Scale-Up of a Titanium Carbonitride Coating System for Titanium Alloys.

The objectives of this program were to design, construct, and qualify a new, large reactor suitable for coating titanium alloy compressor components with titanium carbonitride Ti-Cote C on a production basis. Materials Technology Corporation MTC, the sole source of Ti-Cote C, was responsible for the reactor scale-up and subsequent development effort. Microprobe and metallographic studies, erosion testing, the establishment of an SN curve with coated airfoils, and a determination of the thermal shock resistance of coated airfoils were performed on parts coated in the new reactor. At the conclusion of the program, the scaled up reactor was still unable to deliver the consistent coating quality required for production. Coating coverage, adhesion, and thermal shock resistance were acceptable, but the erosion resistance varied greatly between reactor runs of identical parameters. The problem with the erosion resistance appeared to be related to the somewhat porous and granular microstructure of Ti-Cote C deposited in the new, hot wall reactor. No compositional variations were detected in the coating to explain the grainy structure and inconsistent erosion resistance. MTC performed a parametric study to improve coating reproducibility but it was not entirely successful. Author