选区激光熔化合成Ni-Al合金层的组织与性能

Microstructure and properties of Ni-Al alloy layer synthesized by selective laser melting

采用选区激光熔化技术在20钢基体表面制备了Ni-Al合金层。研究了激光工艺参数对合金层宏观形貌的影响,确定了较优工艺参数。利用扫描电镜(SEM)、X射线衍射(XRD)、能谱仪(EDS)和HVS-1000硬度测试仪等研究了合金层的物相组成、组织形貌、成分分布和硬度。结果表明:在优化工艺参数下利用选区激光熔化技术可在20钢表面制备出组织致密、无明显缺陷且与基体具有良好冶金结合的Ni-Al合金层,合金层主要由Ni3Al和ɑ-Ni两相组成,表层为细小致密的等轴晶,合金层中部为柱状晶,底部为胞状树枝晶,合金层表层显微硬度达到548 HV0. 2,随着与表面距离的增加,显微硬度逐渐降低。脉宽、电流的增加和扫描速率的降低,均可增加合金层宽度;脉宽、扫描速率和电流的增加,合金层的层厚都呈现出先增大后降低的趋势,其中电流180 A,扫描速率150 mm/min,脉宽4. 0 ms,频率12 Hz为最佳工艺。

Ni-Al alloy layer was prepared on the surface of 20 steel substrate by selective laser melting technique. The effect of laser process parameters on macroscopic morphology of the alloy layer was studied,and the optimum process parameters were determined. Phase composition,microstructure,composition distribution and hardness of the alloy layer were studied by means of scanning electron microscopy( SEM),X-ray diffraction ( XRD),energy dispersive spectrometer ( EDS) analysis and HVS-1000 hardness tester. The results show that the Ni-Al alloy layer with dense microstructure,no obvious defects and good metallurgical bonding with the matrix can be prepared on the surface of the 20 steel by selective laser melting under the optimized process parameters. The alloy layer is mainly composed of Ni3Al and ɑ-Ni phases,the surface layer is fine and dense equiaxed crystal,the middle of the alloy layer is columnar crystal, the bottom is cellular dendritic crystal,and the surface microhardness of the alloy layer reaches 548 HV0. 2. With the increase of the distance from the surface,the microhardness of the alloy layer decreases gradually. With the increase of pulse width,current and the decrease of scanning rate,the width of the alloy layer increases,and the thickness of the alloy layer increases at first and then decreases with the increase of pulse width,scanning rate and current,in which current of 180 A and scanning rate of 150 mm/min,pulse width of 4. 0 ms and frequency of 12 Hz are the best processes.