Preparation and Tribological Properties of TZ3Y20A-SrSO4 Ceramic Matrix Composites
|School||Harbin Institute of Technology|
|Keywords||TZ3Y20A-SrSO4 ceramic matrix composites nanoscale SrSO4 particles tribological properties hot-pressing sintering spark plasma sintering|
Nanoscale SrSO4 powders were prepared by chemical precipitation method. ZrO2(3mol%Y2O3)-20wt%Al2O3(TZ3Y20A) ceramic was selected as the matrix due to its high melting point, excellent mechanical properties and wear-resistance. TZ3Y20A-SrSO4 ceramic matrix composites were fabricated by hot-pressing sintering and spark plasma sintering, respectively. The morphology and growth mechanisms of nanoscale SrSO4 crystals and microstructure of TZ3Y20A-SrSO4 composites were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry-thermogravimetry (DSC-TG) measurement. The mechanical and tribological properties of TZ3Y20A-SrSO4 composites were studied by universal testing machine and high temperature friction and wear tester.The nanoscale SrSO4 particles prepared by chemical precipitation method have different morphologies, including flake-like, rod-like and equiaxed shapes. The flake-like SrSO4 particle has a thickness of 100 nm and a length of 200 nm. The rod-like SrSO4 particle has a diameter of 80~150nm and a length of 700~800nm. However, the particle size of equiaxed shape SrSO4 crystal is about 80nm. The diffraction intensity ratio of two low-energy crystal planes of (002) and (210) shows that, different crystal planes exhibit different growth rates, which may directly lead to the formation of flake-like and rod-like SrSO4 crystals. However, the driving force of SrSO4 crystal growth was dispressed with decreasing the reaction concentration, and adding small amounts of Sr-EDTA chelating precursors and PEG dispersive, which results in equiaxed shape SrSO4 polycrystal.The optimum parameters for hot pressing TZ3Y20A-SrSO4 composites are given as sintering temperature of 1150oC and sintering pressure of 40MPa, sintering time of 60 min, and heating rate of 20oC/min. The optimum parameters for spark plasma sintering TZ3Y20A-SrSO4 composites are given as sintering temperature of 1050oC, sintering pressure of 40MPa, sintering time of 5 min and heating rate 50oC/min. TZ3Y20A ceramics consist of t-ZrO2, c-ZrO2 andα- Al2O3 phase. The grain size of TZ3Y20A ceramics is between 100nm and 500nm.The mechanical properties of TZ3Y20A-SrSO4 composites depend mainly on the composition and relative density. The hardness, bending strength and fracture toughness of TZ3Y20A ceramics are distinctly higher than those of TZ3Y20A-SrSO4 composites. However, the hardness, bending strength and fracture toughness of TZ3Y20A-50SrSO4 composite is slightly higher than that of TZ3Y20A-30SrSO4 composite.The friction coefficient of TZ3Y20A ceramics increases with increasing wear test temperature from 0.48 at room temperature to 1.15 at 800oC. With the incorporation of SrSO4 into TZ3Y20A ceramics, the friction coefficients of the composites are located between 0.31 and 0.42 over a broad temperature range of room temperature to 800oC.The wear rates of TZ3Y20A ceramics are 2.31×10-6mm3/N?m at room temperature and 4.77×10-4mm3/N?m at 800oC, respectively. The wear rates of TZ3Y20A-SrSO4 composites are 6.33×10-5 to 6.91×10-5mm3/N?m at room temperature, and 1.17×10-5 to 3.39×10-5mm3/N?m at high temperatures of 600 and 800oC. After high temperature friction and wear test, SrSO4 are distributed uniformly on the worn surfaces of TZ3Y20A-SrSO4 composites, and effectively act as a solid lubricant over a broad temperature range, which significantly improves the friction and wear properties of high temperature structural ceramics.