Wet shot peening for jet engine components

The lifespan of peening media depends on factors including media type, component hardness, cycle frequency, and slurry concentration. Ceramic shot generally fractures more readily than stainless-steel shot, meaning replacement intervals are shorter. As media degrades, particle size distribution shifts, reducing impact energy and compressive residual stress depth. This directly undermines fatigue life improvements in rotating components such as fan blades and compressor discs. A properly engineered wet peening system continuously classifies and replenishes media to maintain a consistent size distribution throughout production runs.

Laser shock peening (LSP) induces compressive residual stresses to greater depths than wet shot peening, making it the preferred choice for applications where subsurface fatigue crack initiation is the primary concern, such as foreign object damage repair zones on fan blades. However, wet shot peening offers significantly lower capital and operating costs, shorter cycle times, and broader OEM approval across MRO and new manufacture workflows. For the majority of rotating engine component applications processed to Rolls-Royce, GE, and Pratt and Whitney specifications, wet shot peening delivers sufficient compressive stress depth at a production-viable cost.

A: AMS 2432 requires intensity to be established via a saturation curve using Almen strips of the appropriate type (N, A, or C) selected according to the target intensity range for the component. For nickel superalloy turbine discs, N-type strips are typically used where intensities fall in the lower range, while A-type strips cover the mid-range intensities common in disc fir-tree slot and bore region peening. The saturation curve must demonstrate that doubling the exposure time produces no more than a 10% increase in arc height, confirming saturation has been reached. Strip placement, holder design, and accessibility within complex disc geometry are critical variables that must be validated during process qualification.

Wet shot peening is generally performed prior to the application of thermal barrier coatings (TBCs) or erosion-resistant coatings, as the process is intended to introduce compressive residual stress into the substrate before any coating is deposited. Peening after coating risks coating delamination or cracking. Where selective peening of uncoated regions on partially coated components is required, masking must be applied to OEM-specified standards, typically defined within the relevant process specification or engineering order. Masking materials must withstand slurry impingement without contaminating the slurry or leaving residue on component surfaces, and their removal must be verified as part of the post-process inspection sequence.

Before a new component geometry enters serial production, a full process qualification is required under the governing specification, typically including saturation curve generation, coverage verification, surface roughness measurement, and residual stress confirmation via X-ray diffraction (XRD) or similar technique. First-article inspection (FAI) documentation must demonstrate that all monitored parameters, including slurry concentration, air pressure, nozzle standoff, and cycle time, were held within specification throughout the qualification run. For AMS 2432 compliant systems, the computer monitoring records form part of the auditable FAI package. OEM-specific requirements from Rolls-Royce, GE, or Pratt and Whitney may impose additional witness testing, laboratory analysis, or approved supplier list (ASL) registration steps before production release.