激光直接烧结FGH95高温合金冲击韧性试验研究

基于直接激光金属烧结成形技术,进行了FGH95镍基高温合金粉末的快速成形试验,研究了工艺参数对样件冲击韧性的影响,并分析了断口形貌。试验结果表明:激光功率对冲击韧性的影响最为显著,当激光功率为1 000 W和900 W时,样件常温冲击韧性和高温冲击韧性分别达到最大值109.09 J/cm2和101.82 J/cm2;在试验参数范围内,样件高温冲击韧性与常温冲击韧性变化趋势基本一致,数值相差不大;断口呈现典型的韧窝断裂特征。     

选区激光熔化成形用钽粉射频等离子体球化研究

以不规则状钠还原钽粉为原料,采用射频等离子体球化技术制备高纯致密球形钽粉,实现了还原钽粉的球化、致密化和纯化。研究了送粉速率、载气流量、反应室压力等工艺参数对钽粉球化率及粉体特性的影响,并探索了球化钽粉的选区激光熔化成形适用性。结果表明：不规则状钠还原钽粉,经射频等离子体球化处理后可得到表面光滑、内部致密、高纯低氧、球化率可达100%的球形钽粉。球化处理后,钽粉粒度分布变窄。钽粉的球化率随送粉速率的增大而降低,随载气流量的增加先升高后减小。弱负压更有利于获得较高球化率的钽粉。随着球化率的提高,钽粉的流动性能显著改善,松装密度与振实密度明显提高。当送粉速率为30g/min,载气流量为5.0slpm,反应室压力为12.0Psi时,球形钽粉霍尔流速提高到5.98s/50g,松装密度由3.503g/cm_³提高到9.463g/cm_³,振实密度由5.344g/cm_³提高到10.433g/cm_³,且氧含量由0.076%降低至0.0481%。另外,射频等离子体球化钽粉具有良好的选区激光熔化成形适用性,其试样致密度ρ≥99.5%,抗拉强度σ_b=693MPa,屈服强度σ_0.2=616MPa,延伸率δ=28.5%。     

选区激光熔化成形用钽粉的射频等离子体球化

以不规则状钠还原钽粉为原料,采用射频等离子体球化技术制备高纯致密球形钽粉,实现了还原钽粉的球化、致密化和纯化。研究了送粉速率、载气流量、反应室压力等工艺参数对钽粉球化率及粉体特性的影响,并探索了球化钽粉的选区激光熔化成形适用性。结果表明:不规则状钠还原钽粉,经射频等离子体球化处理后可得到表面光滑、内部致密、高纯低氧、球化率可达100%的球形钽粉。球化处理后,钽粉粒度分布变窄。钽粉的球化率随送粉速率的增大而降低,随载气流量的增加先升高后降低。弱负压更有利于获得较高球化率的钽粉。随着球化率的提高,钽粉的流动性能显著改善,松装密度与振实密度明显提高。当送粉速率为30 g/min,载气流量为5.0 L/min,反应室压力为82.7 kPa时,球形钽粉霍尔流速提高到5.98 s/50g,与不规则形钠还原钽粉相比,松装密度由3.503 g/cm~3提高到9.463 g/cm~3,振实密度由5.344g/cm~3提高到10.433g/cm~3,且氧含量由0.076%降低至0.0481%。另外,射频等离子体球化钽粉具有良好的选区激光熔化成形适用性,其试样致密度ρ≥99.5%,抗拉强度σ_b=693 MPa,屈服强度σ_(0.2)=616 MPa,延伸率δ=28.5%。     

Al-Mg-Li合金选区激光熔化成形及热处理工艺

设计并制备了多种不同成分的铝锂合金粉末，对其进行了选区激光熔化(SLM)成形，选取高致密、无裂纹的自研铝镁锂合金成形零件进行了热处理工艺研究。结果表明，第三代Al-Li-Cu系铝锂合金在选区激光熔化成形快速凝固过程中极易产生微裂纹，第二代Al-Li-Mg系合金较为适合选区激光熔化成形，能够得到高致密、无裂纹的成形样件；选区激光熔化成形铝镁锂合金在200℃进行时效热处理，强化相主要为δ′相，时效48 h达到峰时效状态，继续延长时效时间，其力学性能有所下降。     

钽的激光选区熔化成形工艺研究

通过一系列实验探究难熔金属钽的激光选区熔化(Selective?Laser?Melting,SLM)成形工艺,分别选取不同激光功率、扫描速度和扫描间距,进行了单道实验、单层实验以及块体实验.结果表明,SLM成形钽最优工艺参数为激光功率300?W,扫描速度50?mm/s.针对SLM过程中钽层出现不同程度的开裂现象,从热传导及激光选区熔化过程中产生内应力累积方面对钽层开裂的原因进行了定性分析.最终成功制备得钽块体,并采用扫描电子显微镜(SEM)及X射线散射谱(EDX)对SLM成形钽的微观组织及成分分布进行表征.     

激光功率对Al2O3-ZrO2共晶陶瓷成形质量的影响

采用激光近净成形系统成形了Al2O3-Zr O2(Y2O3)共晶陶瓷,研究了激光功率对成形形貌以及陶瓷内部裂纹、气孔的影响规律,利用X射线衍射仪和扫描电镜对样件进行相成分分析和微观组织观察。研究表明,相对较高的激光功率可以得到裂纹以及气孔较少的陶瓷样件;陶瓷样件具有紧凑排列的胞状共晶组织,亚微米级t-Zr O2(Y2O3)纤维均匀分布在胞状共晶组织内部。由于激光近净成形加工具有层层堆积的特点,微观组织呈现出垂直于沉积方向的周期性带状组织。     

ZL114A铝合金激光选区熔化成形工艺

以ZL114A铝合金粉末为研究对象,主要研究激光选区熔化(SLM)成形主要工艺参数如激光功率、扫描速度、扫描间距、铺粉厚度等对ZL114A成形试样致密度的影响。结果表明,SLM成形ZL114A合金试样的致密度随着激光功率的增大而增大;而随着扫描速度的增大,试样的致密度则呈现先增大后减小的趋势;当激光功率为450 W,扫描速度为2 000 mm/s,扫描间距为0.09 mm,铺粉厚度为0.05 mm时,试样致密度最大可达到99.92%,其SLM沉积态合金的常温平均抗拉强度为402.7 MPa,伸长率为6.0%。进一步引入能量密度模型,综合表征能量输入与试样致密度之间的作用关系,当能量密度在35～100 J/mm~3范围内,其致密度均可达99%以上。     

金属粉末选区激光熔化球化现象研究

球化现象是选区激光熔化(SLM)成形中的常见缺陷,是影响零件致密度及力学性能的关键因素之一。目前,国内外对SLM成形方面还处于初步阶段,对SLM成形中球化的成形理论、成形过程及控制方法研究还不够深入。本文从金属液与固体表面的润湿性问题和SLM成形中液滴飞溅两个方面阐述了球化的成形理论;从激光熔化金属粉末是否穿透粉层的角度分析了球化的成形过程;从氧含量和金属粉末熔化量等方面提出了球化的控制方法。     

AlSi10Mg合金选区激光熔化成形参数的选择

选区激光熔化成形技术常用于复杂构件的制造,其成形件的力学性能甚至优于热处理后传统铸造件的。在选区激光熔化成形过程中,易出现球化等缺陷,会降低零件的致密度和力学性能,进而影响产品的使用。以AlSi10Mg合金为例,从材料、设备及工艺等参数选择的角度对如何减少合金选区激光熔化成形件球化现象、提高致密度进行了分析。结果表明,氧含量低和粒度小的粉末颗粒可减少球化现象,选择合适的工艺参数,可提高零件的致密度。     

INCONEL系镍基高温合金选区激光熔化增材制造工艺研究

研究了激光加工工艺参数对选区激光熔化工艺成形的Inconel 718合金试样的致密化行为、显微组织特征、硬度及摩擦磨损性能的影响。结果表明:当激光线能量密度(η)较低时,球化效应的出现使试样的致密度水平较低;在较高的线能量密度与合适的加工参数下,可获得接近完全致密的Inconel 718合金试样。同时,随着激光线能量密度的增加,SLM成形Inconel 718合金试样的显微组织经历了粗大的柱状树枝晶、聚集的枝晶、细长而均匀分布的柱状枝晶等变化过程。在优化工艺参数下,成形试样的显微硬度高达397.8 HV0.2;摩擦系数和磨损率较低,分别为0.40和4.78×10-4mm3/Nm;且试样内部显微组织均匀细小,摩擦试样的表面形成摩擦保护层,使试样的摩擦磨损性能较好。     

Microstructure of a Ti–50wt% Ta alloy produced via laser powder bed fusion

Ti-Ta alloys have been widely studied for biomedical applications due to their high biocompatibility and corrosion resistance.In this work,nearly fully dense and in situ alloyed Ti-50 wt% Ta samples were fabricated by the laser powder bed fusion(LPBF) of mechanically mixed powders.With increased exposure time,and thereby increased laser energy density,insoluble Ta particles were almost dissolved,and a Ti-50 wt% Ta alloy was formed.Cellular and dendritic structures were formed due to constitutional undercooling,which was caused by the high cooling rate of LPBF process.Both retained βphases and α " phases were observed in the LPBFed Ti-50 wt% Ta alloy.The α" phase was found at the boundary of the cellular structures,where the tantalum content was not high enough to suppress the bcc lattice transition completely but could suppress the β phase→α' phase transition.     

Selective laser sintering of high carbon steel powders studied as a function of carbon content

Optimum conditions for laser irradiation to achieve fully dense high carbon steel SLS (selective laser sintering) specimens have been investigated as a function of carbon content in steel powders with the use of steel powders with different carbon contents in the range of 0.33–1.05 mass%C (corresponding to S33C, S50C, S75C and S105C in the JIS standard). Full densification is found to be easily achieved by SLS processing for all high carbon steel powders. The energy density during the SLS process required for full densification decreases as the carbon content increases from 400 J/mm³ for 0.33 and 0.50 mass%C to 267 J/mm³ for 0.75 and 1.05 mass%C. This is considered to be due to the increased wettability of molten Fe–C alloys for the higher carbon contents. The values of microhardness and yield stress of fully dense SLS specimens tend to increase as the carbon content in steel powders increases. At a given carbon content, the values of microhardness and yield stress of fully dense SLS specimens tend to be higher for those produced with a lower energy input (with higher laser scan speeds and larger scan spacings).     

Laser Powder Deposition Parametric Optimization and Property Development for Ti-6Al-4V Alloy

In this study, Ti6Al4V alloy was produced via laser powder deposition (LPD). To obtain Ti6Al4V alloy with maximum density, LPD parameters for preparing Ti6Al4V samples were optimized using the Taguchi method. Results were analyzed on the basis of the signal-to-noise (S/N) ratios and analyses of variance. A high energy density should be used to achieve higher levels of densification. The optimal combination of parameters for density was a scanning speed of 550 mm/min, laser power of 160 W, powder feeding rate of 0.99 g/min, and shield gas flow of 8 L/min. An almost fully dense Ti6Al4V sample was prepared using the optimized LPD process, and the relative density was greater than 99%. In addition, the microstructure and properties of Ti6Al4V samples prepared by optimized LPD process were investigated. The microstructure investigation revealed that the LPD-prepared Ti6Al4V sample was predominantly composed of fine acicular α phase and lath-type α phase. Tensile and microhardness tests indicated that the LPD sample had higher mechanical properties than the traditional cast Ti6Al4V alloy because of the acicular martensitic phase and smaller grain size.     

Ni-CuSn混合粉末选区激光烧结试验

通过对双组分Ni-CuSn混合粉末进行激光烧结试验,表明此组粉末体系成形机制是粉末半熔化状态下的液相烧结机制。详细讨论了激光工艺参数对成形机制及烧结质量的影响,结果表明,将激光功率和扫描速率控制在适宜的范围内,才可实现预期的成形机制,并获得较好的烧结质量。对烧结件显微组织分析表明,组分M和CuSn间存在较为明显的熔点差、及两者之间较高的固溶度,是保证液相烧结机制、获得较高烧结致密度的前提。     

Effects of selective laser melting parameters on surface quality and densification behaviours of pure nickel

The effects of laser power and scanning speed on the forming characteristic of scanning tracks, densification behaviours and surface roughness of pure nickel fabricated with selective laser melting (SLM) were studied. The results indicate that the scanning tracks showed continuous, regular and flat surface with increasing laser power and decreasing scanning speed in a specific range, which could avoid the defects (like holes and balling structures) forming in SLM processing. The optimal process window was identified as the scanning speed of 900 mm/s and the laser power of 255?275 W by comparing the surface qualities and densification behaviours. With the suitable processing parameters, the relative density could achieve 99.16%, the tensile strength was (359.49±2.74) MPa, and the roughnesses of the top and side surfaces were (12.88±2.23) and (14.98±0.69) μm, respectively.     

Fabrication and microstructure characterization of selective laser‐melted FeAl intermetallic parts

Selective laser melting was considered in this study with the goal to manufacture dense parts with mechanical properties comparable to those of bulk materials, directly from FeAl intermetallic powder. Based on a series of single line scans, the processing window was first explored, paying attention to the melting mechanisms. Then, FeAl samples were produced using various selected parameters according to the previously established processing map. These samples were investigated in terms of microstructure, surface roughness, densification and microhardness. Observations revealed that these characteristics are strongly dependent on the processing parameters. Finally, interesting FeAl specimens with a relatively high density (98% of the theoretical value), high microhardness and smooth surface were obtained using a laser power of 90 W and a scanning speed of 0.2 m/s, corresponding to a continuous melting mechanism of the powder bed.     

Selective Laser Melting of in-situ TiC/Ti5Si3 composites with novel reinforcement architecture and elevated performance

A novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti₅Si₃ in-situ composites starting from Ti/SiC powder system. The influence of the applied laser energy density on densification, microstructure, and mechanical performance of SLM-processed composite parts was studied. It showed that the uniformly dispersed TiC reinforcing phase having a unique network distribution and a submicron-scale dendritic morphology was formed as a laser energy density of 0.4 kJ/m was properly settled. The 96.9% dense SLM-processed TiC/Ti₅Si₃ composites had a high microhardness of 980.3HV_0.2, showing more than a 3-fold increase upon that of the unreinforced Ti part. The dry sliding wear tests revealed that the TiC/Ti₅Si₃ composites possessed a considerably low friction coefficient of 0.2 and a reduced wear rate of 1.42 × 10^− 4 mm³/Nm. The scanning electron microscope (SEM) characterization of the worn surface morphology indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer. The densification rate, microhardness, and wear performance generally decreased at a higher laser energy density of 0.8 kJ/m, due to the formation of thermal cracks and the significant coarsening of TiC dendritic reinforcing phase.     

3D printing of tantalum parts based on low molecular mass organic gel system

In this study, 3D gel printing based on a low molecular mass organic gel system was employed to fabricate complex-shaped Ta parts. As opposed to a polymeric gel system, this system was initiated by heat transition. To obtain suitable printing slurry with 62 vol% solid content, 2.5 wt% resin was introduced to improve green body strength and 0.55 wt% oleic acid was added to modify the viscosity. As a result, the printed samples had relatively good surface quality without defects or pores observed on the surface. Ta particles were closely bound by dibenzylidene sorbitol (DBS) gelators. After sintering, a uniform shrinkage was obtained with a shrinkage of 11%, but the surface quality of the as sintered samples was improved. Sintering decreased the surface roughness from 4.0 μm to 2.8 μm. Besides, the as-sintered Ta samples had a relatively dense and homogenous microstructure. The relative density of the as-sintered sample was about 98%. Therefore, 3D gel printing is a promising method to prepare complex-shaped Ta parts with minimal material waste.     

On grain refinement of a γ-TiAl alloy using cryo-milling followed by spark plasma sintering

A fully dense fine-grained γ-TiAl based alloy was fabricated by cryo-milling pre-alloyed powders followed by spark plasma sintering. The consolidation was performed at 1050 or 1200 °C. The effect of cryo-milling on the densification kinetics and final microstructure was studied. Results indicate that cryo-milled (8 h) powder is fully densified at a temperature nearly 125 °C lower than that of un-milled powder. The microstructure of the alloy fabricated at different temperatures consisted of fine grains of γ-TiAl and α₂ (Ti₃Al) phases in different volume fractions. The average grain size of cryo-milled powders compacted at 1050 and 1200 °C were determined as 0.6 and 0.9 μm, respectively. It is inferred that the reduction in crystallite and particle size induced by cryo-milling is the likely reason for such enhancement in densification and grain refinement.     

Rapid sintering of ultra fine WC and WC-Co hard materials by high-frequency induction heated sintering and their mechanical properties

Using a high-frequency induction heated sintering (HFIHS) method, the densification of binderless WC and WC-x wt.%Co (x=8, 10, 12) hard materials were accomplished using an ultra fine powder of WC and WC-Co. The advantages of this process are that it allows very quick densification close to the theoretical density and prohibits grain growth in nano-structured materials. Nearly fully dense WC and WC-Co with a relative density of up to 99.9% could be obtained with a simultaneous application of 60 MPa pressure and induced current (within 2 min) without a significant change in grain size. The average grain size of WC was approximately 270 nm for WC-x wt.%Co. The hardness and fracture toughness of the dense WC and WC-Co composites produced by HFIHS were investigated.