Study on microstructures and mechanical performance of laser transmission welding of poly-ether-ether-ketone (PEEK) and carbon fiber reinforced PEEK (CFR-PEEK)

The reliable assembly of poly-ether-ether-ketone (PEEK) and carbon fiber-reinforced PEEK (CFR-PEEK) is crucial to effective load transfer within lightweight and high-stiffness structures, which are commonly demanded in aeronautical, automobile, and medical industries. In this work, laser transmission welding of PEEK and CFR-PEEK has been performed by using a 1070 nm Nd:YAG fiber laser. The effects of process parameters including laser power, laser scanning speed, and clamping pressure on joining quality have been investigated via mechanical, morphological, and thermal characterization. Results show that strong bonds have been formed by entanglements of polymer chains at the joining interface and the mechanical embedment between carbon fibers and PEEK. The formation mechanisms of bubble defects have been classified into three types. One of them was eliminated by scanning the joints twice, which significantly improved joints' mechanical performance and hermeticity with the maximum joining strength reaching 11.6 MPa. Also, a comparative study between PEEK/PEEK and PEEK/CFR-PEEK joints shows that the existence of carbon fibers within the CFR-PEEK significantly increased joints' decomposition threshold, joining region, and strength due to their great thermal conductivity. Besides, the influence of the welding process on the crystallinity of PEEK was analyzed, which was then improved from 11.7% to 34.1% through annealing.