The erosion resistance of infrared transparent materials

Abstract

Studies in the Cavendish Laboratory over the years have demonstrated the poor erosion resistance of most infrared (IR) transparent materials. A number of methods for increasing this erosion resistance have been investigated by various laboratories and these are assessed in the following study. These techniques include producing high–quality surface finishes, generating surface compressions and the application of coatings. The results emphasise that considerable care and effort is needed to produce even minor improvements in the liquid impact damage threshold velocity (DTV). The magnitude and time–scale of the impact stresses dictate that significant reductions in crack size are required to cause a significant improvement in DTV. The effectiveness of the coatings can be reduced by poor adhesion and tensile residual stresses weakening the substrate material. The recent development of chemical vapour deposited diamond (CVDD) as an erosion resistant infrared transparent material is also discussed.