粉末形貌对选区激光熔化316L不锈钢力学性能的影响

以气雾化316L不锈钢粉为原料,结合等离子球化和选区激光熔化技术制备了不锈钢块体,并用XRD、SEM、激光粒度仪、振实密度仪和万能力学试验机等对等离子球化粉体和选区激光不锈钢块的组织结构和性能进行了表征.结果表明:316L不锈钢粉经等离子球化处理后,不规则扁平状颗粒数量减少,球形颗粒数量增加,振实密度与松装密度的比值(...     

激光选区熔化316L奥氏体不锈钢微观组织和冲击韧性的各向异性研究

利用光学显微镜（OM）、X射线衍射(XRD)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和金属摆锤试验机等观察和分析激光选区熔化316L不锈钢的物相、织构、微观组织及冲击韧性各向异性。结果表明：激光选区熔化成形316L不锈钢的组织和冲击韧性存在着明显的各向异性。垂直和平行于构建方向试样的物相均为γ-Fe相,垂直于构建方向的组织呈“棋盘状”形貌,晶粒大多数为等轴晶且晶粒得到了细化(dmean=9.177μm),尤其熔池搭接区域晶粒更加细小(6μm以下),平行于构建方向上小角度晶界数目较多,而平行于构建方向为“鱼鳞状”形貌,大多数为柱状晶,晶粒直径较大(dmean=21.247μm)。同时垂直于构建方向织构为强纤维织构< 110 >//RD（强度为7.83）和弱板织构{112}<110>,而平行于构建方向为强纤维织构< 110 >//RD（强度为12.23）。在致密度相同条件下,横向、纵向的冲击韧性分别为62.8±3.2,38.6±4.5,横向明显优于纵向且提高了62.69%。此外晶粒大小、大小角度晶界和织构类型对冲击韧性各向异性有着显著影响,垂直于构建方向的晶粒得到了细化,大角度晶界数目多,韧性较好;纤维织构< 110 >//RD对冲击韧性不利,而板织构{112}<110>有利于韧性,垂直于构建方向的{112}<110>织构强度低且存在弱{112}<110>织构,横向韧性较好。     

选区激光熔化成型316L不锈钢微观组织及拉伸性能分析

选区激光熔化技术在复杂零部件的制造领域显示出强大的优势,但打印件的组织与综合性能还有待于进一步优化。采用选区激光熔化技术制备了316L不锈钢的拉伸试样,分析了试样不同区域的组织特征,测试了其拉伸力学性能。结果表明,其组织形貌主要为胞状晶,但在某些"微熔池"内晶粒生长方向不相同,近乎于相互垂直,从而在同一视野中呈现出典型的细小柱状晶(亚晶)和近似六边形"胞晶"共存的组织特征。试样的抗拉强度与传统工艺相比有较大提高,但延伸率有所降低。这主要是由于选区激光熔化是快速熔化与冷却凝固的过程,其选区熔化的特征使得不同区域的激光入射角度、选区熔化扫描方式、"熔池"散热条件各不相同,导致不同区域呈现复杂的结晶过程,形成不同特征的微区组织。由于冷却速度较快,所得细小柱状晶的直径为亚微米级,致密分布,显著提高了材料的抗拉强度。但由于晶粒生长明显的方向性,使得拉伸过程中晶粒在不同方向的塑性变形不均匀,相互牵制,加之熔合线界面处不可避免的内应力,导致延伸率降低。     

选区激光熔化成形316L不锈钢微观组织及拉伸性能分析

采用选区激光熔化技术制备了316L不锈钢的拉伸试样,分析了试样不同区域的组织特征,测试了其拉伸力学性能.结果表明,其组织形貌主要为胞状晶,但在某些“微熔池”内晶粒生长方向不相同,而近乎相互垂直,从而在同一视野中显示出典型的细小柱状晶（亚晶）和近似六边形“胞晶”共存的组织特征.试样的抗拉强度与传统工艺制备的相比有较大提高,但断后收缩率有所降低.这主要由于选区激光熔化是快速熔化与冷却凝固的过程,其选区熔化的特征使得不同区域的激光入射角度、选区熔化扫描方式、“熔池”散热条件各不相同,导致不同区域呈现复杂的结晶过程,形成不同特征的微区组织.由于冷却速度较快所得的细小柱状晶的直径为亚微米级,致密分布,显著提高了材料的抗拉强度.但由于晶粒生长明显的方向性,使得拉伸过程中晶粒在不同方向的塑性变形不均匀,相互牵制,加之大量熔合线界面处不可避免的内应力,导致断后收缩率有所降低.     

选区激光熔化316L不锈钢的各向组织与性能

对采用选区激光熔化(SLM)制备的316L不锈钢增材制造试样进行了横向、纵向力学性能与微观组织分析。结果表明,增材制造SLM试件亚结构组织由尺寸为0.4 μm左右的胞状组织所构成,组织之间无明显的成分偏析,纵向与横向拉伸强度分别达到808和713 MPa,在经过1050 ℃热处理后,原组织中部分胞状组织消失,纵向及横向强度分别下降到673 MPa及579 MPa,增材制造试样相对传统热轧试样(550 MPa)具有明显的强度优势。SLM试样组织中存在未熔合缺陷,缺陷几何形状的方向性对其在拉应力作用下连接成裂纹有显著影响。热处理后缺陷长度方向与拉伸应力平行的纵向试样伸长率达到47.5%,横向试样伸长率为20%,伸长率指标均显著低于热轧316L钢试样,未熔合缺陷是导致3D打印试件塑性指标降低的主要因素之一。     

热处理对选区激光熔化304L不锈钢组织和力学性能的影响

采用光学显微镜(OM),X射线衍射仪(XRD),扫描电镜(SEM),透射电镜(TEM)等研究了热处理工艺对选区激光熔化(SLM)制备的304L不锈钢微观组织结构与力学性能的影响。结果表明:SLM制备的304L不锈钢的组织结构细小,组织中存在高密度位错、δ铁素体与σ相析出物,其强度和塑性均远高于传统304L不锈钢。对SLM制备的304L不锈钢分别进行1050℃×30 min和1000℃×2 h固溶处理后,其微观组织结构发生了变化,观察到了晶内胞状亚晶组织的长大和析出相的固溶,强度和塑性均有所降低。SLM制备过程产生的大量纳米级胞状亚晶结构,是304L不锈钢具有高强高韧性能的主要原因,析出强化和加工硬化可进一步提高其强度。     

选区激光熔化MnSi2增强316L不锈钢复合材料的表面质量及耐蚀性能

为改善316L不锈钢在海洋环境下的耐腐蚀性能,通过MnSi₂增强316L不锈钢基体,采用选区激光熔化(SLM)制备MnSi₂/316L不锈钢复合材料。利用Image-Pro Plus软件、光学显微镜、扫描电镜(SEM)及电化学工作站研究了激光功率对316L不锈钢金属基复合材料致密度及耐腐蚀性能的影响,通过Tafel极化曲线和阻抗谱表征其耐腐蚀性能的强弱,并通过点蚀形貌揭示了其腐蚀机理。结果表明:添加MnSi₂是提高316L不锈钢耐腐蚀性能的有效途径。随着激光功率的增大,耐腐蚀性能呈现先提高后降低的趋势,当激光功率达到190 W时,2%MnSi₂/316L不锈钢复合材料的致密度为99.80%,其腐蚀电位为－0.053 V (vs SCE)。同时,2%MnSi₂可以显著改善316L不锈钢的成形质量,提高其耐腐蚀性能,其腐蚀形式为氯离子诱导氯化物生成的点蚀,且点蚀产生位置主要集中在孔隙边界处。     

固溶时效对SLM成形316L不锈钢块体件显微组织及硬度的影响

采用选区激光熔化技术(Selective laser melting, SLM)成功制备了316L不锈钢块体件,借助光镜(OM)和扫描电镜(SEM)及维氏硬度计研究了不同时效工艺(时效温度分别为650 ℃和850 ℃)对SLM成形316L不锈钢块体件显微组织以及显微硬度的影响。结果表明,SLM成形316L不锈钢块体件显微组织主要由细小柱状晶和蜂窝状晶粒组成。“层-层”和“道-道”熔池边界清晰可见,经固溶时效后边界基本消失,但晶界清晰可见,再结晶晶粒呈合并生长方式长大。650 ℃时效时,试样中少量M₂₃C₆分布于晶界,显微硬度相对较高;随着时效温度的升高,850 ℃时效后试样的晶粒进一步长大,沿晶界形成了大量不连续M₂₃C₆。     

316L不锈钢表面激光熔覆Stellite-F合金层的电化学腐蚀行为

采用CO₂激光器在316L不锈钢表面熔覆Stellite-F合金,通过电化学方法研究了Stellite-F熔覆合金层在5wt%NaCl溶液中的腐蚀行为。结果表明:与316L不锈钢相比,与基材呈冶金结合的Stellite-F合金层自腐蚀电位较正、自腐蚀电流密度较小,无点腐蚀现象出现,耐海水腐蚀性能较好;研究发现,熔覆合金层物相主要由γ-Co固溶体与Ni₃C、Cr₂₃C₆碳化物构成,在盐溶液中其腐蚀失效机制为选择性腐蚀,即固溶体合金相作为阳极被腐蚀浸出,碳化物相得到阴极保护暴露析出,同时固溶体相中的Co、Ni组分优先被腐蚀浸出,其余组分形成海绵状结构。     

蜂窝状多孔316 L不锈钢的选区激光熔化制备

对含预合金316L不锈钢和NH4HCO3(质量比96:4)的混合粉末进行选区激光熔化,制备多孔材料的实验研究。利用扫描电镜分析试样的微观孔隙特征。结果表明,在较高激光功率(800 W)条件下,可形成蜂窝状的多孔结构,孔径分布均匀(2~5 μm),平均孔径约3.5 μm。分析激光功率对多孔结构特征的影响,讨论选区激光熔化蜂窝状多孔结构的形成机制     

Electropolishing of 316L stainless steel for anticorrosion passivation

316L stainless steel is deemed an indispensable material in the semiconductor industry. In many instances, the surface of the production equipment needs to be treated for low-corrosion passivation, good finish, weldability, and cleanliness. The process characteristics of electropolishing meet these requirements well. The current study investigates the effects of the major processing parameters on the anticorrosion performance and the surface roughness. The electrolyte with 10% water content and a ratio between H₂SO₄ and H₃PO₄ of 4 and 6 has been proven to be successful, showing no corrosion pitting points on the specimen surface. The electrolyte temperature of 85±10 °C and the electrical current density of 0.5 to 1.0 A/cm² are found to be optimal. The processing time beyond 3 to 5 min produces no further improvement. The addition of 10% glycerin provides a very fine surface (maximum roughness of 0.05 μm), while the anticorrosion performance is deteriorated. The results obtained are useful for the manufacture of the semiconductor equipment.     

Laser ultrasonic testing for near-surface defects inspection of 316L stainless steel fabricated by laser powder bed fusion

The laser powder bed fusion (L-PBF) method of additive manufacturing (AM) is increasingly used in various industrial manufacturing fields due to its high material utilization and design freedom of parts. However, the parts produced by L-PBF usually contain such defects as crack and porosity because of the technological characteristics of L-PBF, which affect the quality of the product. Laser ultrasonic testing (LUT) is a potential technology for on-line testing of the L-PBF process. It is a non-contact and non-destructive approach based on signals from abundant waveforms with a wide frequency-band. In this study, a method of LUT for on-line inspection of L-PBF process was proposed, and a system of LUT was established approaching the actual environment of on-line detection to evaluate the method applicability for defects detection of L-PBF parts. The detection results of near-surface defects in L-PBF 316L stainless steel parts show that the crack-type defects with a sub-millimeter level within 0.5 mm depth can be identified, and accordingly, the positions and dimensions information can be acquired. The results were verified by X-ray computed tomography, which indicates that the present method exhibits great potential for on-line inspection of AM processes.     

电弧喷涂316L不锈钢涂层的结构与性能

采用电弧喷涂优化工艺制备316L不锈钢涂层,利用扫描电镜、能谱仪和X射线衍射仪等对涂层的组织及物相进行分析,同时对涂层的硬度、结合强度进行了测定。结果表明：涂层具有典型的层状形貌,涂层截面较为致密,局部区域出现粗大孔洞;涂层与基体之间主要为机械结合,结合强度较高;涂层硬度的最大值出现在涂层中部,靠近界面的基体组织发生加工硬化。     

Corrosion behavior of GO-reinforced TC4 nanocomposites manufactured by selective laser melting

To improve the corrosion resistance of Ti–6Al–4V (TC4) matrix, the influence on the corrosion behavior, microhardness, and microstructure of graphene oxide (GO)-reinforced TC4 nanocomposites manufactured by selective laser melting was systematically investigated in this study. Microhardness tester, profilometer, X-ray diffractometer, scanning electron microscopy, and electrochemical workstation were used to characterize the association between microhardness, pore microstructures, hard phases, and corrosion resistance of GO/TC4 nanocomposites. It can be observed that the incorporation of GO promotes the in situ formation of hard phases, such as TiC, TiO₂, Al₂O₃, and so forth, and it also changes the microstructure of the matrix as well as increases its porosity. Nevertheless, GO/TC4 nanocomposites perform the best corrosion resistance when the mixing content of GO is 0.5 wt%, and its microhardness is greatly improved with the addition of GO. All experimental results suggest the efficacy of added GO.     

Determination of susceptibility to intergranular corrosion and electrochemical reactivation behaviour of AISI 316L type stainless steel

In this study, double loop electrochemical potentiokinetic reactivation (DLEPR) test was applied to determine the degree of sensitization in 316L type stainless steel, where obtained results were correlated with revealed microstructures after oxalic acid test and weight loss measurements of Streicher and Huey acid tests. Best agreement was provided with test parameters which are 1 M H₂SO₄ and 0.005 M KSCN at 0.833 mV/s scan rate at 30 °C. Specimens were classified structurally as absence of chromium carbides - step, no single grain completely surrounded by carbides - dual and one or more grain completely surrounded by carbides - ditch, in the as-etched structure, if the I_r:I_a (×100) ratios were obtained to be between 0 and 0.2, 0.2 and 5.0 and 5.0 and higher, respectively. It was also found that at high KSCN concentrations, reactivation current profile skewed to higher potentials where this was attributed the formation of metastable pits, during the anodic scan of the test procedure.     

Corrosion of type 316L stainless steel in molten LiCl–KCl salt

Pyrochemical reprocessing in molten chloride salt medium has been considered as one of the best options for the reprocessing of spent metallic fuels. The AISI 316L stainless steel (SS) is envisaged as a candidate material for the fabrication of components for various unit operations like salt preparation vessel, electro‐refiner and cathode processor, on which ceramic coatings with metallic bond coat will be applied by the thermal plasma spraying. The unit operation like electro‐refining is carried out in the molten lithium chloride–potassium chloride (LiCl–KCl) eutectic salt at 773 K in argon atmosphere. The corrosion behaviour of the container vessel in molten chloride salts is therefore important, hence corrosion tests were carried out in a molten salt test assembly under argon gas atmosphere. The present paper discusses the corrosion behaviour of 316L SS in the molten LiCl–KCl eutectic salt at 873 K. The 316L SS samples were immersed in the molten LiCl–KCl eutectic for 25, 100 and 250 h, while 316L SS with yttria stabilized zirconia coating was exposed for 1000 h. The exposed samples were examined by optical and scanning electron microscope for corrosion attack. The X‐ray mappings of the cross‐section of the degraded layer onto the 316L SS indicated that the mechanism of corrosion corresponds to the selective diffusion of Cr to the surface with the formation of voids below, and the formation of chromium compounds at the surface. The results of the present study indicated that the yttria stabilized zirconia coating onto the 316L SS exhibits a better corrosion resistance in molten chloride salt than with uncoated 316L SS.     

高温酸性溶液中316L不锈钢/Ni-Cu-P镀层的耐蚀性能

为了改善316L 不锈钢在高温酸性溶液中的耐蚀性,采用化学镀技术在316L 不锈钢表面沉积高铜高磷Ni?Cu?P 镀层。采用扫描电镜(SEM)、能谱仪(EDS)和 X 射线衍射仪(XRD)对其结构进行分析,利用极化曲线、阻抗谱(EIS)及浸泡腐蚀试验对其在高温酸性溶液中的耐蚀性进行研究。结果表明,Ni?Cu?P 镀层由铜含量分别为19.98%和39.17%(质量分数)两种类型的胞状组织组成;在高温酸性溶液中,这种新型Ni?Cu?P镀层可显著改善316L不锈钢的耐蚀性;镀态镀层的耐蚀性优于热处理态的;镀态镀层和经673 K热处理镀层的腐蚀机制是选择性腐蚀,而经773和873 K热处理镀层的腐蚀机制为点腐蚀。     

Effects of geometrical characteristics on defect distributions in alloy components produced by selective laser melting

Selective laser melting (SLM) has been applied to manufacture various alloy components with excellent properties, but its further application is restricted by the intrinsic defects. In this work, the internal defect distributions in samples of three alloys (316L stainless steel, AlSi10Mg and Inconel 718) were investigated respectively, considering the effects of geometrical characteristics of the samples. The defects in the 316L stainless steel sample tend to be formed densely in the central part with large wall thickness, indicating a strong sensitivity to heat accumulation. Contrarily, the Inconel 718 sample shows a higher relative density with homogeneous defect distribution, indicating better formability for the SLM process. For the AlSi10Mg sample, the defect density keeps increasing as the deposition goes on. Typically, the defect density located at sample edges shows an abnormally high level comparing with the inner part, especially in the top sections of AlSi10Mg and Inconel 718 samples. The results are helpful for the geometrical design, the adjustment of building orientation and the further optimization of process parameters in the SLM process.     

表面机械研磨处理对316L不锈钢组织和性能的影响

对2.8mm厚的316L不锈钢板的上下表层进行机械研磨处理(SMAT),对经过不同时间的SMAT后的样品的表层组织进行金相观察,并测量SMAT不同时间的样品的硬度、抗拉强度.结果表明,经过表面机械研磨处理不同时间后,在316L不锈钢板表层获得了不同厚度的表面强化层,强化层组织为沿厚度方向由纳米晶层向微米晶层过渡的梯度组织;随着SMAT时间的增加,总的强化层厚度增加;表面组织的变化导致了表面硬度明显增加,整体材料的屈服强度增加;表面机械研磨处理时间对性能的影响并非线性增加,表面硬度和整体材料的屈服强度在处理5min时增加显著,处理时间继续增加到15、30和60min,它们的增加速度很小.拉伸断口表面形貌的扫描电镜观察表明,经过5min处理后的样品,表层的剪切唇变形区域面积增加,断口微观特征为长条状的韧窝,但是随着处理时间的增加,剪切唇区的尺寸并没有继续增加,而是开始下降,表面硬化区域的增加造成了塑性变形能力的下降.