Metallographic Preparation of Additive Manufactured Parts

Also known as 3D printing, additive manufacturing refers to technologies that grow 3D objects one superfine layer at a time. Each successive layer bonds to the preceding layer of melted or partially melted material to create components, parts, or complete products.

The characteristics of additive manufacturing materials

Initially, the metals available for additive manufacturing were connected to the industries driving the development: the automotive, aerospace, and medical industries. However, multiple new and redeveloped alloys keep entering the market. In general, additive manufactured parts have the same or better mechanical properties and densities than traditional manufactured parts. The most common defects and deviations related to additive manufacturing can be categorized into these three groups:

• Surface quality: Without post-processing, additive manufactured parts have high surface roughness.
• Geometry and dimension deviation: Thermal shrinkage due to cyclic heating may lead to dimensional deviations.
• Microstructure defects: Porosities can be an issue, typically caused by gas or a lack of fusion

MATERIALOGRAPHY OF ADDITIVE MANUFACTURED PARTS

Additive manufacturing is one of the newest and fastest growing component manufacturing techniques. Although primarily used for the creation of prototypes and one-off designs, it is increasingly being used in general manufacturing to produce high-strength and lightweight single-component parts with complex geometries.

As a relatively ”young” production technique, additive manufacturing presents new challenges to the professional materialographer. Generally, materialographic investigation is performed on feedstock powders or representative test specimens as part of quality control. These specimens are often very small, so high precision cutting and clamping equipment is recommended.

Many different metals and alloys can be used in additive manufacturing. As a rule of thumb, preparation should be similar to standard preparation methods for that material. However, the methodology may differ depending on the specific specimen. In the full application note, you can find a detailed description of preparing additive manufactured parts for materialographic analysis. As well as a comprehensive description of the general challenges and solutions, the application note includes proven methods and techniques for different additive manufactured materials and alloys.

TARGET PREPARATION

With additive-manufactured specimens, it is often important to investigate microscopic attributes in the microstructure. These targets include pores, cracks, or inclusions from laser sintering, as well as impurities from different feedstock materials. Epoxies with fluorescent powders are a useful solution when visualizing porosity and cracks open to the surface. We recommend:

• Heating up the epoxy to 50-60°C to increase viscosity.
• Using active cooling during curing to improve impregnation and lower shrinkage and gap formation.

Using fluorescent dye with this technique requires a special feature in the microscope.