High-pressure torsion (HPT) on nanocomposite produced by multi-pass friction stir process (MP-FSP): Microstructure evolution and wear behaviors
Behrouz Bagheri Vanani, Mahmoud Abbasi, Amin Abdollahzadeh, Melika Mohammadkhah, Sandra Klinge
Abstract
This study aims to investigate the effect of high-pressure torsion (HPT) as a post-treatment process on microstructure, mechanical properties, and wear behavior of mild steel reinforced with graphene nanoparticles (GNP) fabricated by multi-pass friction stir processing (MP-FSP). To investigate microstructural changes, such as grain refinement and nanoparticle distribution, optical microscopy, transmission electron microscopy, and scanning electron microscopy equipped with an EDS system were utilized. The mechanical and wear properties of the nanocomposites were assessed through tensile tests, hardness measurements, and dry sliding tests according to standard procedures. The results revealed that HPT effectively reduced metallurgical defects, alleviated graphene agglomeration, and refined the grain structure due to the severe plastic deformation (SPD), leading to significant improvements in the mechanical properties of the specimens. HPT increased the hardness of the MP-FSP specimens from 428 HV to 930 HV (about 120% increase in hardness), both of which were considerably higher than the base material (BM) hardness of approximately 160 HV. More importantly, the wear loss and wear rate of the MP-FSP specimens were significantly reduced after HPT (from 3.45×10 -5 to 1.01×10 -5 mm 3 /Nm for triple pass of FSP), demonstrating a notable improvement in wear resistance. The uniform distribution of reinforcing particles and the formation of an ultra-fine grain (UFG) structure suggest an abrasion wear mechanism for the mild-steel/GNP composite. The post-HPT processing of the MP-FSP-ed St37/GNP composite presents a promising method to enhance the performance of mild steel nanocomposites. This could have significant industrial applications.