选区激光熔化成型Ni50.8Ti49.2形状记忆合金的组织和性能研究

Investigation on Microstructure and Properties of Selective Laser Melting NiTi Shape Memory Alloys

单位体积能量输入随试验变量激光功率和扫描速率的变化而变化,探究了选区激光熔化工艺参数的改变对沉积态块状Ni50.8Ti49.2样品组织及性能的影响。考虑到不同能量输入对样品组织的影响,分别对样品扫描方向和沉积方向进行了组织观察,发现随能量输入的升高,金相组织的缺陷逐渐降低,沿沉积方向显微组织由短粗的柱状晶演变为细长的柱状晶。利用XRD考察其室温相组成,结果表明样品常温下为B2母相,部分样品含少量Ti3Ni4相。同时显微硬度测试表明,除激光功率外,第二相的引入能显著提高显微硬度值。利用差示扫描量热仪考察不同样品的相变温度。采用万能力学试验机对圆柱样品进行压缩测试,结果表明,样品的断裂应变最高达42%,高能量输入样品断裂应变略低。而室温超弹性能随能量输入的提高而显著提高,压缩应变10%时,超弹回复率高达90.2%。

The energy input per unit volume changes with the laser power and scanning rate. The change of the process parameters on the influence of microstructure and properties of the selective laser melting(SLM) is investigated for the as-deposited Ni50.8 Ti49.2. Considering the influence of different energy inputs on the sample microstructure of the scanning direction(SD) and deposition direction(BD), samples are observed by optical microscopy, it was found that with the increase of energy input, the defects of the metallographic structure gradually decreased along the deposition direction. The microstructure evolved from short, thick columnar crystals to slender columnar crystals. Phase constitution at room temperature is investigated by XRD. Most of the samples are B2 parent phase at room temperature, and some samples contained a small amount of Ti3 Ni4 phase. At the same time, the microhardness test of the sample shows that the introduction of Ti3 Ni4 phase increases the microhardness value in addition to the laser power. The transformation temperatures of different samples are investigated by differential scanning calorimetry(DSC). The cylindrical samples were subjected to compression test using a universal testing machine. The results show that the fracture strain of the sample was up to 42%, and the fracture strain of the high energy input sample is slightly lower. The superelasticity at room temperature increases significantly with the increase of energy input. When the compression strain is 10%, the superelastic recovery rate is as high as 90.2%.