Anomalous Tensile Strength and Fracture Behavior of Polycrystalline Iridium from Room Temperature to 1600 °C

• Published in: Advanced engineering materials Vol. 20; no. 7
• Main Authors: Yang, Jieren, Wang, Hu, Hu, Rui, Li, Shuangming, Liu, Yi, Luo, Ximing
• Format: Journal Article
• Language: English
• Published: 01.07.2018
• Subjects: Anomalous strength; Ductile‐to‐brittle transition; Fracture behavior; Polycrystalline Iridium
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.201701114

The nature of the brittleness of Iridium crystal is still unclear. The aim of this study is to explore the mechanism of ductile‐to‐brittle transition (DBT) and the fracture behavior in polycrystalline Iridium. Tensile tests are conducted from room temperature to 1600 °C. Furthermore, fracture morphology and deformation substructures are characterized by OM, SEM, and TEM. The results show that the tensile strength increases anomalously below 600 °C and then decreases with the increasing temperature. The elongation increases slowly from room temperature to 700 °C, and it then changes sharply from 9.88% at 700 °C to 31% at 800 °C. Below 700 °C, the polycrystalline Iridium exhibits intergranular and partial transgranular cleavage fracture pattern. In contrast, the ductile fracture morphologies associated with microvoids coalescence are observed between 800 and 1600 °C. Massive tangling screw dislocations form at 700 °C and less tangles appear when stretching at 900 °C, manifesting that the DBT is around 800 °C in polycrystalline Iridium. The strain–stress curves of polyacrystalline Iridium in (a) indicate that the ductile‐to‐brittle transition occurs as the stretching temperature increasing from 700 to 900 °C. Massive tangling screw dislocations appear at lower temperatures. The results are of interest to understand the brittle fracture mechanism in Iridium.