Sisa Pityana

Microstructures, hardness and bioactivity of hydroxyapatite coatings deposited by direct laser melting process.

Hydroxyapatite (HAP) coatings on bioinert metals such as Ti-6Al-4V are necessary for biomedical applications. Together, HAP and Ti-6Al-4V are biocompatible and bioactive. The challenges of depositing HAP on Ti-6Al-4V with traditional thermal spraying techniques are well founded. In this paper, HAP was coated on Ti-6Al-4V using direct laser melting (DLM) process. This process, unlike the traditional coating processes, is able to achieve coatings with good metallurgical bonding and little dilution. The microstructural and mechanical properties, chemical composition and bio-activities of the produced coatings were studied with optical microscopy, scanning electron microscope equipped with energy dispersive X-ray spectroscopy, and Vickers hardness machine, and by immersion test in Hanks solution. The results showed that the choice of the laser power has much influence on the evolving microstructure, the mechanical properties and the retainment of HAP on the surface of the coating. Also, the choice of laser power of 750 W led to no dilution. The microhardness results inferred a strong intermetallic-ceramic interfacial bonding; which meant that the 750 W coating could survive long in service. Also, the coating was softer at the surface and stronger in the heat affected zones. Hence, this process parameter setting can be considered as an optimal setting. The soak tests revealed that the surface of the coating had unmelted crystals of HAP. The CaP ratio conducted on the soaked coating was 2.00 which corresponded to tetra calcium phosphate. This coating seems attractive for metallic implant applications.

Microstructure, hardness and corrosion properties of laser processed Ti6Al4V-based composites

Abstract Nb and Ti–13Nb powders were used for improving the surface of Ti6Al4V alloy. The deposition of the powders was carried out at various laser powers. The scanning electron microscopy (SEM)–EDS and optical microscopy were used for characterization. X-ray diffractometer (XRD) was used for analyzing the elemental composition and phase constituents. The hardness, wear and corrosion properties were achieved. The corrosion and the wear behaviours of the deposited layers were studied in a Hanks solution (simulated body fluid, SBF). The microstructures of Nb coatings reveal the presence of orthorhombic, dendritic α” and metastable β-Nb phases which produce uneven hardness with an average of HV 364. For Ti–13Nb coatings, martensitic α and metastable β-Nb phases with an average hardness of HV 423 were observed. The resistance of wear on dry sliding of Ti–13Nb coating is attributed to the increase in hardness. Experimental results indicate that deposition of Nb and Ti–13Nb on Ti6Al4V grossly reduces the mass fractions of Al and V in all coatings. In SBF, Nb reinforcement produces the best coating that reveals the best wear and corrosion resistances as compared with the substrate. Hence, this coating will perform best for orthopaedic implant material enhancement.

Microstructural and mechanical evaluation of laser-assisted cold sprayed bio-ceramic coatings : potential use for biomedical applications

Bio-composite coatings of 20xa0wt.%, HAP and 80xa0wt.%, HAP were synthesized on Ti-6Al-4V substrates using LACS technique. The coatings were produced with a laser power of 2.5xa0kW, powder-laser spot trailing by 5xa0s. The coatings were analyzed for the microstructures, microhardness, composition, and bio-corrosion using SEM-EDS, XRD, hardness tester, and Metrohm PGSTAT101 machine. SEM images indicated least pores and crack-free coating with dark-spots of Ti-HAP for the 20xa0wt.%, HAP as opposed to the 80xa0wt.%, HAP coating which was solid, porous and finely cracked and had semi-melted Ti-HAP particles. The EDS mappings showed high content of HAP for the 80xa0wt.%, HAP coating. The diffraction patterns were similar, even though the Ti-HAP peak was broader in the 80xa0wt.%, HAP coating and the HAP intensities were lower for this coating except for the (004) peak. The hardness values taken at the interface inferred that the 80xa0wt.%, HAP coating was least bonded. It was possible to conclude that when this phase material increased the hardness dropped considerably. The bio-corrosion tests indicated that the presence of HAP in coating leads to a kinetically active coating as opposed to pure titanium coating.

In situ laser deposition of NiTi intermetallics for corrosion improvement of Ti–6Al–4V alloy

Abstract NiTi intermetallic coatings were fabricated on the surface of Ti–6Al–4V alloy by melting Ni and Ti powders using laser metal deposition (LMD) process. The effects of NiTi reinforcement content on the microstructure, hardness and corrosion properties of the coatings were examined. The results show that the deposited coatings are characterized by NiTi, NiTi 2 and NiTi 3 intermetallic phases. An appreciable increase in corrosion resistance is obtained for all the coatings, and Ti55Ni45 coating shows the highest corrosion resistance; while coatings Ti50Ni50 and Ti45Ni55 follow in that succession. The reinforcement materials are proven to be corrosion resistant in the tested environment, and the effect of Ti is more dominant.

Nd: YAG laser treatment of aluminium —C TiB2 coated: Optimization of corrosion properties

As the reports in the literature regarding corrosion performance of Al/TiB2 MMC are rather contradictory, the optimization of laser surface alloying parameters for these composite coatings seems to be necessary. The characterization of the MMC was carried out by optical microscopy (OM), scanning electron microscopy (SEM/EDS) and x-ray diffraction (XRD). Partial melting of the alloying powder occurred and the chemical reactions with the a-Al in the matrix led to the formation of AlTi and AlB2 phases. Eutectics of TiB2/Al and TiB2/Ti were observed. The results of the tests indicate that TiB2 reinforcement does not give significant increase in microhardness of aluminium. The corrosion resistance of a single laser trackline MMC in a 3.65 % NaCl solution was improved, especially for the sample produced at high scan speed, with the lowest volume fraction of TiB2 particles.

The Microstructural and In Vitro Characterics of Hydroxyapatite Coating Fabricated Using Nd-YAG Laser

Hydroxyapatite (HAP) is the most researched calcium phosphate material in the field of biomaterials to be used for bone re-engineering applications; given its attractive properties. Plasma spraying is the best available industrial method that can be used to deposit HAP coatings on metallic substrates. However, this process is sustained with high heat inputs which decompose HAP into secondary phases. These phases are undesirable for biomedical applications. Lasers are sued as secondary post-laser curing step where they are used to improve the crystallinity of these coatings. The purpose of this study was to establish the optimised setting process parameters necessary for direct laser melting process. Nd-YAG laser was used to directly melt HAP powder beds preplaced on Ti-6Al-4V. The produced coatings were characterised with preserved, mixed morphologies of HAP crystallites that sat on the surface of the coating. These crystals were suspended on the long and short titanium needles according to SEM images. XRD results indicated a mixture of HAP and TTCP in the coating while TEM conclude a hexagonal atomic packing. These results indicated that in addition to laser power and scanning speed, the angle at which the laser beam interacts with material is also a necessary parameter to optimise.

Tribocorrosion Response of Laser Clad TiNiZrO2 Composite Coatings on Ti6Al4V

The design of tribocorrosion resistant composite on Ti6Al4V alloy by laser surface cladding of admixed metal-ceramic powder was successfully achieved using a 2 kW CW ytterbium laser system (YLS). The effects of TiNiZrO2 addition on the tribocorrosion properties of the synthesized composite coatings were investigated in 1 M H2SO4 solution using open circuit potential and potentiodynamic polarization techniques. The experimental results showed that TiNiZrO2 refined the microstructure to flower-like structure. A strong metallurgical bond was obtained between the coatings and the Ti6Al4V alloy substrate with inter-columnar widmansttaten α΄ grains at the interface. There was a significant increase in surface microindentation hardness values of the clad layers. Also, the presence of zirconia shifted the tribocorrosion potential to more noble values and significantly enhanced the tribocorrosion resistance of the composites.