To increase the strength of the laser powder-bed fusion (LPBF) Al-Si-based aluminum alloy, TiB_(2) ceramic particles were selected to be mixed with high-Mg content Al-Si-Mg-Zr powder, and then a novel TiB_(2)/Al-Si-Mg...To increase the strength of the laser powder-bed fusion (LPBF) Al-Si-based aluminum alloy, TiB_(2) ceramic particles were selected to be mixed with high-Mg content Al-Si-Mg-Zr powder, and then a novel TiB_(2)/Al-Si-Mg-Zr composite was fabricated using LPBF. The results indicated that a dense sample with a maximum relative density of 99.85% could be obtained by adjusting the LPBF process parameters. Incorporating TiB_(2) nanoparticles enhanced the powder's laser absorption rate, thereby raising the alloy's intrinsic heat treatment temperature and consequently facilitating the precipitation of Si and βʺ nanoparticles in the α-Al cells. Moreover, the rapid cooling process during LPBF resulted in numerous alloying elements with low-stacking fault energy dissolving in the α-Al matrix, thus promoting the formation of the 9R phase. After a 48 h direct aging treatment at 150℃, the strength of the alloy slightly increased due to the increase of nanoprecipitates. Both yield strength and ultimate tensile strength of the LPBF TiB_(2)/Al-Si-Mg-Zr alloy were significantly higher than that of other LPBF TiB_(2)-modified aluminum alloys with external addition.展开更多
Laser powder-bed fusion(LPBF)of Zn-0.8Cu(wt.%)alloys exhibits significant advantages in the customization of biodegradable bone implants.However,the formability of LPBFed Zn alloy is not sufficient due to the spheroid...Laser powder-bed fusion(LPBF)of Zn-0.8Cu(wt.%)alloys exhibits significant advantages in the customization of biodegradable bone implants.However,the formability of LPBFed Zn alloy is not sufficient due to the spheroidization during the interaction of powder and laser beam,of which the mechanism is still not well understood.In this study,the evolution of morphology and grain structure of the LPBFed Zn-Cu alloy was investigated based on single-track deposition experiments.As the scanning speed increases,the grain structure of a single track of Zn-Cu alloy gradually refines,but the formability deteriorates,leading to the defect’s formation in the subsequent fabrication.The Zn-Cu alloys fabricated by optimum processing parameters exhibit a tensile strength of 157.13 MPa,yield strength of 106.48 MPa and elongation of 14.7%.This work provides a comprehensive understanding of the processing optimization of Zn-Cu alloy,achieving LPBFed Zn-Cu alloy with high density and excellent mechanical properties.展开更多
Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build c...Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build chamber with a single gas inlet exhibits a pronounced tendency for gas to flow upward near the outlet.This phenomenon results in the formation of a large vortex within the build chamber.The vortex leads to the chaotic motion trajectory of the spatter in the build chamber.The design defects of the existing build chamber based on dual gas inlets are shown in this paper.We established a coupled computational fluid dynamics-discrete phase model(CFD-DPM)model to optimize the build chamber by adjusting the position and structure of the second gas inlet.The homogeneity of the flow is increased with a distance of 379 mm between the two inlets and a wider-reaching second inlet.The Coanda effect is also crucial in the spatter-removal process.The Coanda effect is reduced by modifying the right sidewall of the build chamber and increasing the pressure difference between the inlet and outlet.Finally,we found that the spatter-removal rate rose from 8.9%to 76.1%between the conventional build chamber with a single gas inlet and the optimized build chamber with two gas inlets.展开更多
It is well known that laser-based powder-bed fusion(L-PBF) additive manufacturing of magnesium(Mg) and its alloys is associated with high Mg loss due to vaporization(MgLoss) and high incidence of many types of defects...It is well known that laser-based powder-bed fusion(L-PBF) additive manufacturing of magnesium(Mg) and its alloys is associated with high Mg loss due to vaporization(MgLoss) and high incidence of many types of defects in the manufactured parts/samples. Despite this,MgLoss, densification, and defect characteristics have not been holistically considered in the determination of the optimal values of L-PBF processing parameters for Mg and its alloys. This study presents a combined modeling and experimental approach applied for a widely used Mg alloy(WE43) to address this shortcoming in the literature. First, an experimentally calibrated model is proposed to determine MgLoss as a function of the L-PBF processing parameters. The model couples the temperature profile using a double ellipsoidal heat source with a Langmuir vaporization model and is calibrated using the width of the single-track L-PBF process and the measured Mglossusing inductively coupled plasma mass spectrometry(ICP-MS). Second, the densification of the samples is determined using a modification of the Archimedes method that considers the amount of MgLossin the calculation of the relative density. Third, a comprehensive and quantitative study is conducted on the relationships between the characteristics of porosity defects and the L-PBF processing parameters. Finally, the optimized L-PBF processing parameters are determined by considering the MgLoss, densification, and the characteristics of defects. The present study yields 0.23 wt.% MgLosscompared to 2 wt.% MgLossthat was reported in the previous studies. Furthermore, more than 99.5% densification is achieved while only ~2% and ~0.5% of the total defects are characterized as keyhole and lack of fusion defects, respectively.展开更多
Evaluating the recyclability of powders in additive manufacturing has been a long-term challenge.In this study,the microstructure and mechanical properties of a nickel-based superalloy fabricated by laser powder-bed f...Evaluating the recyclability of powders in additive manufacturing has been a long-term challenge.In this study,the microstructure and mechanical properties of a nickel-based superalloy fabricated by laser powder-bed fusion(LPBF)using recycled powders were investigated.Re-melted powder surfaces,satellite particles,and deformed powders were found in the recycled powders,combined with a high-oxygencontent surface layer.The increasing oxygen content led to the formation of high-density oxide inclusions;moreover,printing-induced cracks widely occurred and mainly formed along the grain boundaries in the as-built LPBF nickel-based superalloys fabricated using recycled powders.A little change in the Si or Mn content did not increase the hot cracking susceptibility(HCS)of the printed parts.The changing aspect ratio and the surface damage of the recycled powders might contribute to increasing the crack density.Moreover,the configuration of cracks in the as-built parts led to anisotropic mechanical properties,mainly resulting in extremely low ductility vertical to the building direction,and the cracks mainly propagated along the cellular boundary owing to the existence of a brittle precipitation phase.展开更多
An equiatomic CoCrFeNiMn High Entropy Alloy(HEA)was in-situ deposited by the powder-bed arc ad-ditive manufacturing(PBAAM)process for the first time.Comparative research was conducted on the evolution of phase,crystal...An equiatomic CoCrFeNiMn High Entropy Alloy(HEA)was in-situ deposited by the powder-bed arc ad-ditive manufacturing(PBAAM)process for the first time.Comparative research was conducted on the evolution of phase,crystallographic orientation,dislocation morphology,precipitation,and mechanical performance with the accumulation of inter-layer remelting times.The experimental outcomes mani-fested that the PBAAMed CoCrFeNiMn HEA consists of a stable solid-solution FCC structure,with de-creased lattice parameter but slightly increased(full width at half maximum)FWHM as the accumulation of the inter-layer remelting.The{001}<100>cube texture with a weakened texture intensity was de-tected with an increment of inter-layer remelting frequency from once to 5 times,yet it was transformed into{011}<100>Goss texture with a further increase to 7 times.Additionally,the mean grain diameter distinctly decreased,while the volume fraction of(low angle grain boundaries)LAGBs and dislocation density remarkably added up as the accumulated inter-layer remelts.Predominant cellular substructure generated in all process conditions and could be easily differentiated by elemental segregation.Both theσand M 23 C 6 Cr-rich precipitates in nano-scale and submicron MnS precipitate were detected on the grain boundaries of the PBAAMed deposited components,with a rather sparse distribution.Speaking of mechanical performance,the YS,UTS,and hardening rate are generally increased while the UE is grad-ually decreased as increased inter-layer remelting times.The studied PBAAMed CoCrFeNiMn HEA pos-sesses comparable mechanical performances with the counterparts of laser-deposited and as-cast ones.The strengthening mechanisms of the studied material are predominantly the grain boundary strength-ening and dislocation strengthening.This investigation would be a valuable resource in the research field of fabricating HEA alloys with acceptable microstructure and properties using the PBAAM method.展开更多
Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBF)...Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBF).However,its capabilities for being implemented as a reliable tool for material design,where minor changes in material-related parameters must be accurately captured,is still in question.In the present research,first,a thermo-fluid computational fluid dynamics(CFD)model is developed and validated against experimental data.Considering the predicted material properties of the pure Mg and commercial ZK60 and WE43 Mg alloys,parametric studies are done attempting to elucidate how the difference in some of the material properties,i.e.,saturated vapor pressure,viscosity,and solidification range,can influence the melt pool dynamics.It is found that a higher saturated vapor pressure,associated with the ZK60 alloy,leads to a deeper unstable keyhole,increasing the keyhole-induced porosity and evaporation mass loss.Higher viscosity and wider solidification range can increase the non-uniformity of temperature and velocity distribution on the keyhole walls,resulting in increased keyhole instability and formation of defects.Finally,the WE43 alloy showed the best behavior in terms of defect formation and evaporation mass loss,providing theoretical support to the extensive use of this alloy in L-PBF.In summary,this study suggests an approach to investigate the effect of materials-related parameters on L-PBF melting and solidification,which can be extremely helpful for future design of new alloys suitable for L-PBF.展开更多
激光粉末床熔融(Laser Powder Bed Fusion,LPBF)技术是定制化多孔纯Mo结构的重要技术。然而,LPBF成形纯Mo试样仍面临表面粗糙度值高及耐蚀性差等问题。电化学抛光(Electrochemical Polishing,ECP)是LPBF成形纯Mo的主要环保型后处理工艺...激光粉末床熔融(Laser Powder Bed Fusion,LPBF)技术是定制化多孔纯Mo结构的重要技术。然而,LPBF成形纯Mo试样仍面临表面粗糙度值高及耐蚀性差等问题。电化学抛光(Electrochemical Polishing,ECP)是LPBF成形纯Mo的主要环保型后处理工艺。研究了不同ECP抛光状态对LPBF成形纯Mo的表面粗糙度及降解特性的影响。结果表明:经电化学抛光处理后,试样表面粗糙度由4.55μm显著降低至1.05μm;相比原始态试样,抛光后试样腐蚀电流密度降低了78.4%。失重率从大到小顺序为:原始态>半抛光>抛光,且随着浸泡时间增加,失重率逐渐增加。溶液pH值波动≤0.5,验证了降解过程未引发局部酸化,符合生物医用材料要求。通过采用ECP处理Mo基材料表面,为合理调控其植入体的降解行为及降解速率的均匀性提供了重要理论依据。展开更多
聚醚醚酮(polyetheretherketone,PEEK)材料作为典型的轻质高性能聚合物材料,在医疗航空航天等领域获得了大量应用,PEEK材料的增材制造技术可以实现复杂零部件的结构功能一体化制造。针对聚醚醚酮粉末床熔融(powder bed fusion,PBF)系统...聚醚醚酮(polyetheretherketone,PEEK)材料作为典型的轻质高性能聚合物材料,在医疗航空航天等领域获得了大量应用,PEEK材料的增材制造技术可以实现复杂零部件的结构功能一体化制造。针对聚醚醚酮粉末床熔融(powder bed fusion,PBF)系统加工温度高、易翘曲的难题,开展了聚醚醚酮粉末床熔融系统多工艺参数优化与成形性能研究,通过工艺成形过程模拟仿真,揭示了激光功率等核心参数对温度场的影响规律。在成形工艺仿真基础上,开展了成形工艺参数优化试验,建立了工艺参数与拉伸力学性能以及翘曲率的对应关系,获得了拉伸强度86 MPa,断裂伸长率3.7%的优异力学性能,并最终实现了颅骨植入物的高精度增材制造。展开更多
Large solidification ranges and coarse columnar grains in the additively manufacturing of Al-Mg-Si alloys are normally involved in hot cracks during solidification.In this work,we develop novel crack-free Al-Mg_(2) Si...Large solidification ranges and coarse columnar grains in the additively manufacturing of Al-Mg-Si alloys are normally involved in hot cracks during solidification.In this work,we develop novel crack-free Al-Mg_(2) Si alloys fabricated by laser powder-bed fusion(L-PBF).The results indicate that the eutectic Mg_(2) Si phase possesses a strong ability to reduce crack susceptibility.It can enhance the grain growth restriction factor in the initial stage of solidification and promote eutectic filling in the terminal stage of solidifica-tion.The crack-free L-PBFed Al-x Mg_(2) Si alloys(x=6 wt.%,9 wt.%,and 12 wt.%)exhibit the combination of low crack susceptibility index(CSI),superior ability for liquid filling,and grain refinement.Particularly,the L-PBFed Al-9Mg_(2) Si alloy shows improved mechanical properties(e.g.yield strength of 397 MPa and elongation of 7.3%).However,the cracks are more likely to occur in the region near the columnar grain boundaries of the L-PBFed Al-3Mg_(2) Si alloy with a large solidification range and low eutectic content for liquid filling.Correspondingly,the L-PBFed Al-3Mg_(2) Si alloy shows poor bearing capacity of mechanical properties.The precise tuning of Mg_(2) Si eutectic content can offer an innovative strategy for eliminating cracks in additively manufactured Al-Mg-Si alloy.展开更多
由于稀土(RE)元素在激光粉末床熔融(Laser powder bed fusion,LPBF)制备的WE43合金中具有超高的固溶度,因此本文省去固溶处理过程,直接对其进行T5时效处理,研究了T5时效处理对其微观组织、物相、缺陷以及拉伸性能的影响。结果表明:T5时...由于稀土(RE)元素在激光粉末床熔融(Laser powder bed fusion,LPBF)制备的WE43合金中具有超高的固溶度,因此本文省去固溶处理过程,直接对其进行T5时效处理,研究了T5时效处理对其微观组织、物相、缺陷以及拉伸性能的影响。结果表明:T5时效处理后,WE43合金中的椭圆形和鱼鳞纹组织消失,平均晶粒尺寸由2μm长大至8.5μm,稀土相由点状弥散分布在α-Mg晶体内转变为连续或较小间距的分布在晶界处,形状为碟状或片状、针状,整体分布均匀;T5时效处理后WE43合金的屈服强度、抗拉强度和伸长率相对于LPBF态分别下降了12.6%、10.7%和6.6%,其力学性能降低的原因可归因于以下3个方面:时效后合金的晶粒尺寸增大;时效后连续或较小间距分布于晶界处的脆性析出相破坏了晶界的连续性,以及微孔等缺陷依然存在;时效后稀土元素从α-Mg基体中析出,导致其在α-Mg基体中的固溶度降低;但稀土原子在α-Mg中的固溶度对LPBF制备的WE43合金塑性的影响程度相对较低。展开更多
激光粉末床熔融(laser powder bed fusion,LPBF)成形悬垂结构的应力与变形是实现复杂金属构件高质量、高精度制造的关键问题之一。通过基体预埋应变片的方式实现了悬垂结构LPBF成形过程应变数据的实时测量。基于原位应变测量系统研究了...激光粉末床熔融(laser powder bed fusion,LPBF)成形悬垂结构的应力与变形是实现复杂金属构件高质量、高精度制造的关键问题之一。通过基体预埋应变片的方式实现了悬垂结构LPBF成形过程应变数据的实时测量。基于原位应变测量系统研究了T形悬垂结构、低角度悬垂结构(5°和10°)LPBF过程的原位应变行为。深入研究了不同悬臂长度、不同成形工艺参数对T形悬垂结构原位应变行为的影响,并进一步分析了不同悬垂角度、支撑类型对低角度悬垂结构原位应变行为的影响。结果表明,T形悬垂结构的悬空长度越长,结构的变形越大;采用激光能量梯度、棋盘扫描策略可有效降低T形悬垂结构的变形。支撑结构设计可显著影响低角度悬垂结构的应变行为和成形质量,采用H1支撑设计策略(块体支撑间距0.8 mm+锥体支撑间距0.6 mm)的成形质量最佳。上述结果可为深入理解LPBF成形悬垂结构的变形行为和调控提供有效参考。展开更多
激光粉末床熔融(laser powder bed fusion, LPBF)技术作为金属增材制造领域的前沿工艺,已被成功应用于航空航天等高端制造领域。然而多物理场强耦合效应易引发熔池动态失稳,导致制件内部孔隙缺陷频发,严重影响成形质量稳定性。传统监测...激光粉末床熔融(laser powder bed fusion, LPBF)技术作为金属增材制造领域的前沿工艺,已被成功应用于航空航天等高端制造领域。然而多物理场强耦合效应易引发熔池动态失稳,导致制件内部孔隙缺陷频发,严重影响成形质量稳定性。传统监测手段受限于成本高、部署困难等瓶颈,难以满足工业化生产需求。为此,提出声发射-深度学习融合的在线监测与内部质量智能判别方法。研制了基于声发射传感器的LPBF过程在线监测系统,通过工艺过程全周期声发射信号监测揭示声发射信号特征与成形质量间的映射规律,构建了包含逾8万组样本的熔池声发射数据。针对熔池微弱波动特征提取难题,构建了基于自适应傅里叶神经算子(AFNO)的频域特征提取网络和Kolmogorov-Arnold网络(KAN)的高维特征映射分类器,通过多尺度时域特征融合机制解析熔池动态特性,并借助高维流形精确映射高维特征,实现了声发射信号中微弱波动特征的增强表征和高精度质量判别。试验结果表明:研制的监测系统可有效捕获熔池的动态行为,所提方法质量判别精度达97%以上。展开更多
为研究流态工业固废固化黄土在路基工程中应用的可行性,基于响应面法(RSM),以粒化高炉矿渣粉(GBFS)、循环流化床脱硫粉煤灰(CFBFA)、烟气脱硫石膏(FGD)为影响因素,试件7、28 d无侧限抗压强度(UCS)为响应值建立响应面模型,开展了固化剂中...为研究流态工业固废固化黄土在路基工程中应用的可行性,基于响应面法(RSM),以粒化高炉矿渣粉(GBFS)、循环流化床脱硫粉煤灰(CFBFA)、烟气脱硫石膏(FGD)为影响因素,试件7、28 d无侧限抗压强度(UCS)为响应值建立响应面模型,开展了固化剂中掺10%水泥(OPC)时,各固废材料交互作用对流态固化黄土强度的影响研究;优化了固化剂配合比,并结合XRD、FTIR、TG-DTG和SEM微观试验分析了其强度形成的水化作用机理。结果表明:随GBFS掺量增加,CFBFA掺量减小,7、28 d UCS明显增大,GBFS与CFBFA交互作用对UCS的影响显著;随FGD掺量增加,7 d UCS先增后减,而28 d UCS减小,FGD与GBFS交互作用对UCS的影响从7~28 d由显著变为不显著,而与CFBFA交互作用的影响则相反;基于RSM确定的最佳配比,并考虑强度要求及原材料成本,提出当灰土比为0.15、水固比为0.51,固化剂中掺10%OPC时,GBFS、CFBFA和FGD建议的掺量范围分别为43%~50%、25%~32%和8%~15%;在反应初期,OPC水解产生的OH-与FGD溶解出的Ca^(2+)、SO_(4)^(2-)可激发GBFS与CFBFA表面的火山灰活性,生成钙矾石(AFt)与水化硅(铝)酸钙(C—S—(A)—H)连结黄土颗粒并填充颗粒间孔隙,使试件7 d UCS增大;在反应中后阶段,GBFS、CFBFA持续溶解出Ca^(2+)、[SiO_(4)]^(4-)和[AlO_(4)]^(5-)发生火山灰反应,生成更多C—S—H填充结构孔隙和裂缝,试件28 d UCS进一步增大。实际工程应用中,通过调整固化剂原材料配比或灰土比等制备出的流态固化黄土完全能满足一般台背、涵背回填和一般公路路基对强度的要求。展开更多
文中针对激光粉末床熔融(laser powder bed fusion,L-PBF)制造的GH3536样品,采用了不同的后处理工艺,并对其微观组织、力学性能和残余应力进行了分析.结合激光冲击强化技术,开展了构件表面残余应力调控,探究了热处理与激光冲击强化工艺...文中针对激光粉末床熔融(laser powder bed fusion,L-PBF)制造的GH3536样品,采用了不同的后处理工艺,并对其微观组织、力学性能和残余应力进行了分析.结合激光冲击强化技术,开展了构件表面残余应力调控,探究了热处理与激光冲击强化工艺顺序对残余应力的影响.结果表明,热处理中巨大的冷却应力撕裂了部分孔隙,同时,热处理不能完全消除构件表面约为+90 MPa的残余拉应力.随着冲击次数增加,残余应力的改善效果更显著,冲击两次后构件近表面呈现残余压应力状态,约为−350 MPa.相比在热处理前进行激光冲击强化,在热处理后进行强化更有利于残余拉应力的调控,从而实现性能的综合提升.文中研究结果为GH3536构件的增材制造及后处理工艺提供了新的思路,同时为其在航空航天领域的工程应用奠定基础.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51801079 and 52001140)the National Science Centre,Poland(Narodowe Centrum Nauki)(No.UMO-2021/42/E/ST5/00339).
文摘To increase the strength of the laser powder-bed fusion (LPBF) Al-Si-based aluminum alloy, TiB_(2) ceramic particles were selected to be mixed with high-Mg content Al-Si-Mg-Zr powder, and then a novel TiB_(2)/Al-Si-Mg-Zr composite was fabricated using LPBF. The results indicated that a dense sample with a maximum relative density of 99.85% could be obtained by adjusting the LPBF process parameters. Incorporating TiB_(2) nanoparticles enhanced the powder's laser absorption rate, thereby raising the alloy's intrinsic heat treatment temperature and consequently facilitating the precipitation of Si and βʺ nanoparticles in the α-Al cells. Moreover, the rapid cooling process during LPBF resulted in numerous alloying elements with low-stacking fault energy dissolving in the α-Al matrix, thus promoting the formation of the 9R phase. After a 48 h direct aging treatment at 150℃, the strength of the alloy slightly increased due to the increase of nanoprecipitates. Both yield strength and ultimate tensile strength of the LPBF TiB_(2)/Al-Si-Mg-Zr alloy were significantly higher than that of other LPBF TiB_(2)-modified aluminum alloys with external addition.
基金Project(2022YFC2406000)supported by the National Key R&D Program,ChinaProject(2022GDASZH-2022010107)supported by the Guangdong Academy of Science,China+4 种基金Project(2019BT02C629)supported by the Guangdong Special Support Program,ChinaProject(2022GDASZH-2022010203-003)supported by the GDAS’project of Science and Technology Development,ChinaProjects(2023B1212120008,2023B1212060045)supported by the Guangdong Province Science and Technology Plan Projects,ChinaProject(2023TQ07Z559)supported by the Special Support Foundation of Guangdong Province,ChinaProject(52105293)supported by the National Natural Science Foundation of China。
文摘Laser powder-bed fusion(LPBF)of Zn-0.8Cu(wt.%)alloys exhibits significant advantages in the customization of biodegradable bone implants.However,the formability of LPBFed Zn alloy is not sufficient due to the spheroidization during the interaction of powder and laser beam,of which the mechanism is still not well understood.In this study,the evolution of morphology and grain structure of the LPBFed Zn-Cu alloy was investigated based on single-track deposition experiments.As the scanning speed increases,the grain structure of a single track of Zn-Cu alloy gradually refines,but the formability deteriorates,leading to the defect’s formation in the subsequent fabrication.The Zn-Cu alloys fabricated by optimum processing parameters exhibit a tensile strength of 157.13 MPa,yield strength of 106.48 MPa and elongation of 14.7%.This work provides a comprehensive understanding of the processing optimization of Zn-Cu alloy,achieving LPBFed Zn-Cu alloy with high density and excellent mechanical properties.
基金supported by the Natural Science Foundation of Jiangxi Province(Nos.20224BAB214061 and 20224ACB214008)the National Natural Science Foundation of China(Nos.52165043 and 52166002)+2 种基金the Jiangxi Provincial Cultivation Program for Academic and Technical Leaders of Major Subjects(No.20225BCJ23008)the Anhui Provincial Natural Science Foundation(No.2308085ME171)the University Synergy Innovation Program of Anhui Province(Nos.GXXT-2023-025 and GXXT-2023-026),China。
文摘Mounds of spatter are generated in laser powder-bed fusion(L-PBF)additive manufacturing,which reduces build quality and laser lifetime.Due to the lack of supplemental airflow above the chamber,the conventional build chamber with a single gas inlet exhibits a pronounced tendency for gas to flow upward near the outlet.This phenomenon results in the formation of a large vortex within the build chamber.The vortex leads to the chaotic motion trajectory of the spatter in the build chamber.The design defects of the existing build chamber based on dual gas inlets are shown in this paper.We established a coupled computational fluid dynamics-discrete phase model(CFD-DPM)model to optimize the build chamber by adjusting the position and structure of the second gas inlet.The homogeneity of the flow is increased with a distance of 379 mm between the two inlets and a wider-reaching second inlet.The Coanda effect is also crucial in the spatter-removal process.The Coanda effect is reduced by modifying the right sidewall of the build chamber and increasing the pressure difference between the inlet and outlet.Finally,we found that the spatter-removal rate rose from 8.9%to 76.1%between the conventional build chamber with a single gas inlet and the optimized build chamber with two gas inlets.
文摘It is well known that laser-based powder-bed fusion(L-PBF) additive manufacturing of magnesium(Mg) and its alloys is associated with high Mg loss due to vaporization(MgLoss) and high incidence of many types of defects in the manufactured parts/samples. Despite this,MgLoss, densification, and defect characteristics have not been holistically considered in the determination of the optimal values of L-PBF processing parameters for Mg and its alloys. This study presents a combined modeling and experimental approach applied for a widely used Mg alloy(WE43) to address this shortcoming in the literature. First, an experimentally calibrated model is proposed to determine MgLoss as a function of the L-PBF processing parameters. The model couples the temperature profile using a double ellipsoidal heat source with a Langmuir vaporization model and is calibrated using the width of the single-track L-PBF process and the measured Mglossusing inductively coupled plasma mass spectrometry(ICP-MS). Second, the densification of the samples is determined using a modification of the Archimedes method that considers the amount of MgLossin the calculation of the relative density. Third, a comprehensive and quantitative study is conducted on the relationships between the characteristics of porosity defects and the L-PBF processing parameters. Finally, the optimized L-PBF processing parameters are determined by considering the MgLoss, densification, and the characteristics of defects. The present study yields 0.23 wt.% MgLosscompared to 2 wt.% MgLossthat was reported in the previous studies. Furthermore, more than 99.5% densification is achieved while only ~2% and ~0.5% of the total defects are characterized as keyhole and lack of fusion defects, respectively.
基金This work was financially supported by the National Key Research and Development Program of China(No.2017YFB 0702300)the National Natural Science Foundation of China(No.51871028)the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-003B2).
文摘Evaluating the recyclability of powders in additive manufacturing has been a long-term challenge.In this study,the microstructure and mechanical properties of a nickel-based superalloy fabricated by laser powder-bed fusion(LPBF)using recycled powders were investigated.Re-melted powder surfaces,satellite particles,and deformed powders were found in the recycled powders,combined with a high-oxygencontent surface layer.The increasing oxygen content led to the formation of high-density oxide inclusions;moreover,printing-induced cracks widely occurred and mainly formed along the grain boundaries in the as-built LPBF nickel-based superalloys fabricated using recycled powders.A little change in the Si or Mn content did not increase the hot cracking susceptibility(HCS)of the printed parts.The changing aspect ratio and the surface damage of the recycled powders might contribute to increasing the crack density.Moreover,the configuration of cracks in the as-built parts led to anisotropic mechanical properties,mainly resulting in extremely low ductility vertical to the building direction,and the cracks mainly propagated along the cellular boundary owing to the existence of a brittle precipitation phase.
基金financially supported by the China Scholarship Council (CSC)(No. 201606080014)the University of Wollongong(UOW)the Electron Microscopy center of UOW (EMC)
文摘An equiatomic CoCrFeNiMn High Entropy Alloy(HEA)was in-situ deposited by the powder-bed arc ad-ditive manufacturing(PBAAM)process for the first time.Comparative research was conducted on the evolution of phase,crystallographic orientation,dislocation morphology,precipitation,and mechanical performance with the accumulation of inter-layer remelting times.The experimental outcomes mani-fested that the PBAAMed CoCrFeNiMn HEA consists of a stable solid-solution FCC structure,with de-creased lattice parameter but slightly increased(full width at half maximum)FWHM as the accumulation of the inter-layer remelting.The{001}<100>cube texture with a weakened texture intensity was de-tected with an increment of inter-layer remelting frequency from once to 5 times,yet it was transformed into{011}<100>Goss texture with a further increase to 7 times.Additionally,the mean grain diameter distinctly decreased,while the volume fraction of(low angle grain boundaries)LAGBs and dislocation density remarkably added up as the accumulated inter-layer remelts.Predominant cellular substructure generated in all process conditions and could be easily differentiated by elemental segregation.Both theσand M 23 C 6 Cr-rich precipitates in nano-scale and submicron MnS precipitate were detected on the grain boundaries of the PBAAMed deposited components,with a rather sparse distribution.Speaking of mechanical performance,the YS,UTS,and hardening rate are generally increased while the UE is grad-ually decreased as increased inter-layer remelting times.The studied PBAAMed CoCrFeNiMn HEA pos-sesses comparable mechanical performances with the counterparts of laser-deposited and as-cast ones.The strengthening mechanisms of the studied material are predominantly the grain boundary strength-ening and dislocation strengthening.This investigation would be a valuable resource in the research field of fabricating HEA alloys with acceptable microstructure and properties using the PBAAM method.
基金the financial supports received from Wenner-Gren foundation(UPD2021-0229),JernkontoretSTT(Stiftelsen för Tillämpad Termodynamik).
文摘Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBF).However,its capabilities for being implemented as a reliable tool for material design,where minor changes in material-related parameters must be accurately captured,is still in question.In the present research,first,a thermo-fluid computational fluid dynamics(CFD)model is developed and validated against experimental data.Considering the predicted material properties of the pure Mg and commercial ZK60 and WE43 Mg alloys,parametric studies are done attempting to elucidate how the difference in some of the material properties,i.e.,saturated vapor pressure,viscosity,and solidification range,can influence the melt pool dynamics.It is found that a higher saturated vapor pressure,associated with the ZK60 alloy,leads to a deeper unstable keyhole,increasing the keyhole-induced porosity and evaporation mass loss.Higher viscosity and wider solidification range can increase the non-uniformity of temperature and velocity distribution on the keyhole walls,resulting in increased keyhole instability and formation of defects.Finally,the WE43 alloy showed the best behavior in terms of defect formation and evaporation mass loss,providing theoretical support to the extensive use of this alloy in L-PBF.In summary,this study suggests an approach to investigate the effect of materials-related parameters on L-PBF melting and solidification,which can be extremely helpful for future design of new alloys suitable for L-PBF.
文摘激光粉末床熔融(Laser Powder Bed Fusion,LPBF)技术是定制化多孔纯Mo结构的重要技术。然而,LPBF成形纯Mo试样仍面临表面粗糙度值高及耐蚀性差等问题。电化学抛光(Electrochemical Polishing,ECP)是LPBF成形纯Mo的主要环保型后处理工艺。研究了不同ECP抛光状态对LPBF成形纯Mo的表面粗糙度及降解特性的影响。结果表明:经电化学抛光处理后,试样表面粗糙度由4.55μm显著降低至1.05μm;相比原始态试样,抛光后试样腐蚀电流密度降低了78.4%。失重率从大到小顺序为:原始态>半抛光>抛光,且随着浸泡时间增加,失重率逐渐增加。溶液pH值波动≤0.5,验证了降解过程未引发局部酸化,符合生物医用材料要求。通过采用ECP处理Mo基材料表面,为合理调控其植入体的降解行为及降解速率的均匀性提供了重要理论依据。
文摘聚醚醚酮(polyetheretherketone,PEEK)材料作为典型的轻质高性能聚合物材料,在医疗航空航天等领域获得了大量应用,PEEK材料的增材制造技术可以实现复杂零部件的结构功能一体化制造。针对聚醚醚酮粉末床熔融(powder bed fusion,PBF)系统加工温度高、易翘曲的难题,开展了聚醚醚酮粉末床熔融系统多工艺参数优化与成形性能研究,通过工艺成形过程模拟仿真,揭示了激光功率等核心参数对温度场的影响规律。在成形工艺仿真基础上,开展了成形工艺参数优化试验,建立了工艺参数与拉伸力学性能以及翘曲率的对应关系,获得了拉伸强度86 MPa,断裂伸长率3.7%的优异力学性能,并最终实现了颅骨植入物的高精度增材制造。
基金financially supported by the National Natural Science Foundation of China(Grant No.52071343)the Leading Innovation and Entrepreneurship Team of Zhejiang Province-Automotive Light Alloy Innovation Team(No.2022R01018).
文摘Large solidification ranges and coarse columnar grains in the additively manufacturing of Al-Mg-Si alloys are normally involved in hot cracks during solidification.In this work,we develop novel crack-free Al-Mg_(2) Si alloys fabricated by laser powder-bed fusion(L-PBF).The results indicate that the eutectic Mg_(2) Si phase possesses a strong ability to reduce crack susceptibility.It can enhance the grain growth restriction factor in the initial stage of solidification and promote eutectic filling in the terminal stage of solidifica-tion.The crack-free L-PBFed Al-x Mg_(2) Si alloys(x=6 wt.%,9 wt.%,and 12 wt.%)exhibit the combination of low crack susceptibility index(CSI),superior ability for liquid filling,and grain refinement.Particularly,the L-PBFed Al-9Mg_(2) Si alloy shows improved mechanical properties(e.g.yield strength of 397 MPa and elongation of 7.3%).However,the cracks are more likely to occur in the region near the columnar grain boundaries of the L-PBFed Al-3Mg_(2) Si alloy with a large solidification range and low eutectic content for liquid filling.Correspondingly,the L-PBFed Al-3Mg_(2) Si alloy shows poor bearing capacity of mechanical properties.The precise tuning of Mg_(2) Si eutectic content can offer an innovative strategy for eliminating cracks in additively manufactured Al-Mg-Si alloy.
文摘由于稀土(RE)元素在激光粉末床熔融(Laser powder bed fusion,LPBF)制备的WE43合金中具有超高的固溶度,因此本文省去固溶处理过程,直接对其进行T5时效处理,研究了T5时效处理对其微观组织、物相、缺陷以及拉伸性能的影响。结果表明:T5时效处理后,WE43合金中的椭圆形和鱼鳞纹组织消失,平均晶粒尺寸由2μm长大至8.5μm,稀土相由点状弥散分布在α-Mg晶体内转变为连续或较小间距的分布在晶界处,形状为碟状或片状、针状,整体分布均匀;T5时效处理后WE43合金的屈服强度、抗拉强度和伸长率相对于LPBF态分别下降了12.6%、10.7%和6.6%,其力学性能降低的原因可归因于以下3个方面:时效后合金的晶粒尺寸增大;时效后连续或较小间距分布于晶界处的脆性析出相破坏了晶界的连续性,以及微孔等缺陷依然存在;时效后稀土元素从α-Mg基体中析出,导致其在α-Mg基体中的固溶度降低;但稀土原子在α-Mg中的固溶度对LPBF制备的WE43合金塑性的影响程度相对较低。
文摘激光粉末床熔融(laser powder bed fusion, LPBF)技术作为金属增材制造领域的前沿工艺,已被成功应用于航空航天等高端制造领域。然而多物理场强耦合效应易引发熔池动态失稳,导致制件内部孔隙缺陷频发,严重影响成形质量稳定性。传统监测手段受限于成本高、部署困难等瓶颈,难以满足工业化生产需求。为此,提出声发射-深度学习融合的在线监测与内部质量智能判别方法。研制了基于声发射传感器的LPBF过程在线监测系统,通过工艺过程全周期声发射信号监测揭示声发射信号特征与成形质量间的映射规律,构建了包含逾8万组样本的熔池声发射数据。针对熔池微弱波动特征提取难题,构建了基于自适应傅里叶神经算子(AFNO)的频域特征提取网络和Kolmogorov-Arnold网络(KAN)的高维特征映射分类器,通过多尺度时域特征融合机制解析熔池动态特性,并借助高维流形精确映射高维特征,实现了声发射信号中微弱波动特征的增强表征和高精度质量判别。试验结果表明:研制的监测系统可有效捕获熔池的动态行为,所提方法质量判别精度达97%以上。
文摘为研究流态工业固废固化黄土在路基工程中应用的可行性,基于响应面法(RSM),以粒化高炉矿渣粉(GBFS)、循环流化床脱硫粉煤灰(CFBFA)、烟气脱硫石膏(FGD)为影响因素,试件7、28 d无侧限抗压强度(UCS)为响应值建立响应面模型,开展了固化剂中掺10%水泥(OPC)时,各固废材料交互作用对流态固化黄土强度的影响研究;优化了固化剂配合比,并结合XRD、FTIR、TG-DTG和SEM微观试验分析了其强度形成的水化作用机理。结果表明:随GBFS掺量增加,CFBFA掺量减小,7、28 d UCS明显增大,GBFS与CFBFA交互作用对UCS的影响显著;随FGD掺量增加,7 d UCS先增后减,而28 d UCS减小,FGD与GBFS交互作用对UCS的影响从7~28 d由显著变为不显著,而与CFBFA交互作用的影响则相反;基于RSM确定的最佳配比,并考虑强度要求及原材料成本,提出当灰土比为0.15、水固比为0.51,固化剂中掺10%OPC时,GBFS、CFBFA和FGD建议的掺量范围分别为43%~50%、25%~32%和8%~15%;在反应初期,OPC水解产生的OH-与FGD溶解出的Ca^(2+)、SO_(4)^(2-)可激发GBFS与CFBFA表面的火山灰活性,生成钙矾石(AFt)与水化硅(铝)酸钙(C—S—(A)—H)连结黄土颗粒并填充颗粒间孔隙,使试件7 d UCS增大;在反应中后阶段,GBFS、CFBFA持续溶解出Ca^(2+)、[SiO_(4)]^(4-)和[AlO_(4)]^(5-)发生火山灰反应,生成更多C—S—H填充结构孔隙和裂缝,试件28 d UCS进一步增大。实际工程应用中,通过调整固化剂原材料配比或灰土比等制备出的流态固化黄土完全能满足一般台背、涵背回填和一般公路路基对强度的要求。
