Mechanical and tribological properties of nanoceramics dispersion strengthened 2205 duplex stainless steel

M.Tech. (Chemical Engineering)Abstract: Conventional Duplex Stainless Steel used in industrial applications suffers degradation in wear and mechanical properties. A good approach to solve these problems is the dispersion of second phase nanoparticles into duplex stainless steel matrix to improve its strength and properties. Taking the advantage of the high hardness and high chemical stability of titanium nitride (TiN), efforts were made to disperse varying amounts of TiN nanoparticles into the matrices of SAF 2205 to enhance its properties. Hence the mechanical properties and tribological behaviour of the duplex stainless steel (SAF 2205 DSS) strengthened with varied amounts of titanium-based ceramics using nanoindentation system and tribometers were studied. The elastic and plastic deformation properties of the DSS composite materials were determined with a nanoindenter together with the wear behavior of the DSS samples using the strain-to-break (H/Er) and the plastic deformation (H3/Er2) parameters. Also the wear characteristics were estimated with a Tribometer, and Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) was employed to evaluate the morphology and chemistry of the wear scar of the DSS composite. The TiN nanoceramics reinforced SAF 2205 composites were fabricated using spark plasma sintering using optimized process parameters: sintering pressure (50MPa), sintering temperature (1150 oC), heating rate (100 oC/min) and sintering holding time (15 minutes). The TiN dispersions into the SAF were varied between 0 - 8 wt% at an interval of 2 wt%. Nanoindentation technique was used to access the plastic (H) properties, elastic (E) properties, the strain-to-break parameter (H/Er) and the resistance to plastic deformation parameter (H3/Er2) behaviour of the composites under loading and unloading conditions. The wear properties of coefficient of friction, wear loss, wear and specific wear rates under dry sliding conditions and varying loads and worn surface were investigated. The microstructures and worn surfaces of the composites were then evaluated using JEOL Scanning Electron Microscopy (FESEM, JSM-7600F). The results show that the TiN is evenly dispersed in the duplex matrix with a general tendency to locate itself at the grain boundaries. The mechanical properties improved considerably as the TiN content increased, resulting from grain boundary refinements and better dispersion strengthening mechanisms. The grain boundaries have better hardness and reduced young modulus compared to the grains. Furthermore, the ratios H/Er and H3/Er2 increased as the TiN composition increases which demonstrates that the nanocomposites wear resistance is favourable and it was in good correlation with the wear test data. The worn mechanism was a mixed mode of adhesive-abrasive at lower TiN composition but at higher TiN content, the adhesive mechanism prevails. This study established that increasing the addition of nanosized titanium nitride confers better microstructural properties, nanoindentation properties and wear behaviour on spark plasma sintered SAF 2205. Nanocomposite with DSS–6 % TiN reinforcement is recommended for industrial applications