What Types of Post-Processing Are Necessary After LENS Repairs?

Mandatory Stress Relief and Heat Treatment

The localized high heat input of the LENS process induces significant residual stresses, which can lead to distortion or cracking in service. Therefore, a controlled heat treatment cycle is the first critical post-process. This serves to: 1) relieve these residual stresses, stabilizing the component geometry; and 2) condition the microstructure of the deposited material. For precipitation-hardening alloys like Inconel 718, this involves a full solution treatment and aging cycle to achieve optimal mechanical properties and ensure the repair zone integrates properly with the substrate.

Precision Machining to Restore Form and Function

LENS deposits material in a near-net shape, leaving an as-deposited surface that is rough and oversized. Precision machining is essential to restore the component's final dimensions, critical tolerances, and functional surface finish. This typically involves CNC machining to machine sealing faces, bore diameters, or blade airfoil profiles. Due to the often hard and wear-resistant nature of the deposited alloy, machining may require specialized tooling and parameters. For complex internal repairs, techniques like deep hole drilling or EDM may be necessary.

Surface Enhancement and Functional Coating

After machining, surface enhancement techniques are often applied to improve performance. These may include: • Shot Peening or Laser Shock Peening: To introduce beneficial compressive surface stresses, dramatically improving fatigue life—a critical consideration for repaired rotating parts in aerospace and aviation. • Polishing or Grinding: To achieve a specific surface roughness (Ra) for aerodynamic efficiency, fluid flow, or to meet sanitary standards in pharmaceutical and food applications. • Application of Coatings: For components facing extreme temperatures, a Thermal Barrier Coating (TBC) may be applied over the repaired area to restore full thermal protection.

Rigorous Non-Destructive Inspection (NDE)

Comprehensive inspection is non-negotiable to validate the repair's integrity. This involves a combination of material testing and analysis techniques: • Dye Penetrant Inspection (DPI): To detect surface-breaking cracks or lack-of-fusion at the deposit interface. • Ultrasonic Testing (UT) or X-ray Inspection: To identify sub-surface defects like porosity or incomplete bonding within the clad layer. • Dimensional Inspection: Using Coordinate Measuring Machines (CMM) to verify all critical features meet original equipment manufacturer (OEM) specifications after machining.

Industry-Specific Validation and Recertification

The final step is often performance validation to recertify the component for service. This may involve proof testing (e.g., hydrostatic testing for pressure vessels), microstructural analysis to confirm proper heat treatment, or comparative hardness mapping across the repair zone. For safety-critical industries like power generation and nuclear, this rigorous post-processing and documentation chain is essential to demonstrate the repair meets or exceeds the original component's performance requirements, ensuring reliability and safety.