Powder particle transport in plasma arc powder cladding

Physical problem in powder delivery

The paper by Wang Xibao and Zhang Wenye analyzes powder particle transport during plasma arc powder cladding. The process quality depends not only on arc power and travel speed, but also on how powder particles travel through the plasma arc column. If particles arrive at the melt pool with unsuitable velocity, temperature, or distribution, the deposit can show porosity, unmelted particles, composition variation, or uneven dilution.

Theoretical transport findings

The study applies arc physics and fluid mechanics to examine particle motion in a transferred plasma arc. It calculates axial velocity distribution and radial powder flux distribution for iron based and boride powders. The main finding is that powder particles move much slower than the plasma gas stream. Smaller particles are accelerated more easily and achieve higher average velocity in the arc column. Lower density particles also show higher acceleration and average velocity.

Variable	Effect on particle transport	Process consequence
Particle size	Smaller particles accelerate more readily.	Fine powder may overheat or arrive faster.
Particle density	Lower density increases acceleration.	Lighter powder may follow gas stream more closely.
Current level	Higher current deepens central velocity valley.	Axial powder distribution becomes nonuniform.
Arc column shape	Creates mountain like velocity profile.	Powder flux varies across the melt pool.
Powder type	Iron and boride powders respond differently.	Composition and melting behavior must be considered.

Parameter interpretation

The paper reports that for transferred plasma arcs above 150 A, the axial transport velocity across the arc cross section shows a mountain like distribution. With increasing current, the central valley becomes deeper and wider. This means the powder velocity is not uniform across the arc cross section, and the center of the arc may not correspond to the highest particle velocity. Such nonuniformity can affect powder capture efficiency and melt pool chemistry.

Process implications

For engineering practice, powder transport analysis explains why fine powder may behave differently from coarse powder even at the same feed rate. It also explains why high current plasma cladding can produce uneven dilution if the powder stream is not matched to the arc velocity field. Process development should therefore consider powder size distribution, powder density, carrier gas, nozzle geometry, arc current, and traverse speed as one system.

Study insight

This paper is valuable because it connects plasma cladding defects to the physical behavior of powder in the arc, rather than stopping at empirical parameter adjustment. Engineers often tune current and speed by trial and error, but the underlying issue may be particle velocity mismatch. The practical lesson is that powder selection and nozzle design are as important as arc parameters. A well controlled deposit requires matching the powder trajectory to the arc thermal field.