气–液反应激光原位增材制造TiN增强钛基复合材料组织结构及力学性能研究

本文采用选区激光熔化(SLM)工艺制备了Ti6Al4V合金,并系统研究了激光能量密度(LED)对其致密度、显微硬度、压缩强度和塑性的影响。获得了SLM制备Ti6Al4V合金的最佳LED工艺窗口为84.8–163.6 J/mm_³。在最佳LED窗口内,在不同N₂浓度(3 vol.%、10 vol.%、30 vol.%)工作气氛中,以气–液反应方式SLM制备了TiN为增强相的Ti6Al4V基复合材料。该新工艺制备复合材料的原理为：钛合金高温熔池附近的N₂裂解为N原子/离子,N与熔融状态的Ti原位反应生成均匀分散的TiN增强相,并与熔化–凝固过程中的Ti合金基体复合,最终以SLM逐层成形的方式制备出TiN增强钛基复合材料。本文探究了N₂浓度对钛基复合材料组织结构和力学性能的影响规律。其中,3 vol.%的N₂工作气氛中SLM成形的复合材料的强度和塑性同时得到提升,阐述了其强韧化机理。     

激光增材制造铝合金及其复合材料的研究进展

增材制造中的选区激光熔化技术在未来航天航空、车辆制造、医学生物等方面都具有广阔的应用及发展前景。文中从选区激光熔化铝合金及其复合材料的相对密度、显微组织、力学性能三方面阐述了其研究进展,归纳总结了SLM制备不同铝合金及其复合材料的抗拉强度和伸长率、相对密度。通过文献得出,添加Sc, Zr等元素及纳米增强颗粒的复合铝合金材料,可获得更好的力学性能,并展望了未来研究的趋势。     

激光增材制造钛合金微观组织和力学性能研究进展

激光选区熔化(SLM)技术与激光熔化沉积(LMD)技术在航空航天、生物医疗等领域的应用具有巨大潜力,但由于成形的Ti6Al4V合金构件存在较差的表面质量、较大的残余应力以及内部孔洞等问题,影响了构件的力学性能,从而制约了其大规模的应用。针对这一现状,首先概述了激光选区熔化技术与激光熔化沉积技术的制造原理,比较了2种增材制造技术的成形参数及其特点,并分析了2种不同成形技术的自身优势以及适用场合。其次,从2种增材制造技术成形钛合金的工艺参数入手,综述了激光功率、扫描速度、激光扫描间距、铺粉厚度、粉床温度等参数对SLM工艺成形钛合金的影响,以及激光功率、扫描速度、送粉速率等参数对LMD工艺成形钛合金的影响。发现成形工艺参数直接影响了粉末熔化程度、熔合质量和成形显微结构,从而影响成形件的组织与力学性能。此外,综述了不同的扫描策略对两种增材制造技术成形钛合金的表面质量与力学性能的影响,可以发现在不同扫描策略下同一试样表面的不同区域表面质量、残余应力以及抗拉强度存在较大差异,同一扫描策略下试样的不同表面之间也存在各向异性。最后,探讨了不同热处理工艺对钛合金微观组织和力学性能的影响,通过合适的热处理能够降低成形构件应力,并调控组织相变和性能。     

热处理对增材制造生物纯钛力学性能的影响

选区激光熔化(selective laser melting,SLM)能直接根据CAD模型制备形状复杂的个性化医用植入物.本工作旨在研究SLM和后续热处理后生物纯钛(TAl)的显微组织和力学性能.结果 表明,SLM打印后的TAl合金为针片状a'马氏体组织,且沿建造方向保留初始β柱状晶形貌;热处理后发生再结晶组织转变,形...     

铝基复合材料激光粉末床熔化增材制造研究现状

采用激光粉末床熔化技术制备铝基复合材料在航空航天、军工、交通运输等领域显示出了深远的研究前景,向铝合金引入纳米增强体的种类、引入方式以及含量对铝合金可打印性、组织、力学性能产生的影响是学者们的关注热点。本文主要总结分析了TiB₂、石墨烯、TiC纳米增强体对激光粉末床熔化技术制备铝合金的晶粒形态、晶粒尺寸、相对密度、可打印性和力学性能的影响,进行了不同纳米增强体对打印态铝合金力学性能影响的对比,分析得出以TiB₂为代表的纳米增强体能够提升打印态铝合金的强度、塑性,使其具有良好的综合力学性能,最后提出了该研究领域在未来的进一步发展趋势。     

选区激光熔化TC4试样的力学性能及微观组织分析

采用选区激光熔化技术成形TC4试样,研究了线扫描功率、曝光时间和退火处理对TC4成形试样微观组织和性能的影响。结果表明,试样的缺陷随线扫描功率的升高而减少。线扫描功率在400 W,曝光时间为30μs,经过退火处理后,试样抗拉强度达到1153MPa,高出普通TC4钛合金锻件近300MPa,同时,试样的拉伸断面总体呈脆性断裂。     

SiCf/TC17复合材料断裂机理

利用扫描电镜和光学显微镜研究了C涂层SiC_f/TC17复合材料室温拉伸、高温拉伸(400℃)和高温疲劳(400℃)的断裂机理。结果表明,室温拉伸和高温拉伸断裂机理相似,均为界面脱粘和纤维拔出。室温拉伸断口由高低起伏的大断面组成。高温拉伸断口由众多的小断面组成,纤维拔出高度和界面脱粘程度比室温更剧烈。复合材料、包套和复合材料与包套结合区的组织分别为双态组织、网篮组织和粗大的双态组织,其疲劳性能依次递减,因此高温疲劳断裂中主裂纹萌生于包套与复合材料结合区,呈脆性断裂。主裂纹首先向包套扩展,随后向复合材料扩展,引起界面脱粘和纤维拔出。     

增材制造TiAl合金的研究进展

轻质耐热的TiAl合金是航空航天和民用工业等领域最具潜力的高温结构材料之一。然而,由于其低的延展性和断裂韧性,制造TiAl零部件具有挑战性。目前,增材制造工艺被认为是制造TiAl零件具有前途的技术之一。本文在介绍增材制造技术原理和特点的基础上,综述了激光金属沉积(LMD)、选区激光熔化(SLM)和电子束熔化(EBM)制备TiAl合金的工艺-组织-性能关系,并对该技术未来的发展趋势进行了展望。     

选区激光熔化增材制造In718合金的激光焊接性能

采用光学显微镜、扫描电镜、显微硬度计和力学性能试验等研究了选区激光熔化(SLM)In718合金的激光焊接接头的组织和性能。结果表明:SLM In718合金的激光焊接接头的宏观质量较好,没有发现冶金缺陷的存在。未热处理时,In718合金的SLM构件的组织主要由奥氏体柱状晶及奥氏体柱状晶之间的共晶组织构成,柱状晶的平均尺寸约为5μm×2μm;激光焊接SLM构件的焊缝组织主要由奥氏体柱状晶及奥氏体柱状晶之间的共晶组织构成,柱状晶的平均尺寸约为25μm×5μm;焊缝区显微硬度均值约282 HV,是SLM母材均值335 HV的84.2%;不同厚度焊接试样的抗拉强度为970~983 MPa(均达到SLM母材95%以上),伸长率为20.2%~22.6%(为SLM母材65%以上);固溶+时效处理后,焊接试样抗拉强度均值为1412 MPa(约为SLM母材的98.9%),伸长率均值为13.5%(约为SLM母材的93.7%),与未热处理相比,SLM母材和焊缝显微硬度值分别提高了55.2%和77.3%。     

选区激光熔化TC4合金高温力学性能及腐蚀行为研究

采用选区激光熔化技术(selectivelasermelting,SLM)制备了TC4合金,利用光学显微镜、扫描电子显微镜、X射线衍射仪、万能材料试验机以及电化学测试等技术研究其热处理后的组织、高温力学性能及腐蚀行为,并与铸造TC4合金做了对比。结果表明,SLM与铸造TC4合金物相组成相同,SLM TC4合金组织主要为片层状(α+β)相,平均晶粒面积约为2μm²,而铸造TC4合金表现出典型的魏氏组织,平均晶粒面积约为276μm²。相对于铸造TC4合金,SLM TC4合金的室温及高温力学性能均较优异,且表面形成的钝化膜保护性能更好,腐蚀速率更低。     

WCp/Fe metal matrix composites produced by laser melt injection

Laser melt injection (LMI) was used to produce WC particles (WC_p) reinforced metal matrix composites (MMCs) layer on the mild steel. During the LMI process, different parameters were applied, and the processing window of this technique was obtained. The MMCs layers were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The SEM result reveals that none macro-defects except few pores can be found in the MMCs layer, and the WC_p distribute uniformly in the layer. In addition, some new phases can be found in the MMCs layer, where Fe₃W₃C is the predominant phase. At the same time, the amount of dissolved WC_p plays a key role in the microstructure of the MMCs layer. The WC particle dissolved into the melt pool leads to the appearance of reaction products in the matrix, such as various primary Fe₃W₃C dendrites, and the liquid WC remained on the solid WC particle results in the formation of a thicker reaction layer.     

Microstructures and mechanical properties in laser beam welds of titanium matrix composites

Laser beam welding (LBW) was used to 2 mm thick titanium matrix composites (TMCs) sheets and microstructure, hardness and tensile properties of butt joints were studied. Welded joints without defects were obtained indicating that LBW is a suitable processing method for TMCs. The results reveal that the fusion zone completely consists of α′ martensite causing an increase of more 27% in hardness compared with that of base metal. The heat affected zone consists of a mixture of α′ martensite and primary α phases. Large gradients of microstructures and hardness are found over the narrow heat affected zone dependent on the β-transus temperature during weld cooling. TiB_w with smaller sizes redistribute at grain boundaries in the weld. The joints show excellent strength and they can reach the full strength compared with the base metal with sound welding parameters, which is ascribed to the presence of α′ martensite and refinement of TiB_w in the weld.     

Microstructure of reaction zone in WCp/duplex stainless steels matrix composites processing by laser melt injection

The laser melt injection (LMI) process has been used to create a metal matrix composite consisting of 80μm sized multi-grain WC particles embedded in three cast duplex stainless steels. The microstruture was investigated by scanning electron microscopy with integrated EDS and electron back-scatter diffraction/orientation imaging microscopy. In particular the search of the processing parameters, e.g. laser power density, laser beam scanning speed and powder flow rate, to obtain crack free and WC_p containing surface layer, has been examined. Before the injection of ceramic particles into remelted surface layer, the influence of processing parameters of laser surface remelting on the microstructure and properties of selected duplex steels was also investigated. Although after simple laser surface remelting the austenitic phase is almost not present inside remelted layer, in the case of LMI the austenite was observed in vicinity of WC particles, due to increase of carbon content acting as austenite stabilizer. The diffusion of carbon in the reaction zone results also in a formation of W₂C phase in the neighborhood of WC particles with a strong orientation relationship between them. The maximum volume fraction of the particles achieved in the metal matrix composite layer was about 10% and a substantial increase in hardness was observed, i.e. 575 HV0.2 for the matrix with embedded particles in comparison to 290 HV0.2 for untreated cast duplex stainless steels.     

WCp/Ti-6Al-4V graded metal matrix composites layer produced by laser melt injection

The laser melt injection (LMI) process was explored to produce WC particles (WC_p) reinforced Ti-6Al-4V metal matrix composites (MMC). In particular monocrystalline WC powder was used as injection particles to avoid the intercrystalline cracking often observed in granular or cast WC_p reinforced MMC. WC_p were injected into the extended part of the melt pool just behind the laser beam. The process allowed for the minimization of the WC_p dissolution caused by the direct irradiation of the laser beam, and the decomposition reaction between WC_p and Ti melt. Different parameters were applied, and a processing window of LMI was obtained. WC_p exhibit a graded distribution along the depth direction of the MMC layer. New phases such as TiC and W₂C are observed in the MMC layer, in which TiC is the predominant phase. TiC grains present a continuous decrease in both amount and size with the distance from the surface to the bottom of the MMC layer. Two types of reaction layers around WC_p can be distinguished, namely an irregular reaction layer and a cellular reaction layer. The growth and final morphology of reaction layers are most likely being dominated by the composition of the neighbouring melt pool. A gradual hardness distribution in the depth direction of the composites layer is observed. Moreover, the transition from the MMC layer to the substrate also exhibits a gradual change in the hardness.     

激光增材制造GH3625高温合金激光焊接头组织及力学性能

对激光增材制造GH3625高温合金进行激光对接焊实验,分析了焊接接头的显微组织演变规律和力学性能。结果表明,在热影响区,仅在上层晶界处析出大量Laves相,导致晶界发生明显粗化。沿焊缝上层至下层,熔合区和中间区由上层的胞状晶、柱状晶和等轴细晶逐渐转变为下层的柱状晶,且紧贴熔合线生长的等轴细晶的数量逐渐增多,中心区均为树枝晶。细小颗粒状γ′相弥散分布于焊缝;大量Laves相在中间区枝晶间析出,且形态由上层的条状逐渐转变为下层的颗粒状。接头抗拉强度为872MPa,达到母材抗拉强度的98.2%,伸长率达到母材的90.7%。接头断面近似呈45°斜面,断裂形式为脆性和韧性混合断裂方式。     

Microstructure and mechanical properties of laser additive repaired Ti17 titanium alloy

Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17 titanium alloy with small surface defects. The microstructure, micro-hardness and room temperature tensile properties of laser additive repaired (LARed) specimen were investigated. The results show that, cellular substructures are observed in the laser deposited zone (LDZ), rather than the typical α laths morphology due to lack of enough subsequent thermal cycles. The cellular substructures lead to lower micro-hardness in the LDZ compared with the wrought substrate zone which consists of duplex microstructure. The tensile test results indicate that the tensile deformation process of the LARed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and fracture in the laser repaired zone with a mixed dimple and cleavage mode. The tensile strength of the LARed specimen is slightly higher than that of the wrought specimen and the elongation of 11.7% is lower.     

Load transfer mechanism and mechanical properties of SiCw/Al metal matrix composites

The load transfer mechanism and mechanical properties of SiC whisker reinforced aluminum matrix composites were investigated. A generalized shear-lag model was proposed to analyze the effects of the aspect ratio, misorientation angle and volume fraction of SiC whisker on the mechanical properties of SiCw/Al composites. A new concept on effective aspect ratio was suggested, combining the effects of aspect ratio and alignment of whiskers, to calculate the effective stress acting on the aluminum matrix in SiCw/Al composites. The magnitude and anisotropy of the yield strength of the SiCw/2124Al composite can be estimated more accurately by substituting the average aspect ratio with the effective aspect ratio based on the generalized shear-lag model. The SiCw/2124Al composite with the largest effective aspect ratio showed the lowest minimum creep rate which decreased with increasing effective aspect ratio of SiC whisker, but were found to be almost similar under the same effective stress acting on the Al matrix. It is suggested that the role of SiC whisker is to improve the mechanical properties by reducing the effective stress acting on the Al matrix in the SiCw/Al metal matrix composite. This article is based on a presentation made in the symposium “The 1^st KIM-JIM Joint Symposium: High Strength Ratio Aluminum Alloys”, held at Inha University, Inchon, Korea, October 22. 1999 under the auspices of The Korean Institute of Metals and Materials and The Japanese Institute of Metals.     

Porosity and mechanical properties of porous titanium fabricated by gelcasting

Porous Ti compacts with large size and complex shape for biomedical applications were fabricated in the porosity range from 40.5% to 53.8% by controlling gelcasting parameters and sintering conditions. The experimental results show that the total porosity and open porosity of porous titanium compacts gelcast from the Ti slurry with 34 vol.% solid loading and sintered at 1100℃ for 1.5 h are 46.5% and 40.7%, respectively, and the mechanical properties are as follows： compressive strength 158.6 MPa and Young＇s modulus 8.5 GPa, which are similar to those of human cortical bone and appropriate for implanting purpose.     

Wear resistance of WCp/Duplex Stainless Steel metal matrix composite layers prepared by laser melt injection

Laser Melt Injection (LMI) was used to prepare metal matrix composite layers with a thickness of about 0.7 mm and approximately 10% volume fraction of WC particles in three kinds of Cast Duplex Stainless Steels (CDSSs). WC particles were injected into the molten surface layer using Nd:YAG high power laser beam. As a result the microstructure characterized by hard ceramic particles distributed in a metal matrix with the strong bonding to substrate is formed in the surface layer of the treated metal.Dry sliding wear properties of these metal matrix composites layers were measured and compared with the wear properties of the substrate and with surfaces simply remelted by the laser beam. The observed wear mechanisms are summarized and related to detailed microstructural observations. The layers have been found to show excellent interfacial bonding, coupled with substantially improved tribological properties expressed through the wear resistance increase of 8 times. The amount of WC particles was sufficient to reinforce the matrix and the particles have shown a good bonding to the matrix to support the contact stress in the layer.     

Interface morphology and mechanical properties of Al-Cu-Al laminated composites fabricated by explosive welding and subsequent rolling process

Explosive welding is a well-known solid state method for joining similar and dissimilar materials. In the present study, tri-layered Al-Cu-Al laminated composites with different interface morphologies were fabricated by explosive welding and subsequent rolling. Effects of explosive ratio and rolling thickness reduction on the morphology of interface and mechanical properties were evaluated through optical/scanning electron microscopy, micro-hardness, tensile and tensile-shear tests. Results showed that by increasing the thickness reduction, bonding strength of specimens including straight and wavy interfaces increases. However, bonding strength of the specimens with melted layer interface decreases up to a threshold thickness reduction, then rapidly increases by raising the reduction. Hardness Values of welded specimens were higher than those of original material especially near the interface and a more uniform hardness profile was obtained after rolling process.