Journal of Thermal Spray Technology最新文献

To address the issue of low surface hardness and poor wear resistance of 45# steel, this study applied laser cladding technology to prepare three types of iron-based coatings on the surface of 45# steel: Fe25-30WC, Fe25-30TiC, and Fe25-15WC+15TiC. The microstructure and mechanical properties of the coatings were analyzed using SEM, EDS, XRD, Vickers hardness tester, and a mechanical testing machine. The results indicated that in terms of hardness, the Fe25-30TiC coating exhibited the highest average microhardness of 600 ({HV}_{0.2}), followed by the Fe25-30WC coating (520 ({HV}_{0.2})) and the Fe25-15WC+15TiC coating (480 ({HV}_{0.2})). The bond strength of the Fe25-30WC coating and the Fe25-15WC+15TiC coating to the substrate was roughly the same, about 500 MPa, which is higher than that of the Fe25-30TiC coating (467 MPa). Additionally, the study discussed the abrasive wear characteristics of the three coatings under dry and wet sand conditions. The experimental results showed that under dry sand conditions, the Fe25-30TiC coating had superior wear resistance compared to the Fe25-15WC+15TiC coating and the Fe25-30WC coating. Under wet sand conditions, the Fe25-30WC coating exhibited better wear resistance than the Fe25-30TiC coatings and Fe25-15WC+15TiC coatings.

Dual-phase AlCoCrFeNiSi_0.5 high-entropy alloy powders for thermal spraying were prepared by mechanical alloying (MA). The effect of ball-milling time on MA of AlCoCrFeNiSi_0.5 powder was studied. The formation of solid solution during ball-milling was studied by X-ray diffraction. The grain size (GS), lattice distortion (LS) and dislocation density were calculated. The morphology, microstructure and element content of the powder were analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The GS decreases with the increase in rotating milling time, while the LS and dislocation density change in contrast therewith. The addition of Si increased the hardness and modulus of the powder to 12.33 ± 1.26 and 79.9 ± 6.21 GPa, respectively. The AlCoCrFeNiSi_0.5 powder has BCC and FCC solid solutions, while the FCC phase can be adjusted by annealing treatment. After 2 h solid-solution treatment at 1110 °C, BCC phase content up to 79%, the content of BCC solid solution is much higher than that before solid-solution treatment (46%), the GS increases, the LS and dislocation density decreases, the effects of solid-solution strengthening, dislocation strengthening, and fine-crystal strengthening are significantly enhanced, and the distribution of elements is more uniform. However, due to the reduction of FCC solid solution and σ-phase content, the hardness and elastic modulus of the powder after 1110 °C solid-solution treatment are slightly lower than that beforehand.

In this study, a comprehensive set of characterization techniques are employed to demonstrate that the cold spray deposition process can result in a significant increase in martensite in austenitic stainless steel. The lack of consensus in the literature on the formation of strain-induced martensite in cold spray can be attributed to the diverse processing conditions and measurement techniques used in different studies. In this work, EBSD, neutron diffraction, TEM imaging, and precession electron diffraction were used in combination to examine whether strain-induced martensite is formed during cold spray deposition of 304L stainless steel powder and to give further insight into possible mechanisms controlling this phenomenon. Cold spray was performed at both 350 °C and room temperature (25 °C) to investigate the effects of spray temperature on the martensite transformation. It is shown that the strain-induced martensite formation is significantly suppressed compared to that which would be expected for comparable levels of plastic strain at quasi-static strain rates. Additionally, the spray gas temperature is shown to directly impact the microstructure formed at the prior particle interface and the formation of dynamically recrystallized regions.

Titanium plasma-sprayed (TPS) porous coatings have been used in total hip arthroplasty for decades. They are considered reliable, and very few failure cases have been described so far. This retrieval study described a series of 20 acetabular components—where total or partial debonding occurred during in vivo use and aimed to explain the underlying failure mechanisms. Implants were examined using optical and electron microscopy (SEM), metallographic sections of retrievals were prepared while pathologic samples of periprosthetic tissues were examined for presence of wear debris. Data from metallographic slides indicated that debonding was initiated at free borders of the coating and tended to progress at the interface between the TPS layer and the shell. In some cases, total debonding occurred leading material wear of both the TPS layer and acetabular shell leading to massive release of metallic debris and accelerated polyethylene wear in third body mechanism. SEM examination demonstrated that splats forming the TPS layer exhibited features suggesting a high temperature gradient between the plasma sprayed layer and the substrate material existed, leading to porosity of splats and suboptimal bonding strength. This study demonstrated that coating application parameters and certain design features (screw holes, fins) may promote long-term failure due to debonding. Surgeons should be aware of this complication as it is most likely underreported, while manufacturers should consider more rigorous pre-clinical testing as suboptimal coating bonding may result in failures during long-term clinical use.

Ti-6Al-4 V is commonly used in gas turbine engines and is sometimes subject to wear during operation. To address this, cost-effective and environmentally friendly solutions are being explored, with a focus on solid-state additive manufacturing techniques such as cold spray (CS). CS can create a dense structure; however, the existing porosity adversely affects the mechanical properties. To reduce the need for post-heat-treatment, this paper considers inner-diameter high- velocity air-fuel (ID_HVAF) as an alternative repair method which is a relatively low-temperature HVAF process that can deposit coatings with microstructures close to those observed in CS coatings. ID_HVAF process can deposit particles at high velocities and relatively low temperatures so that a significant portion of the particles forming the coatings are deposited in the solid state. This work is based on the deposition of Ti-6Al-4 V coatings using the ID_HVAF gun. During deposition, increasing the nozzle length increases the particle velocity and substrate temperature. The particles hit a softer surface with higher kinetic energy, thus increasing the density of the samples. However, HVAF will still oxidize some Ti-6Al-4 V particles and produce vanadium oxide. To study the tribological behavior, Ti-6Al-4 V counterballs were used to simulate the dovetail interface. According to the result, the top deposited layers were densified by the application of counterbalance force. Compared to an α-β Ti-6Al-4 V bulk sample, the coatings have a smaller wear track width and a greater wear depth, resulting in less wear on the counterballs. Each of the three samples shows a combination of abrasive and adhesive wear. The low cohesion between the particles in the coatings results in smaller oxide debris with a greater amount on the wear track of the coatings. By acting as a roller between the counter ball and the coating, this debris can slightly reduce the coefficient of friction.

Photoelectrochemical (PEC) water splitting is a viable route for green hydrogen generation. In PEC cells, the electrodes are coated with suitable semiconductor materials, which absorb the sunlight, generating charge carriers that are used to split water molecules into H₂ and O₂. CuFeO₂ is one promising photocathode material for water splitting. However, its performance is limited by electron/hole pairs recombination within the film and at the film/substrate interface. Aerosol deposition (AD) can be employed to minimize charge recombination by spraying dense, thin films and by establishing a good back-contact interface. In this study, CuFeO₂ powders were synthesized through a conventional solid-state technique and sprayed by AD under varied parameter sets. The effect of particle size distributions, carrier gas, gas pressure and substrate temperature was investigated. The best spraying parameter set was then tuned to obtain thin coatings (< 1 µm). Single-particle deformation and coatings microstructure were investigated by scanning electron microscopy. Optical properties of CuFeO₂ films were analyzed by UV–Vis spectroscopy, while photoelectrochemical performances were estimated through amperometry tests under simulated sunlight. The results of this research show that CuFeO₂ photocathodes can be successfully manufactured by AD. Their performance can be optimized by adjusting coating thickness and by annealing in air.

Microstructural modeling at progressive length scales can enable the prediction of thermal and mechanical properties of thermal sprayed coatings with hierarchical features. Object-oriented finite (OOF2) element modeling conducted using microstructural images, although a powerful technique, has been employed to a limited extent in thermally sprayed materials. Consequently, there is little scientific understanding of the efficiency of the OOF2 technique for estimating bulk properties. For the first time, this study provides a comprehensive analysis of these factors’ role in the OOF2 technique’s capability to predict thermal and mechanical properties in ceramic and metallic coatings manufactured by plasma spray, high-velocity oxyfuel (HVOF) spray, wire_arc spray, and cold spray. The prediction efficiency generally increases for larger grain sizes as overall microstructural features are captured even at lower magnifications. The same effect is obtained in microstructures having lower and uniformly shaped pores. The data on the porosity suggest that OOF2 predictions are most accurate when conducted on coatings manufactured using sintered feedstock because of the dense powder. In contrast, OOF2 predictions are the least accurate when hollow spherical (HOSP) feedstock having empty cores is used. These multiscale facets of microstructure, porosity, etc., thus, highlight the importance of the selection of the representative volume element for accurate analysis in OOF2, which, depending upon the process, is captured at 300× − 500× for HVOF and wire-arc spray, and 1000× − 15,000×  magnifications for plasma and cold spray. This overall assessment charts the relative importance of variables such as grain size, porosity, and feedstock as compared to that of the process and anisotropy in the prediction of properties in thermally sprayed coatings. While these conclusions are based on the limited literature of 37 articles, this study makes a bold attempt towards a guidebook for future thermal spray researchers in conducting more accurate OOF2 analysis.

The cumulative deposition characteristic of deformed particles in the cold spray (CSAM) deposits forms unique open pore microstructure and poor bonding quality, which has great influence on the corrosion resistance. This study investigates the influence of heat treatment (HT) on the corrosion and wear behaviors of CSAM FeCoNiCrMn high entropy alloy. The results show that HT improves the bonding quality between particles, turning open micro-pores into closed, and ultimately greatly improves the corrosion resistance, which can reach the level of traditional additive manufacturing and as-cast materials. The wear resistance of the CSAM deposit after HT is improved, and the layer stripping phenomenon is weakened by the increase in interparticle bonding quality. To improve the corrosion resistance of the CSAM deposit, the first consideration is to improve the bonding quality.

Detonation spraying is a technique that uses the high-temperature, high-velocity detonation waves to deposit the molten metal particles onto the target surface. The effect of the detonation spraying is influenced by the structure of the gun significantly. A series of detonation spraying gun two-dimensional (2-D) numerical models with various spray gun structures (slope lengths from 5 to 45 mm with a step of 10 mm) were established in this work, to investigate the spray performance. During the process of gas detonation, the interaction between the detonation wave and obstacles results in the generation of reflected waves, which exerts an accelerating effect on flame. Simultaneously, collisions between the flame front and obstacles introduce energy losses. Based on the above factors, the following results can be obtained: when the slope length at the nozzle diameter change point is 5 mm, the maximum flow velocity is achieved at the spray gun outlet. When the slope length at the transition point of the spray gun is 25 mm, the maximum temperature is reached at the spray gun outlet. When the slope length at the transition point of the spray gun is 45 mm, the maximum pressure is reached at the spray gun outlet. This work can contribute to the design of the detonation gun.