Tribological behavior of the isothermally forged and heat-treated Ti-22Al-25Nb (at. %) orthorhombic alloy with lamellar O microstructures was investigated. The friction experiments using a tribometer (UMT-3 CETR) against Si 3 N 4 and Al 2 O 3 were conducted at the load of 10N from 20 to 750 • C and a constant speed of 0.188 m/s. The experiment results indicated that for the friction pair of Al 2 O 3 , the coefficient of friction (COF) was decreased from 0.906-0.359, and for the friction pair of Si 3 N 4 , COF was decreased from 0.784-0.457 as the friction temperature increased from room temperature to 750 • C. The wear rate of the alloy against Al 2 O 3 is in the range of 2.63-8.15 × 10 −4 mm 3 N −1 m −1 , the wear rate against Si 3 N 4 is in the range of 2.44-5.83 × 10 −4 mm 3 N −1 m −1 , respectively. The wear mechanisms of the alloy were changed from plastic deformation and ploughing at lower temperature (20-400 • C) to adhesive wear and oxidative mechanism at higher temperature (600 and 750 • C). The friction and wear behavior of the Al 2 O 3 friction pair was comparable to that of the Si 3 N 4 friction pair.
This article investigates the tensile and creep behaviors of the Ti-22Al-25Nb (at.%) alloy with equiaxed microstructure. The experimental results show that the equiaxed microstructures are formed by isothermal forging in the α2 + B2 + O phase region, and then heat treating in α2 + B2 + O and B2 + O phase regions. The equiaxed particles are determined by isothermal forging and solution heat treating, and the acicular O phase is obtained by adjusting the aging temperature. The strengths of the alloy are sensitive to the thickness of the secondary acicular O phase. Increase in aging temperature improves strength and reduces the ductility. Deformation of the alloy mainly depends on the volume fraction and deformability of the B2 phase. During the high-temperature tensile deformation, the flow stress decreases with the increasing deformation temperature and increases with the increasing strain rate. The microstructure obtained by higher aging temperature (HT-840) has better creep resistance, due to the coarsening of the secondary acicular O phase.
Ti-6Al-4V alloy (TC4) with different concentrations of graphene nanoplatelets (GNPs) were fabricated by ball milling and spark plasma sintering (SPS). Microstructure characteristics of the composites were characterized by X-Ray Diffraction (XRD), Scanning electron microscopy (SEM), and Raman. Microhardness and the compressive mechanical properties were also investigated. Experimental results showed that in the process of SPS, most of the GNPs were still retained at high pressure and temperature, and a new phase of TiC was presented due to the in-situ reaction between TiC and GNPs. Also, the strength of the composites was depended on the concentration of GNPs in TC4 matrix. Consequently, the composite with 0.8 wt. % GNPs was increased 18% in microhardness. The maximum yield strength and ductility of the composite were increased by 22.2% and 43.2%, respectively. The strengthening mechanism of the composites was further discussed, and the Orowan strengthening mechanism was the main strengthening factor.
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