adhesion strength and physicochemical properties of molybdenum and tantalum coatings on titanium nickelide

The methods of estimating the adhesion strength are considered, the surface morphology is studied, and a layer-by-layer analysis is performed in the near-surface volume of titanium nickelide coated with molybdenum and tantalum films of various thicknesses. The mechanical and adhesion strengths of the coatings are shown to depend on the coating thickness and the chemical compositions of the film and substrate.     

A porous titanium diboride composite cathode coating for Hall-Héroult cells: Part I. Thin coatings

The mechanical, electrical, and electrochemical properties of a porous cathode coating, made by compositing titanium diboride powder and colloidal alumina, are described. Such coatings are expected to be used on the carbon cathodes employed in Hall-Héroult cells. The properties of the composite coating are compared with uncoated carbon cathode reference samples. The bonding properties of the coating with the carbon are also examined. The sodium trapping mechanisms of the coating are explored in this article. An earlier version of this article appeared in TMS Light Metals 1996 Proc., edited by W. Hale. This previous article is cited herein in Ref. 28.     

Wear of steel with ultrasound-induced nanostructuring of the surface layer. Part 1. Mechanical properties and wear resistance

The structural modification and change of wear resistance on friction with boundary lubrication is considered for 110Γ13 steel with and without impact ultrasound treatment. The deformational relief formed on the lateral surface of the samples in compression and in frictional loading is found to be the same. On that basis, the factors responsible for the change in wear resistance are discussed.     

Plasma spraying of ceramic particles in argon-hydrogen D.C. Plasma jets: Modeling and measurements of particles in flight correlation with thermophysical properties of sprayed layers

The behavior of alumina or stabilized zirconia particles in flight in Ar−H₂ d. c. plasma jets (up to 40 kW) has been studied. Measurement of the temperature distributions in the plasma jets (by emission spectroscopy) has shown the importance of the electrodes and are chamber designs on the length and diameter of the jets. The important cooling effect of the surrounding air has also been shown, and the parameters controlling it have been studied. Modeling of the momentum, mass, and heat transfers between plasma and particles as well as measurements of the trajectory, velocity, surface temperature distributions, and particle evaporation have enabled us to determine the influence of the different paramters, such as size and injection velocity distributions, particle morphology,etc., on the particle molten state upon impact. These calculations and measurements on the particles in flight have been correlated to some physical properties of deposits. This paper is based on a presentation made in the T.B. King Memorial Symposium on “Physical Chemistry in Metals Processing” presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS.     

Reinforcement of acrylic resins for provisional fixed restorations. Part I: Mechanical properties

Acrylic resins are commonly used in many dental applications; especially in the fabrication of provisional fixed partial dentures. Among noticed technical drawbacks associated with this material are unsatisfactory mechanical properties. Moreover, if acrylic resins are exposed to moist environment, water sorption results in further mechanical deterioration. In order to improve the mechanical properties, aluminum, magnesium, and zirconium oxide powders and pulverized E-glass particles were separately admixed with pre-polymerized acrylic resin beads prior to mixing with monomer liquid. Particle loading ratios were 1, 2 and 3 vol.% with respect to pre-polymerized beads. Poly(methyl methacrylate), poly(ethyl methacrylate) and poly(isobutyl methacrylate) were used as resin matrices. Furthermore, a metal primer agent was employed in order to form a strong interphase between admixed particles and polymer matrix phase. Samples were subjected to three-point transverse bending tests at a crosshead speed of 10 mm/min. It was concluded that (1) addition of particles generally increases the water sorbed by the composite resins systems, (2) however, two vol.% admixtures in a PMMA resin matrix showed significant improvements in the mechanical properties (p < 0.05), (3) among the oxide particles, zirconia exhibited the greatest improvements in modulus of elasticity, transverse strength, toughness and hardness, and (4) mechanical properties (transverse strength, 0.2% offset yield strength and modulus of elasticity) were linearly correlated to hardness numbers.     

Electrodeposition and characterization of sacrificial copper-manganese alloy coatings: Part II. Structural,mechanical, and corrosion-resistance properties

The structure and properties of electrodeposited Mn-rich Cu-Mn coatings were studied in order to assess their potential to provide sacrificial galvanic protection to steels. It is found that a small amount of codeposited copper can stabilize the ductile as-deposited centered tetragonal γ′ phase against roomtemperature recrystallization to the stable bcc α phase. The time to transformation is increasingly delayed with increasing copper content. Phase transformation of crystalline films does not follow the Johnson-Mehl-Avrami-Kolmogorov equation for nucleation and growth transformation. Amorphous coatings do not show any structural transformation at room temperature. Nanomechanical and tribological measurements showed that Cu-Mn coatings have a lower friction coefficient than reference Cd coatings. Cu codeposition reduces the coating’s hardness and elastic modulus and increases the resistance to plastic penetration with respect to pure Mn. Cu-Mn coatings show a barrier or passive behavior under anodic polarization, while the sacrificial characteristics are still preserved. The corrosion appears uniform, and the formation of MnO₂ and Cu₂O upon anodic polarization may account for the good corrosion performance of the coatings.     

Development and relaxation of stress in surface layers; Composition and residual stress profiles in γ′-Fe4N1−x layers on α-Fe substrates

Composition-depth and (residual) stress-depth profiles were investigated in two different γ′-Fe₄N_1−x surface layers on α-iron substrates. X-ray diffraction analysis was applied. Determination of the actual lattice-spacing depth profiles required correction for the effect of penetration of the X-rays. The dependence of the nitrogen content in γ′-Fe₄N_1−x surface layers on depth below the surface corresponds with that expected for diffusion-controlled layer growth. The formation of porous grain boundaries (channels) in the surface-adjacent part of the layers provides the possibility of nitrogen uptake at “internal” surfaces during nitriding, leading to the development of concave concentration-depth profiles in this part of the layers. Stress buildup in the massive interface-adjacent part of γ′-Fe₄N_1−x layers on a-Fe substrates originates from both the presence of a concentration-depth gradient and the difference in thermal contraction between layer and substrate on cooling from the nitriding temperature to the measurement temperature. Channel/pore development along grain boundaries in the surface-adjacent part of the layers provides a mechanism for stress relaxation during nitriding. On cooling, the channels can also accommodate part of the thermally induced misfit. Lateral strain gradients in the most severely porous part of the layers are revealed by the X-ray diffraction analysis. Formerly Graduate Student, Laboratory of Metallurgy, Delft University of Technology.     

Bauschinger effect and residual phase stresses in two ductile-phase steels: Part II. The effect of microstructure and mechanical properties of the constituent phases on Bauschinger effect and residual phase stresses

A finite-element method has been employed to calculate the effect of the prestrain, particle size, volume fraction, and yield strength ratio of the constituent phases on the Bauschinger effect (BE) and residual phase stresses for ferrite-martensite two-phase steels. The relationships be-tween the BE parameters and residual phase stresses are given, and the basics of inelastic un-loading and the effect of reverse deformation on the BE and residual phase stresses are also discussed. Based on the decaying of the residual phase stresses (commonly called “back stresses”) during reverse loading, the relationship between back stresses and permanent softening has been elucidated. Some of the calculated results are compared with experimental ones, and good agree-ment between them is found.