Hi Mvk
to the Surface Engineering Forum.
Experimenting with atomising air pressures, spray distance, spray angle and amps/voltage should enable you to get quite porous coatings. Whether the nature of the porosity/coating is suitable for your particular application is another matter. May I ask what is the application or function of the coating?
Arc spray co-deposition of a pseudo alloy coating for example zinc and aluminium and then acid leaching zinc out of the coating in a post process. This is very dependent on suitability of substrate material and is very limited in flexibility with regard to changing amount of porosity.
Using same principle but with a powder spray process gives much more flexibility as you can tailor the powder mixture to give desired porosity amount, size and distribution. There also more options for the co-deposit material and method of removal. For example plasma or HVOF spraying aluminium polyester blend and then post heat treatment to burn out polyester. Co-spraying with water soluble material and dissolving out in water as a post process is another possibility.
In the distant past I did some work developing coatings for increasing the nucleate boiling effect for heat transfer surfaces exploring some of the above techniques as well as simply detuning process parameters to give what most would call very poor coatings