激光选区熔化成形钛合金内部缺陷及其演化规律研究

Investigation on realationship between defects and paramaters for titanium alloy fabricated by selective laser melting

摘要:

激光选区熔化(selective laser melting, SLM)成形技术可实现形状复杂、尺寸精度高、力学性能优异零部件的直接成形,但成形工艺参数选择不当,则会在产品中引入缺陷,针对SLM成形钛合金内部缺陷的问题,本文研究了激光功率和扫描速度两个主要成形工艺参数对钛合金内部缺陷类型、尺寸及数量的影响,探索了缺陷的演化规律。结果表明,SLM成形钛合金内部主要有不规则形状、规则球形两种形态的缺陷。低激光功率(≤130 W)、高扫描速度(≥900 mm/s)区域主要为不规则形状缺陷,能量不足是导致形成该类型缺陷的主要原因；高激光功率(≥190 W)、低扫描速度(≤600 mm/s)区域主要为规则球形缺陷,能量过高导致合金元素气化是产生这类缺陷的主要原因。随着能量密度的增加,根据缺陷的演化规律绘制了SLM成形钛合金加工图,其中缺陷的演化呈现三个阶段,即不规则形状缺陷尺度逐渐降低区,微尺度不规则缺陷向微尺度规则球形缺陷过渡区和规则球形缺陷逐渐长大区。

Abstract:

Selective laser melting (SLM) technology can realize the direct fabrication of products with complex shape, high dimensional accuracy, and excellent mechanical properties. However, improper selection of fabrication parameters of SLM will introduce defects in the products. For the problem of defects, this investigation studied the influence of the two main fabrication parameters, laser power and scanning speed, on the type, size and quantity of internal defects in fabricated titanium alloy, and explored the evolution of defects with fabrication parameters. The results shown that there are mainly irregular shape and regular spherical shape defects in the titanium alloy fabricated by SLM. The area with low laser power (≤130 W) and high scanning speed (≥900 mm/s) is mainly irregular shape defects. Insufficient energy is the main reason for formation this type defect. The area with high laser power (≥190 W), low scanning speed (≤600 mm/s) is mainly regular spherical shape defects. The gasification of alloying elements caused by excessive energy is the main reason for formation this type defect. With the increasing of laser energy density, the SLM fabricated titanium alloy processing map was drawn according to the evolution law of defects. The evolution of defects presents three stages for the area of irregular shape defects gradually decreasing, micro-scale irregular defects to micro-scale regular spherical, and regular spherical defects gradually grow up.