article · Materials
This research evaluates the thermal expansion and phase transformation behaviour of metastable titanium alloys containing 15 weight percent molybdenum and varying levels of silicon, from 0 to 2 weight percent. Using dilatometry, five cast alloy formulations were monitored under continuous heating and cooling up to 850 degrees Celsius at heating rates of 5 and 10 degrees Celsius per minute. All cast samples initially displayed an equiaxed beta-titanium phase microstructure. Heating produced distinct reflection points on the dilatometric curves, showing an S-shaped pattern. The introduction of silicon significantly lowered both the starting transformation temperature for omega-phase formation and the final transformation temperature for alpha-phase dissolution. Consequently, higher silicon content reduced the overall beta-transus temperature, demonstrating a direct influence of alloy composition on dimensional changes during thermal cycling.
Metals change phase and shift dimensionally when heated, which can alter their performance in demanding environments. By measuring how silicon changes the transformation temperatures and thermal expansion of titanium-molybdenum alloys, engineers gain baseline data required to predict material behaviour during thermal processing and service.
This work represents early-stage laboratory characterisation aimed at biomedical alloy design. The findings could inform materials developers and implant manufacturers seeking to understand the thermal stability and phase behaviour of beta-titanium alloys modified with silicon, but the abstract does not indicate testing in finished medical devices or direct commercial trials.
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Thermal expansion measurements were used to characterize phase transformations in metastable β-Ti alloys (Ti15MoxSi) without and with various Si additions (where x = 0, 0.5, 1.0, 1.5, and 2 in wt.%) during linear heating at two heating rates of 5 and 10 °C/min up to 850 °C. For this study, five alloys were developed and examined in terms of their presence phases, microstructures, and starting and final transformation temperatures. According to the results, all of the as-cast samples primarily include an equiaxed β-Ti phase. The influence of phase transformation on the material dimensions was discussed and compared with the variations in Si contents. The transformation was investigated using a dilatometric technique for the developed alloys during continuous heating and cooling. The dilatometric curve of heating revealed two distinct reflection points as the heating temperature increased. The starting transformation temperature (Ts) to obtain the ω-phase was reported at 359 °C without Si addition; whereas the final transformation temperature (Tf) of the dissolution of α-phase was obtained at 572 °C at a heating rate of 10 °C/min. At 2 wt.% Si, the first derivative curves reported Ts and Tf transforming temperatures of 314–565 °C (at a 5 °C/min heating rate) and 270–540 °C (at a 10 °C/min heating rate), respectively. The Ts and Tf transforming temperatures were significantly decreased with Si additions, which decreased the β-transus temperature. Moreover, the thermal expansion coefficient curves of the investigated alloys without and with 2 wt.% Si were studied. The transformation heating curves have an S-shaped pattern, according to the results.
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DOI: 10.3390/ma16134768
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