Defects Modification of TiB₂–TiC Composite Phase Coating Resistance Spot Welding Electrode via Friction Stir Processing

Abstract

In this work, surface modification was carried out using friction stir processing (FSP) technique to investigate on the electro-spark deposited (ESD) TiB 2 TiC coated electrode caps for resistance spot welding. The morphology, microstructure, phase composition and resulting mechanical properties of the electrode were examined and characterized. The results showed that treatment with FSP significantly reduced the number of cracks formed on TiB 2 TiC coating and enhanced the interfacial binding force between the TiB 2 TiC coating and the substrate. The micro-hardness and bonding strength of the TiB 2 TiC coating were also improved and the heat affected zone (HAZ) of the substrate disappeared due to the influence of FSP. The improvement mechanism are attributed to a decrease in the number of coating cracks, improved delamination, and refined substrate grains size near the interface.

Improved Properties of TiC Coating Deposited on Copper Alloy via Friction Stir Processing

“…This is in agreement with Y. Morisada and co-workers' work. 20) Additionally, the coarse columnar grains of copper alloy substrate that observed in Fig. 2 (a) are instable, with temperature of the substrate increased, they spontaneously transfer into the equiaxed microstructure.…”

“…912) The recrystallization temperature of pure Ni is about 632°C. 24) Our previous work 20) reported that the substrate temperature generated by FSP didn't exceed the softening point, which indicates that the Ni within the coating may be recrystallized by severe plastic deformation during the FSP, resulting in the elimination of cracks. This is in agreement with Y. Morisada and co-workers' work.…”

“…In present work, due to low rotating rate (600 rpm) it was determined that the substrate temperature generated by FSP didn't exceed the softening point of the Improved Properties of TiC Coating Deposited on Copper Alloy via Friction Stir Processing copper alloy substrate, which was reported in our previous work. 20) Extensive investigations 1419) also showed that the temperature generated by FSP was in range from 400 to 900°C, which under the action of FSP TiC coating was hardly oxidized due to excellent high-temperature oxidation resistance. Ni diffraction peak is not found in the X-ray pattern, which is regarded as the evaporation of some Ni during the ESD, resulting in the decrease of Ni in the coating.…”

“…1419) Our previous work also reported that FSP successfully modified the defects of TiB 2 -TiC composite coating on resistance spot welding electrode. 20) The principle of FSP is almost as same as friction stir welding (FSW). A selected area of a metal plate can be modified by a rotating tool (with or without a pin).…”

Critical Assessment 25: Friction stir processing, potential and problems

“…FSP for microstructure refinement has also been applied to coatings, including Al-Cr-O plasmasprayed composites [24], Al-Al 2 O 3 cold-sprayed composites [25], electro-spark-deposited TiB 2 -TiC composite [26], flame thermal-sprayed Ni-Cr-Al alloy [27], and cemented carbide layers [28]. Other benefits also have been attributed to FSP, such as improved liquation cracking resistance in the heat-affected zones of nickel-based alloys [29], and consolidation of sintered microstructures in powder metallurgy-based metal matrix composites [30].…”