Metallurgical Failure Analysis Helps Prevent Future Failures

当组件失效时, it can affect the delivery of goods 和 the safety of the general public as well as result in costly repairs 和 downtime. Performing 冶金失效分析 to underst和 why a part failed is critical to preventing future failures.

在研究一个失效的部件, the analyst must consider a broad range of possibilities for the failure. Although some faults can be attributed to a single primary cause, it is common for multiple secondary factors to contribute. The failure analyst must evaluate all evidence available to prepare a hypothesis about the causes of failure.

The most common type of failure studied is fracture. Fractures often have the most serious consequences, especially when load-bearing members lose their ability to carry their intended load. Other types of failures may be related to distortion, wear, or corrosion.

故障分析工具

一个装备精良的 材料实验室 will have most of the tools to effectively analyze these types of failures. These tools include a low-power stereomicroscope, 金相设备, 硬度测试人员, 光谱仪, 和 a scanning electron microscope (SEM).

The 冶金失效分析 过程

The 过程 of analyzing a failed part starts with the collection of background information. It is essential to know what the specified requirements for the part 和 the material are. That information is often available in the form of a part drawing 和 referenced material specifications. It is also important to know what the expected performance of the part is 和 how the failed part compares to that expectation. Any changes made to the manufacturing 过程 should be reported to the failure analyst. Examples include vendor changes, design changes, material changes, thermal 过程ing changes, etc. 

The next step in the failure-analysis 过程 is the visual examination of the metal component. 需要注意的特点, 记录, 和 photographed in the visual inspection include fractures, 裂缝成因区, 部件损坏, 残留物的存在, 腐蚀产物, 还有腐蚀坑. 在某些情况下，  无损检测 may be warranted if cracks are not readily visible or if they may be present below the surface. 化学分析 和 硬度测试 are performed in most cases to verify whether the part meets the specified requirements. If enough material is available, 拉伸试验 和 影响测试 are desirable to help underst和 the inherent mechanical properties of the metal.

分析揭示了什么?

Electron microscopy is a critical step in the metallurgical analysis of failed parts. The electron microscope is the best means of verifying the fracture mode. Visual 和 low-power light microscopy is often not adequate to reveal the true morphology of a fracture. For example, consider the fracture surface of a bolt head. The fracture is relatively flat, which is often associated with fatigue cracking.

A closer inspection of the fracture origin region by a low-power stereomicroscope reveals a relatively rough texture, but the morphology of the fracture is still not clear. Examination of the fracture origin region via electron microscopy reveals a mixed fracture morphology of brittle intergranular cracking 和 dimpled rupture. The features revealed by the scanning electron microscope verify that the fracture was not due to fatigue. Further investigation indicated the fracture was due to 氢脆.

Metallography is an important step in the metallurgical 失效分析 过程. Examination of the microstructure can help verify whether proper thermal 过程es were applied to the part. Metallography can also identify whether material anomalies were present in the material that could have had a deleterious effect on the part’s performance.

所有拼图的碎片

After all the information is collected, 分析就完成了, a conclusion can be made based on the evidence available.

The investigation can be thought of as a forensic puzzle. The more pieces of the puzzle that are in place, the more conclusive the test results will be. 人们常常忍不住要问 冶金家 to minimize the amount of testing performed to save time 和 money. It may also be tempting to withhold background information about the part for fear of biasing the 冶金家’s final conclusion. 应该理解, 然而, that restricting the amount of testing 和 withholding important information will effectively take away pieces of the puzzle that can prove critical to achieving the correct final conclusion. If the reasons for failure are not properly understood, corrective actions to prevent future failures may be ineffective.

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