Characterizing relaxation phenomenon and crack propagation during low-temperature harmonic vibrations in heterogeneous metals

This work reveals the relaxation phenomenon induced by the localized atomic segregation during harmonic vibrations, which engenders substantial fluctuations in the dynamic modulus. The relaxation peak occurs when the dynamic modulus undergoes a sudden increase upon temperature reduction to −20 °C. This occurrence is caused by interstitial carbon atoms undergoing segregation and dragging dislocations to accumulate near grain boundaries. It leads to an increase in elastic strain energy, resulting in local stress concentrations and cracks initiation in heat affected zone (HAZ) and weld zone (WZ). The elevated value of the dynamic modulus within the HAZ facilitates a substantial internal accumulation of elastic strain energy. Consequently, this accumulation allows cracks to propagate rapidly along grain boundaries within the HAZ. Secondary cracks form in dispersed localized stress concentration zones in the WZ, which can inhibit crack propagation during harmonic vibration. This work will provide detailed insights and theoretical studies on the harmonic vibrational behavior of heterogeneous metals at low temperatures.