What Properties Should Thermal Spray Powders Have?

In addition to meeting the functional requirements of the coating, the thermal spray powder must also meet the needs of the spraying process: it can be transported into the jet flame flow uniformly, smoothly and stably to ensure a stable and uniform thermal spray coating. Therefore, the basic characteristics of the powder such as shape, particle size and particle size distribution, bulk density, fluidity and surface quality, are important components of the performance of thermal spray powder.

(1) Morphology of powder particles

Most of the thermal spraying alloy powder materials are prepared by the atomization method, and the powder particle morphology mainly refers to the geometric shape and surface characteristics of the powder particles. The geometry can be evaluated by measuring the ratio of the short axis to the long axis (statistical value) of the elliptical spherical particles. The higher the spheroidization degree, the better the solid-state fluidity of powder. Since the degree of powder spheroidization is not only related to the atomization powder milling method and atomization milling process parameters, but also to the chemical composition of the powder itself. Therefore, the spheroidization degree of different types of powders is also different, but it should be ensured that the spraying process can be smooth and even powder feeding.

There are sometimes holes of different sizes inside the thermal spray metal powder particles prepared by atomization, some of which penetrate to the surface, and some are closed inside the particles. If the spraying process is improper, it will have a direct impact on the quality of the coating. To observe such holes, an optical metallographic microscope is usually used. Surface features refer to surface color, smoothness, etc.

(2) Particle size of powder

The selection of powder particle size and its range is mainly determined by spraying process method and spraying process specification parameters. Even if the powder particle size range is the same, the proportion of the particle size grade composition is not necessarily the same. For example: although the powder particle size is in the range of 125μm~50μm (-120mesh~+320mesh), the proportion of powders of three different particle size grades of 100μm~125μm, 80μm~100μm, 50μm~80μm is not the same. The powder particle size range and its particle size grade composition have a direct impact on the coating quality, powder bulk density and fluidity.

(3) Bulk Density of Powder

Powder bulk density refers to the mass per unit volume of powder when it is loosely packed. Since the bulk density of the powder is related to the spheroidization degree of the powder, the size and quantity of the holes inside the powder particles, and the composition of the powder particle size, it also affects the quality of the spray coating.

(4) Fluidity of powder

The fluidity of powder is the time required for a specified amount of powder to flow freely through a standard funnel with a specified aperture. It is usually characterized by the time (s) required for 50g powder to flow through a standard funnel with a diameter of 2.5mm. It has certain influence on spraying process and spraying efficiency.

Chengdu Huarui Industrial Co., Ltd. 

Email: sales.sup1@cdhrmetal.com 

Phone: +86-28-86799441