选区激光熔化成形12CrNi2合金钢的显微组织和力学性能

利用选区激光熔化(SLM)技术制备了12CrNi2合金钢. 借助金相显微镜、扫描电子显微镜、透射电子显微镜、显微硬度仪、室温拉伸试验等方法研究了激光能量密度对合金钢显微组织和力学性能的影响. 结果表明,成形合金钢的宏观组织可分为熔池区与热影响区两部分,微观组织为回火马氏体和少量残余奥氏体. 随激光能量密度(E_V)增加,成形合金钢的孔洞缺陷逐渐减少,致密度逐渐增加,最高可达到99.87%;同时,熔池体积增大,寿命增加,冷却速度降低,导致回火马氏体板条宽化,热影响区变宽,合金钢的显微硬度和强度降低,塑性增加. 在E_V为81.34 J/mm3条件下,SLM成形12CrNi2合金钢具有最优强塑性,抗拉强度和屈服强度分别为1098和882 MPa,断后伸长率为20.07%. 采用SLM技术成形12CrNi2合金钢可获得比激光熔化沉积(LMD)和铸造成形更佳的综合力学性能.     

选区激光熔化Zr改性Al-Si-Mg合金组织和力学性能

针对选区激光熔化（SLM）高Mg含量AlSiMg3合金成形性差的缺点,通过Zr进行合金化,研究了工艺参数对SLM成形高Mg含量Al-Si-Mg-Zr合金的成形性及时效处理对合金组织和力学性能的影响。结果表明,SLM成形Al-Si-Mg-Zr合金的熔池边界处形成了大量的细小等轴晶,从而有效地避免了样品在成形过程中裂纹的产生,增加了样品的SLM成形性,不同激光功率和激光扫描速度下获得样品的孔隙率均低于0.3%。拉伸测试结果表明,成形态样品的屈服强度（YS）为(426±8) MPa,极限抗拉强度（UTS）为(464±12) MPa。经165℃时效处理后,由于α-Al晶粒内部纳米强化相的增多,样品的强度增加明显,时效样品的最大YS和UTS分别为(482±11)MPa和(522±10)MPa。本研究获得SLM成形Al-Si-Mg-Zr样品的强度高于目前商用的SLM成形Al-Si-Mg合金。     

Microstructure and mechanical properties of laser additive manufactured novel titanium alloy after heat treatment

A novel α+β titanium alloy with multi-alloying addition was designed based on the cluster formula 12[Al-Ti₁₂](AlTi₂)+5[Al-Ti₁₄](AlV_1.2Mo_0.6Nb_0.2) which was derived from Ti-6Al-4V.The nominal composition of this novel alloy was determined as Ti-6.83Al-2.28V-2.14Mo-0.69Nb-6.79Zr.In this study,the novel alloy and Ti-6Al-4V alloy samples were prepared by laser additive manufacturing.The microstructure,micro-hardness,room/high temperature tensile properties of the as-deposited samples were investigated.Compared to Ti-6Al-4V,the novel alloy has much higher room and high temperature (600℃) tensile strengths,which are 1,427.5 MPa and 642.2 MPa,respectively;however,it has a much lower elongation (3.2%) at room temperature because of the finer microstructure.To improve the elongation of the novel alloy,heat treatment was used.After solution at 960℃ or 970℃ for 1 h followed by air cooling and aging at 550℃ for 4 h followed by air cooling,a unique bi-modal microstructure which contains crab-like primary α and residual β phase is obtained,improving the compression elongation by 80.9% compared to the as-deposited samples.The novel alloy can be used as a high-temperature and high-strength candidate for laser additive manufacturing.     

激光选区熔化组织分析及人工神经网络力学性能预测

采用激光选区熔化技术（selective laser melting,SLM）制备18Ni300时效模具钢.通过扫描电子显微镜（scanning electron microscope,SEM）,研究试样的枝晶生长取向和凝固组织状态.利用人工神经网络对激光功率、扫描速度和扫描间距进行重要性分析,同时采用BP （back propagation,BP）神经网络以工艺参数为特征对材料的抗拉强度进行预测,应用遗传算法（genetic algorithm,GA）对神经网络权值和阈值进行寻优.结果表明,试样组织主要呈树枝柱状生长,外延生长明显,组织取向主要取决于熔池底部的凝固条件;熔池顶部易发生柱状晶向等轴晶转变（columnar to equiaxed transition,CET）,可以通过调节工艺参数来控制转变区的大小;热毛细对流导致熔池其它区域也出现枝向转变区.人工神经网络重要性预测结果由大到小的顺序是激光功率、扫描速度、扫描间距,BP拟合结果与实际结果较为接近,决定系数R2=0.73.     

Microstructure,cracking behavior and control of Al-Fe-V-Si alloy produced by selective laser melting

Selective laser melting(SLM) technology based on atomized powder was used to fabricate Al-8.5Fe-1.3V-1.7Si(wt%) alloy parts.The microstructure and crack characterization of SLM samples fabricated at various conditions were presented.Results show that the cracks appear periodically along the building direction,initiate preferably at the outer edges of the as-built samples and propagated along the remelting border zone(RBZ) into deposited layers.Solid-phase cracking is proposed according to the fr...     

激光熔化沉积TC2钛合金显微组织及力学性能

采用激光熔化沉积直接成形技术制备了TC2钛合金中空薄壁盒,通过光学显微镜和X射线衍射仪分别分析了显微组织和相组成,并测试了室温拉伸性能.结果表明,激光熔化沉积TC2钛合金具有细小的网篮组织和优异的室温拉伸性能,但其塑性存在明显的各向异性,纵向伸长率较横向提高约42.5%.     

Microstructure and properties of AlSi7Mg alloy fabricated by selective laser melting

The AlSi7Mg alloy was fabricated by selective laser melting (SLM), and its microstructure and properties at different building directions after heat treatment were analyzed. Results show that the microstructure of SLM AlSi7Mg samples containes three zones:fine grain zone, coarse grain zone, and heat affected zone. The fine-grain regions locate inside the molten pool, and the grains are equiaxed. The coarse-grain regions locate in the overlap of molten pools. After T6 treatment, the microstructure at the molten pool boundary is still the network eutectic Si, but the network structure becomes discrete, and is composed of intermittent, chain-like eutectic Si particles. The yield strength at three directions (xy, 45°, z direction) of the AlSi7Mg alloy samples fabricated by SLM is improved after T6 heat treatment. The fracture mechanism of the samples is a mixed ductile and brittle fracture before heat treatment and ductile fracture after heat treatment.     

Microstructure and mechanical properties of additive manufactured steel-Al structure materials with nickel gradient layers

The microstructure and mechanical properties of steel/Al structure material produced by additive manufacturing(AM) was investigated in this work based on the cold metal transfer welding.The results show that the microstructure gradually changed from the steel side to the aluminum side.The microstructure in the steel layer consisted of vermiform like 8ferrite and austenite structure,while in the aluminum layer the microstructure was constituted by α-Al grains and typical reticulate distributive Al-Si eutectic structure.Besides,a 7 μm thickness Ni-Al intermetallic compound layer was emerged at the interface of nickel and aluminum layer.The maximum room-temperature tensile strength of the Steel-Al structure materials was found to be 54 MPa,the rupture morphology showed a brittle fracture characteristic.     

Microstructure analysis of high density WC-Co composite prepared by one step selective laser melting

WC-Co composite, also well known as cemented carbide, is one of the most challenging materials for one step additive manufacture process, such as selective laser melting (SLM). Up until now, defect free cemented carbide has never been successfully synthesized yet using one-step SLM. In this study, the critical effect of the morphology of feedstock carbide granules on the microstructure was initially investigated for SLM processed carbides. Crack free WC-20Co cemented carbide with high density has been successfully synthesized using one-step SLM without further heat treatment. The density is significantly high for SLM processed carbides although still unsatisfactory yet compared to conventional liquid phase sintered carbides. Spherical granules are more favorable than non-spherical granules in obtaining a higher final density. The SLM process results in inhomogeneous and rapid WC grain growth, which is attributed to the non-uniform temperature distribution and varying amount of time experienced by the material in the liquid state during the SLM process.     

选区激光熔化成形Inconel 625合金的激光焊接头组织及高温蠕变性能

采用光学显微镜、扫描电镜、X射线衍射仪和能谱仪等对选区激光熔化 (SLM) 成形Inconel 625合金的激光焊接头组织特征及高温蠕变性能进行研究分析. 结果表明,SLM成形Inconel 625合金的激光焊接头质量良好,无明显的制造缺陷存在. SLM成形Inconel 625合金激光焊焊接试样的组织主要由母材区的等轴奥氏体组织以及焊缝区的柱状枝晶组成. 高温蠕变试验结果显示,试样的蠕变时间随着应力的增大急剧下降. 较高的应力水平（200 MPa）对合金在同一温度下的蠕变性能影响很大,会导致蠕变变形直接进入蠕变第三阶段——加速阶段,引发试样较早发生断裂. 断口分析表明,所有试样断裂均发生在母材区或近热影响区,母材区观测有大量二次裂纹,熔覆区未观察到明显裂纹. 蠕变断口形貌呈冰糖块状特征,表明断裂模式主要为沿晶断裂. 高温下晶界滑移引发的形变位移是晶界空洞形核的主要机制.     

选区激光熔化法制备的M2052锰铜合金的组织与性能

使用真空感应熔炼气雾化法(VIGA)制备M2052锰铜粉末,通过选区激光熔化技术(SLM)直接成形合金试样,经固溶时效处理和热等静压加工,从热力学计算、显微组织分析及力学性能测试等方面对SLM法制备的锰铜合金进行了研究。研究发现SLM法成形的锰铜合金的抗拉和屈服强度较高,但冲击吸收能量低,塑性差。经过热等静压处理后,合金的综合力学性能明显提高。     

激光增材制造GH3625高温合金激光焊接头组织及力学性能

对激光增材制造GH3625高温合金进行激光对接焊实验,分析了焊接接头的显微组织演变规律和力学性能。结果表明,在热影响区,仅在上层晶界处析出大量Laves相,导致晶界发生明显粗化。沿焊缝上层至下层,熔合区和中间区由上层的胞状晶、柱状晶和等轴细晶逐渐转变为下层的柱状晶,且紧贴熔合线生长的等轴细晶的数量逐渐增多,中心区均为树枝晶。细小颗粒状γ′相弥散分布于焊缝;大量Laves相在中间区枝晶间析出,且形态由上层的条状逐渐转变为下层的颗粒状。接头抗拉强度为872MPa,达到母材抗拉强度的98.2%,伸长率达到母材的90.7%。接头断面近似呈45°斜面,断裂形式为脆性和韧性混合断裂方式。     

激光熔化沉积CrMnFeCoNi高熵合金组织和低温力学性能

采用激光熔化沉积和铸造技术分别制备了CrMnFeCoNi高熵合金。通过X射线衍射(XRD)、金相腐蚀、扫描电镜(SEM)和力学拉伸实验等分析手段对不同方法制备的CrMnFeCoNi高熵合金相组成、微观组织及力学性能进行了对比研究。结果表明:通过激光熔化沉积和铸造技术制备的CrMnFeCoNi高熵合金均为面心立方(FCC)单相固溶体结构;采用激光熔化沉积技术制备的CrMnFeCoNi高熵合金具有更为均匀的元素分布;随着温度从293 K降低到77 K,激光熔化沉积技术制备的CrMnFeCoNi高熵合金的拉伸强度与塑性分别从518 MPa、55%提升到878 MPa、95%,表现出优异的低温力学性能。     

Corrosion behaviour of 316L stainless steel manufactured by selective laser melting

This work investigates the electrochemical behaviour of an AISI 316L stainless steel produced by selective laser melting (SLM) and compares its behaviour with that of wrought stainless steel with similar chemical composition. The SLM stainless steel specimens are tested in the as‐produced condition without stress relief or recrystallization heat treatments. The electrochemical tests are carried out in two electrolytes: 3.5 wt% NaCl solution with neutral pH and with pH of 1.8. At the macroscale, the microstructure of the SLM specimens is determined by the laser scanning pattern and displays an overlapping network of melt pools. At the microscale, the SLM specimens exhibit a cellular/columnar dendritic structure with submicrometric cell size. Electrochemical measurements highlight a more extended passive range for SLM stainless steel in both neutral and acid electrolytes indicating higher protective properties of the oxide film on SLM specimens. In contrast to the wrought material, the refined microstructure of the SLM specimens promotes a very shallow morphology of attack without deep penetration in the bulk.     

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.     

Microstructure and mechanical properties of Ti6Al4V alloy prepared by selective laser melting combined with precision forging

To improve the mechanical properties of Ti6Al4V alloy prepared by selective laser melting (SLM) process, the precision forging was conducted at 950 °C and different strains and strain rates. The microstructure evolution of as-built samples and forged samples in both horizontal and vertical sections was visualized and analyzed by optical microscope and X-ray diffraction. The microstructure was improved by the precision forging and subsequent water quenching. The porosity in each section was accounted. It can be seen that high strain rate and large deformation result in low porosity, consequently contributing to a better fatigue performance. The micro-hardness was lowered after precision forging and water quenching, while the difference of microhardness between the horizontal and vertical sections became smaller, which illustrated that this process can improve the anisotropy of structural components fabricated by SLM.     

激光熔化沉积2195铝锂合金微观组织演变及力学性能

采用激光熔化沉积技术对2195铝锂合金进行制备,通过单道以及搭接试验分析激光熔化沉积2195铝锂合金的最佳工艺参数,并利用光学显微镜(OM)等表征方法对其微观组织进行系统研究。结果表明,最佳沉积工艺参数为扫描功率1400 W,扫描速度480 mm/min,扫描间距1.6 mm。利用最佳工艺参数进行5层堆叠块体打印所得激光熔化沉积2195铝锂合金的微观组织中会出现沿晶界分布的析出相TB(Al₇Cu₄Li)相;激光熔化沉积2195铝锂合金经450℃固溶2 h后,合金中的第二相发生回溶;155℃时效32 h水冷后,合金中的不稳定过饱和固溶体Al₇Cu₄Li相会析出稳定的第二相,形成稳定时效态组织,硬度比固溶处理试样明显增加。     

Microstructure and mechanical properties of laser additive repaired Ti17 titanium alloy

Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17 titanium alloy with small surface defects. The microstructure, micro-hardness and room temperature tensile properties of laser additive repaired (LARed) specimen were investigated. The results show that, cellular substructures are observed in the laser deposited zone (LDZ), rather than the typical α laths morphology due to lack of enough subsequent thermal cycles. The cellular substructures lead to lower micro-hardness in the LDZ compared with the wrought substrate zone which consists of duplex microstructure. The tensile test results indicate that the tensile deformation process of the LARed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and fracture in the laser repaired zone with a mixed dimple and cleavage mode. The tensile strength of the LARed specimen is slightly higher than that of the wrought specimen and the elongation of 11.7% is lower.     

纳米铝热体系制备陶瓷复合钢管组织及性能

采用纳米铝热体系制备了陶瓷复合钢管,研究了纳米铝热剂中添加4%Na2B4O7+2%、4%、6%、8%(质量分数)纳米SiO2对其组织性能的影响。XRD分析结果表明,陶瓷层主相为α-Al2O3和FeAl2O4,杂相为Al2SiO5和B2O3;金相显微镜和SEM观察表明,α-Al2O3枝晶较细,排布密集,FeAl2O4呈晶间分布;测试结果表明陶瓷致密度可达95%,压溃强度和压剪强度分别可达499 MPa、22.6 MPa。     

Effect of powder reuse on mechanical properties of Ti-6Al-4V produced through selective laser melting

Metallic powder reuse presents attractive economic and environmental advantages for direct metal laser sintering (DMLS). However, continuous recycling of powder raises concerns of powder quality and sintered part performance, and complicates process validation. Efforts to examine the mechanical response of parts built with reused feedstocks are increasingly common in the technical literature, but none have optimized process parameters in DMLS to control for changes in material properties. In this paper, titanium powder reuse was investigated with the objective of optimizing the additive manufacturing (AM) process for reuse. Virgin Ti-6Al-4V powder was cycled a total of eight times through conditions representative of industrial DMLS machines. A full 2³-factorial design of experiments (DOE) approach was employed to identify how parameter settings affect mechanical behavior, and include reuse as a process variable. The independent factors (laser power, laser speed, and hatch distance) did not significantly affect mechanical properties; however, measurements of ductility were found to be influenced by some interaction between the factors. These results were attributed to the narrow operating envelope which was required for successfully sintered specimens. Density and chemistry measurements further demonstrated no significant change with respect to reuse. The findings suggest that titanium powder can be reused up to eight times without any noticeable loss in strength or ductility.