Preparation and selective laser sintering of nylon-12 coated metal powders and post processing

A dissolution–precipitation process was successfully developed to prepare nylon-12 coated carbon steel powders. The SEM and laser diffraction particle size analysis results show that the metal particles are well coated by nylon-12 resin; therefore, an effective method for preparing nylon-12 coated metal powders is provided. Green parts were formed from the coated powders by selective laser sintering (SLS) process, and when the nylon-12 content in the coated powder was 1.0 wt% and the applied laser energy density was 0.06 J/mm², the SLS green parts had sufficient strengths for features as small as 0.1 mm to be built and post-processed, and relatively high dimensional accuracy. The SLS green parts were post-processed by binder decomposition and epoxy resin infiltration, and the obtained epoxy-infiltrated parts have the dimensional errors in the X, Y and Z directions of −0.30, −0.32 and −0.25% respectively, and the bend strength, bend modulus, tensile strength and impact strength of 93.4 MPa, 14.7 GPa, 70.3 MPa and 12.4 MPa respectively.     

成形气氛中氧含量对激光沉积TA15钛合金组织及力学性能的影响

采用激光沉积制造技术制备了TA15钛合金厚壁件,通过光学显微镜(OM)和扫描电子显微镜(SEM)及拉伸试验对其显微组织、断口及力学性能进行分析,研究成形气氛中氧含量对激光沉积TA15钛合金组织及力学性能的影响。结果表明:随着气氛中氧含量增加,沉积态和退火态试样的显微组织均为典型网篮组织无明显变化。沉积态试样的室温抗拉强度提高而塑性下降,氧含量保持在5×10~(-5)以下能获得较好的综合力学性能。退火态试样的显微硬度低于沉积态且两者均随氧含量增加逐渐提高。室温拉伸断口的断裂机制随着氧含量增加由韧性断裂变为半解理半韧性断裂。     

SLS和FDMS制造超薄金刚石锯片对比研究

提出了一种使用增材技术制造金刚石工具的新思路,即使用熔融沉积成型烧结(FDMS)工艺来制造超薄金刚石锯片.详细介绍了选择性激光烧结(SLS)工艺和FDMS工艺在超薄金刚石锯片制造中的应用,并从主要设备仪器、工艺原理、工艺步骤以及成型材料、成本与生产应用等角度,对2种工艺进行比对.研究发现:在选择合适材料的条件下,2种工...     

Selective laser sintering of HIPS and investment casting technology

A selective laser sintering (SLS) pattern made of polystyrene (PS) is not suitable for investment casting of complex parts due to its poor mechanical properties. Therefore, high impact polystyrene (HIPS) should be used to make complex parts. The sintering characteristics of HIPS are as good as those of PS, and the mechanical properties are much higher than those of PS. In order to further improve the performance, post-processing is employed infiltrating with wax in this study. Through post-processing, the void fraction is decreased from 52.8% to 8.1%, correspondingly the tensile strength and impact strength are increased 64% and 97%, respectively.Because of high-melting temperatures and high-melting viscosities, it is very difficult to dewax completely for the SLS pattern. In order to avoid carbonization residues, the proper dewaxing technology is developed in this study: (1) the wax is removed first at low temperature, (2) the temperature is then increased to 200–250 °C to allow most of the HIPS to flow out and finally (3) baking is performed at a temperature higher than 500 °C. Furthermore, examples are performed to illustrate the settings of slag extraction risers, riser vents and associated running channels for producing complex parts.     

Laser pressure welding of Al alloy and low C steel

Abstract

This study was performed to obtain fundamental knowledge concerning the development of laser pressure welding technology for the joining of dissimilar metals. Laser pressure welding of Al alloy A6061 and low C steel SPCC sheets was carried out to investigate the effects of the roller pressure, laser beam scanning speed and irradiation position on the tensile shear and peel strength of welded joints. The interfaces of the joints were observed and analysed by SEM and EDX, and the formation phases on the peeled surfaces were identified with XRD. It was revealed that prevention and suppression of oxidation during welding was extremely important to the production of a sound joint with good mechanical properties. The highest tensile strength and the highest peel strength of joints were obtained at a laser power of 1·8 kW, laser scanning speed of 30 Hz, laser irradiation position at the centreline, roller pressure of more than 245 MPa and welding speed of 0·5 m min^?1 in an Ar atmosphere. The fracture occurred not in the welded zone but in the A6061 base alloy specimen.     

2024铝合金粉末选区激光熔化成形工艺研究

采用自主研发的金属增材制造设备对2024铝合金粉末进行了选区激光熔化成形,研究了不同工艺参数下该合金的显微组织及室温拉伸性能。结果表明,激光功率为260 W,扫描速度900 mm/s,扫描间隔0.12 mm时,2024铝合金显微组织细小,结构致密,抗拉强度为372 MPa,伸长率为6.1%,具有较高的室温力学性能。     

GTi70与TC4异种钛合金材料激光焊缝组织与性能分析

研究了GTi70与TC4异种钛合金材料激光焊接性能,通过接头常温、高温拉伸强度检测,焊缝组织XRD、OM、SEM检测分析,拉伸断口以及剪切断口形貌SEM分析,论证了异种材料的可焊性. 试验结果显示,异种材料接头常温拉伸强度高于GTi70母材,500,600和750 ℃高温拉伸强度高于TC4母材,焊缝拉伸断口、剪切断口均为韧性断裂,两种材料激光焊接性能良好. 脉冲激光焊缝组织更为细小,焊缝热影响区较窄,母材损伤小,焊缝强度与塑性优于连续激光焊缝.     

激光冲击TC17钛合金叶片的微观组织/应力演变及缺口振动疲劳性能

目的 提高航空发动机叶片的抗疲劳性能。方法 采用高功率密度短脉冲激光冲击某型发动机TC17钛合金整体叶盘叶片模拟件,并采用飞秒激光在进气边预制缺口。通过扫描电子显微镜和透射电子显微镜表征激光冲击前后的表层微观组织。通过X射线衍射和三坐标测量仪分别测量激光冲击强化过程中的残余应力演变和宏观塑性变形,并由一阶弯曲振动疲劳对激光冲击强化效果进行评价。结果 激光冲击在TC17钛合金叶片表层诱导产生了高密度位错组织,但由于冲击次数的控制,未产生明显的晶粒细化效应。激光冲击叶盆面后,叶盆面呈现压应力状态,残余应力为330.5 MPa,叶背面呈现拉应力状态,其值为55.5 MPa。进一步激光冲击叶背面后,叶背面的拉应力转变为压应力,其值达到了267.0 MPa,叶盆面残余压应力减小,由330.5 MPa变为261.9 MPa。激光冲击叶盆面后,进气边与叶尖交点偏离初始位置0.119 1、0.129 1 mm;冲击叶背面后,位移偏离初始位置减小,分别为0.071 08、0.099 mm。激光冲击强化后,缺口振动疲劳寿命显著提升,平均循环次数由56 696周次增加到199 515周次,出现了明显的裂纹闭合效应。结论 激光冲击强化在TC17钛合金表层引入了高密度位错组织和双面贯穿式残余压应力,并将叶片宏观塑性变形控制在0.1 mm以内,在疲劳性能上获得了显著的提升。     

扫描速度对激光沉积ER630丝材修复层力学性能与显微组织的影响

采用直接激光沉积法(DLD)在45钢基材上激光沉积ER630丝材,研究了扫描速度对ER630丝材修复层力学性能和组织的影响。结果表明,随着扫描速度的不断提高,ER630修复层中夹渣逐渐增多,且尺寸逐渐增大;扫描速度对ER630丝材修复层密度的影响可忽略不计。在30 mm/s扫描速度下,组织主要为板条柱状马氏体和少量圆胞状奥氏体,随着扫描速度的提高,板条柱状马氏体减少,圆胞状奥氏体逐渐增多。在30 mm/s扫描速度下,激光沉积丝材试样的力学性能与550 ℃时效处理的630不锈钢相当。随着扫描速度的提升,屈服强度与硬度均呈下降趋势,30 mm/s时屈服强度最大,为961.07 MPa,40 mm/s时硬度最大,为428.88 HV。拉伸断口形貌为韧窝断裂或准解理断裂,可见DLD工艺可实现优异的冶金结合;比较30 mm/s扫描速度下的强度,当沉积效率提高至2倍时,仍能得到较好的修复强度。     

Generation and characterization of T40/A5754 interfaces with lasers

Laser-induced reactive wetting and brazing of T40 titanium with A5754 aluminum alloy with 1.5 mm thickness was carried out in lap-joint configuration, with or without the use of Al5Si filler wire. A 2.4 mm diameter laser spot was positioned on the aluminum side to provoke spreading and wetting of the lower titanium sheet, with relatively low scanning speeds (0.1–0.6 m/min). Process conditions did not play a very significant role on mechanical strengths, which were shown to reach 250–300 N/mm on a large range of laser power and scanning speeds. In all cases considered, the fracture during tensile testing occurred next to the TiAl₃ interface, but in the aluminum fusion zone. The interfacial resistance was then evaluated with the LASAT bond strength tester, based upon the generation and propagation of laser-induced shock waves. A 0.68 GPa uniaxial bond strength was estimated for the T40/A5754 interface under dynamic loading conditions.     

Fabrication of parts and their evaluation using a dual laser in the solid freeform fabrication system

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process for SLS extended application to machinery and automobiles, whose production involves the use of various materials. For the fabrication of a large surface using the SFF system, the dual-laser approach has been introduced in this paper. Since the building room is divided into two regions, each scan path for the dual-laser system is generated based on a single-laser scan path. The scan paths for both lasers have to be synchronized, and the mechanical strength of the large surface must be considered to prevent fracture at the interface region. This paper addresses the generation of a single-laser scan path for special cases such as those involving unnecessary scan points, and the generation of a dual-laser scan path according to various divided regions so to enhance the mechanical strength of the large surface. Moreover, the tensile strength of the specimen manufactured through single-laser scan path system has been compared with the specimen manufacture through dual-laser scan path and the effect of overlapping region with respect to tensile strength is also highlighted.     

成形速度对7050铝合金锻件力学性能和断口形貌的影响

通过光学显微镜(OM)、扫描电镜(SEM)、室温拉伸试验等研究了成形速度对7050铝合金锻件显微组织、力学性能和断口形貌的影响。结果表明,随成形速度的增加,7050铝合金锻件的晶粒截面形貌逐渐由圆形过渡到细长状,且局部出现粗化。抗拉强度和屈服强度随成形速度增加呈先增加后减小的趋势,伸长率随成形速度的增加逐渐减小;当成形速度为2 mm/s时,抗拉强度、屈服强度分别达到608 MPa和560 MPa,伸长率为12.7%;当成形速度分别为2 mm/s和8 mm/s时,拉伸后试样的断裂形式以穿晶断裂为主,伴随着少量的第二相粗大颗粒和晶间断裂,且随着成形速度的减小,韧窝数量不断增加,韧窝深度也逐渐变深。实际热模锻生产成形速度宜选择2~8 mm/s。     

铝合金激光熔化沉积应力场及力学性能分析

采用激光熔化沉积工艺对6 mm厚的ZL114A铝板中的通槽进行了修复试验. 试验中采用AlSi10Mg粉末作为沉积过程的填充材料. 为了选择合适的激光扫描方法,通过数值模拟的方式,探究了不同扫描路径下产生的残余应力情况. 模拟结果显示,相比于自一侧向另一侧平行扫描,自下向上逐层扫描方式更有助于减小残余应力,残余应力分布也更均匀. 采用自下向上的逐层扫描方式实现了铝板通槽的激光熔化沉积的工艺试验,并探索了缺陷及热输入对试件力学性能的影响. 结果表明,通过工艺试验得到的沉积试件,最优性能的试件抗拉强度为268 MPa,达到母材的89%. 试件断裂并未沿着沉积区与母材的界面处断裂,而是在沉积区内部层与层界面间的搭接区域断裂.     

Joint performance of CO2 laser beam welding 5083,H321 aluminum alloy

Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam autogenoas welding and wire feed welding are conducted on 4 mm thick 5083- H321 aluminum alloy sheets at different welding variables. The mechanical properties and microstructure characteristics of the welds are evaluated through tensile tests, micro-hardness tests, optical microscopy and scanning electron microscopy （SEM）. Experimental results indicate that both the tensile strength and hardness of laser beam welds are affected by the constitution of filler material, except the yield strength. The soften region of laser beam welds is not in the heat-affected zone （ HAZ ）. The tensile fracture of laser beam welded specimens takes place in the weld zone and close to the weld boundary because of different filler materials. Some pores are found on the fracture face, including hydrogen porosities and blow holes, but these pores have no influence on the tensile strength of laser beam welds. Tensile strength values of laser beam welds with filler wire are up to 345.57 MPa, 93% of base material values, and yield strengths of laser beam welds are equivalent to those of base metal （264. 50 MPa）.     

基于SLS技术的金属零件快速制造研究

介绍利用ＳＬＳ技术制作精密铸造用熔模,通过熔模铸造快速获得金属零件的工艺方法。并对零件作了相应性的性能分析。绍     

聚碳酸酯激光透射焊接力学性能分析

为研究聚碳酸酯激光透射焊接力学性能,采用10 W半导体端泵浦全固态激光器进行了透明与不透明聚碳酸酯的焊接.采用光学金相显微镜(OM)、场发射扫描电子显微镜(SEM)、显微硬度仪和电子万能实验拉力机分析测试了接头的显微形貌、断口形貌、显微硬度分布及拉伸抗剪强度.结果表明,随着激光面能量的增加,接头的连接形式由焊接接头演化为类似粘接接头;分层和气孔是影响接头力学性能的主要原因,通过控制面能量,可获得力学性能良好的焊接试样,在面能量为0.23 J/mm²时,拉伸抗剪强度达到44 MPa,约为母材强度的68%,且接头的显微硬度与母材相当;接头的断裂机制为混合断裂机制.     

Effect of Hydrogen on Mechanical Properties of 23Co14Ni12Cr3Mo Ultrahigh Strength Steel

In order to evaluate the effect of hydrogen on mechanical properties of 23Co14Ni12Cr3Mo ultrahigh strength steel, the specimens were electrochemically hydrogen charged for different times. The tensile property, fatigue fracture behavior, fatigue crack growth (FCG) behavior, and threshold stress intensity (ΔK _th) of the samples were studied. The fracture morphology was characterized by scanning electron microscopy. It was shown that tensile strength decreases from 2300 to 2000 MPa, critical fatigue stress from 577 to 482 MPa, and ΔK _th from 27.4 to 14.3 MPam^0.5 with the increasing hydrogen contents from 0.0001 to 0.0008 wt.%. Hydrogen enhances the FCG rate from 2.4 × 10^?3 to 3.6 × 10^?3 mm/cycle at ΔK = 80 MPam^0.5 in the hydrogen-charging range. Microscopic observation showed that the tensile fracture is a combination of overload microvoids and some intergranular regions for 0 h, and isolated areas of transgranular (TG) fracture are observed with brittle cleavage for 24-72 h. The fatigue fracture is ductile for the uncharged specimens, while the hydrogen-charged specimens show mainly brittle TG fracture. These results suggest that hydrogen degrades the fracture behavior of 23Co14Ni12Cr3Mo ultrahigh strength steel.     

退火处理及沉积方向对激光沉积TA15钛合金性能和组织的影响

以TA15钛合金粉末为原料,利用激光沉积制造方法制备TA15钛合金拉伸试样厚壁件。通过光学显微镜(OM)、扫描电子显微镜(SEM)和X射线衍射(XRD)等方法研究退火温度及沉积方向对TA15钛合金组织、拉伸性能的影响,以及α相变形机制。结果表明：随着退火温度升高,显微组织中α相长宽比呈上升趋势;激光沉积成形TA15钛合金厚壁件在沉积和垂直沉积方向上的力学性能存在差异,沉积方向上的抗拉强度明显均低于垂直沉积方向上的抗拉强度;柱状晶晶界对α片层的受力变形有一定的阻碍作用;α片层通过挤压变形和滑移变形两种机制发生变形或断裂;两种方向上拉伸断裂方式不同,沿沉积方向上断裂为韧性断裂,沿垂直沉积方向上断裂为半解理半韧性断裂。     

基于光纤激光的LY12铝合金焊接试验分析

在飞机制造领域,铝合金主要用于制造飞机蒙皮、梁、桁条和框架等结构.采用多模光纤激光器进行了1.4 mm厚LY12铝合金的激光焊接试验,研究了焊接工艺参数对铝合金焊缝形貌的影响规律,并对焊接接头的显微硬度及断口形貌进行了分析.结果表明,大功率高速度连续激光焊缝的成形具有不稳定性,当功率为2 200 W,焊接速度为55 mm/s,保护气体流量为10 L/min时,可以获得成形良好且无宏观缺陷的焊接接头.接头的平均抗拉强度约为388 MPa,达到母材抗拉强度的63.98%,断裂类型为韧脆混合型断裂.     

1Cr18Ni9Ti激光选区熔化成形工艺参数对致密度的影响

采用正交试验,结合典型缺陷形成原因和微观组织,研究了激光选区熔化成形工艺参数(激光功率、扫描速度和扫描间距)对1Cr18Ni9Ti不锈钢致密度的影响,分析了各工艺参数对致密度的影响规律。结果表明,粉末熔化的能量输入密度主要取决于激光功率和扫描速度;在激光功率325~340 W、扫描速度1 000~1 200 mm/s、扫描间距0.12 mm的工艺参数下,SLM技术可制备致密度高于99.9%的1Cr18Ni9Ti不锈钢零件。采用优化后的SLM工艺参数成形1Cr18Ni9Ti不锈钢试棒的力学性能优于QJ501A-98标准,抗拉强度Rm≥709 MPa,屈服强度Rp0.2≥547 MPa,断后伸长率A≥41%。