Tungsten (W) and stainless steel (SS) are well known for the high melting point and good corrosion resistance respectively. Bimetallic W-SS structures would offer potential applications in extreme environments. In this study, a SS→W→SS sandwich structure is fabricated via a special laser powder bed fusion (LPBF) method based on an ultrasonic-assisted powder deposition mechanism. Material characterization of the SS→W interface and W→SS interface was conducted, including microstructure, element distribution, phase distribution, and nano-hardness. A coupled modelling method, combining computational fluid dynamics modelling with discrete element method, simulated the melt pool dynamics and solidification at the material interfaces. The study shows that the interface bonding of SS→W (SS printed on W) is the combined effect of solid-state diffusion with different elemental diffusion rates and grain boundary diffusion. The keyhole mode of the melt pool at the W→SS (W printed on SS) interface makes the pre-printed SS layers repeatedly remelted, causing the liquid W to flow into the sub-surface of the pre-printed SS through the keyhole cavities realizing the bonding of the W→SS interface. The above interfacial bonding behaviours are significantly different from the previously reported bonding mechanism based on the melt pool convection during multiple material LPBF. The abnormal material interfacial bonding behaviours are reported for the first time.

分别对厚度为1.0，1.5，2.0 mm的不锈钢-碳钢层合板进行激光弯曲试验。采用金相显微镜、电子探针和扫描电镜能谱仪对激光弯折区的元素扩散现象进行分析；采用纳米压痕试验测得过渡层附近的纳米硬度及弹性模量分布，对过渡层处纳米硬度、弹性模量和屈服强度的变化进行了分析。结果表明，弯折区过渡层处元素沿板厚方向连续稳定扩散，Fe、Ni、Cr元素扩散范围相近，1.0，1.5，2.0 mm厚层合板的过渡层厚度分别增加了2.5，3.5，3.0 μm。元素扩散促进了过渡层的冶金结合，保证了层合板过渡层的材料性能。

在无填充、不开坡口条件下，以5 kW 光纤激光作为热源，研究激光扫描速度对YG20硬质合金与45#钢的焊缝组织与元素扩散的影响规律。分析了YG20/45#钢焊缝成形、组织及元素扩散。讨论了激光扫描速度对于热胀系数差异较大的异质材料焊接的焊缝成形的影响规律。研究结果表明，当被焊材料厚度为2 mm 时，采用激光功率P=1.93 kW、激光扫描速度v=2.40 m/min，离焦量-8 mm 时，可以获得冶金结合良好的YG20/45#钢焊接接头；随着焊接热输入的增加，硬质合金/焊缝侧界面的碳化钨晶粒粗化，裂纹倾向增加。主要分布在焊缝和硬质合金侧热影响区，降低焊接接头的性能。线扫描分析结果表明，硬质合金中的W、Co 与钢中Fe 发生了互相扩散，使整个接头达到了很好的冶金结合。

采用激光熔覆工艺将不锈钢粉末熔覆在碳钢板上，制备不锈钢-碳钢层合板。通过金属材料性能检测试验，对不锈钢-碳钢层合板的金相组织、元素扩散、显微硬度及拉伸断口形貌等性能进行分析。结果表明，激光熔覆制备层合板获得了致密均匀的覆层；结合面两侧Fe、Cr、Ni 等元素呈梯度扩散，扩散区域约为12 μm ，表明激光熔覆复合材料为扩散型冶金结合；覆层到基体硬度逐渐减小，这使覆层与基体之间应力平稳过渡，提升了其整体力学性能；其屈服强度为405 MPa，超过轧制层合板的326 MPa。基体和扩散区断口形貌为韧性断裂，而覆层表现为脆性断裂，进一步表明激光熔覆层合板结合面结合性能良好。