A Study on Surface Modification of Al7075-T6 Alloy against Fretting Fatigue Phenomenon

Aircraft engines, fuselage, automobile parts, and energy saving strategies in general have promoted the interest and research in the field of lightweight materials, typically on alloys based on aluminum. Aluminum alloy itself does not have suitable wear resistance; therefore, it is necessary to enhance surface properties for practical applications, particularly when aluminum is in contact with other parts. Fretting fatigue phenomenon occurs when two surfaces are in contact with each other and one or both parts are subjected to cyclic load. Fretting drastically decreases the fatigue life of materials. Therefore, investigating the fretting fatigue life of materials is an important subject. Applying surface modification methods is anticipated to be a supreme solution to gradually decreasing fretting damage. In this paper, the authors would like to review methods employed so far to diminish the effect of fretting on the fatigue life of Al7075-T6 alloy. The methods include deep rolling, shot peening, laser shock peening, and thin film hard coatings. The surface coatings techniques are comprising physical vapor deposition (PVD), hard anodizing, ion-beam-enhanced deposition (IBED), and nitriding

Hydroxyapaptite layer formation on titanium alloys surface using micro-arc oxidation

In recent years, research on titanium and its alloys had increased significantly for hard tissue replacement and dental applications due to their excellent mechanical properties such as high strength to weight ratio, low density and biocompatibility. However, there are some surface originated problems associated with titanium (Ti): poor implant fixation, lack of osseoconductivity, wear and corrosion in physiological environment. As the interaction between the implant and host bone is a surface phenomenon, surface properties play a prominent role in determining both the biological response to implant and the material response to the biological condition. To improve osseointegration of titanium with bone, hydroxyapatite (HA) has been widely used due to its close similarity to bone mineral. Promising new studies have been reported regarding coating titanium implant with HA using various surface modification techniques to improve the long term stability of titanium implants. Micro-arc oxidation (MAO) has attracted a lot of interest owing to its ability to produce a thick microporous oxide layer on titanium implants. The significant part of MAO is that HA can be incorporated in the oxide layer when processed in electrolytes containing calcium and phosphorous ions. The oxide layer containing hydroxyapatite can be subsequently increased via hydrothermal treatment. The HA produced on titanium surfaces has attractive features such as high porosity and adherent layer which facilitate good clinical outcomes. This review presents the state of the art of MAO and possible further suggestion of MAO for the production of HA on titanium implants

Assessment of nano-indentation method in mechanical characterization of heterogeneous nanocomposite materials using experimental and computational approaches

This study investigates the capacity of the nano-indentation method in the mechanical characterization of a heterogeneous dental restorative nanocomposite using experimental and computational approaches. In this respect, Filtek Z350 XT was selected as a nano-particle reinforced polymer nanocomposite with a specific range of the particle size (50 nm to 4 µm), within the range of indenter contact area of the nano-indentation experiment. A Sufficient number of nano-indentation tests were performed in various locations of the nanocomposite to extract the hardness and elastic modulus properties. A hybrid computational-experimental approach was developed to examine the extracted properties by linking the internal behaviour and the global response of the nanocomposite. In the computational part, several representative models of the nanocomposite were created in a finite element environment to simulate the mechanism of elastic-plastic deformation of the nanocomposite under Berkovich indenter. Dispersed values of hardness and elastic modulus were obtained through the experiment with 26.8 and 48.5 percent average errors, respectively, in comparison to the nanocomposite properties, respectively. A disordered shape was predicted for plastic deformation of the equilateral indentation mark, representing the interaction of the particles and matrix, which caused the experiment results reflect the local behaviour of the nanocomposite instead of the real material properties

Experimental and modelling study of ultra-fine grained ZK60 magnesium alloy with simultaneously improved strength and ductility processed by parallel tubular channel angular pressing

Ultrafine grained ZK60 magnesium (UFG–ZK60 Mg) tubes were successfully fabricated by a parallel tubular-channel angular pressing (PTCAP) process. The number of pass effects on the phase composition, microstructural features and mechanical properties were examined. Also, two types of Artificial Neural Network known as Radial Basis Function (RBF) and Multi-Layer Perceptron (MLP) were employed to accurately estimate mechanical behavior of the PTCAP-processed ZK60 Mg alloy. The results showed that all the processed tubes had more refined microstructure with ~ 7 to 0.9 µm grain sizes, which consist of an average crystallite size between 68 ± 8 and 51 ± 8 nm, compared to the as-received specimen with a mean grain size of ~ 90 µm. Similar XRD profiles were achieved following different PTCAP passes, however, some discrepancies were observed as the number of passes increased, which corroborated the structural changes during the PTCAP process. The microscopic observations also revealed the microstructural changes by increasing the PTCAP passes. The hardness of the processed tubes increased with the number of PTCAP passes, from 77 ± 2 HV for the unprocessed alloy to a maximum of 111 ± 2 HV at three PTCAP passes. The PTCAP process increased not only mechanical strength but also the ductility of the processed tubes, where the highest yield strength (sYS = 320 MPa), ultimate tensile strength (sUTS = 397 MPa) and elongation to failure (d = 14%) values were obtained at the second pass of PTCAP. However, with increasing number of PTCAP passes to three, d reached 4% and sYS and sUTS decreased by 31% and 11%, respectively. Findings from the neural based-predictive models indicated that both RBF and MLP can be employed for accurately estimating the mechanical properties of the PTCAP-processed ZK60 Mg alloy