CASE FILE ENTRY // MATERIAL FAILURE LOG

Overview: Each case highlights metallurgical failures—voids, porosity, cracking—observed in aerospace-grade forging environments.

Approach: I applied NDT, thermal history tracing, and process diagnostics to determine root causes. Visuals are based on simulated micrographs for clarity.

Note: All examples are fictionalized for instructional use and comply with NDA requirements. No proprietary data is shown.

⚠️ Note: All entries are educational and NDA-safe. No client identifiers used.

Metallographic Simulations — Aluminum Alloy

Subsurface Void — Edge Defect

This simulation presents a void located near the edge of an aluminum billet. The defect was identified during a failure investigation following machining deviations.

  • Material: Simulated aluminum alloy
  • Inspection: Cross-sectioned, polished, examined under 20× magnification
  • Void dimension: Approx. 0.0004 in wide
  • Formation mechanism: Casting or rolling-induced porosity

Interpretation: Edge-located voids can disrupt tool engagement and dimensional control. Their early detection supports upstream process optimization.

⚠️ All visuals are fictionalized simulations for educational use only. No proprietary or client-specific data is included.

💻 Corrosion Comparison Dashboard

Compare common corrosion and failure types in aluminum and steel alloys. Learn visual cues, estimated depths, and forge-related causes to better diagnose material integrity issues.

⚫ Pitting Corrosion — 6261-T6 Aluminum

Localized corrosion initiating at grain boundaries or reheated zones in aluminum billets.

📝 Pit dimensions: 41.2 µm × 16.6 µm
🔍 Visual cue: Isolated elliptical void with dark rim, often adjacent to microstructural transitions.

📎 Cause: Poor passivation + chloride exposure + thermal cycling (especially in wet forge environments).

🟠 Surface Corrosion — 304 Stainless Steel

Uniform corrosion with even material loss. Passive chromium oxide layer deteriorates in high-moisture or chloride environments.

📏 Depth: ~54.9 µm
🌊 Visual cue: Smooth matte finish, etched grain texture, no isolated pits.

📎 Cause: Long-term exposure + humidity + uncoated storage — commonly observed in parts left outside prior to machining or welding.

🔵 Advanced Surface Attack — Steel Alloy

Trench-like corrosion with jagged, structural loss. Accelerated by press misalignment, coating failure, and environmental contamination.

📏 Depth: ~129.5 µm
⚠️ Visual cue: Rough-edged void, often spanning multiple grains or wall surfaces.

📎 Cause: Coating breakdown + mechanical stress + electrolyte pooling during storage or forming.

🧲 Galvanic Corrosion — Bimetallic Joint

Dissimilar metals in electrical contact corrode at different rates. Common in bolted assemblies with aluminum and stainless steel.

🔩 Visual cue: Corrosion halo at fastener or joint contact.
⚡ Cause: Electrochemical potential difference + electrolyte presence.

🔧 Material Pair: Aluminum bolt (anode) + Stainless steel washer (cathode)

🔬 Damage Morphology: Circular pitting and halo effect surrounding the fastener head, focused on the aluminum interface

🌧️ Environment: Humid air with periodic condensation, creating an electrolyte bridge between dissimilar metals

💥 Why It Failed: The aluminum, being less noble, corroded preferentially in the galvanic couple. Moisture enabled ion flow, initiating and sustaining anodic attack while the stainless steel remained protected.

🔍 Magnification: 10x | Observation: Moisture ingress along threads facilitated localized corrosion underneath the washer.

⚪ Hydrogen Embrittlement — High-Strength Steel

Atomic hydrogen diffuses into the metal lattice, causing delayed cracking under stress. Often occurs during acid cleaning or plating of hardened components.

⚡ Visual cue: Subsurface cracks or brittle fracture in high-strength parts.
📋 Cause: Hydrogen absorption combined with tensile stress.

🔧 Material: Hardened steel rod (high-strength alloy, post-plating)

🔬 Damage Morphology: Intergranular cracking near the surface, with jagged crack fronts extending along stress paths

🧪 Environment: Acid cleaning and electroplating processes introduced atomic hydrogen into the microstructure

💥 Why It Failed: Absorbed hydrogen atoms diffused into the steel lattice, concentrating at areas of high tensile stress and leading to brittle, delayed failure under load. Crack propagation occurred without significant plastic deformation.

🔍 Magnification: 50x | Observation: Fracture originated beneath the surface and propagated outward in a brittle pattern.

📊 Quick Comparison Table

Material Corrosion Type Depth / Risk Visual Cue Cause
6261-T6 Al Pitting 41.2 × 16.6 µm Isolated elliptical void Cl– ingress + thermal cycling
304 S.S. Surface Attack ~54.9 µm Matte grain etch Humidity + oxide breakdown
Steel Alloy Trench Corrosion ~129.5 µm Jagged trench void Mechanical + coating failure
Al/Stl Joint Galvanic Variable Halo at fastener zone Electrochemical mismatch
High-Strength Steel Embrittlement Crack propagation Subsurface fracture Hydrogen + stress

Simulated reference cases — NDA-safe visuals.

🔬 Alpha Case in Titanium — Root Cause & Visuals

Alpha case is a brittle, oxygen-enriched surface layer found in titanium alloys after high-temperature exposure. It must be minimized in aerospace and critical applications.

It forms when oxygen diffuses into titanium at forging or heat treat temperatures above 1000°F. While it can reduce ductility and fatigue life, not all alpha case is catastrophic. If within allowable limits (typically ≤0.002"), it may be tolerable or removable through surface finishing processes. Judgment depends on location, depth, and application criticality.

🧪 Simulated Microstructural Snapshots

  • Material: Ti-6Al-4V alloy (forged, NDA-safe simulation)
  • Prep: Polished, etched, illuminated under LED ring
  • Magnification: 20x objective lens
  • Focus: Identify oxidized surface depth and grain boundary patterns

© 2025 Audrey Enriquez. All content is shared for educational and documentation purposes only.
No proprietary or confidential information is disclosed. All rights reserved.