Surface modification of titanium 6-aluminum 7-niobium alloy with biodegradable polymer coatings

The aim of the study is to determine the effect of long-term exposure to Ringer's solution on the physical properties of biodegradable polymer coatings on the titanium 6-aluminum 7-niobium alloy substrate. 30 day, 60 day and 90 day research periods are applied. The work is performed on a titanium 6-aluminum 7-niobium alloy modified by sandblasting and anodic oxidation. Three biodegradable polymer coatings: poly(glycolide-ϵ-caprolactone); poly(glycolide-ϵ-caprolactone-L,L-lactide) and poly(D,L-lactide-glycolide), containing ciprofloxacin are used in the study. The coatings are deposited by dip-coating method. Topography, wettability, and adhesion of the coatings are analyzed. The analysis of the test results indicates that regardless of the type of coating and the number of dips, the obtained coatings are continuous, hydrophilic, map the topography of the substrate, and slight change roughness after exposure to Ringer's solution. After three months of exposure to Ringer's solution, an increase in wettability and, at the same time, a significant decrease in adhesion is observed. The poly(D,L-lactide-glycolide) coatings are characterized by the greatest adhesion to the substrate.     

Influences of size and position of defects on the fatigue life of electron beam welded-aluminum alloy joints

Defects such as pores influence the fatigue life of electron beam-welded aluminum alloy joints. In this paper, the influences of pore size and position on the fatigue life of aluminum overlap joint are studied. A finite element model (FEM), combined with experimental data, is established to evaluate the fatigue life of overlap joints. By employing this FE model, the effects of pore size and position on fatigue lives of overlap joints are investigated and discussed. From the present study, when pore position is closer to the weld bead tip or the faying surface, the fatigue life decreases. Also, there is a critical size for the pore; when the pore size is larger than the critical value, the fatigue strength decreases sharply.     

Thermomechanical and flexural properties of chopped silk fiber-reinforced poly(butylene succinate) green composites: effect of electron beam treatment of worm silk

The effect of electron beam treatment on the thermomechanical and flexural properties of chopped silk fiber-reinforced poly(butylene succinate) (PBS) green composites was studied for the first time in this work. The surface topological changes in worm silk fibers before and after the electron beam irradiation at various doses (5–100?kGy) were observed. Dynamic mechanical and flexural properties and thermal expansion behavior of neat PBS and silk/PBS green composites were investigated by means of dynamic mechanical analysis, three-point flexural test, and thermomechanical analysis. The irradiated silk/PBS composite result was compared with neat PBS and un-irradiated silk/PBS counterparts. It was concluded that use of electron beam irradiation at an appropriate dosage may contribute to an enhancement of the dynamic mechanical and flexural properties as well as to the thermodimensional stability of silk-based green composites. The result revealed that the property enhancement was most profound at the electron beam absorption dose of 20?kGy.     

Measurement of the heat of fusion of titanium and a titanium alloy (90Ti-6Al-4V) by a microsecond-resolution transient technique

A microsecond-resolution pulse heating technique was used for the measurement of the heat of fusion of titanium and a titanium alloy (90Ti-6Al-4V). The method is based on rapid (50- to 100-s) resistive self-heating of the specimen by a high-current pulse from a capacitor discharge system and measuring, as functions of time, current through the specimen, voltage across the specimen, and radiance of the specimen. Melting of the specimen is manifested by a plateau in the measured radiance. The time integral of the net power absorbed by the specimen during melting yields the heat of fusion. The values obtained for heat of fusion were 272 J · g^–1 (13.0 kJ · mol^–1) for titanium and 286 J · g^–1 for the alloy 90Ti-6Al-4V, with an estimated maximum uncertainty of ±6% in each value.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

A study on hybrid bioceramic coatings of HA/poly(vinyl acetate) co-deposited electrochemically on Ti–6Al–4V alloy surface

A novel electrochemical co-deposition approach was developed to prepare hybrid bioceramic coating of hydroxyapatite (HA)/poly(vinyl acetate) on the surface of Ti–6Al–4V alloy. The aim is to improve the adhesion between the HA coating and the metal substrate. Surface characterization showed that the composition of inorganic phase in the composite bioceramic coatings was mainly HA and the content of organic phase was more than 4% (W/W). Significant surface morphology changes were observed. The shear-testing experiments indicated that the bonding strength of the hybrid coating to metal substrate was increased by as much as 3 MPa.     

Effect of high-energy electron beam irradiation on the properties of AZO thin films prepared by rf magnetron sputtering

We investigated that high-energy electron beam irradiation (HEEBI) performed in air at room temperature affected remarkably the properties of Al-doped ZnO (AZO) films grown on SiO₂ substrates by radio frequency magnetron sputtering techniques. Hall and photoluminescence measurements revealed that the n-type conductivity was preserved in HEEBI treated films with low dose up to 10¹⁵ electrons/cm² and converted to p-type conductivity with further increase in the amount of dose. X-ray photoelectron spectroscopy confirmed the conversion of conductivity by showing that in-diffusion of O₂ from the ambient as well as out-diffusion of Zn from the films took place as a result of HEEBI treatment at high dose of 10¹⁶ electrons/cm². X-ray diffraction analysis indicated that all as-grown films were found to have compressive stress, which was enhanced by HEEBI treatment with the increase of doses. It was also found that worse crystallinity with a smaller grain size was observed in HEEBI treated films with a higher dose, which was correlated with rougher surface morphologies of films observed by an atomic force microscope.     

Structure‐property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications. Part II: Resistance to fatigue crack propagation and fracture

Investigations were continued on the dissimilar laser beam welds of AA6056 and Ti6Al4V, fabricated by inserting Ti‐sheet into the profiled Al‐sheet and melting AA6056 alone. By using microstructure, hardness and strength as the criteria, sites exhibiting non‐uniform microstructure and localized plastic deformation due to strength mismatch were investigated in two orientations: ? crack parallel to the weld and ? crack perpendicular to the weld for fatigue crack propagation and fracture toughness at room temperature. Effect of temper of AA6056 on these properties was studied for two conditions; welding in T4 followed by post weld heat treatment T6, and welding in T6 and naturally aged for a defined period. The orientation “crack parallel to the weld” was investigated in 3 locations on the side of AA6056: the interface and the two changeovers on the Al‐side. Firstly, between the fusion zone and the heat affected zone (3 mm from the interface) and secondly, between (primary) heat affected zone and towards the base material (7 mm from the interface). Although brittle intermetallic TiAl₃ had been formed at the interface, uncontrolled separation or debonding at the interface was not observed. Insofar the bond quality of the weld was good. However, the ranking of interface was the lowest since fatigue crack propagation was relatively faster than that in the fusion zone and heat affected zone, and fracture toughness was low. Therefore, unstable fatigue crack propagation is observed when the crack propagates perpendicular to the weld from AA6056 towards Ti6Al4V. The results have shown that the dissimilar joints exhibit improved performance when laser beam welded in the T6 condition.     

The surface characteristics of organoclays and their effect on the properties of poly(trimethylene terephthalate) nanocomposites

Biobased materials developed in conjunction with nanotechnology are poised to achieve a significant presence in the world market for polymeric materials. An example of an engineering polymer that can be partially derived from biomass is poly(trimethylene terephthalate). One of its raw materials, 1,3-propanediol, can be derived from corn sugar. In the present study we used a fully petroleum-based resin as an analog to the biobased material. Five organically modified montmorillonite clays were characterized via moisture uptake studies to determine the hydrophilic/hydrophobic nature of their surfaces. Nanocomposites were produced via melt compounding followed by injection molding with 5 wt.% organoclay loading to determine which modification gave the best balance of mechanical and thermal properties. It was found that the tensile modulus increased by up to 35% and the tensile stress at break by up to 50%. The heat deflection temperature of the nanocomposites versus the neat polymer increased by up to 33 °C. From these results, one organoclay was selected for detailed study over a loading range of 0–5 wt.%. The testing revealed that over this range, changes in the mechanical properties may go through a maximum (e.g. strength) or increase/decrease to a plateau (e.g. modulus, elongation at break). X-ray diffraction and transmission electron microscopy were also used to characterize the nature of the organoclay/polymer interaction. Biobased poly(trimethylene terephthalate)/organoclay nanocomposites are expected to exhibit properties similar to the petroleum-based resin.     

The effect of bi-modal and lamellar microstructures of Ti-6Al-4V on the behaviour of fatigue cracks emanating from edge-notches

This paper is aimed at evaluating the influence of bi‐modal and lamellar microstructures on the behaviour of small cracks emanating from notches in α+β titanium Ti‐6Al‐4V alloy. Pulsating four point bending tests were performed at a nominal stress ratio of 0.1 and a frequency of 15 Hz on double‐edge‐notched specimens. The conditions of initiation and early propagation of fatigue cracks were investigated at two relatively high nominal stress levels corresponding to 88 and 58% of the 0.2% material yield stress. Crack closure effects were measured by an extensometric technique and discussed. Variations in crack aspect ratio were determined and considered in the ΔK calculation. Corresponding results were discussed by considering the effect of the yielded region at the notch tip calculated by elastic–plastic finite element modelling of the fatigue tests. The importance of the bi‐modal and lamellar microstructures on the material damage was highlighted and correlated to the observed oscillations in the crack growth rate. The crack growth rate data obtained were compared with those measured using standard C(T) specimens (long crack).     

Influence of laser power on the corrosive behavior of laser metal deposited Ti6Al4V+Cu in artificially prepared sea water

Titanium alloy is an excellent corrosion resistance material due to its greater affinity with oxygen when exposed to an aggressive medium such as sea water. The protection against attack is due to the oxidizing fume formed into its surface. This paper reports the effect of laser power on the corrosive behavior of laser metal deposited Ti6Al4V alloy with 5 weight percent (wt. %) copper in freshly prepared artificial sea water. The open circuit potential, potentiodynamic polarization curves, and the scanning electron microscope (SEM) morphologies of the entire Ti6Al4V+5 Cu alloy samples had been investigated and reported. From the results obtained, it can be deduced that the laser power is inversely proportional to the corrosion rate. Sample PL3 deposited with a laser power of 1600 W exhibited the best corrosion rate of 0.0123 mm/year when exposed to sea water under aerated condition. The morphologies of the entire laser deposited samples of the scanning electron microscope (SEM) unveiled typical passivity due to the strong inter-atomic bonds between the α/β phases formed with the copper inclusion within the lattices of the titanium alloy.