A Ti-15Mo/TiB metal–matrix composite was produced by spark plasma sintering at 1400 °C. The fractions of the elements in the initial powder mixture were 80.75 wt.% Ti, 14.25 wt.% Mo, and 5 wt.% TiB2. The initial structure of the synthesized composite was composed of bcc β titanium matrix and needle-like TiB reinforcements with an average thickness of 500 ± 300 nm. Microstructure and mechanical properties of the composite were studied after laser beam welding (LBW) was carried out at room temperature or various pre-heating temperatures: 200, 400, or 600 °C. The quality of laser beam welded joints was not found to be dependent noticeably on the pre-heating temperature; all welds consisted of pores the size of which reached 200–300 µm. In contrast to acicular individual particles in the base material, TiB whiskers in the weld zone were found to have a form of bunches. The maximum microhardness in the weld zone (~700 HV) was obtained after welding at room temperature or at 200 °C; this value was ~200 HV higher than that in the base material.
A Ti-15Mo/TiB metal matrix composite was produced by the spark plasma sintering process at 1400 °C using a Ti-14.25 wt.% Mo-5 wt.% TiB2 powder mixture. The microstructure and mechanical properties of the composite were studied after non-isothermal rolling of specimens heated to 1000 °C to a thickness strain of ~0.7. Transmission and scanning electron microscopy, as well as X-ray analysis were used for microstructure examination; mechanical properties were evaluated using tensile testing and microhardness measurement. In the initial condition, the Ti-15Mo/TiB composite consisted of 8.5 vol.% of TiB needle-like particles heterogeneously distributed within the β matrix. A small volume of fractions of the α″ and ω phases was also found in the microstructure. Microstructure evolution of the composite during hot rolling was associated with dynamic recrystallization of the bcc titanium matrix and shortening of the TiB whiskers by a factor of ~2. The Ti-15Mo/TiB composite after hot rolling showed considerable improvement in ductility without substantial loss of strength and hardness. The hot rolled specimen was not fractured during the compression test even after 45% thickness reduction, while in the initial condition, the compression ductility was 22%. The yield strength for both conditions was quite similar (~1350 MPa). The hot rolled composite also showed some improvement in ductility to ~12% elongation at elevated temperature (500 °C) compared to the initial condition, the tensile elongation of which did not exceed 2%. The observed difference in the mechanical behavior was associated with the presence of the metastable α″ and isothermal ω phases in the initial condition and the more stable α phase in the hot rolled condition.
Crack formation process in the Ti-23Al-23Nb-1.4V-0.8Zr-0.4Mo-0.4Si (at.%) alloy based on orthorhombic titanium aluminide (Ti2AlNb), especially in the weld zone (WZ), heat-affected zone (HAZ), and base metal (BM), during laser beam welding (LBW) at room temperature was considered. It was determined that the crack spread in the WZ throughout the crystallites of β-phase. In the HAZ, cracks spread throughout the globular β-phase crystals body and along the edges of globular α2- and O-phases. The cracking stopped in BM due to a mechanism similar to shear ligament toughening. Cracking can be effectively suppressed by increasing the LBW temperature.
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