Uncovering the Intrinsic High Fracture Toughness of Titanium via Lowered Oxygen Impurity Content

• Published in: Advanced materials (Weinheim) 2024-10, Vol.36 (40), p.e2408286-n/a
• Main Authors: Zou, Xiao‐Wei, Han, Wei‐Zhong, Ma, En
• Format: Article
• Language: English
• Subjects: Austenitic stainless steels; c+a〉 slip; Crack initiation; Crack tips; Damage tolerance; Fracture toughness; Impurities; Oxygen; Oxygen content; Plastic deformation; Plastic zones; Titanium; twinning
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202408286

Titanium (Ti) and its alloys are known to exhibit room‐temperature fracture toughness below 130 MPa m1/2, only about one half of the best austenitic stainless steels. It is purported that this is not the best possible fracture resistance of Ti, but a result of oxygen impurities that sensitively retard the activities of plasticity carriers in this hexagonal close‐packed metal. By a reduction of oxygen content from the 0.14 wt% in commercial purity Ti to 0.02 wt%, the mode‐Ι fracture toughness of the low‐oxygen Ti is measured to be as high as KJIc ≈ 255 MPa m1/2, corresponding to J‐integral‐based crack‐initiation toughness of up to JIc ≈ 537 kJ m−2. This extraordinary toughness, reported here for the first time for pure Ti, places Ti among the toughest known materials. The intrinsic high fracture resistance is attributed to the profuse plastic deformation in a significantly enlarged plastic zone, rendered by the pronounced deformation twinning ahead of the crack tip along with ample twin‐stimulated 〈c+a〉 dislocation activities, in the absence of impeding oxygen. Controlling the content of a property‐controlling impurity thus holds the promise to be a readily applicable strategy to reach for unprecedented damage tolerance in some other structural alloys. Here it is revealed that the low‐oxygen titanium (Ti) has an intrinsic fracture toughness of 255 MPa m1/2. The low oxygen concentration promotes deformation twinning, and the numerous twin boundaries further stimulate the 〈c+a〉 slip at the crack tip. The operation of these two 〈c〉‐axis deformation modes enhances the uniform deformation abilities, resulting in a remarkable leap in fracture resistance of Ti.