Ultra-fine hydroxyapatite powders were successfully synthesized using radio frequency (RF) suspension plasma spraying (SPS). This novel technique utilises the inherent characteristics of the RF plasma to axially feed and spheroidise a liquid suspension to produce spherical ultra-fine HA powders. This offers an alternative approach over conventional D.C. and flame spheroidising techniques which are better suited for solid feed stocks. Rietveld analysis was subsequently applied using Rietquan Quantitative Analysis software package to determine the amount of decomposed phases and amorphous content of the as-sprayed powder. This was also compared against quantitative XRD analysis employing internal and external standards. However, pure phases needed for calibration is scarce and amorphous calcium phosphate (ACP) is virtually impossible to isolate. In addition, the long and laborious task of obtaining calibration curves makes this technique unpopular. Nevertheless, conventional quantitative phase analysis (QPA) was carried out, using relative peak height ratios of HA and the phase involved, but the calculated decomposition only shows relative trends for a particular parameter variation. Determining the actual phase content is critical because of possible variations in biological responses when used as coatings and inserts in restorative orthopaedic implants. Varying tissue responses can arise from decomposed phases such as α and β-tricalcium phosphate (TCP) and tetra-calcium phosphate (TTCP) as well as ACP which generally have higher solubility as compared to crystalline. QPA via the Rietveld method provides a powerful tool that offers the user simultaneous quantitative phase determination of multiphase systems containing amorphous content. Unlike XRD QPA, the amorphous content could be indirectly calculated using crystalline alumina standard. XRD QPA results showed that decomposition generally rose with plate power without considering the amorphous content. With Rietveld QPA, the results showed an initial rise in decomposition before decreasing at higher plate powers. The amorphous phase content was calculated at different plate powers and concentration of suspension with the aid of alumina as an external standard. Results showed that the amorphous content increased substantially at higher powers. This study demonstrates the ability of Rietveld analysis to completely quantify all associated amorphous and crystalline phases within a multiphase system for any thermally treated material.

A novel thermal plasma process, based on inductively coupled plasma torch is employed for producing nano-sized calcium phosphate powders from spray-dried hydroxyapatite (HA) feedstock. The phases during plasma process of HA feedstock under different working conditions have been studied. It is revealed that amorphous calcium phosphate is predominant in the nano-sized powders. HA, α-TCP and CaO are also detected in the nano-sized powders. After heat treatment at 800 °C in air, β-Ca 2 P 2 O 7 (β-DCP) and HA are found to dominate in the powders. The presence of β-DCP is attributed to the HA feedstock directly decomposed into DCP in the plasma flame, and this phase formed amorphous calcium phosphates region by the rapid quenching process. This region crystallized into β-DCP after heat treatment.

In recent studies, titania has been added to hydroxyapatite (HA) coatings to impart photocatalytic properties. The benefits of such additions are maximized when titania is in nanocrystalline anatase form. In this study, nano-titania was synthesized in-flight from a liquid precursor consisting of ethanol and titanium isopropoxide. The precursor and HA powder were fed into a plasma gun, forming nano-titania particles that embedded in the HA. Coatings of pure titania and titania-embedded HA were deposited under different spray conditions on titanium coupons and then characterized via XRD and SEM analysis. The titania coatings contained ultrafine anatase and rutile particles with anatase being favored by more power input and rapid quenching. The composite coatings contained dispersed ultrafine titania particles in a matrix consisting primarily of HA with trace amounts of calcium phosphate and amorphous phases. The effect of spraying parameters on phase and microstructure evolution is discussed as well.

In this work, a TiO 2 coating with nanostructured surface was obtained through plasma sprayed nano-sized TiO 2 powder. Its bonding strength onto Ti-6Al-4V substrate is high up to 38 MPa. At same time, we have successfully improved the bioactivity of plasma sprayed TiO 2 coating with nanostructured surface using hydrogen ion implantation and UV illumination. Bone-like apatite can form on the surface of the post-treated TiO 2 coatings after they are soaked in simulated body fluid for a period of time. Introduction of surface bioactivity (bone conductivity) to plasma-sprayed TiO 2 coatings which are generally recognized to have excellent biocompatibility and corrosion resistance as well as high bonding to titanium alloys makes them more superior than many current biomedical coatings such as plasma-sprayed hydroxyapatite.

Nanostructured hydroxyapatite (HA) and HA/nano-zirconia powders were sprayed by both plasma and HVOF spraying. Microstructure characterization on the nanostructured coatings were conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and Raman spectroscopy. Results showed that the nanostructures of the HA feedstock retained to some extent after the thermal spraying depending on the melt state of the powders. The microstructural features of individual HA splats were also characterized through TEM observing both as-sprayed and ion-milled splats. A nanostructure (with ~ 30nm grains) within the surrounding parts of the HA splats was revealed, while significant grain growth (a size up to 5 µm) depending on flattening state was found at the center of the splats. It also revealed that the nano-sized zirconia particles (< 90 nm) retained their fine size after HVOF deposition, and were evenly distributed within the coating. The crystallite size of tetragonal zirconia in the coating was found to be less than 13 nm. The biocompatibility of the coatings was characterized using in vitro incubation testing in simulated body fluid and osteoblast cell culturing. It showed that the presence of the nanostructures in the coatings improved the stability of the coatings (delayed the dissolution). The addition, the presence of the nanostructures contributes to improved mechanical properties.

In this paper, nano-structured TiO 2 coatings have been successfully deposited onto titanium alloy substrates by atmospheric plasma spraying technology using optimized plasma parameters. A chemical treatment method was employed to induce bioactivity on the TiO 2 surface. The bioactivity of as-sprayed and chemical treated TiO 2 coatings were evaluated by investigating the formation of apatite on their surface after they were soaked in simulated body fluids (SBF) for a period of time. Microstructure and the phase composition of the as-sprayed coating and apatite were analyzed by Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDS). The results obtained indicate that as-sprayed TiO 2 coating consists of rutile, anatase and suboxide such as Ti 3 O 5 . The surface of nano-TiO 2 coating is covered by nano particles of about 50nm in size. The bonding strength of TiO 2 coating with Ti alloy substrate is as high as 40 MPa. The corrosion resistance performance of nano-coating in SBF is better than that of Ti-6Al-4V alloy. The surface of as-sprayed TiO 2 coating can not induce bone-like apatite formation. Chemical treatment, such as acid and alkali, can improve bioactivity of TiO 2 coating surface.

Thermal spraying of suspensions containing particles of submicron or nano-size offers new possibilities in functional coating development and enables new application fields. Spraying of suspensions containing bioceramic materials by hypersonic flame spraying (HVSFS), result in coatings with a refined microstructure. A layer thickness ranging from 10 - 50 µm can be achieved. Thermally sprayed HAp coatings are widely used for various biomedical applications due to the fact that HAp is a bioactive, osteoconductive material capable of forming a direct and firm biological fixation with surrounding bone tissue. Bioceramic coatings (e.g. Hydroxyapatite HAp, Tricalcium Phosphate TCP or Bioglass) were thermally sprayed on Ti plates by high-velocity suspension flame spraying. The deposited coatings were mechanically characterized. The bond strength of the layer composites was analyzed by the pull-off method and compared for different spraying conditions.

Inductively coupled radio frequency (RF) plasma spraying, powered by high-frequency oscillating electrical current, performed an important role in fine powder manufacture. It was used in the present study to prepare fine spherical bioceramic powders of hydroxyapatite (HA) whose chemical composition similar to those of natural bone. The as-sprayed powders consisted of both micron-sized spherical particles and nano-sized particles. In addition to the spheroidization effect, rf plasma treatment led to the decomposition of HA into secondary calcium phosphate phases including tri-calcium phosphate (TCP), tetra-calcium phosphate (TTCP) and calcium oxide (CaO). The microstructure investigation showed that the spheroidized particles were either fully dense or hollow structure with a shell. The reason for the formation of hollow spheres was contributed to the higher density of the solidifying surface layer compared with the molten phase during solidification.

The aging baby boomer population coupled with an increase in life expectancy is leading to a rising number of active elderly persons in occidental countries. As a result, the orthopedic implant industry is facing numerous challenges such as the need to extend implant life, reduce the incidence of revision surgery and improve implant performance. This paper reports results of an investigation on the bioperformance of newly developed coating-substrate systems. Hydroxyapatite (HA) and nano-titania (nano-TiO 2 ) coatings were produced on Ti-6Al-4V and fiber reinforced polymer composite substrates. In vitro studies were conducted in order to determine the capacity of bioactive coatings developed to sustain osteoblast cells (fetal rat calvaria) adherence, growth and differentiation. As revealed by SEM observations and alkaline phosphatase activity (ALP), cell adhesion and proliferation demonstrated that HA coatings over a polymer composite are at least as good as HA coatings made over Ti-6Al-4V substrate in terms of osteoblast cell activity. Nano-TiO 2 coatings produced by high-velocity oxy fuel (HVOF) spraying led to different results. For short term cell culture (4.5 and 24 hrs), the osteoblasts appeared more flattened when grown on nano-TiO 2 than on HA. The surface cell coverage after 7 days of incubation was also more complete on nano-TiO 2 than HA. Preliminary results indicate that osteoblast activity after 15 days of incubation on nano-TiO 2 is equivalent to or greater than that observed on HA.

Most of ductile metals can be deposited by cold spray (CS). For brittle ceramic, such solid-state deposition process is still questionable, but some recent work on Ti0 2 or hydroxyapatite powders have shown that micrometric ceramic powder could be deposited by CS. In this work, it is claimed that the nature and the porous architecture of a ceramic powder with agglomerated ultra-fine grains play an important role on the impact behaviour. The aim of this work is to investigate the deformation behaviour of ceramic agglomerated powders under high velocity impact. Two different powders, respectively 3YSZ and Y 2 O 3 , were selected in order to study their architectures (particle size, porosity, density, crystallite size, etc.). Cold spray “splats” experiments, with various spraying distances to vary the particles velocities upon impact, were carried out to observe the deformation and fragmentation. In case of Y 2 O 3 , cold spray with dynamic vacuum surrounding atmosphere up to 3kPa were also prepared to evaluate the role of the atmosphere on the resulting impact. In parallel, in situ SEM micro-compression tests at 10 −2 s −1 on cross-sectioned 3YSZ particles involving flat-punch nano-indentation and micropillar compression were performed. By modelling the compression tests, the aim is to identify a Drücker-Prager behaviour law suitable for an agglomerated ceramic powder under quasi-static compression. Such deformation behaviour could help to better understand the compaction behaviour of agglomerated powders.

In this study, hydroxyapatite (HA) coatings were deposited on stainless steel by suspension plasma spraying. Coating samples and suspensions were examined by means of electron microscopy, XRD analysis, and FTIR and Raman spectroscopy. The results show that the coatings are porous and nanostructured with no impurity phases when low H 2 flow rates are used. They also contain a significant amount of OH - and CO 3 2- , which facilitates the formation of well-crystallized HA and improves bioactivity and compatibility in implant applications.

In the High Velocity Oxygen Fuel (HVOF) technology, the coating properties are sensitive to the behaviors of in-flight particles, which are mainly influenced by the processing parameters. However, due to the complex chemical and thermodynamic reactions, the real-time optimization of the coating properties during the HVOF process is still a challenging issue. This study focused on establishing an Artificial Neural Networks (ANN) model to analyze the influence of the processing parameters on the characteristics of in-flight particles. Hydroxyapatite (HA) powders were selected to deposit onto the stainless steel substrates via an improved HVOF spraying system. Combined with an Accuraspray-g3 system applied to acquire the temperature and velocity of inflight HA particles, the artificial neural network algorithm was well trained to predict the velocity and temperature of in-flight particles. The relationship between the variations of the operating parameters (gas flow rates and fuel-to-oxygen ratio) and the behaviors of in-flight HA particles was investigated, which therefor contributes to analyzing and optimizing the mechanical performance and crystallinity of the HA coatings.

In this investigation, bioactive ceramic materials, including dicalcium silicate, titania, and zirconia, were deposited on titanium substrates by plasma spraying in order to determine their effect on the bioactivity of metal implants. Cell-seeding tests show that MG63 osteoblast-like cells grow and proliferate well on each of the coating materials. In the case of Ca 2 SiO 4 , the presence of silicon ions is thought to be the key to this behavior. In regard to TiO 2 and ZrO 2 , the bioactivity is thought to result from the nanostructured surfaces and special surface compositions.

Magnesium light weight alloys are currently being studied as implants due to their biodegradability. However, its applications are limited by high rate hydrogen evolution during corrosion. Coating on this substrate is one of the ways to reduce the rate of corrosion and increase the life of this type of implant. Hence, hydroxyapatite (HA) was coated on the substrates by using high velocity oxy- fuel (HVOF) spraying. The main purpose of such coatings is increasing bioactivity as well as corrosion resistance of the Mg alloy. Crystal structure was characterized by X-ray diffraction (XRD). Crystallinity of the coating was about 70% in which HA is dominant phase. The amounts of hydrogen gas released during magnesium corrosion tests in simulated body fluid (SBF) were measured to evaluate the corrosion resistance of the coated samples. This coating could decrease hydrogen evolution from 100 per cm 2 .mL to about 15 per cm 2 .mL after 29h of immersion time.

Ultra-fine hydroxyapatite (HA) powders were produced with radio frequency (RF) suspension plasma spraying (SPS). This novel technique utilizes the inherent properties of the RF plasma enabling axial feeding of the suspension into the plasma producing spherical ultra-fine HA powders. These powders were examined by XRD and Rietveld analysis using the Rietquan 2.3 Quantitative Analysis software package. The aim of the analysis was to determine the various amounts of decomposed phases and amorphous content after SPS of HA. Results showed that the amount of decomposed phases rose up to a plate power of 15 kW there after decreasing at higher plate powers. The amorphous phase however kept increasing with plate power reaching about 35 wt.% in the powders sprayed at 21 kW. These trends have led to the belief that the phase content and hence, the characteristics of the powders are controlled mainly by the competitive processes of decomposition and melting and evaporation within the plasma. The morphology of the powders was also observed through TEM and changes in molecular structure were investigated by FTIR. DSC was carried out to observe the crystallisation of amorphous calcium phosphate into HA.

Aerosol cold spraying (ACS) is modification of low-pressure cold spray technology which allows to deposit ceramic and metal-based coatings. ACS technology in vacuum possesses the formation of films from sub-micro and nanoparticles directly at room temperature. The ACS technology is still under development to cover more application and discover solutions of spraying different kind of powders on different types of material substrate and optimizing spraying conditions to obtain the best results. The main objective of the present work is to develop a new ACS cold spray technology of Hydroxyapatite (HA) and Copper powder deposition onto both the implants and ceramic substrates. The new AD spraying system with radial injection of particles to be deposited is constructed and tried. An influence of technology parameters on the coating structure and properties are presented. In addition, the combined cold spray and sintering technology technique is further investigated for additive manufacturing applications.

In this study, titania and hydroxyapatite nanopowder mixtures are deposited on medical grade titanium substrates by HVOF spraying. To assess bioperformance, human mesenchymal stem cells (hMSCs) were cultured from 1 to 21 days on the surface of HVOF-sprayed TiO 2 and TiO 2 -HA samples. Plasma sprayed HA and uncoated Ti-6Al-4V substrates were used as controls. The active cultures were evaluated for cell proliferation, cytoskeleton organization, and cell-substrate interaction. The results for HVOF-sprayed TiO 2 -HA nanocomposite coatings show strong evidence of bone growth, proliferation, and attachment with cell-substrate interaction levels superior to those of air plasma sprayed HA coatings. Although there are no clear explanations for this favorable behavior, the topography and chemical composition of the surface of the coating appear to be playing important roles.

Nanostructured titania (TiO 2 ) coatings were produced by high velocity oxy-fuel (HVOF) spraying. They were engineered as a possible candidate to replace hydroxyapatite (HA) coatings produced by air plasma spray (APS) on implants. They exhibited mechanical properties, such as hardness and bond strength, much superior to those of APS HA coatings. In addition to these characteristics, the surface of the nanostructured coatings exhibited regions with nanotextured features originating from the semi-molten nanostructured feedstock particles. This nanotexture is considered an asset, due to its better interaction with the adhesion proteins of the osteoblast cells, such as fibronectin, which exhibit dimensions in the order of nanometers. Osteoblast cell culture demonstrated that this type of coating supported osteoblast cell growth and did not negatively affect cell viability.

This study examines the influence of nano- and near-nano grains in bulk powder metal processing thus providing a baseline for understanding the potential of nanopowders for thermal spray application. Two light alloys (Al and Ti) and two tungsten carbide blends (WC-NiCrBSi and WC-CoCr) are cryomilled into nanocrystalline powders. The nanopowders are consolidated via hot isostatic pressing or spark plasma sintering and tested along with consolidated forms of virgin (micron scale) grains, shedding light on property improvements achieved through nanograined materials. HVOF coatings produced from nano- and micro-crystalline powders are tested as well, and the results are correlated with the improvements observed in the consolidated material forms.

In this study, hydroxyapatite (HA) and HA-SiO 2 coatings are applied to unalloyed Ti by atmospheric plasma spraying and corrosion resistance is assessed by immersion in Ringer’s solution for 24 h. The results show that the HA coating improves corrosion resistance, which is further improved with the addition of SiO 2 . An analysis based on Scherrer’s equation confirms an observed increase in crystallite size in the coated samples.