Besides metal powders, can finished printed parts also be tested for carbon and sulfur content?
Yes, finished 3D printed parts can and often are tested for carbon and sulfur content, particularly for high-value, safety-critical components. This type of analysis serves as a crucial final verification to ensure that the manufacturing process, including all thermal cycles, has not adversely altered the chemical composition in a way that compromises the part's integrity.
Methods for Testing Finished Parts
Testing solid parts requires destructive methods, as a sample must be taken for combustion analysis. The approach varies depending on the information being sought.
Bulk Analysis: This is the most common method and determines the average carbon and sulfur content throughout the part's cross-section. It is directly comparable to the powder's original certification.
Procedure: A sample is precisely cut from the part, often from a designated witness coupon or a non-critical section. This sample is then cleaned to remove any surface contamination (e.g., from machining or handling) and machined into fine chips or filings using a tool like a lathe or mill. This ensures the entire sample mass is homogeneous and will combust completely in the analyzer.
Localized Analysis (Less Common for C/S): While techniques like Laser-Induced Breakdown Spectroscopy (LIBS) can provide elemental maps, combustion analysis is the gold standard for accurate, quantitative carbon and sulfur results. For localized concerns, a small, specific feature can be sampled for bulk analysis.
The Purpose and Importance of Testing Final Parts
Verifying the chemistry of a finished part provides several key assurances that powder testing alone cannot.
Verification of Process Stability: The high-energy Powder Bed Fusion process takes place in a protected atmosphere; however, minor leaks or contamination can potentially alter the surface chemistry. Testing the final part confirms that no significant carbon pick-up or loss occurred during printing.
Validation of Post-Processing: Certain post-processing treatments can affect chemistry. For instance, Heat Treatment in a carbon-rich atmosphere could cause carburization, while treatments in air could lead to decarburization. Testing the final part validates that these processes were controlled correctly.
Correlation with Mechanical Properties: The results from the finished part test are directly correlated with the mechanical test data from witness coupons. This provides a complete material pedigree, proving that the part not only started with the correct chemistry (powder) but also finished with it, ensuring the reported mechanical properties are valid.
When is this Level of Verification Necessary?
This additional, destructive testing is reserved for the most demanding applications where material consistency is non-negotiable.
Aerospace and Aviation: For flight-critical components, this test provides the final confirmation of material compliance before installation.
Medical and Healthcare: For permanent implants, verifying the final chemistry is part of the comprehensive biocompatibility and performance certification.
Failure Analysis: If a part fails, this analysis is essential to rule out chemical composition as a root cause.
In summary, while powder certification is the first and primary control, testing the finished part is the definitive method to close the quality loop, providing irrefutable evidence that the final component conforms to all specified chemical requirements.
