Rotating gliding arc plasma: Innovative treatment for adhesion improvement between stainless steel heating elements and thermoplastics in resistance welding of composites

Rotating gliding arc plasma treatment was conducted on a stainless-steel heating element (HE) for the resistance welding of carbon fiber/polyetheretherketone (CF/PEEK) thermoplastic composites. The lap shear strength of 51.7 MPa, corresponding to an improvement of 14.63 % compared to that of joints welded using untreated HE, was successfully achieved after the plasma treatment. The results of the surface characterization tests revealed that owing to the cleaning and oxidation effects, the hydrophilicity as well as the surface bonding of the HEs were remarkably improved after plasma treatment. Moreover, the reduction of void defects within the welded joints was disclosed via nondestructive inspection of cross-sections, indicating that the enhancement of HE hydrophilicity resulted in the improved resin impregnation and void elimination. Besides, according to the fractographic analysis, the main failure mode changed from the HE/PEEK interfacial damage to a CF/matrix interfacial failure, indicating that the HE/matrix interfacial adhesion was highly strengthened after plasma treatment.