Plasma Spray Forming Research Articles

Thermal Shock and Ablation Behavior of Tungsten Nozzle Produced by Plasma Spray Forming and Hot Isostatic Pressing

Tungsten nozzle was produced by plasma spray forming (PSF, relative density of 86 ± 2%) followed by hot isostatic pressing (HIPing, 97 ± 2%) at 2000 °C and 180 MPa for 180 min. Scanning electron microscope, x-ray diffractometer, Archimedes method, Vickers hardness, and tensile tests have been employed to study microstructure, phase composition, density, micro-hardness, and mechanical properties of the parts. Resistance of thermal shock and ablation behavior of W nozzle were investigated by hot-firing test on solid rocket motor (SRM). Comparing with PSF nozzle, less damage was observed for HIPed sample after SRM test. Linear ablation rate of nozzle made by PSF was (0.120 ± 0.048) mm/s, while that after HIPing reduced to (0.0075 ± 0.0025) mm/s. Three types of ablation mechanisms including mechanical erosion, thermophysical erosion, and thermochemical ablation took place during hot-firing test. The order of degree of ablation was nozzle throat > convergence > dilation inside W nozzle.

Ablation Properties of ZrO<sub>2</sub>-MgO and Mo Nozzle Produced by Plasma Spray Forming

ZrO2-MgO and Mo powder coating on a substrate material prepared by an high temperature plasma spraying forming (PSF) for lease-shaped engine nozzles, and its total thickness is about 300 μ m. The surface coating changes of microstructure were investigated by a small solid rocket motor static ablation and the results were discussed for preliminary ions after ablation. The results show that the plasma spraying throat coat is a layer structure and the pore consist in micro-gap between layer and layer.That throat coating erosion is so severe were found after the ablation test , which is because of the metal oxide particles caused by mechanical denudation and high temperature thermal chemical ablation.Whereas the coating interface have no significant cracks after erosion, so that the composite coating of ZrO2-MgO and Mo wear good erosion performance.

Near-Net-Shape Tungsten–Rhenium Alloy Parts Produced by Plasma Spray Forming and Hot Isostatic Pressing

Near-Net-Shape Tungsten–Rhenium Alloy Parts Produced by Plasma Spray Forming and Hot Isostatic Pressing

Improving mechanical properties of near-net-shape aluminum/MWCNT nanocomposites fabricated by plasma spray forming using electroless copper coating of MWCNT

The growing demand for using high-performance materials for industrial sheet parts manufacturing actuated us to fabricate wave-formed sheets nanocomposite. A combination of impregnation method and plasma spray forming (PSF) was used for manufacturing of Al/multiwall carbon nanotube (MWCNT) sheets nanocomposite. By addition of 5 wt.% MWCNT to pure Al matrix, microhardness increased to 34.5 (VHN) compared to 30 (VHN) for monolithic pure Al. The effect of using coated MWCNT as a reinforcement material was also investigated. Our results showed that applying coated MWCNT not only lead to significant increase of microhardness (50 VHN), but also less defect was generated on the MWCNT sidewalls.

Simulation Analysis of Splat Deposition in Plasma Spray Forming

Splat deposition is an important part influencing coating quality in plasma spray forming. Flatten behavior of a single Ni droplet falling on a smooth substrate is evaluated by numerical simulation of ANSYS software, this paper meanwhile researches a single Ni particle deposition in the surface of flattened Al2O3 sheet and thin Al particles, the impact factors of particles flattening and the mechanism of the interaction between particles are also studied. The results have benefit to improving the coating porosity and bond strength between particles.

Sintering Behavior of Tungsten Heavy Alloy Products Made by Plasma Spray Forming

Refractory metallic thin-walled products of 95W–3.5Ni–1.5Fe (in mass%) were fabricated by plasma spray forming (PSF) in argon atmosphere at 1.01×105 Pa followed by high temperature sintering (1200, 1300, 1400 and 1465°C). Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), Archimedes method, differential scanning calorimetry (DSC) and X-ray diffractometer (XRD) have been employed to study microstructure, solubilities, density, solidus and liquidus temperatures and phases of the parts. Lamellar structure consisting of vertical columnar grains and fine particles was found in PSF deposits. Supersaturated solid solutions were formed in the deposits with the relative density of 88±2%. Solidus and liquidus temperatures of γ phase were measured to be 1392 and 1412±5°C, respectively. Initial lamellar structure was remained in the tested samples after sintering at lower temperatures (1200°C/90 min, 1300°C/90 min and 1400°C/15, 90 min) and turned into granular structure at 1465°C/5, 15, 30, 90 min. In addition, the relative densities of deposits, after sintering at 1200, 1300, 1400 and 1465°C for 90 min, were increased from 88 to 90, 92, 94 and 98±2%, respectively. A five-stage sintering mechanism proposed by us previously has been re-validated and double checked by experimental results.

Near-Net-Shape Molybdenum Parts Produced by Plasma Spray Forming

Complex and thin-walled refractory metallic parts including molybdenum (Mo) rocket nozzle and crucible were fabricated using plasma spray forming (PSF) followed by hot isostatic pressing (HIPing). Optical microscope (OM), scanning electron microscope (SEM), Archimedes method, Vickers hardness and tensile tests have been employed to study microstructure, density, micro-hardness and mechanical properties of the parts. A lamellar structure consisting of vertical columnar grains, micron-sized pores, partially melted particles and rough interlamellar contacts with gaps of sub-micron sizes between lamellae were found in PSF Mo deposits. Relative density, micro-hardness and ultimate tensile strength (UTS) of the deposits were about 89%, 150 HV0.025 and 44 MPa, respectively. After low-pressure and two-step HIPing, those changed up to about 92%, 250∼400 HV0.025 (interior ∼ exterior layers), 93 MPa, and 97%, 325 HV0.025 and 170 MPa, respectively. Moreover, a four-stage mechanism of HIPing for PSF parts including heating up, recrystallization, lamellae movement, plastic yielding and creep has been proposed and discussed in detail.

Effect of Mandrel Rotation on the Accuracy of Computed Temperature Profile during Near Net Shape Forming by Plasma Spraying

Near net shape processing by the plasma spray forming (PSF) is a rapid prototyping technique that involves deposition of ceramic coating on the mandrel and its removal as a free-standing structure. This process requires a precise control of the temperature attained by the mandrel during spraying. This article describes the improvement in the accuracy of the temperature prediction of the mandrel by considering the effect of solid rotation inside the fluid during conjugate heat transfer. The computation model was modified by incorporating a no-slip interface boundary condition instead of a tangential slip condition. The transient temperature profiles of the mandrel computed with tangential slip and no-slip interface conditions were validated by experimentally measured temperature profiles. The accuracy of the computed temperature results increased to 95% for the no-slip condition compared to 79% for the tangential slip condition.

Near-net-shape 95W–3.5Ni–1.5Fe thin-walled products produced by plasma spray forming

Tungsten heavy alloy 95W–3.5Ni–1.5Fe (in wt.%) refractory metallic thin-walled products (diameter ≤100 mm, length ≤150 mm and wall thickness ≤5 mm) were produced using plasma spray forming (PSF) covered in argon atmosphere at a pressure of 1.01 × 10 5 Pa followed by vacuum liquid phase sintering at 1465, 1485 and 1500 °C for 90 min, respectively. A lamellar structure consisting of vertical columnar grains and some fine particles was found in PSF deposits. Relative density of the deposits was about 87.70% with poor mechanical property. Upon vacuum liquid phase sintering, their density and property have been improved significantly. The microstructures of PSF deposits before and after vacuum sintering were found to consist with tungsten and (Ni, Fe)-rich phase. Volume fraction of (Ni, Fe)-rich phase was decreased due to vaporization that occurred in plasma spraying and vacuum liquid phase sintering. Their fracture surfaces were dominated by intergranular rupture. The lamellar structure remained in the deposits during early stages of sintering (solid state sintering and initial of liquid phase sintering). Particle rearrangement and rapid densification of the deposits did not occur until the surface of tungsten particles being modified and changed into spheroids by solution and precipitation. In the end, the PSF deposits have been transformed from lamellar structure into two phase composites with dispersed spheroidal tungsten grains embedded in a continuous network of (Ni, Fe)-rich phase.

An experimental and computational methodology for near net shape fabrication of thin walled ceramic structures by plasma spray forming

Near net shape (NNS) fabrication by plasma spray forming (PSF) is a rapid prototyping technique to fab- ricate engineering components having axi-symmetric geometry out of ceramics and refractory metals which are difficult to manufacture by conventional techniques. This study establishes an experimen- tal and computational protocol to manufacture thin walled ceramic (Al2O3) structures on the graphite mandrel (substrate) via plasma spray forming. The combination of experimental and computational approaches reduces currently used empirical methods for the similar purpose. Thermal profiles gen- erated during plasma spraying of Al2O3 on the graphite mandrel for various mandrel designs and cooling conditions were computed by solving the conjugate problem of computational fluid dynamics and 3D unsteady heat transfer. Entire plasma spraying booth was modeled as per actual dimensions to consider the effect on the thermal profile of the mandrel/coating system. The computed temperature profile was compared with the experimentally measured temperature. The corresponding thermal stresses in the mandrel and spray deposited Al2O3 layer were computed. Computed thermal stresses were compared with the fracture strength of Al2O3 to prevent cracking of the spray formed structure during spraying and its successful removal from the mandrel. An optimum temperature increase rate (TIR) during plasma spray forming is defined for the successful deposition and removal of the freestanding ceramic structure.

Plasma Spray Forming 공정에 의해 제조된 텅스텐 성형체의 미세조직 형성 거동

Plasma spray forming is recently explored as a near-net-shape fabrication route for ultra-high temperature metals and ceramics. In this study, monolithic tungsten has been produced using an atmospheric plasma spray forming and subsequent high temperature sintering. The spray-formed tungsten preform from different processing parameters has been evaluated in terms of metallurgical aspects, such as density, oxygen content and hardness. A well-defined lamellae structure was formed in the as-sprayed deposit by spreading of completely molten droplets, with incorporating small amounts of unmelted/partially-melted particles. Plasma sprayed tungsten deposit had 84-87% theoretical density and 0.2-0.3 wt.% oxygen content. Subsequent sintering at 2500<TEX>$^{\circ}C$</TEX> promoted the formation of equiaxed grain structure and the production of dense preform up to 98% theoretical density.

Tensile properties of carbon nanotube reinforced aluminum nanocomposite fabricated by plasma spray forming

Uniaxial tensile tests were performed on plasma spray formed (PSF) Al–Si alloy reinforced with multiwalled carbon nanotubes (MWCNTs). The addition of CNTs leads to 78% increase in the elastic modulus of the composite. There was a marginal increase in the tensile strength of CNT reinforced composite with degradation in strain to failure by 46%. The computed critical pullout length of CNTs ranges from 2.1 to 19.7 μm which is higher than the experimental length of CNT, leading to relatively poor load transfer and low tensile strength of PSF nanocomposites. Fracture surface validates that tensile fracture is governed strongly by the constitutive hierarchical microstructure of the plasma sprayed Al–CNT nanocomposite. The fracture path in Al–CNT nanocomposite occurs in Al–Si matrix adjacent to SiC layer on CNT surface.

Application of RBF Network for Forecasting Characteristics of In-Flight Particles by Plasma Spraying

The main factors that influence the deposition efficiency and forming quality are the state of in-flight particles, which are directly effected by process parameter during plasma spray forming. In this study, plasma spraying of ZrO2 powder was employed according to the method of orthogonal experiments, and the relationship between spray parameters and characteristics of in-flight particles, which were monitored by an optical monitoring system of CCD camera, were investigated. Radial basis function (RBF) neural network model had been designed to forecast the temperature and velocity of in-flight particles, and optimized spray parameter. The comparison of the simulations with the experimental results shows the validity of the model.

Structure and property evaluation of a vacuum plasma sprayed nanostructured tungsten–hafnium carbide bulk composite

Vacuum plasma spray (VPS) forming of tungsten-based metal matrix nanocomposites (MMCs) has shown to be a cost effective and time saving method for the formation of bulk monolithic nanostructured thermo-mechanical components. Spray drying of powder feedstock appears to have a significant effect on the improved mechanical properties of the bulk nanocomposite. The reported elastic modulus of the nanocomposite nearly doubles due to the presence of HfC nano particulates in the W matrix. High resolution transmission electron microscopy (HRTEM) revealed the retention of nanostructures at the select process conditions and is correlated with the enhanced mechanical properties of the nanocomposite.

Carbon Nanotube Reinforced Aluminum Nanocomposite via Plasma and High Velocity Oxy-Fuel Spray Forming

Free standing structures of hypereutectic aluminum-23 wt% silicon nanocomposite with multiwalled carbon nanotubes (MWCNT) reinforcement have been successfully fabricated by two different thermal spraying technique viz Plasma Spray Forming (PSF) and High Velocity Oxy-Fuel (HVOF) Spray Forming. Comparative microstructural and mechanical property evaluation of the two thermally spray formed nanocomposites has been carried out. Presence of nanosized grains in the Al-Si alloy matrix and physically intact and undamaged carbon nanotubes were observed in both the nanocomposites. Excellent interfacial bonding between Al alloy matrix and MWCNT was observed. The elastic modulus and hardness of HVOF sprayed nanocomposite is found to be higher than PSF sprayed composites.

Carbon Nanotube Reinforced Aluminum Nanocomposite via Plasma and High Velocity Oxy-Fuel Spray Forming

Free standing structures of hypereutectic aluminum-23 wt% silicon nanocomposite with multiwalled carbon nanotubes (MWCNT) reinforcement have been successfully fabricated by two different thermal spraying technique viz Plasma Spray Forming (PSF) and High Velocity Oxy-Fuel (HVOF) Spray Forming. Comparative microstructural and mechanical property evaluation of the two thermally spray formed nanocomposites has been carried out. Presence of nanosized grains in the Al–Si alloy matrix and physically intact and undamaged carbon nanotubes were observed in both the nanocomposites. Excellent interfacial bonding between Al alloy matrix and MWCNT was observed. The elastic modulus and hardness of HVOF sprayed nanocomposite is found to be higher than PSF sprayed composites.

In-flight behaviors of ZrO 2 particle in plasma spraying

In recent years, on-line measurement of particle in-flight behaviors including temperature, velocity and spatial distribution is one of the most important research fields, which can be used to directly analyze the influence of spray parameters and to control the coating quality real-time during plasma spray forming. According to the method of orthogonal experiments, plasma spraying of ZrO 2 has been carried out under different spray parameters in this paper. The particle in-flight behaviors have been measured by a two-color emission technique to analyze the influence of argon flow rate, hydrogen flow rate and electrical current on the particle temperature and velocity. The molten state of the particle has been analyzed. The results showed that the particle velocity increased remarkably with the increase of the argon flow rate. The particle temperature was mainly influenced by the hydrogen flow rate, and increasing electrical current resulted in the increase of the particle temperature and velocity to some extent. The molten state of the particle, affected by the particle in-flight behaviors in the plasma jet, could be used to analyze the deposition efficiency and coating quality.

Plasma spray formed near-net-shape MoSi 2–Si 3N 4 bulk nanocomposites—structure property evaluation

This article, for the first time, presents the challenges toward the successful consolidation of near-net-shape bulk MoSi 2–Si 3N 4–SiC nanocomposite using plasma spray forming. A detailed characterization of the spray formed bulk nanocomponent has been performed using optical microscopy (OM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and Vickers hardness testing. Vickers hardness (900 Hv) and fracture toughness (∼>5 MPa m 1/2) of the nanocomposite showed a little deviation from the expected, which might be due to the difference in the particle (Si 3N 4) size and their distribution in the MoSi 2 matrix as a function of component thickness. Relatively higher hardness is attributed to the retention of the nanostructure in the composite. In addition, the as fabricated bulk nanocomposite showed enhanced oxidation resistance.

Plasma spray forming

The technology of plasma spray forming (PSF) is introduced, and the technical processes of plasma spray for fabricating parts and moulds are investigated emphatically in this paper. The technological characteristics of PSF are summarized, including original prototype fabrication and surface treatment, post-treatment of a formed workpiece and demoulding methods. Also, some important factors affecting the qualities of workpiece formed by plasma spraying have been analyzed and evaluated in detail based on experiments. Finally, some experiments of PSF have been carried out.

The spray forming of nanostructured Aluminum Oxide

Research Summary Nanostructured ceramics and their composites possess improved properties such as tensile strength, fatigue strength, hardness, and wear resistance. Freestanding, near-net shape, nanostructured Al2O3 components can be synthesized via plasma-spray forming. In this study, plasma-spray parameters were optimized and an innovative substrate cooling technique was developed to retain nanosize Al2O3 in the spray deposit. Nanosize Al2O3 particles were partially melted and trapped between the fully melted coarser, micrometersize Al2O3grains. Densification of the spray-deposited Al2O3occurred via solidification and sintering. A similar processing approach can be adopted for fabrication of near-net shapes of a variety of nanostructured materials (metals, ceramics, and intermetallics) and their combinations by selecting suitable powder-treatment and plasmaspray parameters.