Preparation of nickel-chromium-chromium-carbide coatings by supersonic spraying

Supersonic spraying is an advanced surface engineering technology that uses high-temperature, high-speed jets to melt or partially melt coating materials and then deposits them onto a substrate surface at high speed to form a high-performance coating. Among these, nickel-chromium/chromium carbide coatings prepared by supersonic flame spraying are particularly widely used in industrial applications.

I. Technical Principles Supersonic flame spraying technology utilizes the intense combustion of fuel (such as kerosene, propane, or hydrogen) with high-pressure oxygen in a combustion chamber to generate a high-temperature, high-pressure gas stream. This gas stream is accelerated to supersonic speeds as it passes through a specially designed Laval nozzle, forming a stable high-speed jet. The composite powder of nickel-chromium alloy and chromium carbide used in the spraying process is fed into this jet, rapidly heated to a molten or semi-molten state, and impacts the pre-treated (e.g., sandblasted) substrate surface at extremely high speeds (typically exceeding 600 m/s). The molten particles flatten on the substrate, rapidly cool, and stack and solidify, ultimately forming a dense, tightly bonded cermet coating.

II. Core Coating Characteristics The nickel-chromium/chromium carbide coating prepared using this process possesses the following outstanding properties:

Excellent Mechanical Properties: The coating combines high hardness with good toughness. Its microhardness typically ranges from 760 HV to 995 HV. The nickel-chromium alloy, acting as the binder phase, provides excellent toughness and bonding strength, while the dispersed chromium carbide hard phase provides the main wear-resistant support. The average bonding strength between the coating and the substrate exceeds 60 MPa.

Dense microstructure: Due to the extremely high velocity of the sprayed particles, they deform fully upon impact, resulting in a tight superposition and allowing the coating porosity to be controlled at an extremely low level of 1-2%. Low porosity is key to the coating's excellent corrosion resistance and oxidation resistance.

Superior high-temperature performance: This coating maintains stable performance over a long period within an operating temperature range of 538℃ to 900℃. It exhibits high high-temperature hardness retention and significant resistance to oxidation and gas erosion. Studies show that at a high-temperature environment of 620℃, its resistance to solid particle erosion is several to ten times higher than that of ordinary heat-resistant steel substrates.

Good environmental resistance: The nickel-chromium alloy binder phase itself has good oxidation and corrosion resistance. When combined with chromium carbide, the coating effectively resists high-temperature oxidation, sulfur corrosion, and erosion from various salt sprays and chemical media.

III. Main Application Areas

Aerospace: Used for wear-resistant and abrasion-resistant seals on hot-end components such as engine compressor blades and turbine casings.

Energy & Power: Widely used for high-temperature protection and life extension of boiler pipes in coal-fired and gas-fired power plants, steam turbine blades, and gas turbine transition sections.

Industrial Manufacturing: Applied to key components such as metallurgical rolls, high-temperature valves, sintering furnace guides, petrochemical pump shafts, and mechanical seal rings.

IV. Nickel-Chromium-Chromium Carbide Materials Suitable for Supersonic Spraying.