Fracture in Focus: Mapping Fatigue in Ti-6Al-4V

Seeing the Story Behind the Failure

Fatigue cracks do not form randomly. Their initiation and growth depend on the material’s structure and composition, loading conditions, and environmental factors such as corrosion. While both optical and conventional electron microscopes can face contrast and resolution limits, with UHR SEM you get to the finest details with great contrast. Understanding the cracking mechanism requires both an overall view of the fracture surface and high-resolution detail to reveal nanometer-scale striations.

To identify crack origins, track propagation paths, and understand how and where a part fails, researchers need a reliable, detail-rich imaging workflow.

SEM imaging strategy to trace fatigue failure across all fracture stages

The sample was a Ti-6Al-4V alloy component that failed under cyclic loading. Imaging was performed using a Tescan CLARA UHR SEM, with a focus on collecting clear data across three key regions:

Key technical elements:

• Secondary electron imaging to highlight surface morphology

• Wide Field Mode™ for broad overview and site selection

• Variable magnification, with detailed imaging of features like striations and dimples

• No coating or special prep needed

Each region was analyzed to identify telltale fracture patterns and to correlate visual features with the material’s response under stress.

Reading the Fracture in Layers

The initiation point of the crack shows typical crystallographic crack growth and fine striations, each marking a step in the fatigue cycle. In the propagation region, the presence, spacing, and orientation of striations revealed the direction and rate of crack growth and reflected the severity of the loading conditions. The measured striation spacing indicated the local crack propagation rate, and once the crack reached a critical length, a final fracture occurred, marked by ductile dimple formation and high plasticity at failure.

Because imaging was performed across scales and magnifications using Wide Field Mode™, researchers could study both the big picture and the fine detail. The clarity of striation patterns and dimple shapes confirmed that SEM fractography provides not just images, but insight.

This kind of analysis is invaluable for root-cause investigation, lifetime prediction, and materials development.

.