增材方向对激光粉末床熔融钨材料抗高热负荷性能的影响

激光粉末床熔融(LPBF)作为一种新兴的增材制造技术,为未来聚变堆偏滤器mono-block的制备提供了新的成形方法。本研究利用LPBF,采用水平增材和竖直增材2种方式对纯钨样品进行了制备。研究发现,在15 MW/m2的热负荷下,竖直增材样品发生了明显的熔化和飞溅现象,水平增材样品只发生少许开裂和轻微溅射。通过微观组织表征发现,LPBF过程中不同方向组织的差异导致了钨热导率的各向异性。对于水平增材样品,热流方向平行于增材方向,沿该方向生长的柱状晶有利于热量传导;对于竖直增材样品,热流方向垂直于增材方向,晶界及以网格状分布的裂纹阻碍热量传导,热量在表面积累并导致熔化。因此,增材方向对利用LPBF制备偏滤器mono-block部件有着重要的影响。     

异种钛合金协同送丝等离子增材制造试验

采用双丝协同等离子增材系统实现了TC4-TA2异种钛合金的增材成形,期望制备的增材构件具有良好的沉积形貌及优异的力学性能. 采用了体视显微镜、扫描电镜、EDS、XRD、拉伸及硬度等测试方法分析其组织及性能. 结果表明,增材构件中存在两种微观组织形态,即分布在沉积层交界处的α相集束组织和分布在沉积层中心的α + β相片层组织. 构件在竖直和水平方向上的抗拉强度分别为998和1 037 MPa,断后伸长率为9.2%和5.7%,断裂呈现为脆性解理断裂. 试验结果证明,等离子增材制造技术能够实现异种钛合金协同增材成形.     

粉末床激光熔融304L不锈钢的热处理工艺

采用激光粉末床熔融(LPBF)技术制备了 304L不锈钢,并对其分别进行了 600、800、1000 和1300℃保温2 h 的热处理,研究了热处理温度对其显微组织的影响.结果表明:样品的晶粒尺寸随温度升高呈长大趋势.当热处理温度为1300℃时,样品的晶粒明显粗化.由于LPBF 的快速凝固使304L 不锈钢中生成了 6...     

不锈钢增材制造件的激光超声表面波声速研究

利用激光超声技术对增材制造件进行无损检测具有重要的理论和应用价值.因此,针对不同激光功率下制备的316L不锈钢增材制造样品进行试验.利用激光超声在样品不同成型方向上测试,对表面波声速进行了表征.结果表明:不同激光功率下制备的316L不锈钢增材制造件的成型质量与表面波传播速度有着密切的关系,而且同一增材制造件在不同成型方...     

增材制造技术制备梯度材料研究现状

梯度材料是一种新型复合材料,其组成成分、微观组织和性能在空间上呈梯度变化.增材制造所具有的离散-堆积工艺为梯度材料的制备提供了新的路径,与传统的梯度材料制备工艺相比,增材制造方法可以实现一个或多个方向上梯度材料的制备,同时具有制备复杂结构件的能力.梯度材料增材制造工艺主要包括激光增材制造、电子束增材制造和电弧增材制造,其中激光增材制造是目前研究最多且应用最广的工艺.路径规划对梯度材料成分梯度、质量和成形精度有重要的影响,已成为梯度材料增材制造研究的一个重要方向.综述了梯度材料增材制造方法、梯度微观组织,以及制造过程中路径规划的国内外研究现状,可以为梯度材料增材制造研究提供参考.     

高熵非晶材料及其增材制造技术研究进展

高熵非晶合金具有独特的物理、化学和力学性能以及更好的热稳定性,因而其制备技术成为国内外重要的研究热点之一. 然而利用传统技术制备高熵非晶材料时会产生晶粒粗大及材料浪费等缺点,难以满足工艺生产需要. 而增材制造技术的精准制造和快速冷却等特点可以解决这一问题,制备出各项性能优越的高熵非晶合金. 简要介绍了高熵非晶材料的研究体系和常用制造方法,着重阐述了高熵非晶材料的断裂强度、耐腐蚀性和热稳定性的研究,对增材制造技术的工艺特征和优势,以及利用增材制造技术制备高熵非晶合金的科学难点作出了总结. 结果表明,利用增材制造技术有利于获得致密均匀的高熵非晶材料,但对于非晶相形成的解释仅限于高熵合金4大效应.最后阐述了近年来利用常用的两种增材制造手段制造高熵非晶合金的研究,并对增材制造技术制备高熵非晶材料的发展趋势提出了展望.     

焊接电流对等离子弧增材制造Inconel690合金性能的影响

采用等离子弧增材制造系统进行了Inconel690合金材料的薄壁件电弧增材制造。分析了不同焊接电流对Inconel 690电弧增材制造薄壁件成形、显微组织及力学性能的影响。结果表明:随着电流的增加,薄壁试样的宽度增加而层高降低,晶粒尺寸逐渐变大。增材制造试样的伸长率较Inconel690焊丝理论伸长率高而拉伸强度相对较低,不同方向的力学性能差异显著,水平方向拉伸强度约为500 MPa,优于竖直方向的450 MPa,水平方向伸长率为66%,低于竖直方向的75%,不同电流下拉伸试样的断裂机理不同。     

冷金属过渡(CMT)增材制造2219铝合金性能

采用CMT电源的四种模式CMT,CMT-P(脉冲),CMT-ADV(交流)和CMT-PADV(交流脉冲),以2219铝合金丝材为原材料进行增材制造工艺研究。深入分析了不同焊接模式对增材制造时气孔率、孔径分布、显微组织演变和力学性能的影响。为了测试基于CMT电弧增材2219铝合金制件的力学性能,成形了多组单道多层薄壁墙试样,测试结果表明,CMT-PADV模式下制件气孔面积分布率最小,几乎没有直径较大的气孔,制件的晶粒更加均匀细密,析出了细小的第二相Al2Cu颗粒。试样的X射线衍射和力学性能分析表明,CMT-PADV模式下的试样晶格参数最小,溶质Cu的含量最高,试样水平方向的抗拉强度与竖直方向的抗拉强度相差小于5 MPa,并且与其他3种模式相比力学性能有明显提高。     

光固化增材制造技术在熔模铸造中的应用

增材制造工艺可以实现复杂形状直接成形,其中光固化增材制造技术具有成形精度高的优势.利用光固化增材制造技术制备熔模,然后与熔模铸造工艺相结合,可以更好地发挥两种工艺的优势,缩短工艺周期.利用光固化增材制造技术制备熔模铸造用陶瓷型芯、型壳,可实现熔模铸造工艺的快速响应.文中简介了光固化增材制造技术的相关设备及成形原理,并分...     

坡莫合金增材制造及其磁性能研究现状分析

坡莫合金作为磁性能优良的软磁材料,具有十分广阔的应用前景.从坡莫合金的磁化机理出发,分别讨论了晶粒尺寸、元素含量以及内应力等因素对于磁性能的影响.分析了坡莫合金增材制造技术的研究现状,讨论了采用增材制造技术制备坡莫合金时的优势以及不足,并对增材制造制备坡莫合金的磁性能以及工艺改进措施进行了研究.针对目前坡莫合金增材制造急需解决的问题,总结出今后坡莫合金增材制造研究的重点,并分析与展望了坡莫合金增材制造的前景.     

电子束选区熔化成形纯钨的显微组织与晶体取向研究

采用增材制造技术中的电子束选区熔化成形方法制备了高致密度纯钨试件,分析了电子束选区熔化成形纯钨的传热过程和显微组织特点,重点研究了在几种热传导的共同作用下,纯钨的显微组织特点和晶体的取向分布。结果表明,电子束选区熔化纯钨的显微组织为以外延生长的方式形成的柱状晶。在样品内部,沿成形方向向下为最主要的热传导方向,温度梯度最大,柱状晶生长方向与热流方向相反,形成完全竖直生长的柱状晶;在样品外侧面,沿成形方向向下的热传导和向侧面粉床的热传导共同作用,使得热传导的方向与成形方向出现一定偏差,因此柱状晶组织与成形方向呈30-45_⁰夹角。同时,电子束选区熔化成形纯钨沿着成形方向,形成[111]和[100]方向的择优取向。     

Deformation-Induced Strengthening Mechanism in a Newly Designed L-40 Tool Steel Manufactured by Laser Powder Bed Fusion

The microstructural and mechanical properties of a newly designed tool steel (L-40), specifically designed to be employed in the laser powder bed fusion (LPBF) technique, were examined. Melt pool boundaries with submicron dendritic structures and about 14% retained austenite phase were evident after printing. The grain orientation after high cooling rate solidification is mostly < 110 >  _α∥ building direction (BD). Then, the heat treatment converted the microstructure into a conventional martensitic phase, reduced the retained austenite to about 1.5%, and increased < 111 >  _α∥BD texture. The heat-treated sample exhibits higher tensile strength (1720 ± 14 MPa) compared to the as-printed sample (1540 ± 26 MPa) along the building direction, mainly due to hardening caused by a lower volume fraction of retained austenite phase and precipitation of carbides. As a consequence of the strength-to-ductility trade-off, the heat-treated sample showed lower elongation (10% ± 2%) than that of the as-printed sample (18% ± 2%). It was observed that transformation-induced plasticity (TRIP) occurs in both the as-printed and heat-treated samples during tensile testing, which dynamically transforms the retained austenite into martensite, leading to improved ductility. The minimum driving force to initiate the displacive phase transformation is about 6000 J/mol, which was achieved during tensile testing. The strength and ductility of LPBF-produced L-40 were compared with the other LPBF-produced tool steels in literature; the data indicate that heat-treated L-40 has an excellent combination of strength and ductility complemented with high printability.     

The relationship between the microstructure and thermal diffusivity of plasma-sprayed tungsten coatings

Tungsten and tungsten alloy coatings are candidate materials for plasma facing components of divertor plates in future fusion reactors. In normal operation, the sprayed coatings will be submitted to intense heat fluxes and particle bombardment. This work investigated the relationship between the microstructure of plasma-sprayed tungsten coatings and their thermal diffusivity as determined by the laser flash method. The microstructural investigation was carried out on copper-infiltrated coatings. Such a preparation technique permitted the measurement of the total true contact area between the lamellae within the tungsten coatings. The spraying atmosphere was found to strongly influence the interfacial contact between lamellae and coating thermal diffusivity.     

Helium Bubble Growth in He+ Ions Implanted 304L Stainless Steel Processed by Laser Powder Bed Fusion During Post-Irradiation Annealing at 600 °C

The abundancy of defect sinks in the microstructure of laser powder bed fusion (LPBF) processed austenitic stainless steels was found to be beneficial for helium resistance. In the current study, the influence of the novel microstructure in LPBF processed 304L on the helium bubble growth behaviour was investigated using transmission electron microscopy in samples implanted with He⁺ ion and post-irradiation annealing treated at 600 °C for 1 h. Two variants of LPBF processed 304L samples were used, one in as-built condition and the other solution-annealed. The comparison between the two samples indicated that the helium bubble growth was inhibited and remained stable in the as-built sample but coarsened significantly in the solution-annealed sample. The sub-grain boundaries and oxide nano-inclusions acted as defect sinks to trap helium atoms and inhibited the growth of helium bubble in the as-built sample under the post-irradiation annealing conditions used.     

工艺参数对蠕墨铸铁激光熔凝淬火带裂纹率和形貌的影响

采用3 kW固体光纤激光器在蠕墨铸铁基体上进行了激光熔凝淬火试验,分析了淬火带的裂纹率、熔凝区形貌、显微硬度和组织.结果表明,当保护气体流量一定时,提高激光功率或降低扫描速率有利于降低激光熔凝淬火带的裂纹率;而激光功率一定时,不同的扫描速率对应的最佳保护气体流量大小不同.随着激光功率的增加,淬火带形貌会向基体扩展,扩展规律是先主要沿熔凝区宽度和深度方向扩展,然后沿其它方向扩展,到一定程度后,又沿着宽度和深度方向扩展,如此循环,熔凝区总面积不断增加,淬火带形貌也由扁平状逐步变化为帽子状.     

Microstructure and mechanical properties of molybdenum-titanium-zirconium-carbon alloy TZM processed via laser powder-bed fusion

Molybdenum, processed by laser powder-bed fusion (LPBF), is susceptible to hot cracking because segregated oxygen impurities significantly weaken grain boundaries through the formation of MoO₂. The present study reports on the LPBF processing of the most important molybdenum alloy TZM, whose alloying elements—titanium, zirconium, and carbon—lead to particle and solid solution strengthening. Results of investigations into the resulting microstructure and mechanical properties when processing TZM by LPBF are presented. The alloying elements suppress the segregation of oxygen to the grain boundaries so that crack-free samples with a density of 99.7 ± 0.3% may be produced. The microstructure shows grains that are columnar due to epitaxial grain growth and a weak 〈111〉 fiber texture parallel to the building direction. Mo₂C and ZrO₂ particles with a size of <50 nm are precipitated in the grain interior. Oxygen is not only bound by ZrO₂. Research has shown that the ternary molybdenum‑titanium carbide, which can be found in LPBF – TZM – as is the case with pressed/sintered TZM—can dissolve oxygen. While the bending strength is 591 ± 26 MPa for samples in which only pores with a diameter of <50 μm could be detected on the fracture surface, the bending strength drops to 267 ± 50 MPa for samples with defects of 400 μm. In both cases, the fracture mode is transgranular brittle.     

The effect of hot isostatic pressing on thermal conductivity of additively manufactured pure tungsten

The crack-healing behaviors and microstructure evolution of pure tungsten produced by laser powder bed fusion (LPBF) were studied and compared before and after post hot isostatic pressing (post-HIP) treatment. An average thermal conductivity of 133 W·m⁻¹·K⁻¹ at room temperature (RT) was obtained after HIP, which was 16% higher than that of as-built sample (115 W·m⁻¹·K⁻¹). Although the HIP process had little effect on density, it resulted in a large grain size of >300 μm accompanied by a decrease in dislocation density and crack healing, which led to a substantial improvement of thermal conductivity of pure tungsten. The positive correlation between relative density and thermal conductivity of as-built tungsten was reported.     

X-ray microbeam transmission/fluorescence method for non-destructive characterization of tungsten coated carbon materials

Tungsten erosion, its subsequent transport and redeposition are of great interest, because a full tungsten divertor is foreseen to be used during the deuterium–tritium operational phase of ITER. The erosion of tungsten and carbon marker layers was extensively studied in the outer divertor of ASDEX Upgrade (AUG), and work is currently in progress to completely replace the existing JET CFC tiles with tungsten-coated tiles within the JET ITER-like wall project. The need for fast and non-destructive method which allows the quantitative determination of the thickness of a tungsten coating on a carbon material on large areas led us to evaluate a combined absorption/fluorescence X-ray (XRTF) technique. The method can provide fast analysis, high spatial resolution and a material selective detection of deposited layers and inclusions. It was applied on W coated fine grain graphite (FGG) tiles from AUG's divertor. It is proved that the method is able to provide information about the uniformity of the tungsten coating on a graphite or CFC substrate whilst the technique can be used to determine the thickness of the tungsten and other marker materials coatings. It represents a unique instrument for the post-mortem analysis of the coatings.     

Observation of keyhole-mode laser melting in laser powder-bed fusion additive manufacturing

Laser powder-bed fusion additive manufacturing of metals employs high-power focused laser beams. Typically, the depth of the molten pool is controlled by conduction of heat in the underlying solid material. But, under certain conditions, the mechanism of melting can change from conduction to so-called “keyhole-mode” laser melting. In this mode, the depth of the molten pool is controlled by evaporation of the metal. Keyhole-mode laser melting results in melt pool depths that can be much deeper than observed in conduction mode. In addition, the collapse of the vapor cavity that is formed by the evaporation of the metal can result in a trail of voids in the wake of the laser beam. In this paper, the experimental observation of keyhole-mode laser melting in a laser powder-bed fusion additive manufacturing setting for 316L stainless steel is presented. The conditions required to transition from conduction controlled melting to keyhole-mode melting are identified.     

强流脉冲离子束作用下超细晶钨的抗瞬态热负荷性能评价(英文)

采用高能球磨和放电等离子体烧结技术制备纯钨、氧化物弥散强化钨和碳化物弥散强化钨。为了评价钨在瞬态热冲击下的性能,采用强流脉冲离子束,在热流密度高达160MW/(m2·s-1/2)的条件下对4种不同晶粒尺寸的钨进行抗热冲击试验。与商品钨相比,弥散强化钨在瞬态高热流作用下显现出不同的行为。氧化物弥散强化钨显现出较差的抗热冲击性能,这主要是由于低熔点的第二相Ti和Y2O3的引入,从而使得钨的表面发生熔融、起泡和开裂。而碳化物弥散强化钨合金则显现出较好的抗热冲击性能。