Effect of post heat treatment on the microstructure and properties of as-annealed Ti75 alloy
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摘要: 为了研究后处理对退火态Ti75合金性能的影响,采用不同后处理温度和冷却速率对退火态Ti75合金进行处理,利用OM、SEM分析了显微组织演变,并研究了显微组织对拉伸、冲击性能的影响。结果表明,后处理温度较低时,等轴α相的体积分数无明显变化;当温度升至足够高时,等轴α相开始溶解,其体积分数随着温度的升高逐渐降低。退火态Ti75合金经750~950 ℃处理后空冷的强度、冲击韧性变化趋势与炉冷基本相同。屈服强度、抗拉强度随后处理温度的升高呈现先降低后升高又降低的趋势,强度升高的主要原因是β转变组织中数量较多的细小α相难以变形;冲击韧性在低温区无明显变化,而后随温度的升高而逐渐升高。退火态Ti75合金经相同温度处理后空冷的强度高于炉冷;在低温区,空冷后的冲击韧性高于炉冷,高温区则呈现相反的规律。Abstract: In order to study the effect of post heat treatment on the properties of annealed Ti75 alloy, different post treatment conditions including annealing temperatures and cooling rates were selected to treat the annealed Ti75 alloy. The microstructure evolution was analyzed by OM and SEM, and the influence of microstructure on tensile properties and impact toughness of Ti75 alloy was studied. The results show that the volume fraction of equiaxed α phase has no obvious change when alloy is annealed at low temperature. When the annealing temperature is high enough, the equiaxed α phase begins to dissolve and its volume fraction decreases gradually with the increase of temperature. The evolution of strength and impact toughness of annealed Ti75 alloy after air cooling by different annealing temperature at 750 - 950 ℃ is basically the same as that of furnace cooling. The yield strength and tensile strength decrease firstly, then increase a little and then decrease again with the increase of temperature. The main reason for strength increasing is that a large number of fine α phases exists in the β transformation matrix structure which are difficult to deform. The impact toughness has no obvious change when alloy is annealed at low temperature region and then increases with the increase of temperature. The strength of annealed Ti75 alloy after annealing and air cooling is higher than that of furnace cooling. The impact toughness of annealed Ti75 alloy after annealing at low temperature region and air cooling is higher than that of furnace cooling, while at the high temperature region it shows the opposite changing tendency.
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Key words:
- as-annealed Ti75 alloy /
- post heat treatment /
- microstructure /
- strength /
- impact toughness
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表 1 Ti75合金化学成分
Table 1. Chemical composition of Ti75 alloy ingot
% Ti Al Mo Zr N H C O Fe Si Bal. 2.87 1.87 2.15 0.005 <0.001 0.0078 0.099 0.176 0.033 表 2 Ti75合金后处理工艺
Table 2. Post heat treatment process used for as annealed Ti75 alloy
编号 后处理工艺 温度/ ℃ 时间/h 冷却方式 HT1 750 2 AC HT2 750 2 FC HT3 800 2 AC HT4 800 2 FC HT5 850 2 AC HT6 850 2 FC HT7 900 2 AC HT8 900 2 FC HT9 925 2 AC HT10 925 2 FC HT11 950 2 AC HT12 950 2 FC -
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