高速钢刀具激光熔覆AlTiN/NiCoCr涂层的组织及性能分析

为了提高高速钢刀具的综合性能,通过激光熔覆的方式在其表面制备AlTiN/NiCoCr涂层,通过实验测试的方式表征了该涂层的组织结构与各物相成分,并测定了其界面结合性能。研究结果表明:激光熔覆AlTiN/NiCoCr涂层形成致密组织,各层间形成紧密结合状态,陶瓷层厚度接近146μm,形成200μm左右粘结层。在陶瓷层内形成了大量无序排列的等轴晶,获得更高强度的陶瓷层。涂层中主要存在α-Al₂O₃,还有部分Al₂Ti₅N与Rutile-TiN。采用激光熔覆工艺有效降低了界面的空隙比例,获得更加致密的界面组织。陶瓷相内含有Al、N、Ti三种元素,在微孔粘结层内存在Co与Ni。AlTiN/NiCoCr涂层获得了比NiCoCr涂层更高结合力和更小的残余应力。试样发生了台阶断裂,形成了凹凸变化的表面。AlTiN/NiCoCr涂层形成更加平整断裂界面,在断裂面区域形成了众多微孔。

Modification of High Speed Steel Surface with Laser Cladded AlTiN/NiCoCr Bilayers

The porous AlTiN ceramic layer and compact NiCoCr alloy layer were consecutively synthesized by laser cladding on substrate of high speed steel.The influence of the adhesive transition AlTiN-layer on the microstructures,interfacial adhesion and residual stress was investigated with X-ray diffraction and scanning electron microscopy.The preliminary results show that the AlTiN transition layer makes the difference.For example,the 146 μm thick AlTiN layer,comprising the randomly oriented equiaxed grains,in α-Al₂O₃/Al₂Ti₅N/Rutile-TiN phases,and quite a few Co and Ni diffused into and deposited on the pore surfaces,significantly increased the mechanical-strength/interfacial-adhesion and considerably decreased the pore-sizes and residual stress,possibly because the interfacial diffusion/segregation/reaction/reconstruction greatly increased the compactness/density/bonding of the 200 μm thick adhesive layer.In addition,the stepped fracture was observed.