Al 2 O 3-TiB 2 composites were synthesized using high-energy ball milling from starting powders containing Al, TiO 2 , and B 2 O 3. To explore the effect of the addition of another ductile metallic phase during milling, 15 wt.% Ni was added to a sample of the starting powders. The phase transformations and microstructure of the milled powder mixtures were investigated using X-ray diffraction and electron microscopy. The results showed that the Ni addition facilitated the mechanochemical reaction between the Al, TiO 2 , and B 2 O 3. Before the appearance of the Al 2 O 3-TiB 2 composite, the intermediate product NiAl was formed by a gradual exothermic reaction. With continued milling, the final phases of Al 2 O 3-TiB 2 and Ni were obtained.
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.
a b s t r a c tTo improve electrode life during the resistance spot welding of galvanized steel plates, an Al 2 O 3 -TiB 2 composite coating was synthesized on the surfaces of spot-welding electrodes through an electrospark deposition process. The microstructure, elemental composition, phase structure, and mechanical properties of the coating were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and microhardness testing. It was found that extensive cracking occurred in the monolithic Al 2 O 3 -TiB 2 coating and at the coating-electrode interface. When the Al 2 O 3 -TiB 2 coating was deposited on electrodes precoated with Ni, the number of defects decreased significantly. Further, delamination did not occur, and fewer cracks were formed. The average hardness of the multilayered Al 2 O 3 -TiB 2 /Ni coating was approximately 2200 HV and higher than that of the monolithic Al 2 O 3 -TiB 2 coating (1100 HV).
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