Effect of HVOF spraying parameters on the structural-phase composition and mechanical properties of ZrCN coating

This study aimed to understand the influence of small amount of Zr doping of amorphous carbonitride (a-CN) coatings on the structure, and mechanical and tribological behavior. The coatings were prepared using a four-target close-field unbalance magnetron sputtering system; two graphite, one Ti and one Zr targets were used. GDOS, SEM, XRD and XPS were used. A surface profilometer, a nanohardness tester, and a pin-on-disk wear tester were used. It was found the Zr doping resulting in the formation of ZrC and ZrN phases within the coating and the increase in the sp3 bonding fraction. The nanohardness was increased and the wear performance was largely improved.

The parameters optimization and abrasion wear mechanism of liquid fuel HVOF sprayed bimodal WC–12Co coating

The effects of powder types and HVOF spray systems used to produce Cr3C2-NiCr coating on the relationships between spray parameters and wear performance were investigated based on the effect of fuel gas conditions on abrasive wear and erosion wear. The relationships between spray parameters and wear properties were obtained by orthogonal regression experimental design method. Four types of powders and two HVOF spray systems were used. It is found that with the increase in fuel gas flow or pressure the abrasive wear and erosion of Cr3C2-NiCr coatings change following a concave curve. The Cr3C2-NiCr coating with the best wear performance will be deposited under intermediate fuel gas condition. It is experimentally confirmed that by different types of powders and HVOF systems applicable to HVOF spraying of Cr3C2-NiCr coating, although the optimized fuel gas conditions to deposit coating with the best wear performance will be influenced by types of starting powders.

HVOF sprayed tungsten carbide (WC) thermal spray coatings are finding increasing acceptance for replacement of electroplated chromium on aircraft landing gear parts. In order to replace chrome plating by an HVOF WC coating, the latter should exhibit wear and fatigue characteristics at least as good as those of chrome plating. Sliding wear performance and fatigue life of tungsten carbide coated parts depend on morphology and phase composition of the coating which in turn depend on spray parameters such as powder characteristics, powder feed rate, gas flow rates, and spray distance. A Design of Experiments (DOE) approach for a Jet Kote™ HVOF spray system was used to identify optimal spray parameters for WC-Co and WC-Co-Cr coatings based on best sliding wear and best fatigue characteristics. Best sliding wear was defined as minimum block loss in the standard ASTM-G77 wear test in which a rotating WC coated ring is tested against a stationary Al-Ni-Bz block. Best fatigue characteristics were defined as compressive residual stresses in the coating in the range 250 to 450 MPa. Spray parameters found to strongly affect wear were powder feed rate, oxygen flow rate, powder size, and a powder type-powder size interaction. Spray parameters strongly affecting residual stresses include powder type, hydrogen flow rate, and powder feed rate. Some spray parameters were found to be orthogonal with respect to wear behavior and residual stress. This means some parameters can be adjusted to maximize one performance criterion (wear or residual stress) without adversely affecting the other.

HVOF sprayed Ni–Mo coatings improved by annealing treatment: microstructure characterization, corrosion resistance to HCl and corrosion mechanisms

Impact of atmospheric plasma spraying parameters on microstructure, mechanical properties and thermal cycling performance of YSZ coatings

The use of zirconium carbonitride (ZrCN) coatings has demonstrated a significant increase in hardness and wear resistance of 65G and U8G steels. High velocity oxygen fuel (HVOF) has proved to be an effective method of formation of dense coatings with high adhesion, which contributes to a significant improvement in the performance characteristics of treated surfaces. It was found that microhardness of samples depends on HVOF spraying parameters, as it increases 1.5-2 times after coating. In particular, the microhardness of 65G steel after ZrCN application reached 456.6 HV, and for U8G steel this index was 649.7 HV. The obtained results confirm the high efficiency of ZrCN in improving the mechanical and operational properties of steels, which is due to their significant hardness, increased wear resistance and high adhesion. This makes these coatings promising for application in conditions of intensive mechanical and abrasive impact.

This paper is intended to continue the studies of magnesium effects on the structural phase composition, physical and mechanical properties of the nanostructured strain-hardened aluminum-magnesium alloys modified with C60 fullerene [1]. Previously obtained mechanically alloyed composite powders [1] were consolidated by direct hot extrusion method. Consolidation parameters were chosen based on previous studies of the structure and phase composition formation during mechanical alloying and heat treatment. It was found that an increase in magnesium concentration improves mechanical properties of extruded nanosructured composite materials, and additives modified by C60 fullerene stabilize the grain structure and slow down decomposition of α solid solution of magnesium in aluminum to 300 °C. Under similar thermobaric treatment Al82Mg18 (AMg18) not modified with C60 demonstrates a reduced α solid solution lattice constant and an increased average crystallite size. These processes are accompanied by sequential formation of γ, β′, and β phases, while γ and β′ are intermediate phases. The grain structure of extruded samples is typical for materials obtained in this way – grains are closely packed, elongated and oriented along the extrusion axis. The grain structure of extruded samples inherits the morphology of mechanically alloyed powders. Thus, mechanical alloying methods followed by intense plastic deformation (extrusion) improved mechanical properties significantly. Materials with ultimate tensile strength of 880 MPa; ultimate bending strength of 1100 MPa; microhardness up to 3300 MPa; and with the same density of 2.4–2.6 g/cm3 were obtained. This result demonstrates the prospects for using powder metallurgy techniques in the production of new nanostructured composite materials modified by C60 fullerene with improved physical and mechanical properties.

Desilicated zirconia has a great variety of applications. The maximum SiO2 content in desilicated zirconia is <7 mass%. The present techniques to produce zirconia are always accompanied by many drawbacks. So the authors have developed a new plasma process. Desilicated zirconia (88.6 ~ 96.9 mass% ZrO2) and magnesia‐stabilized zirconia (> 91.54 mass% ZrO2, < 5.39 mass% MgO) were produced successfully from zircon using a 150 kW plasma rotating furnace. The effects of time and carbon content on the desilication degree were investigated. The mixture treated in the plasma furnace included condensed phases Zr, ZrC, ZrN, ZrO2, C, Si, SiC, SiO2 and gaseous phases SiO, O2, N2, CO. The established phase equilibrium diagrams of the Si‐C‐N‐O and Zr‐C‐N‐O systems suggest that the formation of Si3N4 is thermodynamically impossible, and the formation of ZrC and ZrN is thermodynamically possible in the central high‐temperature region of the plasma furnace. Experimental results supported the analyses.

Research and selection the performance requirements for the coating, at the same time obtain the WC-Co powders with high efficient spray rate and low cost, through research on the relation between the WC-Co powders sprayed by the HVOF in different morphology and in different manufacturing process and the spraying parameters and structures of coatings. Abstract only; no full-text paper available.

Hardmetal-like coatings of the TiC-Ni system are potential for use as wear, corrosion and heat resistant coatings in various operation conditions. Our previous works [1-12] have shown that these materials are well sprayable using different thermal spray processes such as plasma, D-Gun and HVOF spraying. Since HVOF spraying is today the most important process used to apply carbide based coatings, this study was carried out in order to evaluate more systematically the sprayability of these novel spray powders and the influence of HVOF spray parameters on some coating properties. Coating samples were prepared by using DJ Hybrid gun with propane as a fuel gas, and a CDS gun with hydrogen fuel gas. Oxygen flow rate was varied in both cases for changing the flame temperature. Microstructure, phase composition, hardness, and abrasion wear resistance of the coated samples were investigated. The results showed that both HVOF processes used give satisfactory coating properties and that the use of high oxygen flow rates is beneficial for improving the wear resistance of the coatings. Powders with fine particle size are beneficial in the DJ Hybrid process; the use of coarse powders results in coatings with somewhat higher wear rates. The optimum spray condition for the TiC-Ni system powders differs from that typically used for conventional WC-Co and Cr3C2-NiCr powders by a higher flame temperature.

This study compares high-velocity oxygen fuel spray MJP5000 and MJP 6000 (Patented by Metallizing Equipment Company Pvt Ltd.) using powder WC-Co-Cr. The microstructure and phase composition of powders and coatings will be analyzed by scanning electron microscopy and X-ray diffraction. Coatings were also characterized by their hardness, bond strength, roughness, deposition efficiency. Therefore, coating of high hardness and wear resistance can be produced with all HVOF spray system when the proper spray powder and process parameters are chosen. The results demonstrate that the powder exhibits various phase transformation during the spray process depending on type of powder, spray system and spray parameters.

The deposition parameters of WC-17%Co coatings produced using the JP-5000 liquid-fuel HP/HVOF system (Eutectic TAFA) were investigated with the initial purpose of parameter improvement and optimization. The coating microstructures, porosities, phase compositions, and abrasion resistance were characterized. Preliminary work using the Taguchi statistical experimental design method aimed at optimizing the spray parameters in terms of the microstructure and phase composition was unsuccessful. The variations in the measured properties were too small to be correlated with the spray parameters. Subsequent experiments showed this was primarily due to the fact that the properties, particularly the abrasion resistance, of the WC-Co coatings were not primarily influenced by variations in the spray parameters, but were more dependent on the powder composition, particle size range, and manufacturing route. Hence, the application of Taguchi techniques would have been more effective over a much wider parameter space than was originally used. This result is valuable because it suggests that this process is robust and can be used for WC-Co coatings without large investments in spray parameter optimization and control once the coating and powder type have been fixed.

It was known for long that Ni-Al composite powders can be used to deposit self-bonding coating as a bond coat for common ceramic coatings due to the exothermic reaction between Ni and Al. However, it was found that with commercial Ni-Al composite powders with a large particle size, it is difficult to ignite the self-propagating reaction between Ni and Al to form Ni-Al intermetallics by plasma spraying. In this study, Ni-Al composite powder particles of different sizes were used to prepare Ni-Al intermetallics-based coatings by plasma spraying. The dependencies of the exothermic reaction between Ni and Al and the coating microstructure on powder particle size and spray parameters were investigated. The phase composition, microstructure, porosity and oxide content of the coatings were characterized by x-ray diffraction, scanning electron microscope and image analyzing. The results show that particle size of Ni-Al composite powders is the dominant factor controlling the exothermic reaction for the formation of Ni-Al intermetallics during plasma spraying. When the powders larger than about 50 μm are used, the reaction forming aluminide cannot complete even by heating of plasma flame generated at high plasma arc power. However, when smaller powders less than 50 μm are used, the exothermic reaction can completely occur rapidly in plasma spraying, contributing to heating of Ni-Al droplets to the highest temperature for development of the self-bonding effect. The positive relationship between molten droplet temperature and tensile adhesive strength of the resultant coatings is recognized to confirm the contribution of high droplet temperature to the adhesive or cohesive strength.

Diamond particle-reinforced Zr-alloyed Cu matrix (diamond/Cu-xZr) composites were produced by a gas pressure infiltration route, with x = 0.0, 0.3, 0.5, 0.75, and 1.0 wt.%. The x-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterization confirms the formation of ZrC at the diamond/Cu interface. With increasing Zr content, the tensile, bending, and compressive strengths of the diamond/Cu-Zr composites are found to firstly increase and then decrease. The maximum tensile, bending, and compressive strengths at 0.75 wt.% Zr are 108, 360, and 441 MPa, respectively. The variation of the mechanical properties is attributed to the formation of interfacial ZrC. The increase in amount of ZrC strengthens the interface, but large ZrC particles formed at high Zr content are harmful to the interfacial bonding. The result suggests that the mechanical properties of diamond/Cu composites can be enhanced by Cu matrix alloying with Zr.