Following the findings of nanoscale originof hydrogen blistering at room temperature (Nature Materials, 2015) and themechanism of hydrogen-dislocation interaction (Nature Communications, 2016),researchers in CAMP-Nano recently revealed the microscopic mechanism ofhydrogen induced interface failure at elevated temperatures. This work ispublished in Nature Communications on Feb. 20, 2017.
Figure1. a, the homemade ultra-stable MEMS heating chip, b, the formation of giantcavity of hydrogenated pillar after heating
As the lightest element in the world,hydrogen can easily get into other materials, causing interface failure orforming internal porosity, and hence greatly degrade material performance.These processes are usually related to temperature variation, such as inpetrochemical factories, nuclear plants, and metallurgical process. However,despite its huge industrial significance, the underlying physical mechanism ofhydrogen effect at elevated temperature remain elusive, especially at atomisticscale due to the limitation of technology.
Figure2, Schematic illustration of the giant cavity formation process.
Under the supervision of Prof. Zhiwei Shan,Meng Li, a Ph.D student of CAMP-Nano, collaborated with Prof. Xixiang Zhang inKAUST, Saudi Arabia, and developed a quantitative home-made ultra-stable MEMSheating device, which overcame the multiple challenges of large thermal drift,inaccurate temperature and difficulty in bulk sample preparation in current in-situheating devices. This device has the minimum thermal drift comparing withexisting devices, and can easily prepare samples from bulk material, henceenabling in-situ monitoring of microstructure evolution in response totemperature change at unprecedented high spatial resolution. With this uniquedevice, by heating hydrogenated aluminium inside an environmental transmissionelectron microscope, Meng Li and Dr. Degang Xie found that hydrogen exposure ofjust a few minutes can greatly degrade the high temperature integrity ofmetal–oxide interface. Moreover, there exists a critical temperature of ~150°C, above which the growth of cavities at the metal–oxide interface reverses toshrinkage, followed by the formation of a few giant cavities. Although thesechanges proceed vigorously under the surface oxide layer, they do not cause anyobvious changes to the exterior surface morphology. Consequently, thesecavities may escape routine optical or SEM inspection and can therefore imposea significant threat to the reliability of the material, such as oxide scalespalling off from turbine blades or accelerated corrosion. Vacancysupersaturation, activation of a long-range diffusion pathway along thedetached interface and the dissociation of hydrogen-vacancy complexes arecritical factors affecting this behaviour. These results enrich theunderstanding of hydrogen-induced interfacial failure at elevated temperatures.
This work is done by Ph.D student Meng Li, Dr. Degang Xie, Prof. Zhiwei Shan, Prof.Evan Ma, Prof. Ju Li and Prof. Xixiang Zhang. The paper can be accessed at http://www.nature.com/articles/ncomms14564.