Cold Spray vs. Thermal Spray

In high-end industrial sectors such as aerospace, energy equipment, and automotive manufacturing, surface coating technology is crucial for enhancing the service life and performance of components. As two of the core technologies in materials surface engineering, cold spray and thermal spray are often compared with each other. This article will provide an in-depth analysis from multiple perspectives—including technical principles, performance parameters, and application scenarios—to help you precisely match the right technological solution.

Aerospace Engine Blade Flame Erosion Testing System

The “Aeroengine Blade Flame Erosion Testing System” has passed acceptance testing at East China University of Science and Technology in Shanghai. It is used to evaluate the high-temperature erosion and ablation performance of aeroengine blades.

Development of Cold Spray and the Current Research Status at Home and Abroad

The concept of cold spraying was proposed in 1990, originating from experiments conducted in the mid-1980s at a Soviet research institute. During supersonic wind-tunnel tests using tracer particles, researchers observed that when the particle velocity exceeded a certain critical threshold, the interaction between the tracer particles and the target surface shifted from erosion to accelerated deposition.

U.S. Cold Spray Technology Used to Refurbish Aging Bombers

South Dakota School of Mines & Technology and Ellsworth Air Force Base have signed a formal partnership to jointly undertake project research aimed at modernizing aging bombers. To date, four B-1 bombers have been refurbished, enabling them to remain in service and saving the military millions of dollars.

The U.S. Air Force is evaluating two cold spray processes.

The U.S. Air Force Research Laboratory has recently, through evaluation, validated two cold-spray deposition technologies that make it possible to apply tungsten carbide–cobalt (WC-Co) coatings to high-strength steel components in aircraft. If subsequent tests are successful, these technologies could serve as an alternative to electroplated hard chrome (EHC).

HVOF Supersonic Flame Process: In supersonic flame spraying, oxygen and aviation kerosene are mixed in a premixing system and then burned in a high-pressure combustion chamber. The resulting flame jet, combined with high-pressure air passing through a Laval nozzle, generates a high-temperature, high-velocity flame stream that heats metal-ceramic powders to a semi-molten state.

[Coating Preparation] Wear-resistant Coating

Thermal Barrier Coating Preparation Methods

Plasma Spraying—Plasma spraying involves feeding metal or ceramic powders into a high-temperature plasma flame, where the plasma jet heats the spray material to a molten or highly plastic state. Guided by the high-speed plasma jet, these particles rapidly impact the surface of the workpiece. During the spraying process, the spray material first undergoes heating, reaching either a fully molten or semi-molten state; then enters a flight phase propelled forward by the gas stream; and finally strikes the substrate surface with sufficient kinetic energy, resulting in intense collisions that flatten the particles into a thin, planar layer and cause them to solidify instantly. The resulting coating consists of countless deformed particles interlaced and stacked in a wavy, layered structure. There are inevitably some voids or pores between the particles, with porosity typically ranging from 4% to 20%. The coating also contains oxides and inclusions. By employing a high-temperature plasma arc heat source, supersonic speeds, and low-pressure or protective atmospheres during spraying, these defects such as voids and pores can be significantly reduced. Since the coating has a layered structure, its performance exhibits certain directional characteristics. The bonding between the coating and the substrate surface is generally considered to occur in two ways: mechanical bonding, where the flattened particles formed by collision interlock with the irregularities on the substrate surface, creating a mechanical “anchoring” effect; and metallurgical bonding, which occurs when diffusion and alloying take place at the interface between the coating and the substrate, forming intermetallic compounds or solid solutions at the bonding zone. Among these bonding mechanisms, plasma-sprayed coatings primarily rely on mechanical bonding. The performance of the coating is closely related to both the quality of the spray powder and the spraying process itself. Therefore, the treatment of the spray powder is extremely important. The spraying process itself also greatly influences the coating’s performance. If the power is too high during spraying, the coating becomes dense, and improper control of the substrate temperature can lead to residual stresses, causing the coating to peel off and fail. Electron Beam Physical Vapor Deposition (EB-PVD)—In recent years, EB-PVD thermal barrier coatings have been developed. These coatings are produced by heating and vaporizing ceramic sources using a high-energy electron beam, with the ceramic vapor deposited onto the substrate atom by atom. When preparing gradient thermal barrier coatings, this method enables a continuous transition in both structure and composition between the metallic bond coat and the ceramic layer. After subsequent high-temperature treatment, diffusion occurs between the bond coat and the ceramic layer, effectively eliminating the internal interface. The resulting coating microstructure features columnar crystals oriented perpendicular to the substrate surface. The bonding between the columns and the substrate is metallurgical, providing excellent stability. Moreover, at high temperatures, the columnar microstructure demonstrates outstanding strain tolerance, greatly enhancing the coating’s resistance to thermal fatigue. In thermal cycling tests, coating failure is typically caused by cracking within the Al2O3 layer. Additionally, the coating surface is smooth and requires no further machining, the process parameters are easy to control, and the coating is repairable—all of which represent significant advantages compared to thermal barrier coatings prepared by plasma spraying. However, drawbacks such as uncontrollable coating thickness, complex surface cleaning procedures, expensive and sophisticated equipment, relatively low deposition rates, and cumbersome processing procedures still require further research and improvement. Schematic diagram of the EB-PVD principle—EB-PVD columnar crystal structure. Liquid Injection Plasma Spraying—Liquid injection plasma spraying is a promising coating preparation method that has emerged in recent years. Although there are almost no domestic reports on this technique, some exploratory studies have been conducted abroad. The principle behind liquid-injection plasma spraying for thermal barrier coatings is that a zirconium salt solution is drawn out by a conveying motor and, under the action of a carrier gas, passes through an atomizing nozzle before entering the plasma. Within the hot plasma, physicochemical reactions occur, and the material is deposited onto the metal substrate. Conventional thermal barrier coatings prepared by powder injection can withstand approximately 400 thermal cycles, while EB-PVD-prepared coatings can endure around 780 cycles. The new liquid-injection-based thermal barrier coatings can withstand an average of 1018 thermal cycles, significantly improving their thermal cycling performance. The phase structure of the coating mainly consists of a non-transformative tetragonal phase, and no phase transformation occurs even at 1121°C during thermal cycling. The width of cracks increases with the number of thermal cycles. The hardness of the coating initially rises during the early stages of thermal cycling. The columnar crystal structure of the coating remains intact throughout the thermal cycling process. The depth of penetration of the liquid into the plasma nozzle greatly affects the deposition efficiency of the coating. Coating failure primarily occurs within the ceramic top layer, near the interface between the ceramic layer and the bond coat. Overall, thermal barrier coatings prepared by the liquid-injection plasma spraying process exhibit the following characteristics: (1) A unique microstructure: The grain size of the coating is 10–30 nm; it features uniform nanopores and micropores; contains longitudinal microcracks; and lacks layered particle structures or lamellar grain boundaries; (2) The growth of nanocrystals is inhibited; (3) The coating displays excellent thermal shock resistance. Sol-Gel Composite Slurry Hot-Press Filtration Method for Preparing Ceramic Coatings—By using the sol-gel composite slurry hot-press filtration method, we can prepare Al2O3-ZrO2-Y2O3 composite coatings featuring YPSZ particles embedded within an Al2O3-Y2O3 spatial network membrane structure. This approach combines the advantages of both Al2O3-Y2O3 and ZrO2-Y2O3 coatings, achieving superior overall performance. The PYSZ coatings prepared by the hot-press filtration method possess a nano/micro/microporous composite structure, effectively reducing phonon thermal conduction and convective heat transfer, thus delivering enhanced thermal barrier performance. The thermal barrier effect of the coating increases with the increase in sol content within the slurry. In the Al2O3-ZrO2-Y2O3 composite coating, the Al2O3-Y2O3 network membrane can block oxygen ion transport, while the embedded YPSZ helps adjust the thermal expansion match between the coating and the substrate. Meanwhile, the nano/micro/microporous composite structure of the coating facilitates stress relaxation. As a result, the Al2O3-ZrO2-Y2O3 composite coating demonstrates exceptional resistance to high-temperature oxidation and spalling of oxide layers. Materials, Equipment, Processes, and Solutions—We have accumulated extensive experience in coating applications and are currently replicating these successful cases. We will guide you through the entire coating manufacturing transformation process, ensuring: rapid production start-up; a reliable supply solution covering materials, equipment, and processes; coating trials conducted either on-site at your facility or at our technical center; and consistently high coating quality and efficiency. Start collaborating with us today and reap success tomorrow!

[Coating Preparation] Erosion-Resistant Coating To achieve an ideal sealing condition between the blades and the casing of high-speed rotating machinery (such as compressors and gas turbines) and thereby maximize the hydrodynamic pressure differential, erosion-resistant coating technology can be employed to enhance overall machine efficiency, reduce energy consumption, and extend service life.

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