Oxide layer or some inclusion can definitely block or affects the diffusion of atoms in its path. Because of its huge difference in melting point, for example melting point of Aluminium oxide is about 2070 degrees Celsius whereas the sintering temperature is nearly 4 times lower.

So the oxide layer will not take part in the diffusion process. So high quality of powder is essential for the PM process.

Oxide layer or some inclusion can definitely block or affects the diffusion of atoms in its path. Because of its huge difference in melting point, for example melting point of Aluminium oxide is about 2070 degrees Celsius whereas the sintering temperature is nearly 4 times lower.

So the oxide layer will not take part in the diffusion process. So high quality of powder is essential for the PM process.

There are several factors which could affect the oxide formation during the powder production. For example, the oxygen in liquid metal could lead to precipitation of oxide inclusions. Also during the gas / water atomization treatment, the oxygen from gas/water could also lead to the oxidation on the powder surface. Once oxide layer precipitated on the powder (e.g. Cr2O3, etc.), it will prevent the mass diffusion during the sintering process and decrease the sintering efficiency. Although the sintering can be enhanced by increasing the sintering temperature or/and time, it will lead to an increasing of grain growth as well. There is certain balance among these process parameters. Thus, it is significant to decrease the oxide formation during the powder production or use extra treatment steps to remove the oxide layer on the powder surface.

Surface diffusion governs a sintering process at relatively low temperatures, mainly - at initial sintering stages. Of course, surface oxidation of the powder to be sintered in strongly undesirable, because the oxide layer on the powder's particles is a diffusion barrier, which - obviously - causes an overall slowing of the sintering process.