Abstract
The processes used to protect hot section components in modern gas turbines range from single element chemical vapour deposition diffusion processes requiring low–technology plant and equipment to very sophisticated computer operated processes capable of depositing closely controlled alloy compositions. Regardless of the level of technology involved, all of the processes demand good quality control and efficient working practices at each stage of the procedure to ensure that an adequate standard of coating is produced. For example, good surface preparation is important in every case and can influence the cleanliness, integrity (defect level), and surface finish of both chemical and physical vapour deposited coatings. Microexamination of testpieces is still widely used for monitoring coating characteristics such as coating thickness, but non–destructive techniques based on surface wave phenomena (e.g. thermography and ultrasonics) raise interesting prospects for the future. Ultimately, it is envisaged that automated processing methods with in–built process control and real time non–destructive monitoring and data storage will be standard practice.
MST/285
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