Volume 37, Issue 6

This manuscript has provided an overview of the development of TiNi alloys and their applications in biomedicine. The microstructures and properties of TiNi alloys are first introduced. The breakthroughs in the manufacturing and applications in biomedicine of TiNi alloys in recent years have been achieved by scientists and are presented in the present paper. It is well known that the properties of TiNi alloys are affected by the modification methods on the surface of bulk TiNi alloys. The main preparation technologies of TiNi alloy coatings are evaluated, with particular attention to several spray technologies. Then, the biocompatibility, strong anticorrosion and antiwear properties, and mechanism of TiNi alloys are also described in detail. Several advanced manufacturing processes of TiNi alloys are also briefly outlined such as selective laser melting and spark plasma sintering. The performance of TiNi alloy coatings prepared by thermal spraying techniques are fully qualified for medical applications. Thermal spraying techniques have great prospects in reducing the cost and improving the quality of TiNi alloy medical products.

This review paper considers the research conducted in the past 30 years in the field of corrosion under insulation (CUI). CUI is a significant challenge in many industries for reasons of high cost and risk because it proceeds undetected under insulation. CUI is an unavoidable problem which may potentially cause personnel injury or even fatalities. Presently, CUI counts for as much as 40 to 60% of pipeline-repairing cost. The use of coating under the insulation has been shown very efficient in the mitigation of CUI. Moisture and ion penetration, particularly chlorides, through the insulation and coating may produce stress corrosion cracking of austenitic stainless steels. The process of applying insulating materials on metal surfaces and the precautions that need to be taken are explained. Beside visual inspection, techniques such as neutron backscatter, capacitive imaging and pulsed eddy current can be used to detect the presence of CUI. The strength and limitations of the available commercial detection techniques are evaluated. A comprehensive list of industrial standards dealing with CUI is provided.

The efficacy of nano-TiO 2 -containing zinc phosphate coatings on low-carbon steel is investigated. Zinc phosphate coatings are electrodeposited on low-carbon steel (AISI 1015) keeping current density, deposition time and wt % nano-TiO 2 at their respective levels. Corrosion protection performance of these coatings was assessed using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl electrolyte. The morphology, the composition and the growth process of the zinc phosphate coating is investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD) and electrochemical measurements. The XRD study reveals that the obtained phosphate layer contains traces of hopeite and phosphophylite. The formed zinc phosphate coating offers high corrosion protection in 3.5% NaCl solution, which is well supported by EIS studies. The presence of nano-TiO 2 in the phosphate bath anticipated to offer a better surface coverage and reduction in porosity and forms more homogeneous coating, which is in agreement with the SEM studies. The optimization of the electrodeposition phosphating process for achieving better responses in terms of corrosion rate and coating resistance is addressed in this paper.

This paper reports on the influence of heat treatment on the corrosion properties of CuAlMn alloy in 0.1%, 0.9% and 1.5% NaCl solution (pH = 7.4). Heat treatment of alloy samples was performed by samples annealing at 900°C for 30 min. Electrochemical methods of investigations included measuring the open circuit potential ( E oc ) and linear and potentiodynamic polarisation. Optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to study the morphology and composition of the corroded surfaces, along with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Heat-treated samples have slightly more positive values of E oc , slightly lower values of corrosion current density and higher values of polarisation resistance compared with the as-cast alloy. The microscopic analysis showed the rough surfaces due to corrosion processes. Increasing the electrolyte concentration leads to an increase in alloy surface damage. AFM and SEM examinations showed that the surface was covered with interlaced layers of corrosion products, as well as cracks and ducts formed by their dissolution. EDX and XPS analyses showed that corrosive products consist mainly of aluminium and manganese oxides and chlorides. Annealed CuAlMn alloy samples have significantly lower copper content compared with the as-cast CuAlMn alloy.