The mechanical properties of Ti-6Al-4V can be improved by microstructural control through the heat treatment in α+β region. The heat treatment was carried out with a variety of heat treatment temperatures and holding times to find the optimized heat treatment conditions and it was analyzed by linking the microstructural characteristics and mechanical properties. The part of β phase with 10 ± 2 wt% vanadium was transformed into α'' martensite phase after quenched, so the hardness and tensile properties were decreased below 900 o C. The higher the heat treatment temperature is, the smaller is the vanadium-rich region, which leads to transformation into hcp α' martensite above 900 o C. The hardness and tensile properties were improved due to the hard α' martensite. As the holding times were longer, the hardness and tensile properties decreased below 900 o C because of the softening effect by the grain growth. When varying the holding times above 900 o C, the change of mechanical properties was slight because the softening effect of grain growth and the strengthening effect of α' phase were counteractive. Therefore, the best conditions of heat treatment, which is in the range of 920~960 o C, 40 min, WQ, can effectively improve the mechanical properties of Ti-6Al-4V.

These In this paper, the evaluation of a seleniumbased flat-panel digital X-ray detector is described. The prototype detector has a pixel pitch of 139 ㎛ and a total active imaging area of 14 inches × 8.5 inches, making up a total of 3.9 million pixels. Several quantitative parameters have been devised that correlate with the abilities of imaging devices to perform clinical tasks. The concepts of MTF, NPS, and DQE have been well described and are very useful descriptors of resolution, noise, and signal-to-noise ratio transfer ability. Such parameters (sensitivity, leakage current, MTF, NPS, DQE) were examined to evaluate the performance of this system. The sensitivity of 4.82 nC/mR/cm 2 was measured at 10 V/㎛, while leakage current was measured at 270 pA/cm 2 . The measured MTF at 2 lp/mm was 40%, and the DQE at 1.5 lp/mm was 16%.