Self-healing metal is not just the stuff of science fiction and movie animation anymore. A research team from the Sandia National Laboratories and Texas A&M University has unveiled how, through the process of cold welding, cracked metal can fuse back together at the nanoscale, without the need for human intervention. The findings were recently published in the Nature Journal.
The research team revealed how fatigue cracks in pure metals can undergo intrinsic self-healing. Pieces of pure platinum and copper spontaneously healed cracks caused by metal fatigue during nanoscale experiments that had been designed to study how such cracks form and spread in metal placed under stress, Reuters reported. The cracks were also observed to heal by a process described as crack flank cold welding.
"This was absolutely stunning to watch first-hand," said Sandia materials scientist Brad Boyce. "What we have confirmed is that metals have their own intrinsic, natural ability to heal themselves, at least in the case of fatigue damage at the nanoscale."
The findings could mean a major change in engineering: Could self-repairing infrastructure and vehicles be a reality one day?
"From solder joints in our electronic devices to our vehicle's engines to the bridges that we drive over, these structures often fail unpredictably due to cyclic loading that leads to crack initiation and eventual fracture," Boyce said. "When they do fail, we have to contend with replacement costs, lost time, and, in some cases, even injuries or loss of life. The economic impact of these failures is measured in hundreds of billions of dollars every year for the U.S."
As more dynamic research and testing is underway, standards help support metal fatigue and metal particle testing. As an example, the international standard ISO 11782-1:1998, Corrosion Of Metals And Alloys - Corrosion Fatigue Testing - Part 1: Cycles To Failure Testing, provides guidance and instruction on corrosion fatigue testing of metals and alloys in aqueous or gaseous environments and is concerned with cycles to failure testing. Crack propagation testing is considered in ISO 11782-2. The standard was prepared by International Organization for Standardization (ISO) Technical Committee (TC) 156, Corrosion of metals and alloys. The ANSI accredited U.S. Technical Advisory Group (TAG) Administrator to the ISO TC is the Association for Materials Protection and Performance.
ASTM E10-18, Standard Test Method For Brinell Hardness Of Metallic Material, covers the determination of the Brinell hardness of metallic materials by the Brinell indentation hardness principle. This standard, published by ASTM International, provides the requirements for a Brinell testing machine and the procedures for performing Brinell hardness tests.
Standards developed by various standards developing organizations for metal particle testing cover metallic powders, metal surface inspection, and magnetic particles. SAE International has worked on a number of standards related to steel, bars, forgings, and tubing and magnetic particles, including SAE AMS 2442A-2007, Magnetic Particle Acceptance Criteria For Parts. This specification establishes acceptance criteria for discontinuities revealed by magnetic particle inspection of parts made from wrought, ferromagnetic materials. These criteria are intended typically for, but not limited to, aerospace parts that require magnetic particle inspection following the completion of fabrication operations.
The researchers report that a lot remains unknown about the self-healing process, including whether it will become a practical tool in a manufacturing setting.
Michael Demkowicz, a researcher who has been studying self-healing metals for some time, noted: “My hope is that this finding will encourage materials researchers to consider that, under the right circumstances, materials can do things we never expected.”