Chemico-structural properties and biomineralization of hydroxyapatite coatings produced by high power laminar plasma spray process.

U ovom radu je izvršeno nanošenje hidroksiapatitnih (HA) prevlaka primenom visokoenergetskog laminarnog plazma sprej postupka. Glavni ciljevi rada su bili: (i) da se ispita uticaj nekoliko parametara procesa nanošenja na hemijska, strukturna i morfološka svojstva HA prevlaka i (ii) da se ispita uticaj ljudskih proteina albumin i gama globulin na početni stadijum procesa biomineralizacije koji se javlja na površini dobijenih HA prevlaka u modifikovanim Kokubo rastvorima (simulirane telesne tečnosti) u kojima je vrednost pH bila aktivno regulisana pomoću CO2...In the present work, hydroxyapatite coatings (HACs) were deposited by using the high power laminar plasma spray process. Major objectives were: (i) to estimate effects of several deposition parameters on chemical, structural, and morphological properties of HACs and (ii) to evaluate effects of human proteins albumin and gamma globulin on the early stage of the biomineralization process on the surface of HACs in modified Kokubo solutions (simulated body fluids) in which the pH value was actively regulated using CO2

Simulated Body Fluids Prepared with Natural Buffers and System for Active pH Regulation

The current study focuses on creating an initial highly alkaline simulated body fluid whose pH can be decreased to a physiological range by adding CO2 (protein-free simulated body fluid) or a combination of CO2 and human proteins (protein-containing simulated body fluid). The effects of dissolved human proteins, Ca2+ ions, and immersed plasma-sprayed hydroxyapatite coatings on the pH and chemical instability of prepared simulated body fluids were investigated. The physiological concentration of dissolved human proteins decreased the pH instability in prepared simulated body fluids by 60% and the physiological concentration of dissolved Ca2+ ions by 15%. The effect of immersing the hydroxyapatite coatings was negligible. In terms of chemical instability, the dissolution of Ca2+ ions caused the blurring of protein-free simulated body fluids after 0.6-1.0 h. In protein-containing simulated body fluids, this phenomenon was undetectable due to their opacity. The effects of human protein presence on the carbonated-apatite-forming ability on the surfaces of immersed hydroxyapatite coatings in the prepared simulated body fluids were also assessed. The experiments validated the bioactivity of plasma-sprayed hydroxyapatite coatings in the prepared simulated body fluids, regardless of protein presence. On the other hand, under the different experimental conditions (unregulated or regulated pH), the human protein presence had an inhibitory (unregulated pH) or indifferent/promoting (regulated pH) influence on the carbonated-apatite-forming ability. The results of the present study are discussed, as well as the strengths and shortcomings of the prepared simulated body fluids, and are compared to those of previous relevant investigations

PLASTIC DEFORMATION AND HEAT TREATMENT OF THIN WALLED CENTRIFUGALLY CAST HIGH STRENGTH CrMoNb STEEL TUBES

This work deals with effects of hot plastic deformation process and subsequent heat treatment on structure and mechanical properties of centrifugally cast (CC) high strength CrMoNb steel tubes. Plate samples, taken from CC tubes, were homogenized and subsequently hot rolled. One serie of samples was soft-annealed (SA) and other series oil-quenched and tempered (QT) between 373-923 K. Primary and secondary structures, non-metallic inclusions in radial direction and prior austenite grain size were analyzed using bright-field and polarized light microsopy. Experimental mechanical properties of SA and QT samples were modeled by means of polynomial functions and correlated with structure properties

Analysis of floating-head heat exchanger bolts failure

As-received floating-head heat exchanger bolts were broken (BB) and deposite-coated. The aim was to estimate a cause of their failure. The new bolts of the same material were used as a reference material (reference bolt – RB). After visual and radiographic examination, their chemical composition, structure and room-temperature mechanical properties were determined and compared. Comparison was made with the values set by standard, as well. Afterwards, fractography was performed on fractured surfaces of tensile specimens and originally (during exploitation) BBs to try to get an impression about bolts failure mechanism. Qualitative analysis of deposite was employed in order to confirm was there any possible influence of surroundings during their failure in terms of corrosion-assisted cracking. Chemical composition of RB and BB materials was analyzed by use of spectrophotometry and structure properties with light optical microscope (LOM). Fractured surfaces of tensile specimens and of BBs, as well as deposite chemistry, were analyzed by use of Scanning Electron Microscopy with Energy Dispersive System (SEM-EDS). BBs had an approximately three times higher sulphur content and lesser manganese content, lower ductility and higher strength values comparing to those of the RBs. Generally, fracture surfaces of both, RB and BB tensile specimens have a similar rosette-like macro-appearance. The only difference is that the radial marks in the case of the RBs are rougher. The surface has a more fibrous area and shear lip presence. Fracture mode can be characterized as dimple rupture and micromechanism as microvoid coalescence. In the case of BB tensile specimens, the mixed presence of dimples and cleavage facets was noticed. The macrofractography of originally broken surfaces shows a rough and complex topography of fracture surfaces indicating on a possibility that bolts failure has been a result of complex loading conditions. Presence of sulphur- and chlorine-containing particles on the fracture surfaces of BBs and in deposite reveals a possibility that failure was environmentally-assisted

Chemico-structural properties and biomineralization of hydroxyapatite coatings produced by high power laminar plasma spray process.

U ovom radu je izvršeno nanošenje hidroksiapatitnih (HA) prevlaka primenom visokoenergetskog laminarnog plazma sprej postupka. Glavni ciljevi rada su bili: (i) da se ispita uticaj nekoliko parametara procesa nanošenja na hemijska, strukturna i morfološka svojstva HA prevlaka i (ii) da se ispita uticaj ljudskih proteina albumin i gama globulin na početni stadijum procesa biomineralizacije koji se javlja na površini dobijenih HA prevlaka u modifikovanim Kokubo rastvorima (simulirane telesne tečnosti) u kojima je vrednost pH bila aktivno regulisana pomoću CO2...In the present work, hydroxyapatite coatings (HACs) were deposited by using the high power laminar plasma spray process. Major objectives were: (i) to estimate effects of several deposition parameters on chemical, structural, and morphological properties of HACs and (ii) to evaluate effects of human proteins albumin and gamma globulin on the early stage of the biomineralization process on the surface of HACs in modified Kokubo solutions (simulated body fluids) in which the pH value was actively regulated using CO2

Characterization and comparison of the carbides morphologies in the near surface region of the single- and double layer iron-based hardfaced coatings

The properties of the high-chromium white iron (HCWI) hardfaced materials, such as hardness, toughness and wear resistance, are affected by the morphology of their reinforcing phase, the Cr-carbides. In this work, the influence of the 1) welding parameters, 2) welding procedures and 3) chemical composition on the near-surface Cr-carbides morphology is presented. Additionally, the effects of the nucleo C® formula (Castolin Eutectic Ltd.) of unknown composition are evaluated. The hardfaced coatings are deposited by using the submerged metal arc welding (SMAW) process. The obtained near-surface structures are observed with scanning electron microscope with energy dispersive system (SEM-EDS). The structure morphological parameters are quantitatively determined by use of the ImageJ software. In the single-layer HCWI hardfaced coatings, larger heat input per unit length (≈ 4.1 kJ/mm) is leading to a formation of the hypoeutectic structures. An approximately two times lower heat input (≈ 1.8 kJ/mm) stimulates the solidification of the near-eutectic structures with presence of spheroidized eutectic and primary Cr-carbides (the Nucleo C effect). The double-layer coatings deposited with the ≈ 1.8 kJ/mm possess the hypereutectic structures with blade-like primary and needle-like eutectic carbides (the absence of the Nucleo C effect). The lower heat input (≈ 1.4 kJ/mm) and increase of the chromium and carbon content result in a formation of the hypereutectic structures with presence of the primary rod-like Cr-carbides embedded in the eutectic matrix with coarser and irregular eutectic Cr-carbides. The influence of the nucleo C® formula on the Cr-carbides morphology is more pronounced in the single-layer HCWI hardfaced coatings than in the double-layer coatings

The effects of aging on the precipitation of the W-rich phase in the matrix of the 92.5W-5Ni-2,5Fe powder metallurgy heavy alloys

The precipitation behavior of W-rich phase on the specific matrix locations of Co-free and Co-containing 92.5W-5Ni-2.5Fe heavy alloys is investigated during aging of the as-quenched samples. The aging treatment is performed between 600 °C (873 K) and 800 °C (1073 K) and for aging time up to 9 hours. The average chemical composition of tungsten heavy alloys was determined by using the atomic absorption spectrophotometry (AAS) and the Leco apparatus. The Energy Dispersive X-ray (EDX) analysis was employed to analyze the chemistry of the existing phases. The changes in structure as a function of aging time and temperature have been examined by using the light microscopy (LM) and the scaning electron microscopy (SEM). The macro- and micro-hardness measurements were performed, as well. The local changes in matrix structure and various morphologies of the precipitates are observed. The aging has caused only a minor changes of the micro-hardness of the existing phases (γ and W-rich) as well as the macro-hardness of the investigated alloys. In the case of the Co-free 92.5W-5Ni-2.5Fe heavy alloy, at lower temperatures and for shorter time of aging, there is a dominant presence of lamellar and Widmanstätten morphology of W-rich precipitates within the γ-matrix grains. At higher temperatures and for longer time, there is a significant precipitation of W-rich precipitates at the matrix grain boundaries (γ/γ). In the case of 92.5W-5Ni-2.5Fe heavy alloy micro-alloyed with Co, it is dominant precipitation of W-rich phase at the matrix grain boundaries (γ/γ), especially at higher aging temperatures and for longer aging time

Deposition of the DLC Structures In The Low-pressure Oxy-acetylene Flat Flame

The morphology and phase composition of the diamond-like carbon (DLC) structures as a function of a deposition process parameters are investigated. The DLC was deposited in the low-pressure oxy-acetylene flat flame onto molybdenium substrates. It was done with the designed flame burner by spreading the flame over the area of 40 mm in diameter with the overall acetylene and oxygen flow up to 4 l/min and by changing the substrate distance and the O2/C2H2 ratio. The morphology and the phase composition of the DLC coatings sighnificantly depend on the deposition parameters, especially on the O2/C2H2 ratio

Assessment of Safety Valve Springs Failure

The aim was to investigate the cause of failure of as-received ultra-high strength steel springs, which were deposite-coated. The qualitative analysis of surrounding environment was performed. Springs were visually and radiographically examined. Their chemical composition was determined using spectrophotometer, primary and secondary structure by use of bright-field reflected light microscope with vertical illumination source, and fracture mechanism by scanning electron microscope with energy dispersive system. Macro-hardness measurements were employed, also. The phases present in deposite were identified using X-ray Powder Difractometry and Electron Microprobe analysis. The safety valve springs failure is caused probably by corrosion-assisted process with presence of overloading