Laser Peening Technology Has Come of Age

摘要

It is well known that placing residual compressive stress into the surface of metals provides performance benefits including increased fatigue lifetime, increased fatigue strength, resistance to stress corrosion cracking and resistance to general corrosion. For many years, shot peening has been the mainstay of surface treatment, providing a level of compressive residual stress (CRS) in the skin that is a large fraction of the yield strength of the material and typically extending 10 mils into the surface. This CRS, although shallow, significantly resists crack initiation and gives excellent resistance to stress related corrosion failures. However, in many situations, the depth of residual stress provided by shot peening is too shallow. Cracks can grow past the peened depth or flaws in the material or damage created in use, such as scratches or corrosion, create initiation sites that penetrate beyond the protective layer of compressive stress. In many applications a deeper level of compressive stress is needed. Laser peening has emerged in the past three years as a very viable and important technology for inducing compressive residual stress that is much deeper and more precisely controlled and is able to retain a high quality surface finish. In laser peening, an intense beam of laser light impinges on a surface ablating material from a thin applied sacrificial layer to create a tailored shock wave that impresses a deep but highly controlled level of residual compressive stress into selected areas of metal surfaces. During processing there is essentially no heating of the part, just a shock wave traveling through it. The laser peening technology is finding a major application in jet engine components and is finding expanded applications in aircraft structures and landing gear as well as uses in military, automotive, medical and energy systems. The high repeatability and excellent quality control/quality assurance of the process strongly suggest that surface treatment can be incorporated directly into the design of high performance components.