In Situ Elimination of Pores During Laser Powder Bed Fusion of Ti–6.5Al–3.5Mo–l.5Zr–0.3Si Titanium Alloy

The printing quality of components manufactured using laser powder bed fusion(LPBF) generally depends on the presence of various defects such as massive porosity. Thus, the efficient elimination of pores is an important factor in the production of a sound LPBF product. In this study, the efficacy of two in situ laser remelting approaches to eliminating pores during the LPBF of a titanium alloy Ti–6.5 Al–3.5 Mo–l.5 Zr–0.3 Si(TC11) was assessed both experimentally and computationally. These two re...     

灰铸铁件激光熔覆NiCuFeBSi合金的气孔行为

通过对比分析45钢与HT250两种基体成形熔覆层内气孔形态,研究了熔覆层内气孔气体类型、分布规律以及影响因素.结果表明,熔覆层内气孔气体为CO,由石墨和氧或氧化物反应生成,气孔形状不规则、具有棱角状特征.气孔上浮形式并非垂直上浮,而是弥散式上浮.熔池内部强对流是影响气孔分布的内在因素.气孔运动幅度取决于熔池对流加速度,熔池温度越高,熔池表面张力梯度也越大,熔池对流的加速度越大.激光熔覆工艺是影响气孔分布的外在因素,适当降低激光功率和扫描速度、提高灰铸铁预热温度可有效消除熔覆层气孔缺陷,降低孔隙率.     

稀土 CeO2 含量对 Al 合金激光熔覆层组织形貌的影响

目的研究稀土氧化物CeO2的含量对铝合金表面Ni基激光熔覆层组织形貌的影响,降低Ni60熔覆层的气孔、开裂等组织缺陷。方法采用激光熔覆技术,在6063Al表面制备CeO2含量不同的Ni60熔覆层,对熔覆层的表面形貌、截面形貌及微观组织进行对比分析。结果 CeO2质量分数低于3%时,难以获得表面良好的熔覆层,0%~2%时易出现裂纹;CeO2质量分数在4%~5%的熔覆层形貌最好,无明显气孔和裂纹,尤其4%时具有相对较好的截面形貌;CeO2质量分数在5%~10%的熔覆层主要缺陷为气孔,且气孔、脱落等缺陷较少。结论添加CeO2可以改善铝合金表面Ni60熔覆层的组织形貌,尤其4%的CeO2可以改善Ni60熔覆层的组织结构,促进熔覆层的晶粒细化和组织分布均匀,是较佳的添加量。     

直流横向磁场作用下钴基合金的组织及性能

为了提高堆焊层的性能,研究直流横向磁场对等离子弧堆焊层的组织和性能的影响.在低碳钢表面进行钴基合金粉末等离子弧堆焊时施加直流横向磁场,焊后对堆焊层进行硬度、磨损、显微组织以及X射线衍射分析,并系统地分析直流横向磁场对等离子堆焊层硬度和耐磨性的影响规律.结果表明,施加磁场时堆焊层性能比无磁场时堆焊层性能好.当堆焊电流为1...     

激光熔覆层宽度对汽轮机转子表面综合跳动特性的影响

为解决大型汽轮机转子轴轴颈磨损的修复问题,基于同轴送粉半导体激光熔覆再制造系统,采用激光熔覆再制造方法,以汽轮机转子轴材料为基体,利用激光熔覆再制造专用粉末作为实验材料,针对不同激光熔覆层宽度对汽轮机转子综合跳动的影响进行实验研究与机理模拟验证。结果表明,综合跳动特性与探头直径和激光熔覆层宽度相关,激光熔覆层宽度决定了汽轮机转子表面磁力线、电涡流密度与磁通量密度分布。当激光再制造层宽度小于8mm时,由于磁力线与表面电涡流密度受基体的干扰,磁通量密度在激光熔覆层的边缘出现突变,实际综合跳动的测量值为基体与激光熔覆层综合作用的结果,造成测量结果偏大。根据数值模拟计算被测金属体表面磁通量密度分布结果,激光熔覆层宽度的临界值为9.82mm。     

激光熔覆在AlN陶瓷表面制备铜基金属覆层缺陷分析及控制

通过脉冲式YAG激光器在AlN陶瓷表面制备铜基金属覆层,分析熔覆层的缺陷,并研究如何能控制熔覆层缺陷的发生,熔覆试样的缺陷主要表现为陶瓷基板炸裂、熔覆层成形不完整、熔覆层微观裂纹和气孔.结果表明,通过调节激光熔覆的热输入可以保证陶瓷基板的完整性并且熔覆层成形良好;通过焊前预热和焊后缓冷的工艺可以降低熔覆层微观裂纹和气孔的形成几率.通过优化激光熔覆工艺参数和工艺方法,可以形成良好的熔覆层,并且AlN陶瓷基板和铜基金属覆层之间形成过渡层,形成良好的冶金结合.     

交流电磁场作用下液体金属液面稳定性的研究

为了控制电磁铸造过程中液体金属液面的稳定性 ,借助于激光测量传感器研究低熔点伍德合金在 2 5 0 0Hz交变电磁场作用下液面波动情况及液面形状 ;通过实验发现 ,电磁场作用下沿液面半径方向各点的波动规律相似 ,当金属液面与感应线圈上平面平齐 ,并且施加适当功率的电磁场时 ,能获得更好的液面形状 ,并使液面波动更平缓。     

A three-dimensional finite element analysis of the temperature field during laser melting of metal powders in additive layer manufacturing

Simulating the transient temperature field in additive layer manufacturing (ALM) processes has presented a challenge to many researchers in the field. The transient temperature history is vital for determining the thermal stress distribution and residual stress states in ALM-processed parts that utilise a moving laser heat source. The modelling of the problem involving multiple layers is equally of great importance because the thermal interactions of successive layers affect the temperature gradients, which govern the heat transfer and thermal stress development mechanisms. This paper uses an innovative simulation technique known as element birth and death, in modelling the three-dimensional temperature field in multiple layers in a powder bed. The results indicate that the heated regions undergo rapid thermal cycles that could be associated with commensurate thermal stress cycles. Deposition of successive layers and subsequent laser scanning produces temperature spikes in previous layers. The resultant effect is a steady temperature build-up in the lower layers as the number of layers increases.     

1420铝锂合金激光焊接气孔抑制技术

分别采用气体和固体两种类型、三台激光器对1420铝锂合金消除气孔的焊接工艺进行了试验研究.结果表明,1420铝合金表面氧化膜对产生气孔有很大影响,化学清理可以获得气孔较少的焊缝.保护气体种类、气体流量、焊接速度对1420铝锂合金气孔都有影响.适宜的双激光束焊接工艺可以获得成形美观且无气孔的优质1420铝锂合金焊缝,是1420铝锂合金焊接较为理想的焊接工艺.     

Production of glassy metallic layers by laser surface treatment

This work aims to investigate if glassy surface layers can be obtained when glass forming alloys are submitted to laser surface treatment techniques. Three types of alloys, with different glass forming abilities, were investigated: Zr-, Mg- and Al-based alloys. X-ray diffraction analysis shows that vitreous phases can be formed in the Zr- and Mg-based alloys, when the treatments are made using laser scanning speeds larger than 2 m/s.     

激光能量输入对直接激光沉积莫来石陶瓷组织性能的影响

研究了激光能量密度对直接激光沉积熔体自生莫来石陶瓷孔隙/密度、微观组织和力学性能的影响.结果表明,较低激光能量密度(15 J/mm2)所制备的陶瓷样件边缘分布有尺寸较大的气孔,使得样件整体孔隙率较高,且表面粘粉严重,这与成形扫描速度大和硅酸盐熔体粘度高有关.而较高激光能量密度(90 J/mm2)虽然可以获得表面光滑、莫...     

Laser sintering of Fe-Ni nanocomposites

The laser sintering of powders is one of new technologies of producing surface coatings from nanostructural materials. In this work, we used methods of transmission and scanning electron microscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy to study the structure of layers synthesized using laser sintering of an ultradispersed powder consisting of Fe-Ni nanocomposites. For explaining the specific characteristics of the structure that was formed as a result of high-energy laser action, we carried out a mathematical simulation of the processes of heat transfer with the application of the model of a two-phase (mushy) zone. The coatings synthesized possess a multilevel system of connected pores and can be used in catalytic reactions and hydrogen power engineering.     

间断高频磁场作用下连铸铸型内金属液的运动和铸坯的表面质量 Ⅰ.液体金属弯月面运动对铸坯表面质量的影响

为了消除连铸钢坯的表面缺陷，提出了在铸型外部加间断高频交流磁场的铸造方法.用液体Ga作为钢液的模拟物，借助于激光测位仪研究了外加间断磁场对铸型内液体金属运动的影响.通过Sn的连续铸造模拟实验，探讨了弯月面波动和铸坯的表面质量之间的关系.结果表明，外加间断磁场能控制铸型内液体金属的运动，改善铸坯的表面质量控制弯月面的运动，可使铸坯表面形成和间断频率fi相应的条纹.当fi接近于实验系统的固有频率时，电磁场抑制液面运动的效果最好，铸坯的表面质量最佳.     

MOTION OF MELT IN CONTINUOUSLY CASTING MOLD AND SURFACE QUALITY OF INGOT UNDER INTERMITTENT HIGH FREQUENCY MAGNETIC FIELD Ⅰ. Effect of the Motion of Melten Meniscus on Surface Quality of Ingot

为了消除连铸钢坯的表面缺陷，提出了在铸型外部加间断高频交流磁场的铸造方法，用液体Ｇａ作为钢液的模拟物，借助于激光测位仪研究了外加间断磁场对铸型内液体金属运动的影响。通过Ｓｎ的连续铸造模拟实验，探讨了月弯月面波动和铸坯的表面质量之间的关系。     

铝合金表面激光熔覆CeO_2+Ni60A熔覆层的组织及耐磨性

利用激光熔覆技术,在6063铝合金表面制备了添加不同CeO2含量的Ni60A合金熔覆层,分析了CeO2+Ni60A熔覆层的显微组织及硬度,筛选了最佳稀土添加量,并研究了其耐磨性能。结果表明:Ni60A熔覆层中稀土CeO2含量低于2%(质量分数)时易出现气孔,高于2%时易开裂;添加CeO2的含量为2%时,熔覆层的组织缺陷较少,表面硬度较高,微观组织均匀且晶粒细小;熔覆层中稀土的含量不宜超过4%,过量的CeO2对硬度的提高作用不大,而CeO2的含量在0%~2%的范围内随着其含量的增加,硬度升高明显;在相同磨粒磨损条件下,2% CeO2+Ni60A熔覆层的耐磨性是铝合金基体的7.1倍,是Ni60A熔覆层的1.6倍;激光熔覆Ni60A可以显著降低表面摩擦系数,而添加Ce能提高熔覆层的摩擦系数稳定性,从而改善耐磨性能。     

添加TiC对激光粒子沉积WC-Co-Cr 和WC-Ni涂层性能的影响

研究了激光熔覆TiC增强双相不锈钢上WC涂层的机理。分析了激光工艺参数对复合涂层的影响。采用SEM和EDX手段分析了喂料粉末以及复合涂层的形态和微观组织。采用维式硬度计测试了复合涂层的表面硬度,采用动电位曲线法研究了涂层在3.5%NaCl溶液中的耐腐蚀行为。由于激光熔覆处理,在不锈钢表面形成了与基材结合良好的硬陶瓷粒子。添加TiC到WC中得到的复合涂层没有裂缝、孔洞和金属间化合物,没有出现这些对涂层性能不利的缺陷。结果表明,涂层具有较高的显微硬度,且大部分涂层的腐蚀电位变得更负。     

中频电磁场作用下金属液面稳定性的研究

为了控制电磁铸造过程中金属液面的稳定性 ,借助于激光测量传感器研究了低熔点伍德合金在 2 5 0 0Hz交变电磁场作用下液面波动情况及液面形状。试验发现 ,在电磁场作用下沿金属液面半径方向各点的波动规律相似 ,当金属液面与感应线圈上平面平齐 ,并且施加适当功率的电磁场时 ,能获得更好的液面形状 ,并使液面波动更平缓。     

Magnetic anisotropy of Co/Cu/Co nanocrystalline films upon magnetic annealing

The magnetic anisotropy of Co/Cu/Co films with the thickness of the copper spacer corresponding to the antiferromagnetic and ferromagnetic indirect exchange coupling between Co layers has been studied. The films deposited on naturally oxidized (111) Si single crystals were produced by magnetron sputtering. The films were annealed at 240°C. Such an annealing virtually neither changes the grain size nor leads to the mixing of layers; i.e., no disturbance of the coupling type between the cobalt layers takes place. Changes in the surface and induced magnetic anisotropy and in the effective energy of indirect exchange coupling have been studied upon annealing in the presence and absence of a magnetic field. It has been found that the shape of surface inhomogeneities in the films changes upon annealing in the magnetic field applied along the film plane, which substantially affects, the surface anisotropy. In the films characterized by antiferromagnetic coupling, the easy axis of magnetization is induced only in the magnetic fields exceeding the saturation field. The induced-anisotropy constant estimated theoretically agrees well with those determined experimentally.     

铝合金激光表面处理

综述了铝合金激光表而处理的工艺方法和特点,包括激光重熔、激光合金化、激光熔覆等;阐述了铝合金激光表面强化层的组织特征、硬度变化及其耐磨、耐蚀性能;总结了国内外在该研究领域的最新进展和激光处理过程中存在的问题,并阐明了改进方法.     

Magnetic properties of plasma-electrolytic iron-containing oxide coatings on aluminum alloy

Applications of the plasma-electrolytic oxidation technique for the formation of magnetically active oxide coatings on aluminum and titanium are reviewed. Specimens of aluminum-, iron-, and tungsten-containing oxide layers on aluminum substrates with ferro- and ferrimagnetic properties are experimentally produced and studied, as well as specimens that can be remagnetized at certain external magnetic field intensities and specimens the magnetization of which is opposite to the external field. The existence of nano- and microscale crystallites, in which aluminum and metals from the electrolyte are accumulated, are found in pores of the coatings. The crystallites supposedly determine the magnetic properties of the specimens. A correlation between the Fe/Σ(W, Al) atomic ratio in crystallites and the magnetic properties of the systems studied is discovered.