Cr_(3)C_(2)对激光选区熔化316L合金组织及力学性能的影响

Effect of Cr_(3)C_(2)Particles on Microstructure and Mechanical Properties of 316L Alloy Fabricated by Selective Laser Melting

目的研究添加Cr_(3)C_(2)颗粒对激光选区熔化316L合金的硬度、强度及耐磨性能的影响。方法采用激光选区熔化(Selective Laser Melting,SLM)技术制备316L合金及10%(质量分数)Cr_(3)C_(2)颗粒增强316L合金(Cr_(3)C_(2)/316L),通过X射线衍射仪(XRD)、光学显微镜(OM)、扫描电子显微镜(SEM)、透射电镜(TEM)、维氏显微硬度计、双立柱电子万能试验机和摩擦磨损试验机分别对2组合金试样的组织结构、硬度、拉伸性能以及耐磨性能进行测试与分析。结果316L合金主要由γ-Fe相组成,Cr_(3)C_(2)/316L合金中除γ-Fe相外,还存在Cr_(23)C_(6)和Cr_(3)C_(2)相。316L和Cr_(3)C_(2)/316L合金的显微组织均由柱状晶和等轴晶组成,Cr_(3)C_(2)/316L的组织中等轴晶比例增多,且组织产生了细化。Cr_(3)C_(2)/316L合金的显微硬度为327HV0.1,相比316L合金(265HV0.1)增加了23%。Cr_(3)C_(2)/316L合金的屈服强度和抗拉强度分别为687 MPa和1029 MPa,较316L合金均提高了约50%。Cr_(3)C_(2)/316L合金的磨损率相比316L合金减小了50%。结论在SLM过程中,由于添加的Cr_(3)C_(2)颗粒在激光选区熔化316L合金过程中所产生的非自发形核和提高过冷度的作用,促使了316L合金组织发生明显细化和等轴化。添加的Cr_(3)C_(2)颗粒所产生的细晶强化、沉淀强化和固溶强化作用,使316L合金的硬度、强度和耐磨性都得到有效提升。

The application of 316L alloy is limited due to its low strength and low wear resistance.The addition of Cr_(3)C_(2)particles is beneficial to the improvement of strength,hardness,and wear resistance of 316L alloy.As an advanced metal additive manufacturing technology,selective laser melting(SLM)has the characteristics of an extremely high cooling rate and micro-molten pool solidification,which makes the forming samples have a fine microstructure and good mechanical properties.The work aims to study the phase composition,microstructure,hardness,strength and wear resistance of 316L alloy and Cr_(3)C_(2)/316L alloy fabricated by SLM and discuss the effect of Cr_(3)C_(2)particles on the microstructure and properties of 316L alloy.In this study,10wt.%Cr_(3)C_(2)powder was mechanically mixed with 316L powder,and the samples were fabricated by the SLM machine(Hanbang HBD-150D).The preparation process was carried out under the protection of argon.The process parameters were as follows:laser power of 350 W,layer thickness of 30μm,scanning speed of 2000 mm/s,hatching space of 60μm,checkerboard scanning strategy,and rotation angle of 67°between each layer.Pure 316L alloy was prepared under the same process parameters.The phase of the two alloys was analyzed by X-ray diffraction(KYOWAGLAS H-12).The microstructure was observed by optical microscopy(Leica DM4000),scanning electron microscopy(Nova NanoSEM 430),and transmission electron microscopy(Tecnai G2 F20).The hardness was tested by Vickers hardness tester(HMV-2T),and the tensile property at room temperature was tested by Instron 5565 double-column electronic universal testing machine,and the tensile fracture was observed.The dry sliding wear tests were performed on friction and wear tester(UMT TriboLab).The wear morphology was observed and the wear rate was calculated.The results showed that the 316L alloy was mainly composed of theγ-Fe phase.In addition to theγ-Fe phase,the Cr_(3)C_(2)/316L alloy also contained Cr_(23)C_(6)and Cr_(3)C_(2)phases.The microstructures of both the 316L and the Cr_(3)C_(2)/316L alloys were composed of columnar grains and equiaxed grains.With the addition of Cr_(3)C_(2)particles,the coarse columnar grains in the Cr_(3)C_(2)/316L alloy were reduced,the equiaxed grains were increased,and the microstructure of the Cr_(3)C_(2)/316L alloy was refined obviously.The addition of Cr_(3)C_(2)particles increased the microhardness of the Cr_(3)C_(2)/316L alloy.The hardness of the Cr_(3)C_(2)/316L alloy was 327HV0.1,and that of the 316L alloy was 265HV0.1.The hardness of the Cr_(3)C_(2)/316L alloy was 23%higher than that of the 316L alloy.The yield strength and tensile strength of the Cr_(3)C_(2)/316L alloy were 687 MPa and 1029 MPa,which are about 50%higher than those of the 316L alloy.The Cr_(3)C_(2)/316L alloy also improved wear resistance compared to the 316L alloy,with a 50%reduction in wear rate.The addition of Cr_(3)C_(2)particles in the rapidly solidified SLM process leads to the non-spontaneous nucleation and the increase of overcooling degree which leads to the obvious refinement of the microstructure.The increase in hardness,strength and wear resistance of the Cr_(3)C_(2)/316L alloy is the result of the combined effect of fine grain strengthening,solid solution strengthening,and precipitation strengthening produced by the addition of Cr_(3)C_(2)particles.