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为了满足纯钨块体激光选区熔化致密成型的要求,开展了纯钨基板/粉体单层激光熔化/凝固实验,探索了参数窗口,观察了熔滴球化现象,并运用熔滴铺展/凝固竞争模型解释了球化机制。纯钨熔滴具有较高的粘度和表面张力,铺展过程较慢,且钨的热导率和熔点较高,凝固过程十分迅速,熔滴来不及完成铺展而具有快速凝固球化的倾向。增强基板/粉体对激光的吸收有助于提高熔滴峰值温度并延长凝固时间,从而减弱球化倾向。脉冲激光作用下,相对于扫描速度,调整激光作用时间更加合理。当激光作用时间为300μs时,由于平衡的熔滴体积和温度梯度,可以形成较为良好的熔化轨迹。
In order to meet the requirement of compact compact forming of pure tungsten bulk laser, a laser melting / solidification experiment of pure tungsten substrate / powder monolayer was carried out. The parameter window was explored, the phenomenon of droplet spheroidization was observed, and the droplet spreading / solidification The competitive model explains the spheroidization mechanism. Pure tungsten droplet has higher viscosity and surface tension, spreading process is slower, and the thermal conductivity and melting point of tungsten is higher, the solidification process is very rapid, the droplet is too late to complete the spread and has the tendency of rapid solidification. Enhanced substrate / powder absorption of the laser helps to increase the droplet peak temperature and extend the solidification time, thereby reducing the tendency of spheroidization. Pulse laser effect, relative to the scanning speed, adjust the laser action time is more reasonable. When the laser action time is 300μs, a better melting trajectory can be formed due to the balanced droplet volume and temperature gradient.