The dual role of martensitic transformation in fatigue crack growth

Abstract

Deformation-induced martensitic transformation (DIMT) has been used for designing high-performance alloys to prevent structural failure under static loads. Its effectiveness against fatigue, however, is unclear. This limits the application of DIMT for parts that are exposed to variable loads, although such scenarios are the rule and not the exception for structural failure. Here we reveal the dual role of DIMT in fatigue crack growth through in situ observations. Two antagonistic fatigue mechanisms mediated by DIMT are identified, namely, transformation-mediated crack arresting, which prevents crack growth, and transformation-mediated crack coalescence, which promotes crack growth. Both mechanisms are due to the hardness and brittleness of martensite as a transformation product, rather than to the actual transformation process itself. In fatigue crack growth, the prevalence of one mechanism over the other critically depends on the crack size and the mechanical stability of the parent austenite phase. Elucidating the two mechanisms and their interplay allows for the microstructure design and safe use of metastable alloys that experience fatigue loads. The findings also generally reveal how metastable alloy microstructures must be designed for materials to be fatigue-resistant.

Recent developments and perspectives of advanced high-strength medium Mn steel: from material design to failure mechanisms

“…The effects of martensitic transformation on the toughness should be similar to that in low-alloy steels, except that MMS usually contains a higher fraction of retained austenite. The beneficial effects of martensitic transformation can be explained by: (a) the additional energy absorbed when metastable austenite transforms into martensite at the crack tip [86]; and (b) the volume expansion during martensitic transformation that leads to compressive stress for suppressing crack initiation and growth [87]. For example, Antolovich and Singh [86] estimated that martensitic transformation can contribute up to 39%-60% of fracture toughness.…”

Influence of Heat and Thermochemical Treatment Parameters on C75 Steel Fatigue Resistance

“…A good balance between ductility and strength derives from the transformation of martensite induced by deformation (DIMT). To prevent structural defects under static loads, high-performance alloys are designed with the formation-induced martensitic transformation method, as explained in paper [ 13 ], revealing the dual role of DIMT in increasing fatigue cracks through in situ observations.…”

Model for deformation-induced martensitic transformation in irradiated materials

“…The formation of the martensite phase during DIMT is responsible for the increased plasticity, which is known as the transformation-induced plasticity (TRIP) effect. This effect attracts considerable interest since it not only raises the work hardening capacity and ductility of steels [10] but also substantially influences the fatigue crack growth and the stress corrosion crack behaviour [11,12]. On the other hand, nano-voids can be introduced by irradiation methods such as helium injection at high temperatures, which has also been proven to be a promising way to tailor material properties by affecting DIMT behaviour [13,14].…”