Photothermal Evaluation of Diffusion Coatings

Chromized and chrome-aluminized coatings, applied to 2.25 Cr-1 Mo and 9 Cr-1 Mo steel substrates by a pack-diffusion process, are being considered for advanced heat exchanger (heat recovery) systems of coal gasifiers [1]. The materials used in this application must have good corrosion resistance and high mechanical strength for prolonged operation at high temperatures (up to 650°C) in the presence of aggressive gas mixtures. The combination of coatings of oxide-forming elements such as Cr and Aℓ (which protect against corrosion) and low-alloy steels (which provide mechanical strength) is economically attractive. The pack-diffusion process is well suited to the application of these coatings to large, complex-shaped components of heat exchangers