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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

estarted when the

estarted when the pressure dropped below 95 MPa, leading to the stepped curve of Pmet in Figure 4.46. P P(MPa) s (mm) met met /MPa, s plunger plunger /mm 175 150 125 100 75 50 25 0 T preform 0 5 10 450 15 141 P met T centre T edge s plunger Time t t / (s) s Figure 4.46 Process parameters during preform infiltration with melt IS. Metal pressure Pmet , plunger displacement splunger and temperatures in the vicinity of the surface of the bottom punch (Tcentre, Tedge) and in the preform (Tpreform) are shown. The temperature in the bottom punch varied with position as shown by Tcentre and Tedge. At the edge, the temperature increased to a maximum of 555°C within the first 1.5 seconds and then cooled to 535°C at the end of recording. As the maximum of Tedge was reached, the temperature in the centre Tcentre increased steeply to 585°C with no further significant change until the end of the recording period. The temperature increase in the centre occurred as the main movement of the plunger terminated, whereas the temperature at the edge reached its maximum at about half of the maximum plunger displacement. 4.8.3 Evaluation of infiltration behaviour The first 2 seconds of the infiltration process were investigated more precisely in order to compare the preform-specific infiltration behaviours. To allow comparison, all infiltration parameters were kept constant and only the preform type was changed. The infiltration 800 750 700 650 600 550 500 Temperature T /°C (°C)

pressure was recorded as a function of the preform saturation curves were recorded and examples are given in Figure 4.47 for TOPC10 and AOPC20 preforms infiltrated with IS. The saturation point was taken to be the point at which the maximum pressure of 100 MPa was first reached and then the volume intruded calculated by displacement. Displacements above this point came from solidification shrinkage and were about 6% by volume for IS (1) . Pressure Pmet P/MPa (MPa) met 100.0 10.0 1.0 AOPC20 TOPC10 0.1 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 Saturation S () Figure 4.47 Infiltration curves of the preforms AOPC20 and TOPC10 when infiltrating with molten IS alloy. After the point of complete saturation was determined, the melt volume necessary for full infiltration was subtracted, leading to the zero point equivalent to no saturation. This point corresponded to the starting point of melt intrusion into the preform. This procedure was applied to the data determined during infiltration of AOPC20 and TOPC10 with the IS alloy. The infiltration curves in Figure 4.47 showed two regions of unsteady filling. The first region was below the saturation of 0.1 where a steep increase was observed up to a pressure of about 1 and 2 MPa for AOPC20 and TOPC10 preforms respectively. A second region in which the 142

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