Carrier liquid composition control for suspension plasma spraying

A method comprising:

• controlling a first ratio of a first liquid to a second liquid to form a first suspension comprising a powder and a first carrier liquid composition comprising at least one of the first liquid or the second liquid;
• directing the first suspension comprising the first carrier liquid and the powder to a plume of a thermal spray device;
• forming a first portion of a coating comprising the powder on a substrate from the first suspension;
• controlling a second ratio of the first liquid to the second liquid to form a second suspension comprising a second carrier liquid composition and the powder, wherein the second carrier liquid composition includes the first liquid and the second liquid;
• directing the second suspension comprising the second carrier liquid composition and the powder to the plume of the thermal spray device;
• and
• forming a second portion of the coating comprising the powder on the substrate from the second suspension,
• wherein the first ratio and the second ratio are controlled such that the first portion of the coating exhibits a first microstructure and the second portion exhibits a second microstructure different from the first microstructure,
• wherein the first ratio of the first liquid to the second liquid in the first carrier liquid composition is different from the second ratio of the first liquid to the second liquid in the second carrier liquid composition,
• wherein one of the first microstructure and the second microstructure is a columnar microstructure, and another of the first microstructure and the second microstructure is a dense microstructure having a density of less than about 5 volume percent, and
• wherein the first ratio and the second ratio are selected such that a surface tension of the second suspension is different than the first suspension.