The competitive formation of allotriomorphic α along the prior β grain boundaries, secondary α-phase and the growth of globular primary α is described for the Ti-6Al-4V alloy during continuous cooling. The formation kinetics of the different morphologies of the α-phase is related to the nucleation rate of allotriomorphic α and secondary α as well as with the V supersaturation at the β matrix. A mesoscale physical model is developed for the allotriomorphic α and secondary α based on classical nucleation and growth of platelets. The growth of the primary α is modelled as the growth of a spherical particle embedded in a supersaturated β matrix. Continuous cooling tests at two different holding temperatures in the α+β field, 930 °C and 960 °C, and five different cooling rates, 10, 30, 40, 100 and 300 °C/minutes, are conducted. Additionally, interrupted tests are conducted at different temperatures to determine the progress of growth of primary α and formation of allotriomorphic and secondary α-phases during cooling. The size of primary α increases, while its circularity decreases with decreasing cooling rate. The area fractions of primary α decrease with increasing cooling rate and increasing holding temperature. Moreover, the lower the cooling rate, the thicker the plates of allotriomorphic α and secondary α. The growth of primary α, as well as the formation of allotriomorphic α plates is observed at the beginning of the cooling stage. The formation of secondary α occurs at last and is nearly negligible for very low cooling rates. The model is able to accurately predict the different α-phase formation behaviours and the obtained results show good agreement with the experimental ones.

The growth kinetics of allotriomorphic α along the prior β grain boundaries and of globular primary α in Ti-6Al-4V during continuous cooling is described. A physical model is developed based on classical nucleation and growth of platelets for the allotriomorphic α. The growth of the primary α is modelled based on the growth of spherical particle immerged on a supersaturated β-matrix. Continuous cooling tests at two different holding temperatures in the α+β field, 930°C and 960°C, and five different cooling rates, 10, 30, 40, 100 and 300°C/min, are conducted to validate the proposed models and elucidate the growth sequence of those α morphologies. Additionally, interrupted tests at different temperatures are conducted to determine the progress of growth of primary α and formation allotriomorphic α during cooling. The size of primary α increases while its size distribution broadens with a decrease in cooling rate. Area fractions of primary α decrease with increasing cooling rate and increasing holding temperature. Moreover, the lower the cooling rate, the thicker the plates of allotriomorphic α. At the beginning of the cooling, growth of primary α, as well as formation of allotriomorphic α plates is observed. The experimental and modelled results show good agreement.

<div class="section abstract"><div class="htmlview paragraph">Increasing demands regarding the efficiency and emissions of internal combustion engines will require higher peak firing pressures and increased indicated mean effective pressures in the future. Adaptation of these parameters will result in higher thermal and mechanical loads that act on core engine components. To meet the future requirements, it is essential to make changes to the design of the tribological system, which is composed of the piston, piston rings, liner and lube oil, while maintaining the robustness and reliability of the engine and its components. Modification of the tribological system requires in-depth knowledge of wear and friction.</div><div class="htmlview paragraph">This paper presents the setup of a model of the tribological system (piston, piston rings, liner and lube oil) of a large gas engine in the commercial software AVL EXCITE™ Piston&amp;Rings as well as its calibration and validation with data obtained from a test bed. Initial analysis of necessary input data has revealed a high number (&gt;300) of different parameters, some of which are known and others that have to be determined. Strategies are identified for how missing input data can be specified or generated with appropriate tools. The model is calibrated with respect to blow-by and lube oil consumption data measured on the test bed at two different load points. Subsequent validation shows satisfactory agreement between simulation and measurements. A final summary proposes how the extensive and time-consuming process of setting up, calibrating and validating the presented model could be complemented by the integration of data-driven models and sensitivity analysis approaches.</div></div>