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Proceedings Papers
ITSC2023, Thermal Spray 2023: Proceedings from the International Thermal Spray Conference, 567-573, May 22–25, 2023,
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Material’s tensile strength can be improved by the presence of a body-centered cubic (BCC) phase, which is essential in highstrength applications and highly corrosive environments. Thus, synthesizing a BCC single-phase, equiatomic AlCoCrFeNi high-entropy alloy (HEA) feedstock particle using a highenergy mechanical alloying (HE-MA) method was investigated. The transient alloy particles were developed using a planetary mill at a constant rotational speed of 580 rpm employing milling times in the range of 4 to 24 hours. During the process, stearic acid of 3 wt.% of the precursor composition was used as a process-controlling agent (PCA). Two HE-MA manufacturing regimes were utilized: i) conventional (milling constituent elements simultaneously), and ii) sequential (progressive milling while adding elements in a certain order). In addition to the conventional method, a sequential regime was employed to develop FeNiCoCrAl, wherein individual elements were added every 4 hours to the starting/milled Fe + Ni mixture. Based on the results, the HE-MA FeNiCoCrAl showed a BCC single-phase formation after 24 hours, with no intermetallic or contamination traceability. Finally, a nanoindentation hardness measurement was carried out to support the observed phase transformation before and after the HE-MA process.
Proceedings Papers
ITSC 2021, Thermal Spray 2021: Proceedings from the International Thermal Spray Conference, 447-453, May 24–28, 2021,
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Ni-Al intermetallics have excellent corrosion and oxidation resistance, but their use in thermal spraying has been limited due to issues with in-flight oxidation. In this study, a novel approach is proposed to remove oxide from Ni-Al droplets in-flight by adding a deoxidizer (diamond) to the feedstock powder. A mixture of nickel, aluminum, and diamond powders was mechanically alloyed using a combination of cryogenic and planetary ball milling. The resulting Ni/Al/diamond composite powder was then plasma sprayed via the APS process, forming Ni-Al coatings on Inconel 738 substrates. Phase composition, microstructure, porosity, and microhardness of the coatings were characterized by X-ray diffraction, scanning electron microscopy, image analysis, and hardness testing, respectively. Oxygen content measurements showed that the coatings contained significantly less oxygen than coatings made from ordinary Ni/Al powders. In-flight particle temperatures were also measured and found to be higher than 2300 °C. The low oxygen content in the coatings is attributed to the in-situ deoxidizing effect of ultrahigh temperature droplets which are also oxide-free.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 232-236, May 10–12, 2016,
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In this study, arrested reactive milling (ARM) is used to prepare Al-Ni composite powder for deposition on copper liners via kinetic spraying. Among the main goals are to obtain a better understanding of how the milling process affects deposition efficiency and the reactivity of the coatings and to find a way to reduce the amount of remaining solid lubricant after milling. Al-Ni powders were produced under a wide range of conditions and heated to various temperatures to eliminate stearic acid. The powders were sprayed using fixed process parameters and deposition efficiencies, reactivities, and heat values were measured and are compared along with coating microstructures. The procedures used are described and the findings of the study are presented and discussed.
Proceedings Papers
ITSC2014, Thermal Spray 2014: Proceedings from the International Thermal Spray Conference, 849-854, May 21–23, 2014,
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In the present work, a mechanical alloying (ball milling) method was developed to synthesize NiCrBSi-WC composite powders for HVOF spraying. Coating properties and microstructure are shown to vary with composition and initial powder size prior to ball-milling. With nanometric particles, metallic and carbide powders appear to be intimately linked with WC, forming a highly protective layer. Conversely, with micrometric powders, ball-milled particles appear more fractured and regularly dispersed inside the matrix.
Proceedings Papers
ITSC 2013, Thermal Spray 2013: Proceedings from the International Thermal Spray Conference, 16-21, May 13–15, 2013,
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This study compares the deposition and oxidation behavior of two oxide-dispersed CoNiCrAlY powders, one commercially obtained, the other prepared in a high-energy attrition ball mill using CoNiCrAlY and nanosize α-alumina powders. The custom powder was deposited by HVOF spraying using two sets of parameters, one optimized for CoNiCrAlY powder, the other for fine alumina. Coatings produced under the latter conditions were found to be porous, which can be attributed to a low degree of melting in the dispersed alumina. Isothermal oxidation testing at 1373 K for up to 1000 h in air caused oxidation not only at the surface, but also inside the coatings due to the movement of oxygen through the pores. The coatings deposited under the other set of parameters, i.e., at higher power levels, were free of pores. Isothermal oxidation tests were also carried out on coatings produced from the commercial powder, in this case, by HVOF and as well as vacuum plasma spraying. The coatings obtained by HVOF spraying were found to have a thinner thermally grown oxide layer than not only the VPS coatings, but also conventional metallic bond coats. Internal oxidation in the HVOF coatings is due to insufficient cohesion of the spray particles. Furnace cycling tests were conducted on specimens with an additional ceramic thermal barrier coating. Specimens with VPS bond coats produced from commercial oxide-dispersed powder achieved almost same number of cycles to delamination as specimens with conventional metal bond coats.
Proceedings Papers
ITSC 2013, Thermal Spray 2013: Proceedings from the International Thermal Spray Conference, 620-625, May 13–15, 2013,
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This study evaluates a method for producing carbon fiber composite feedstocks suitable for cold gas spraying. Powders consisting of Al-Si particles and carbon nanofibers were attrition milled at 16.5 Hz and 27.5 Hz for up to 12 h at room and cryogenic temperature. Particle shape and size were examined every hour and carbon fiber integration in the Al-Si matrix was assessed. Detailed results are presented and discussed. In all cases, cryomilled powders had smoother surfaces.
Proceedings Papers
ITSC 2013, Thermal Spray 2013: Proceedings from the International Thermal Spray Conference, 677-683, May 13–15, 2013,
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The aim of this work is to fabricate a particle-reinforced FeAl composite coating by cold spraying. Fe, Al, and WC powders were placed in a ball mill and mechanically alloyed for up to 36 h in order to obtain a nanostructured Fe(Al) solid solution reinforced with a high volume fraction of WC particles. The powder was examined and then cold sprayed on stainless steel substrates using N 2 as the accelerating gas. The as-sprayed deposits exhibited rough surface morphology and dense cross-sectional microstructure with dual-scale WC dispersoids distributed uniformly in the Fe(Al) matrix. The coatings were annealed at 650 °C and subsequently reexamined. In-situ phase transformation from the solid solution to an intermetallic compound occurred after the post-spray treatment along with an improvement in microstructure.
Proceedings Papers
ITSC 2013, Thermal Spray 2013: Proceedings from the International Thermal Spray Conference, 684-689, May 13–15, 2013,
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In this study, Al-SiC composite coatings are produced by cold spraying ball-milled Al powders with different volume fractions of SiC particles. The morphology and microstructure evolution of the powder during ball milling are evaluated along with the effect of SiC content on the microstructure and wear behavior of the coatings. The results show that dense Al-SiC coatings with different volume fractions of SiC particles can be fabricated by cold spraying and that abrasive wear resistance is improved by raising the volume fraction of SiC particles. Wear surfaces indicate that the predominant wear mechanism is gouging of the soft Al matrix in the early stages and cracking and spalling of SiC particles in the latter stages. The dispersed SiC particles serve to protect the matrix from wear products thus raising the wear resistance of the coatings.
Proceedings Papers
ITSC 2010, Thermal Spray 2010: Proceedings from the International Thermal Spray Conference, 352-357, May 3–5, 2010,
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C-BNp/NiCrAl composite coating was deposited by cold spraying using a mechanically alloyed composite powder. To modify coating microstructure, especially the bonding at the interfaces between c-BN particles and NiCrAl alloy matrix, and bonding at the sprayed particle/particle interface, annealing treatment at series of temperatures in Ar atmosphere was carried out. The results show that a zigzag interface layer is formed at the interface between c-BN particle and NiCrAl matrix after annealing at 825°C for 300 min through reaction of c-BN with NiCrAl. It is also observed that the thickness of the interface reaction layer increases with the increasing annealing temperature. Moreover, the interface between spray particles and the plastic deformation ability of the cermet coating can be improved through post-spray annealing. Vickers microhardness test shows that the hardness decreases with increasing annealing temperature due to the reduction of work hardening effect and grain growth of NiCrAl alloy matrix resulting from recovery and recrystallization during annealing treatment.
Proceedings Papers
ITSC 2009, Thermal Spray 2009: Proceedings from the International Thermal Spray Conference, 986-991, May 4–7, 2009,
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In this study, WC-12Co powders with multimodal-sized WC particles were prepared by ball milling and deposited onto stainless steel substrates by cold spraying. Microhardness and fracture toughness were measured on cross-sections by the indentation approach. Coatings produced from powders with small carbide particles, resulting from long milling times, were found to exhibit high microhardness and high fracture toughness. Deposits sprayed with high porosity powders produced by cold compaction had low microhardness, but high fracture toughness.
Proceedings Papers
ITSC 2009, Thermal Spray 2009: Proceedings from the International Thermal Spray Conference, 1030-1035, May 4–7, 2009,
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This work demonstrates the capabilities of oxide dispersion strengthened MCrAlY coatings and the process used to produce the feedstock powders. Mechanically alloyed powder mixtures were prepared in a high-energy ball mill using commercial NiCoCrAlY and YPSZ powders combined in different amounts. A high-velocity oxyfuel torch was used to deposit the powders on Inconel substrates that were then heat treated for 6 h at 1050 °C. Samples were also produced from unaltered NiCoCrAlY powder to serve as a reference. In high-temperature erosion tests, the strengthened coatings had a mass loss of 47 mg/cm 2 after 30 sec compared to 38 mg/cm 2 for the unstrengthened sample. High-temperature corrosion tests showed that the strengthened coatings were not dense enough to protect the substrate from oxidation. The hard phases inhibited sintering and diffusion effects during heat treatment. As a result, dislocations, defects, and voids could not move and were used by oxygen for diffusion. In further investigations, the strengthened coatings will be treated at a higher temperature to achieve a better sintering effect.
Proceedings Papers
ITSC 2009, Thermal Spray 2009: Proceedings from the International Thermal Spray Conference, 1183-1188, May 4–7, 2009,
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In this work, mechanically alloyed Al–12Si/TiB 2 /h-BN composite powder was deposited onto an aluminum substrate by atmospheric plasma spraying. The results revealed that the mechanical alloying (MA) process has a significant effect on composite powder morphology and in-situ reaction intensity between the selective powders during plasma spraying. In addition, hexagonal boron nitride (h-BN) powder incorporated as a solid lubricant, which has excellent lubricating properties, decomposed into B and N and formed a solid solution after a long period of milling. More specifically, during plasma spraying a large amount of h-BN reacted with Al to form AlN. Unlubricated ball-on-disk testing ring was used to examine the anti wear performance of the coatings. The worn surfaces were examined using scanning electron and energy dispersive spectroscopy to elucidate the wear mechanisms operating at the sliding interface.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 79-82, June 2–4, 2008,
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In this research mechanically alloyed Ni-Al powders were used for production of plasma sprayed coatings and effect of spray distance on the phases, microstructure and hardness of the coatings are examined. Three types of Ni-Al powder were made by METCO, LobaChemi and mechanical alloying, were used for comparing coating properties. Coatings are examined by XRD, SEM, EDAX and microhardness measurements. However intermetallic phases were not found in mechanically alloyed powder, but coatings contained these phases. This shows that heat energy of plasma spray caused formation of NiAl phases during flying of particles to substrate or after reaching to substrate. Comparison of coatings properties indicated that mechanical alloying of powders caused improving mechanical properties and decreasing porosity percentage of coatings. Change of spray distance caused changing in phases, porosity percentage and microhardness of coatings. Best spray distance for spraying of the made powder determined as 11cm.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1132-1137, June 2–4, 2008,
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Increasing requirements on technical components for high-temperature-applications (e.g., turbine blades) demand for new developments in surface engineering. The selective combination of materials with positive and negative thermal expansion coefficients (NTE) will lead to a reversible activation of the surface depending on surface temperature: The generation of a riblet structure (“shark skin”) in operation condition by thermal expansion of the matrix and shrinkage of the NTE-ceramic and self-cleaning of the surface at cool down as a result of the reversal of the process. Due to its hygroscopicity the chosen NTE-ceramic Y 2 W 3 O 12 needs to be embedded into a binder matrix. Therefore a feedstock powder consisting of MCrAlY, WO 3 and Y 2 O 3 is mechanically alloyed in a high-energy ball mill. The powder is deposited on substrates by thermal spraying (VPS and HVOF) and laser cladding as well. After coating process a lateral- and depth-selective ion implantation of tungsten, yttrium and oxygen will force nucleation in predefined areas. A following heat treatment of the specimens supports the in-situ-formation of Y 2 W 3 O 12 .
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1208-1212, June 2–4, 2008,
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Ni/Al alloy powders were synthesized by ball milling of nickel-aluminum powder mixture with a Ni/Al atomic ratio of 1:1. Ni/Al alloy coating was deposited by cold spraying using N 2 as accelerating gas. NiAl intermetallic compound was evolved in-situ through post-spray annealing treatment of cold-sprayed Ni/Al alloy coating. The effect of annealing temperature on the phase transformation behavior from Ni/Al mechanical alloy to intermetallics was investigated. The microstructure of the mechanically alloying Ni/Al powder and NiAl coatings was characterized by scanning electron microscopy and X-ray diffraction analysis. The results show that a dense Ni/Al alloy coating can successfully be deposited by cold spraying using the mechanically alloyed powder as feedstock. The as-sprayed alloy coating exhibited a laminated microstructure retained from the mechanically alloying powder. The annealing of the subsequent Ni/Al alloy coating at a temperature higher than 850°C leads to the complete transformation from Ni/Al alloy to NiAl intermetallic compound.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1480-1484, June 2–4, 2008,
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In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al–12Si and SiO 2 powder was deposited onto an aluminum substrate by atmospheric plasma spraying (APS) to obtain a composite coating consist of in-situ formed alumina reinforced hypereutectic Al-18Si matrix alloy. The effect of arc current on the corrosion behavior of the composite coating has been investigated. Corrosion resistance of the composite coatings was analyzed by using the potentiodynamic polarization scanning (PDS) technique. Surface morphology of the coatings before and after the corrosion test was examined by using metallographic methods and scanning electron microscopy (SEM). Obtained results are discussed in detail.
Proceedings Papers
ITSC 2005, Thermal Spray 2005: Proceedings from the International Thermal Spray Conference, 575-577, May 2–4, 2005,
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An important growth potential in thermal spraying industry consists of the development of new coating materials. Metal- or Ceramic-Matrix-Composites (MMC / CMC) are of special interest due to a variety of properties which can be influenced particularly by the ratio of matrix and reinforcing material. Thermal sprayed coating properties mainly depend on thermal and kinetic energy of the spray particles. An increase in thermal energy of sprayed particles can be obtained by Self Propagating High Temperature Synthesis (SHS) reaction between components of the spray material. Hence a higher adhesive strength, a lower porosity and an increased deposition efficiency can be expected. Aluminium-based spray materials, containing metal oxides, are suitable for the Self Propagating High Temperature Synthesis to produce MMC-coatings. For good contact between the reactants, powders of aluminium and chromium oxide for plasma spraying were prepared by mechanical alloying. Coatings characterization results on the base of optical microscopy, scanning electron microscopy (SEM), X-ray structure analysis (XRD) and measurements of velocity and temperature with a DPV2000 system. The plasma spraying process combined with SHS reaction of the spray material leads to raised enthalpy of spray particles combined with an increased ad-/cohesive strength and a lower porosity as well as an increased deposition efficiency.
Proceedings Papers
ITSC 2005, Thermal Spray 2005: Proceedings from the International Thermal Spray Conference, 710-714, May 2–4, 2005,
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In waste-to-energy power generation plants, increasing the combustion temperature improves plant efficiency. However, due to problems caused by molten chloride corrosion, the combustion temperature cannot be increased. Consequently, in order to increase the temperature, it is first necessary to protect components from molten chloride corrosion. In this study, CoNiCrAlY coating is proposed as a protective film against molten chloride corrosion. Three kinds of specimens were prepared. One was standard coating made from conventional CoNiCrAlY. The others included the addition of Mo to the CoNiCrAlY by two different techniques. One technique is mechanical alloying (MA), and the other is a gas-atomizing technique. The mechanic-chemical reaction that occurs during the mechanical alloying process can be expected to create new functionality for the material. The effect of Mo content was evaluated for corrosion resistance. These specimens were coated by low pressure plasma spraying (LPPS). The specimens were exposed to NaCl-KCl for the molten chloride corrosion test. The results of the corrosion tests show that corrosion resistance improved in only MA CoNiCrAlY coatings. These results reveal that mechanically alloyed CoNiCrAlY-Mo coating has excellent corrosion resistance, and its corrosion resistance behavior is different from that of gas-atomized CoNiCrAlY-Mo.
Proceedings Papers
ITSC 2003, Thermal Spray 2003: Proceedings from the International Thermal Spray Conference, 335-342, May 5–8, 2003,
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This work reports research concerning the production of powder, suitable for reactive HVOF spraying, produced by mechanically alloying Ni(Cr), Ti and C elemental powder constituents. Powder mixing was achieved using a high-energy Uni-Ball II Mill and optimisation of the milling parameters are reported. The composition of the powder, at 50wt.%NiCr-40wt.%Ti-10wt.%C, was such that the application of heat has the potential to cause a SHS (Self propagating High Temperature Synthesis) reaction to take place. The utilisation of SHS reactions to produce TiC particles within metallic matrices is well known in bulk systems. However, this work describes carrying out this reaction in individual powder particles on exposure to the high temperature within the HVOF gun. The powder having undergone the SHS reaction during the spray process was deposited onto mild steel substrates to form a dense, coherent coating. The coatings thus formed were shown to contain nanoscale TiC in a Ni(Cr) matrix, indicating a SHS reaction had taken place. This TiC is much finer than that produced in conventional SHS reactions, which is typically ~5ìm. The percentage of TiC formed, and retained in the coating, was lower than expected from the constituent proportions and explanations for this observation are proposed. The microstructure of the coating is described and compared with a Ni(Cr)-TiC cermet coating sprayed using conventional SHS powder generated from reacted compacts which were crushed, sieved and classified to give sprayable feedstock powder.
Proceedings Papers
ITSC 2002, Thermal Spray 2002: Proceedings from the International Thermal Spray Conference, 1033-1037, March 4–6, 2002,
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This study assesses the wear performance of HVOF-sprayed nanostructured TiB 2 composite coatings and the use of mechanical alloying for powder preparation. In order to prevent the formation of undesired secondary borides, TiB 2 particles are processed with a nickel-base self-fluxing matrix alloy. XRD analysis shows that the minimum average TiB 2 crystal size is 22 nm after high-energy milling and only slightly larger and uniformly distributed after HVOF spraying. The resulting TiB 2 layers are characterized based on morphology and wear behavior and are shown to hold promise for abrasive wear applications. Paper includes a German-language abstract.
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