Kirkendall porosity formation

Diffusion-type interface (film formation) When the interfacial material (interphase material), formed during the deposition of A onto B along with subsequent diffusion, consists of an alloy of A and B with a gradation in composition. See also Interface Interphase material Kirkendall porosity. 

Kirkendall porosity (film formation, adhesion) Porosity that develops in the interfacial region between two materials when the first material diffuses faster into the second than the... 

Over-diffusion (adhesion) When the extent of the interdiffusion of materials causes a weakening of the material in the diffusion zone. Examples Weakening by formation of Kirkendall porosity microfracturing due to stresses caused by phase changes in the diffusion zone. 

There were several types of genuine porosities observed by various researchers. The first type was a void observed in the magnetite layers formed on iron and steel at temperatures below 570°C [91,93], where the gas used could be moist air, dry air or CO2. The voids were very fine in size and were observed at grain boundaries as well as inside magnetite grains. This type of porosity is also known as Kirkendall voids [100]. The formation of voids appeared to be associated with the formation of a duplex scale structure [101]. Recently, some theoretical treatments using conventional diffusion theories were made by Maruyama etal. [102] and Ueda etal. [92] to provide a semi-quantitative and quantitative explanation of their formation mechanism and their location in the scale. 

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