Tailoring sapphire–invar welds using burst femtosecond laser
Xuemin Jia, Yuyang Chen, Zhaoxi Yi, Jiawei Lin, Jinlin Luo, Kai Li, Cong Wang, Ji’an Duan, Dmitry Polyakov, Vadim P. Veiko
Abstract
The efficient and robust joining of transparent metal-dissimilar materials remains a significant challenge in high-performance system integration.A primary barrier is the inherently rough surfaces of metals, which hinder reliable bonding with transparent materials, largely due to the limited understanding of the underlying welding mechanisms.In this study, we demonstrate ultrafast laser joining between sapphire and metal substrates with surface roughness (Sa) up to 2 m, achieving a maximum shear strength of 11.73 MPa.High-speed imaging techniques were employed to conduct the first systematic investigation of coupled absorption dynamics at heterogeneous interfaces.The plasma ejection observed during welding indicated that the molten metal actively confined the interfacial region, transforming the initial free space into a confined space.This transition facilitates the formation of an optical contact condition, significantly improving the joint strength.To further explore the potential of pulse shaping in controlling interfacial behaviour, the effects of temporal shaping (Burst mode) on laser energy deposition, joint strength, and interfacial morphology were examined.Consistent joint quality was achieved across a range of burst parameters, with shear strengths ranging from 9 to 13 MPa.Fractographic analysis indicated that the fracture was predominantly governed by the internal stress within the sapphire, thereby limiting further improvements in joint strength.The revelation of the ultrafast laser welding mechanism for non-optical contact dissimilar materials, along with the exploration of temporal shaping for enhancing welding performance, offers theoretical insights and technical guidance for the development of high-performance heterogeneous material joining.