Development of osteoblast colonies on new bioactive coatings

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-TiO₂) coatings were produced on Ti-6Al-4V and fiber reinforced polymer composite substrates. In vitro studies were conducted to determine the capacity of bioactive coatings developed to sustain osteoblast cells (fetal rat calvaria) adherence, growth, and differentiation. As revealed by scanning electron microscopy (SEM) observations and alkaline phosphatase activity, 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-TiO₂ coatings produced by high-velocity oxyfuel (HVOF) spraying led to different results. For short-term cell culture (4.5 and 24 h), the osteoblasts appeared more flattened when grown on nano-TiO₂ than on HA. The surface cell coverage after seven days of incubation was also more complete on nano-TiO₂ than HA. Preliminary results indicate that osteoblast activity after 15 days of incubation on nano-TiO₂ is equivalent to or greater than that observed on HA. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Effect of Cu2+ doping on photocatalytic performance of liquid flame sprayed TiO2 coatings

Cu²⁺ was added to liquid feedstock to deposit ion doping TiO₂ photocatalytic coatings through liquid flame spraying. The coating microstructure was characterized by x-ray diffraction (XRD), transmission electron microscopy, and x-ray photoelectron spectroscopy (XPS). The photocatalytic performance of coatings was examined by photodegradation of acetaldehyde. The XRD analysis shows that the crystalline structure of coatings is not significantly influenced by Cu²⁺ doping. The photocatalytic activity of the TiO₂ coatings is enhanced by Cu²⁺ doping. It is found that a high concentration of Cu²⁺ doping decreases the activity. The XPS analysis shows that the adsorbed oxygen concentration is increased with the increase of Cu²⁺ dopant concentration and decreases with a further increase of dopant concentration. The enhancement of photocatalytic activity can be attributed to the adsorption ability of oxygen and other reactants on the surface of doping TiO₂ coatings. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Biocompatible nanostructured high-velocity oxyfuel sprayed titania coating: Deposition, characterization, and mechanical properties

Nanostructured titania (TiO₂) coatings were produced by high-velocity oxyfuel (HVOF) spraying. They were engineered as a possible candidate to replace hydroxyapatite (HA) coatings produced by thermal spray on implants. The HVOF sprayed nanostructured titania coatings exhibited mechanical properties, such as hardness and bond strength, much superior to those of HA thermal spray coatings. In addition to these characteristics, the surface of the nanostructured coatings exhibited regions with nanotextured features originating from the semimolten nanostructured feedstock particles. It is hypothesized that these regions may enhance osteoblast adhesion on the coating by creating a better interaction with adhesion proteins, such as fibronectin, which exhibit dimensions in the order of nanometers. Preliminary osteoblast cell culture demonstrated that this type of HVOF sprayed nanostructured titania coating supported osteoblast cell growth and did not negatively affect cell viability. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Thermomechanical behavior of nanostructured plasma sprayed zirconia coatings

Retaining nonmelted nanoparticles of zirconia in nanostructured coatings has been a challenge in the past. Recently an air plasma spray process was developed to produce coatings that retain up to 30–35% by volume nonmelted particles, resulting in a unique structure. The creep/sintering behavior of such thermal barrier coatings deposited from nanostructured feedstock has been measured and compared with deposits produced from hot oven spherical particles (HOSP). Both feedstocks contain 6–8 wt.% Y₂O₃ as a stabilizer. Flexure and compression creep testing were conducted under several different loads and temperatures to obtain creep exponents and parameters. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Characterization of microstructure of Nano-TiO2 coating deposited by vacuum cold spraying

Control of the microstructure of TiO₂ coatings through preparation methods significantly influences the coating performance. In this study, a vacuum cold-spray process, as a new coating technology, is used to deposit nanocrystalline TiO₂ coatings on conducting glass and stainless steel substrates. TiO₂ deposits were formed using two types of nanocrystalline TiO₂ powders with mean particle diameters of 200 and 25 nm. Coating microstructures were characterized by scanning electron microscopy and x-ray diffraction analysis. Results demonstrate that a thick nanocrystalline TiO₂ coating can be deposited by the vacuum cold-spray process. The coating was found to consist of particles stacked as agglomerates that build up to several hundred nanometers. The coating also presents a mesoporous microstructure that could be effective in such applications as photocatalytic degradation and dye-sensitized solar cells. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Plasma spray synthesis from precursors: Progress, issues, and considerations

Precursor plasma spray synthesis is an innovative and rapid method for making functional oxide ceramic coatings by starting from solution precursors and directly producing inorganic films. This emerging method utilizes molecularly mixed precursor liquids, which essentially avoids the handling and selection of powders, opening up new avenues for developing compositionally complex functional oxide coatings. Precursor plasma spray also offers excellent opportunities for exploring the nonequilibrium phase evolution during plasma spraying of multicomponent oxides from inorganic precursors. Although there have been efforts in this area since the 1980s and early 1990s with the goal of synthesizing nanoparticles, only recently has the work progressed in the area of functional systems. At the Center for Thermal Spray Research an integrated investigative strategy has been used to explore the benefits and limits of this synthesis strategy. Water- and alcohol-based sol/solution precursors derived from various chemical synthesis methods were used as feedstocks to deposit thin/thick films of spherical and nanostructured coatings of yttrium aluminum garnet (YAG), yttrium iron garnet, lanthanum strontium manganate and Zr-substituted yttrium titanates, and compositions of Y₂O₃-Al₂O₃ and their microstructural space centered around stoichiometric YAG. A detailed discussion of the salient features of the radiofrequency induction plasma spraying approach, the results obtained in the investigations to develop various functional oxide coatings, and process issues and challenges are presented. This article was originally published inBuilding on 100 Years of Success: Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Comparison of the photocatalytic behavior of TiO2 coatings elaborated by different thermal spraying processes

This paper proposes a comparative study on the microstructure and photocatalytic performances of titanium dioxide coatings elaborated by various thermal spraying methods (plasma spraying in atmospheric conditions, suspension plasma spraying, and high-velocity oxyfuel spraying). Agglomerated spray dried anatase TiO₂ powder was used as feedstock material for spraying. Morphology and microstructural characteristics of the coatings were studied mainly by scanning electron microscopy and x-ray diffraction. The photocatalytic behavior of the TiO₂-base surfaces was evaluated from the conversion rate of gaseous nitrogen oxides (NOx). It was found that the crystalline structure depended strongly on the technique of thermal spraying deposition. Moreover, a high amount of anatase was suitable for the photocatalytic degradation of the pollutants. Suspension plasma spraying has allowed retention of the original anatase phase and for very reactive TiO₂ surfaces to be obtained for the removal of nitrogen oxides. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Nanostructured photocatalytic titania coatings formed by suspension plasma spraying

This paper describes formation of titanium dioxide coatings designed for photocatalytic applications, obtained by suspension plasma spraying (SPS), an alternative of the atmospheric plasma spraying (APS) technique in which the material feedstock is a suspension of the material to be sprayed. Two different TiO₂ powders were dispersed in distilled water and ethanol and injected in Ar-H₂ or Ar-H₂-He plasma under atmospheric conditions. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) analyses were performed to study the microstructure of the titania coatings. Photocatalytic efficiency of the elaborated samples was evaluated from the conversion ratio of different air pollutants: nitrogen oxides (NOx) and sulfur dioxide (SO₂). The morphology and crystalline structure of the deposits depended mainly on the nature of the solvent (water or alcohol) used in the preparation of the slurries. Dense coatings were obtained starting from aqueous suspensions and porous deposits were elaborated by plasma spraying of a PC105 alcoholic suspension. A significant phase transformation from anatase to rutile occurred when ethanol was used as a solvent. Different photocatalytic performances were observed as a function of the nature of the liquid material feed-stock, the spraying parameters, and the nature of the pollutant. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Suspension plasma spraying of nanostructured WC-12Co coatings

Nanostructured WC-12% Co coatings were deposited by suspension plasma spraying of submicron feedstock powders, using an internal injection plasma torch. The liquid carrier used in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to thin coatings with a fine surface finish. A polyethylene-imine (PEI) dispersant was used to stabilize the colloidal suspension in an ethanol carrier. In-flight particle states were measured for a number of operating conditions of varying plasma gas flow rates, feed rates, and standoff distances and were related to the resulting microstructure, phase composition (EDS, SEM, XRD), and Vickers hardness. High in-flight particle velocities (>800 m/s) were generated, leading to dense coatings. It was observed that the coating quality was generally compromised by the high temperature and reactivity of the small particles. To compensate for this shortcoming, the suspension feed rate was adjusted, thereby varying the thermal load on the plasma. Results showed that a slightly larger agglomerate size, in conjunction with low particle jet temperatures, could somewhat limit the decomposition of WC into brittle W₂C/W₃C and amorphous cobalt containing binder phases. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Corrosion and Electrochemical Behavior of Composite Electrolytic, Iron-Based Coatings

The corrosion and electrochemical properties of composite electrolytic iron coatings containing Al₂O₃ on the steel substrate are investigated (in comparison to the purely iron ones) in 0.05 M Na₂SO₄ and 5% NaCl solutions. Adding a finely dispersed Al₂O₃ phase to the composition of iron coatings leads to some improvement in their corrosion characteristics, that is, a positive shift of E _cor, and lowered anodic dissolution currents. The corrosion rate of the composite coating is lower than that of the purely iron one. The effect is analyzed.     

Properties and Performance of High-Purity Thermal Barrier Coatings

It has been found that reducing the level of impurity oxides (particularly SiO₂ and Al₂O₃) in 7YSZ, from about 0.2 wt% to below 0.1 wt% raises the sintering resistance and the phase stability of plasma-sprayed coatings. The implications for the usage of these coatings at elevated temperatures are examined. It is concluded that using relatively high-purity powder of this type is likely to confer substantial benefits in terms of the thermomechanical stability of the coatings under service conditions. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Influence of Annealing on Photocatalytic Performance and Adhesion of Vacuum Cold-Sprayed Nanostructured TiO2 Coating

Composite powder was prepared using primary nanoTiO₂ powder and polyethylene glycol (PEG). The nanoTiO₂ coating was deposited through vacuum cold spray using both the composite powder and the primary nanopowder. The influence of annealing on the coating adhesion and photocatalytic activity was investigated. The coating adhesion was evaluated through erosion test by water jet. The photocatalytic performance of the coatings was evaluated through photodegradation of phenol in water. Results showed that annealing of the coating at a temperature from 450 to 500 °C yielded both higher activity and better adhesion. The adhesion of the coating deposited using the composite powder was better than that using the primary nanoTiO₂ powder. It was found that the TiO₂ coating, resulting from the composite powder, presented much higher activity than that deposited with the primary nanopowder. The better activity is attributed to the existence of large pores resulting from the stacking of composite powder, which benefits the reactants’ transportation through the porous coating. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Effect of reinforcement size on the scratch resistance and crystallinity of HVOF sprayed nylon-11/ceramic composite coatings

The high-velocity oxyfuel (HVOF) combustion spraying of dry ball-milled nylon-11/ceramic composite powders is an effective, economical, and environmentally sound method for producing semicrystalline micron and nanoscale reinforced polymer coatings. Composite coatings reinforced with multiple scales of ceramic particulate material are expected to exhibit improved load transfer between the reinforcing phase and the matrix due to interactions between large and small ceramic particles. An important step in developing multiscale composite coatings and load transfer theory is determining the effect of reinforcement size on the distribution of the reinforcement and the properties of the composite coating. Composite feedstock powders were produced by dry ball-milling nylon-11 together with 7, 20, and 40 nm fumed silica particles, 50 and 150 nm fumed alumina particles, and 350 nm, 1, 2, 5, 10, 20, 25, and 50 μm white calcined alumina at 10 vol.% overall ceramic phase loadings. The effectiveness of the ball-milling process as a function of reinforcement size was qualitatively evaluated by scanning electron microscopy+energy dispersive x-ray spectroscopy (SEM+EDS) microanalysis and by characterizing the behavior of the powder during HVOF spraying. The microstructures of the sprayed coatings were characterized by optical microscopy, SEM, EDS, and x-ray diffraction (XRD). The reinforcement particles were found to be concentrated at the splat boundaries in the coatings, forming a series of interconnected lamellar sheets with good three-dimensional distribution. The scratch resistance of the coatings improved consistently and logarithmically as a function of decreasing reinforcement size and compared with those of HVOF sprayed pure nylon-11. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Influence of Silver Doping on Photocatalytic Activity of Liquid-Flame-Sprayed-Nanostructured TiO2 Coating

Silver ion was added to liquid feedstock to deposit Ag⁺-doped-nanostructured TiO₂ photocatalytic coatings through liquid-flame spraying. The coating microstructure was characterized by x-ray diffraction (XRD). The photocatalytic performance of coatings was examined by photodegradation of acetaldehyde. The XRD analysis showed that the phase structure of coatings was not significantly influenced by the silver ion doping. However, a shift was found for XRD peaks of anatase TiO₂. The photocatalytic activity of the TiO₂ coatings increased and then decreased with the increase of dopant concentration. The photocatalytic activity of doped coatings was higher than that of pure TiO₂ coating, regardless of the dopant concentration. The enhancement of photocatalytic performance of doped coatings is attributed to co-doping of Ag⁺ ion and metallic Ag. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Modeling of motion and heating of powder particles in laser, plasma, and hybrid spraying

Mathematical models for simulation of motion and heating of fine ceramic particles in plasma and laser spraying, as well as under conditions of a new technological process, that is, hybrid laser plasma spraying, are proposed. Trajectories, velocities, and temperature fields of fine SiO₂ particles being sprayed using the argon plasma jet, CO₂ laser beam, and their combination have been calculated. It is shown that the space-time distribution of temperature in spray particles greatly depends on the spraying method. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Characterizations and hot corrosion resistance of Cr3C2-NiCr coating on Ni-base superalloys in an aggressive environment

In the current study, Cr₃C₂-NiCr coating was deposited on the Ni-base superalloys by using high velocity oxyfuel (HVOF) process for high temperature corrosive environment applications. Optical microscopy (OM), x-ray diffraction (XRD), scanning electron microscopy/energy-dispersive analysis (SEM/EDAX), microhardness tester, and electro probe microanalyzer (EMPA) techniques were used to characterize the coating with regard to coating thickness, porosity, microhardness, and microstructure. The thermogravimetric technique was used to establish kinetics of corrosion. The hot corrosion behaviors of the bare and Cr₃C₂-NiCr coated superalloys were studied after exposure to aggressive environment of Na₂SO₄-60% V₂O₅ salt mixture at 900 °C under cyclic conditions. The structure of the as-sprayed Cr₃C₂-NiCr coating mainly consisted of γ-nickel solid solution along with minor phases of Cr₇C₃ and Cr₂O₃. Coating has porosity less than 1.5% and microhardness in the range of 850–900 Hv (Vickers hardness). Some inclusions, unmelted and semimelted powder particles were observed in the structure of the coatings. The Cr₃C₂-NiCr coating has imparted necessary resistance to hot corrosion, which has been attributed to the formation of oxides of nickel and chromium, and spinel of nickel-chromium. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Cold gas dynamic spraying of iron-base amorphous alloy

This paper describes recent efforts to synthesize iron-base amorphous alloys coatings using cold gas dynamic spraying. Characterization of the gas-atomized iron-base (Fe-Cr-Mo-W-C-Mn-Si-Zr-B) powder shows that the powder is fully amorphous when the particle diameter is below 20 μm. The coatings produced were composed of the same microstructure as the one observed in the feedstock powder. The overall deformation suggests the occurrence of a localized deformation process at the particle/particle boundary and a possible adiabatic deformation softening inside the powder particles during splat formation. The synthesis of fully amorphous, porous-free coatings using cold gas dynamic spraying was demonstrated in this work. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Liquid plasma sprayed coatings of yttria-stabilized zirconia for SOFC electrolytes

To achieve solid oxide fuel cells (SOFC) at reduced costs, the atmospheric plasma spray (APS) process could be an attractive technique. However, to make dense and thin layers as needed for electrolytes, a suspension is preferably implemented as a feedstock material instead of a conventional powder. Suspensions of yttria-stabilized zirconia particles in methanol have been prepared with various solid loadings and states of dispersion. An external injection system was used to ensure the atomization and radial injection of the suspension into the Ar-H₂ plasma under atmospheric conditions. The coatings morphologies were characterized by scanning electron microscopy, and their porosity was evaluated by the Archimedes method. Differences in the microstructure of the deposits were observed depending on the APS operating conditions. Special attention has been dedicated to assess the influence of the suspension as well as the injection on the layer morphology. For this purpose, the atomization has been investigated and efforts have been made to understand relationships among suspension properties, atomization, and coating microstructure. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Exploring thermal spray gray alumina coating pore network architecture by combining stereological protocols and impedance electrochemical spectroscopy

Complex multiscale pore network architecture characterized by multimodal pore size distribution and connectivity develops during the manufacture of ceramic thermal spray coatings from intra- and interlamellar cracks generated when each lamella spreads and solidifies to globular pores resulting from lamella stacking defects. This network significantly affects the coating properties and their in-service behaviors. De Hoff stereological analysis permits quantification of the three-dimensional (3D) distribution of spheroids (i.e., pores) from the determination of their two-dimensional (2D) distribution estimated by image analysis when analyzing the coating structure from a polished plane. Electrochemical impedance spectroscopy electrochemically examines a material surface by frequency variable current and potential and analyzes the complex impedance. When a coating covers the material surface, the electrolyte percolates through the more or less connected pore network to locally passivate the substrate. The resistive and capacitive characteristics of the equivalent electrical circuit will depend upon the connected pore network architecture. Both protocols were implemented to quantify thermal spray coating structures. Al₂O₃-13TiO₂ coatings were atmospherically plasma sprayed using several sets of power parameters, are current intensity, plasma gas total flow rate, and plasma gas composition in order to determine their effects on pore network architecture. Particle characteristics upon impact, especially their related dimensionless numbers, such as Reynolds, Weber, and Sommerfeld criteria, were also determined. Analyses permitted identification of (a) the major effects of power parameters upon pore architecture and (b) the related formation mechanisms. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Optimization of laser cladding process using taguchi and EM methods for MMC coating production

This study investigates the influence of laser cladding parameters on the geometry and composition of metalmatrix composite (MMC) coatings. Composite coatings are made of a Ni-Cr-B-Si metallic matrix and of WC reinforcement with a volume fraction of 50%. Optical microscopy is used to characterize the coating geometry (height, width, and penetration depth) and to determine the real volumetric content of WC. Laser cladding on low-carbon steel substrate is carried out using a cw neodymium:yttrium-aluminum-garnet (Nd:YAG) laser, a coaxial powder injection system, and a combination of Taguchi and EM methods to design the experiments. This combination explores efficiently the multidimensional volume of laser cladding parameters. The results, which express the interrelationship between laser cladding parameters and the characteristics of the clad produced, can be used to find optimum laser parameters, to predict the responses, and to improve the understanding of laser cladding process. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.