超音速气雾化制备316L不锈钢粉末的表征

利用自行研制的超音速雾化技术制备了316L不锈钢粉末,采用激光粒度仪、扫描电镜、金相显微镜和X射线衍射仪进行了表征.结果表明,316L不锈钢粉末的平均粒度约为24μm,粒度分布的几何标准偏差δ为1.75;粉末内部存在三种典型凝固组织,即具有发达二次枝晶的枝晶组织、胞晶组织以及枝状晶与胞状晶的混合组织;大粒径气雾化316L不锈钢粉末为单一的γ奥氏体相,小粒径粉末由γ奥氏体相+少量δ铁素体相共同组成;熔滴的冷速随着粒径的减小而提高,平均冷却速率为10⁴~10⁷K·s^-1.     

316L不锈钢表面沉积CrCN薄膜的结构及性能研究

利用多弧离子镀技术在316L不锈钢和单晶硅上沉积CrCN薄膜,通过X射线衍射仪(XRD)、扫描电镜(SEM)、X射线光电子能谱仪(XPS)、纳米压痕仪、273A电化学工作站和多功能摩擦磨损试验机等对316L不锈钢及CrCN薄膜的微观结构、力学性能、耐腐蚀性能和摩擦学性能进行表征.结果表明:在316L不锈钢上沉积CrCN薄膜后,硬度从4 GPa提高到22 GPa,H/E和H3/E2分别从0.022和0.002 GPa提高到0.071和0.11 GPa;阳极腐蚀电位从-0.21 V上升到-0.19 V;在大气,去离子水,海水环境下的摩擦系数及磨损率均显著降低,表现出较优异的综合性能.     

Density and porosity control of sintered 316L stainless steel parts produced by additive manufacturing

Abstract

Additive manufacturing (AM) techniques offer the possibility to build complex geometries with integrated functionalities. Three-dimensional (3D) printing of metallic powder is probably the only AM technique that can build controlled porosity sintered parts, such as filter elements and fluid permeable components. Many building and sintering parameters can be set to adjust porous properties of the final part. The effects of particle size, particle shape, sintering temperature and sintering time on the final properties of the sintered parts have been analysed. Correlations have been established between these properties and process parameters.     

选择性激光烧结AISI316L不锈钢制品的致密度

为了提高选择性激光烧结(selective laser sintering,SLS)AISI316L不锈钢制品的致密度,在AISI316L不锈钢粉末中添加微量Si,依次进行SLS、脱脂、冷等静压、1250℃高温液相烧结和热等静压处理.通过致密度测试、扫描电镜观察和能谱分析等手段,探讨等静压压力对AISI316L制品致密度的影响,研究微量Si对制品致密度的作用机理.结果表明:在冷等静压过程中,AISI316L试样致密度随压力增加而提高,压力为100 MPa时,致密度增量最大;压力为500 MPa时,致密度达到80.3％;冷等静压致密化机理为烧结颈破碎、金属颗粒位移与塑性变形等综合作用.经过1 250℃液相烧结,由于微量Si的作用,试样致密度增至93％左右;最后,经过1 250℃/120 MPa热等静压,试样致密度增至约95.3％,满足工程应用要求.因此,采用等静压技术与微量Si的液相烧结可以提高SLS成形的AISI316L制品的致密度.     

316L不锈钢金属间相固溶过程中的微结构表征

利用扫描电镜、X射线衍射仪和电子背散射衍射仪等设备研究了热轧态316L不锈钢金属间相(σ相和χ相)在固溶过程中的微结构演变规律,同时,利用高温激光共聚焦显微镜对金属间相回溶的全过程进行了原位在线观察,确定了最佳固溶温度。结果表明,固溶过程中发生了γ+σ+χ→γ+σ+χ+α/FeCr→γ+α/FeCr的相变过程。金属间相的回溶从1033.1℃开始到1149.5℃结束,回溶时间为21s,消除金属间相的最佳固溶温度约为1150℃。固溶处理前,基体中分布的带状组织形态不规则,χ相和σ相的面积比分别为0.46%和0.94%;固溶处理后,带状组织形态一致,主要分布铁素体和FeCr相,而χ相和σ相不可见。     

Structure and mechanical properties of austenitic 316L steel produced by selective laser melting

The mechanical properties and the impact toughness of austenitic 316L steel produced by selective laser melting at a laser power of 175–190 W have been studied. It is shown that the selective laser melting method makes it possible to significantly increase the strength properties of the steel with some decrease in the ductility and the impact toughness as compared to those of the steel produced by a traditional technology. The laser power influences insignificantly. The methods of making notches and its orientation is found to influence the impact toughness.     

Subgrain microstructures and tensile properties of 316L stainless steel manufactured by selective laser melting

316L stainless steel samples were manufactured by selective laser melting (SLM). The microstructure of SLM-made 316L stainless steel and the room temperature te...     

316L不锈钢冷变形加工硬化机制及组织特征

通过对316L不锈钢的不同变形量的压缩试验,对其冷变形特性进行了研究.利用修正的Ludwik模型对流变应力数据进行非线性拟合,获得了316L不锈钢的真应力应变模型和加工硬化模型.试验结果表明:修正的Luiwik模型能较好的反映316L不锈钢真应力与应变关系;根据流变应力的变化规律,316L不锈钢冷变形流变应力可分为三个阶段,分别为真应变小于0.02的强加工硬化阶段,真应变在0.02与0.29之间的稳加工硬化阶段,以及真应变大于0.29的弱加工硬化阶段.电子显微技术研究表明316L不锈钢三个不同的变形阶段,其加工硬化机制、微观组织特征有所不同.     

316L不锈钢动态再结晶行为

在Gleeble-1500热模拟试验机上,通过高温压缩实验对316L不锈钢的动态再结晶行为进行了系统研究.结果表明:316L不锈钢热变形加工硬化倾向性较大,在真应力应变曲线上没有出现明显的应力峰值σ_p;316L不锈钢在热变形过程中发生了动态再结晶,但只是在局部区域观察到了动态再结晶晶粒.对动态再结晶的实验数据进行拟合,得到316L不锈钢的热激活能和热变形方程,并给出了发生动态再结晶的临界应变和临界应力以及Zener-Hollomon参数和稳态应力的关系.     

316L不锈钢中氮气合金化行为

通过FactSage热力学计算软件和实验室实验研究了在常压和真空条件下温度、氮分压和碳含量对316L不锈钢中氮溶解度的影响.结果表明：钢中氮的溶解度随着温度的降低而升高,随着氮分压的增大而增大,随着钢液碳含量的增加而减少,其中氮分压对钢液氮溶解度的影响最大.不同吹氮条件下氮溶解度实测值与FactSage热力学软件计算值较吻合.生产控氮型316L不锈钢可以在吹氧脱碳阶段实现,生产氮质量分数大于0.10%的中氮型316L不锈钢,只能在氮分压大于30kPa的加料阶段以及破真空后大气微调阶段实现.     

316L不锈钢粉末的温压工艺研究

研究316L不锈钢的温压行为,分析温压工艺参数对压坯密度的影响.结果表明:在粉末加热温度为90℃、模具温度120℃、润滑剂含量0.8%(质量分数)的工艺条件下,压制压力为784 MPa时,压坯密度达6.92 g/cm3:经1130℃烧结后密度为7.06 g/cm3,硬度为HRB76.还对温压与室温模压(添加0.7%硬脂酸锌)后的压坯密度和弹性后效进行了比较:确证温压压坯密度比室温模压密度提高约0.2 g/cm3,弹性后效较室温模压的小.     

Residual stresses and interface strengths in MoSi2/stainless steel 316L joints produced by metallic-glass brazing

The residual stresses in molybdenum disilicide (MoSi₂)/stainless steel 316 L joints were evaluated using X-ray diffraction (XRD) and instrumented indentation techniques. These joints were produced by high-temperature brazing using a cobalt-based metallic glass (METGLAS 2714A). Joining was completed in two different ways, either by feeding excess braze into the braze gap upon heating or by constraining the MoSi₂/stainless steel assembly with an alumina (Al₂O₃) fixture during the heating cycle. These steps were necessary to ensure the production of a high-quality void free joint. The indentation results show higher tensile residual stresses in the stainless steel for the joint with the external constraint, in comparison to the unconstrained state. In contrast, the compressive residual stresses in the MoSi₂ (as measured by XRD) were lower in the constrained state relative to the unconstrained state. These results and a lack of residual stress balance indicate that the stress state in the braze is significantly different under the two joining conditions and the volume of the braze plays an important role in the development of the residual stresses. Push-out tests carried out on these joints gave higher joint strengths in the unconstrained as compared to the constrained condition. The results of this study have important implications on the selection of the appropriate joining process (use of constraint vs extra braze).     

316L不锈钢粉末高速压制行为

采用自行设计制造的18m高落锤式高速压机,研究316L不锈钢粉末的高速压制行为.实验结果表明,冲击速度增大可有效提高生坯密度,对室温粉末进行高速压制,当冲击速度从10 m/s提高到18m/s时,生坯密度从7.18 g/cm3提高到7.61 g/cm3.而在同样冲击速度下,对160℃温粉末进行高速压制时,生坯密度从7.33 g/cm3提高到7.76 g/cm3.同时生坯强度随冲击速度的提高而升高,冲击速度从10 m/s提高到18m/s时,160℃压制的生坯强度从72.5 MPa提高到94.1 MPa,室温压制生坯强度从62.1MPa提高到89.3MPa.通过对生坯SEM照片的分析,得知高速压制过程中粉末会发生严重的塑性变形和碎裂现象,孔隙的形状也会发生改变.该文还对高速压制致密化机理进行了探讨,指出在较高的速度压制时,颗粒间的摩擦和绝热剪切作用使粉末颗粒界面的温度升高,有利于粉末颗粒的塑性变形和焊合,从而有效提高了生坯的密度.     

316L不锈钢/Y-PSZ复合材料的制备与性能

采用粉末冶金方法制备了316L不锈钢/Y-PSZ复合材料,研究了316L不锈钢含量与粉末粒度对复合材料的显微组织、烧结收缩率、密度及硬度的影响.结果表明:随着316L含量的增加,复合材料的密度增高,相对密度和烧结收缩率逐渐降低,试样的HRC硬度值下降;在316L含量一定的情况下,随着316L颗粒尺寸的增大,复合材料的密度略有降低,相对密度和线收缩率逐渐减小,试样的HRC硬度值下降.在本文的研究条件下,所制备复合材料的相对密度值在92.5%~95.5%之间.     

316L不锈钢/Y-PSZ复合材料摩擦磨损特性

在MRH-3型高速环块磨损试验机上研究了粉末冶金方法制备的316L不锈钢/Y-PSZ金属陶瓷复合材料在干摩擦条件下的摩擦磨损性能,并与T10钢(HRC45)的耐磨性能进行了对比.考察了316L不锈钢体积分数(30%~50%)、颗粒尺寸(10.8~51.6μm)及对偶环转速(200~280r·min^-1)对材料耐磨性的影响.结果表明:随着316L不锈钢含量的增加和颗粒尺寸的增大,或随着对偶环转速的提高,复合材料的耐磨性下降.在本文研究条件下,除个别情形外,所制备316L/Y-PSZ复合材料的耐磨性能优于T10钢;当不锈钢体积分数为30%、颗粒尺寸为10.8Ⅱm时,复合材料的耐磨性能达到T10钢的3.0~3.2倍.316L不锈钢/Y-PSZ复合材料的磨损机理主要为316L不锈钢颗粒剥落和Y-PSZ基体层片剥落.     

热处理对SLM-316L不锈钢组织结构及钝化行为的影响机制

对SLM-316L不锈钢在900℃下进行不同时间的热处理,结合热处理后SLM-316L不锈钢的组织结构和腐蚀行为研究,揭示了SLM-316L不锈钢在900℃热处理过程中组织结构的演变规律以及其对钝化行为的作用机制.研究结果表明,900℃热处理时,在组织结构方面,SLM-316L不锈钢晶粒的基本形状和尺寸没有明显变化,但是随着保温时间延长,SLM-316L不锈钢中的位错和亚晶界逐渐消失,同时伴有MnS颗粒物沿晶界析出;在耐蚀性能方面,热处理对SLM-316L不锈钢的耐蚀性能产生重要影响,在含有NaCl的缓冲溶液中,SLM-316L不锈钢的点蚀电位随着保温时间延长逐渐降低,同时电化学阻抗逐渐减小;此外,在钝化膜性质方面,不同热处理时间试样上形成的钝化膜有明显差异,随着保温时间延长,SLM-316L不锈钢钝化膜的厚度逐渐减小,载流子的密度以及扩散系数变大.最后,通过构建不锈钢钝化膜能带结构和空间电荷层的理论模型,讨论了热处理对SLM-316L不锈钢钝化行为的影响机制.     

MlM316L不锈钢致密化和尺寸精度的研究

在Ar,Ar+H_2,N_2,N_2+H_2和低真空5种气氛下对MIM316L不锈钢进行了烧结,讨论了烧结气氛对合金致密化和力学性能的影响;得出烧结气氛的露点显著影响合金的致密化和最终力学性能;烧结气氛中的H_2可以脱去合金中的碳来影响致密化和力学性能;尺寸精度受注射、脱脂和烧结工序的影响;在采用溶剂脱脂时,3个工序对尺寸精度的影响由大至小依次为烧结、注射和脱脂。在不同气氛下,3个工序对尺寸精度的影响相对稳定。     

Inclusion evolution during refining and continuous casting of 316L stainless steel

The formation and characteristics of non-metallic inclusions in 316L stainless steel produced by the AOD (argon oxygen decarburization)–ladle furnace–continuous casting process were investigated. The morphology and composition of inclusions changed significantly during the refining and casting processes. After de-oxidation with Si/Mn additions, spherical complex inclusions mainly consisting of calcium silicates were observed. The contents of MgO and Al₂O₃ in these inclusions continuously increased as the steel moved from the AOD through ladle processing to the tundish. As the temperature decreased from the tundish through to solidification, harmful crystals of MgO/Al₂O₃ spinel were precipitated within the steel melt as well as within the calcium silicate matrix of existing inclusions. The results obtained from thermodynamic calculations carried out using FactSage? commercial software agreed well with the information derived from evaluation of the industrial samples enabling recommendations to be made for the avoidance of detrimental spinel inclusions.