Macro-micro residual stress prediction and hot crack formation mechanism during laser melt injection processing of ZrO2 particles into Ti6Al4V substrate

Laser melt injection (LMI) is a promising technology to produce ceramic particles reinforced metal matrix composites (MMCs) to achieve surface modification and performance upgrading. In this paper, the LMI process was conducted on a Ti6Al4V substrate with ZrO2 particles (ZrO2p) to produce a functionally graded material. Subsequently, a novel finite element model, at both macro and micro scales, was proposed to calculate the thermal-mechanical characteristics during the LMI process to expound on the crack formation mechanism. The differences in experiments, including track dimensions, particle distribution, and crack morphology of the MMC layer, were analyzed, corresponding to varied laser power and scanning velocity. The three-dimensional macro-simulated results showed alternating tensile-compressive residual stresses spread over the heat-affected zone. Besides, the most significant longitudinal tensile stress, the peak values exceeding the yield strength of Ti6Al4V, was distributed on the MMC top surface, leading to cracks. The two-dimensional micro-scale models revealed the residual stress distributed remarkably uniformly in the ZrO2 particles, and the stress values were more significant than those of the Ti6Al4V substrate. Furthermore, there were stress concentration points on the surfaces of ZrO2p, which were the sources of micro-fissure. At the same time, the gaps caused between the Ti6Al4V matrix and the ZrO2p surface also provided the conditions for the formation of microcracks. More conspicuous cracks would be generated after lots of microcracks were gathered.

Automated summary

This paper investigates the laser melt injection (LMI) process for producing ceramic particles reinforced metal matrix composites (MMCs) and proposes a finite element model to analyze the thermal-mechanical characteristics and crack formation mechanism. The experiments show the effects of laser power and scanning velocity on track dimensions, particle distribution, and crack morphology. The results reveal the distribution of residual stresses and the formation of cracks at both macro and micro scales.