Production and characterization of ceramic cushings from Alumina-Toughened yttrium-stabilized tetragonal zirconia composites for projection welding applications

Abstract

In current study, for the first time, it was aimed to produce the ceramic bushings for use of projection bolt welding process in automotive industry. Here, they were manufactured from ready-to-press binder containing granulated alumina-toughened zirconia (ATZ) powders consisted of 20 wt.% alumina (alpha-Al2O3) and 3 mol.% yttria-stabilized tetragonal zirconia polycrystalline components. The ATZ ceramic bushings were densified by pressureless sintering between 1500 and 1600 degrees C with 25 degrees C increments for 2 h under air atmosphere. Physical, mechanical, tribological and microstructural properties of ATZ composites were characterized by different tests, analyses and techniques, i.e., Archimedes' principle, Vickers hardness (HV), indentation fracture toughness (K-Ic), specific wear rate (W), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy. Considering overall results, ATZ ceramic bushings were successfully sintered up to 99% of theoretical density by increasing sintering temperature. The maximum HV and K-Ic values of ATZ composites were determined as 14.62 +/- 0.02 GPa at 1500 degrees C and 6.10 +/- 0.04 MPa m(1/2) at 1600 degrees C, respectively. XRD patterns revealed that ATZ composites comprised of primary t-ZrO2 and secondary alpha-Al2O3 phases with no traces of m-ZrO2 and c-ZrO2. SEM observations showed the homogenous microstructures with high densification including no porosity; however, a slight degree of normal grain growth for t-ZrO2 and alpha-Al2O3 grains. ATZ ceramic bushings also exhibited high wear resistant property with W = 4.71 x 10(-9) m(3) N-1 m(-1) value. They welded over the 500.000 +/- 2.000 bolts to metal sheets in the automatic projection welding machines. This makes the ATZ composites a superior material for projection bolt welding process.