High temperature rise dominated cracking mechanisms in ultra-ductile and tough titanium alloy

Abstract

Extensive use of titanium alloys is partly hindered by a lack of ductility, strain hardening, and fracture toughness. Recently, several β-metastable titanium alloys were designed to simultaneously activate both transformation-induced plasticity and twinning-induced plasticity effects, resulting in significant improvements to their strain hardening capacity and resistance to plastic localization. Here, we report an ultra-large fracture resistance in a Ti-12Mo alloy (wt.%), that results from a high resistance to damage nucleation, with an unexpected fracture phenomenology under quasi-static loading. Necking develops at a large uniform true strain of 0.3 while fracture initiates at a true fracture strain of 1.0 by intense through-thickness shear within a thin localized shear band. Transmission electron microscopy reveals that dynamic recrystallization occurs in this band, while local partial melting is observed on the fracture surface. Shear band temperatures of 1250-2450°C are estimated by the fusible coating method. The reported high ductility combined to the unconventional fracture process opens alternative avenues toward Ti alloys toughening.

The Correlation of Texture and the Formation of the Adiabatic Shear Band in 7XXX Aluminum Alloy during Dynamic Loading

“…is finding also shows that the dynamic loading is similar to the hot rolling process, which is a comprehensive process of heat power. When a certain strain is reached, adiabatic shear band may appear, which is a vantage position for recrystallization nucleation [28,29], leading to the formation of recrystallization texture or the increase of its intensity.…”

Fracture mechanisms in flat and cylindrical tensile specimens of TRIP-TWIP β-metastable Ti-12Mo alloy

“…In a recent study [12], it was shown that the very large ductility of Ti-12Mo results from a large resistance to damage nucleation. Many interfaces are created by the different plasticity mechanisms activated in Ti-12Mo, including both TRIP and TWIP effects, resulting in a rapid nanostructuration of the microstructure, already at a strain level corresponding to the true uniform strain [12]. However, no void nucleates until the formation of a thin localized shear band at the end of the plastic deformation.…”

“…The formation of these shear offsets as well as their final propagation result probably from the exhaustion of the strain hardening capacity of the alloy. The alloy presents an impressive capacity to store the deformation-induced defects during its deformation, resulting in a nanostructure with a very large density of stored defects inside the microstructure [12].…”

“…We showed recently that an incredible resistance to damage nucleation occurs during quasistatic loading of Ti-12Mo, with the total absence of formation of cavities, even after an intense localization occurring after necking [12]. Scarce cavities were observed only in thin localized shear bands, in which a large local temperature rise above the melting temperature of the alloy was highlighted by the observation of Taylor meniscus patterns on the fracture surface and of melted Cu coating on the lateral surface of the fractured tensile specimen [12]. Taylor meniscus patterns are indeed formed during the separation of a fluid layer between two solid surfaces, by the penetration of a less viscous fluid [13].…”

Generative machine learning algorithm for lattice structures with superior mechanical properties

“…Many previous works have tried to develop new materials by introducing physical or chemical bonds between two different materials such as composites and alloys, or tuning microstructures of single materials. [1][2][3][4][5][6] The lattice structure, especially, inspired by the unit cell of crystalline materials in nature, is one of the most lightweight structures compared to conventional engineering materials. 7,8 With the recent development of precise additive manufacturing processes, much work has been devoted to understanding the relationship between microstructure and mechanical properties.…”