Microstructural evolution and mechanical properties of laser melting deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy

A rectangular plate of Ti-6.5A1-3.5Mo-I.5Zr-0.3Si titanium alloy was fabricated by laser melting deposition （LMD） technology. Macrostructure and microstructure were characterized by optical microscope （OM） and scanning electron microscope （SEM）. Room temperature tensile properties were evaluated. Results indicate that the macro-morphology is dominated by large columnar grains traversing multiple deposited layers. Two kinds of bands, named the wide bands and the narrow bands, are observed. The wide band consists of crab-like a lath and Widmanstatten a colony. The narrow band consists of a lath and transformed ft. The formation mechanism of the two bands was explored. The influence of heat effect caused by subsequent deposition layers on microstructural evolution during deposition process was discussed. The room temperature tensile test demonstrates that the strength of laser deposited Ti-6.5A1-3.5Mo-I.5Zr-0.3Si is comparable to that of wrought bars.

Low cycle fatigue behavior of laser melting deposited TC18 titanium alloy

Low cycle fatigue （LCF） behavior of laser melting deposited （LMD） TC18 titanium alloy was studied at room temperature. Microstructure consisting of fine lamella-like primary α phase and transformed β matrix was obtained by double annealed treatment, and inhomogeneous grain boundaryαphase was detected. Fatigue fracture surfaces and longitudinal sections of LCF specimens were examined by optical microscopy and scanning electron microscopy. Results indicate that more than one crack initiation site can be detected on the LCF fracture surface. The fracture morphology of the secondary crack initiation site is different from that of the primary crack initiation site. When the crack grows along the grain boundaryαphase, continuous grain boundaryαphase leads to a straight propagating manner while discontinuous grain boundaryαphase gives rise to flexural propagating mode.

High-cycle fatigue crack initiation and propagation in laser melting deposited TC18 titanium alloy

This article examines fatigue crack nucleation and propagation in laser deposited TC18 titanium alloy. The Widmanstatten structure was obtained by double-annealing treatment,. High-cycle fatigue （HCF） tests were conducted at room temperature with the stress ratio of 0.1 and the notch concentration factor Kt = 1. Fatigue cracks initiated preferentially at micropores, which had great effect on the HCF properties. The effect decreased with the decrease of pore size and the increase of distance from the pore location to the specimen surface. The crack initiation region was characterized by the cleavage facets of a lamella and the tearing of β matrix. The soft a precipitated-free zone formed along grain boundaries accelerated the crack propagation. Subsurface observation indicated that the crack preferred to propagate along the grain boundary α or border of a lamella or vertical to a lamella.

A yttrium-containing high-temperature titanium alloy additively manufactured by selective electron beam melting

A yttrium-containing high-temperature titanium alloy(Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si-0.1Y, mass fraction, %) has been additively manufactured using selective electron beam melting(SEBM). The resulting microstructure and textures were studied using scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and electron backscattered diffraction(EBSD) and compared with the conventionally manufactured form. A notable distinct difference of microstructures is that additive manufacturing by SEBM enables homogeneous precipitation of fine Y2O3 dispersoids in the size range of 50-250 nm throughout the as-fabricated alloy, despite the presence of just trace levels of oxygen(7×10-4, mass fraction) and yttrium(10-3, mass fraction) in the alloy. In contrast, the conventionally manufactured alloy shows inhomogeneously distributed coarse Y2O3 precipitates, including cracked or debonded Y2O3 particles.

Effects of laser surface melting on crystallographic texture, microstructure, elastic modulus and hardness of Ti-30Nb-4Sn alloy

The biocompatibility of orthopedic implants is closely related to their elastic modulus and surface properties.The objective of this study was to determine the effects of cold rolling,recrystallization and laser surface melting(LSM)on the microstructure and mechanical properties of a biphase(α″+β)Ti-30Nb-4Sn alloy.X-ray diffraction(XRD)texture analysis of the cold-rolled substrate revealed the[302]α″//ND texture component,while analysis of the recrystallized substrate showed the[302]α″//ND and[110]α″//ND components.Theβ-phase texture could not be directly measured by XRD,but the presence of the[111]β//ND texture component was successfully predicted by considering the orientation relationship between theα″andβphases.Nanoindentation measurements showed that the elastic modulus of the cold-rolled substrate(63GPa)was lower than that of the recrystallized substrate(74GPa).Based on the available literature and the results presented here,it is suggested that this difference is caused by the introduction of crystal defects during cold deformation.The combined nanoindentation/EBSD analysis showed that the nanoindentation results are not affected by crystal orientation.LSM of the deformed alloy produced changes in hardness,elastic modulus and crystallographic texture similar to those produced by recrystallization heat treatment,creating a stiffness gradient between surface and substrate.

Microstructure evolution of laser deposited Ti60A titanium alloy during cyclic thermal exposure

Cyclic thermal exposure tests of infrared heating to 800 ℃ in 120 s followed by compressed air cooling to 150 ℃ in 60 s were performed for the laser deposited Ti60A （Ti5.54Al3.38Sn3.34Zr0.37Mo0.46Si） alloy. The effects of thermal exposure cycles on length ofβphase, area fraction ofαphase and microhardness of alloy were examined by OM, SEM and EDS. The results indicate that thermal exposure cycles have significant effects on length ofβphase, area fraction ofαphase and microhardness of the alloy. The original fine basket-weaveβand 78.5%αtransform to transient wedge-likeβ, finally leaving granularβand 97.6%coarsenedαwith the increased thermal exposure cycles. The formation mechanism of coarsenedαand broken-upβmicrostructure is discussed. The alloy after 750 thermal exposure cycles has the maximum microhardness, 33.3%higher than that of the as-deposited alloy.

A novel Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy designed using cluster-plus-glue-atom model for laser additive manufacturing

A novel Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy was designed using the cluster formula approach(cluster-plus-glue-atom model)and prepared by laser melting deposition(LMD).Its composition formula 12[Al-Ti_(12)](AlTi_(2))+5[Al_(0.8)Si_(0.2)-Ti_(12)Zr_(2)](V_(0.8)Mo_(0.2)Nb_(1)Ti)features an enhancedβ-Ti via co-alloying of Zr,V,Mo,Nb and Si.The experimental results show that the cluster formula ofαandβphases in the novel alloy are respectivelyα-[Al-Ti_(11.5)Zr_(0.5)](Al_(1)Ti_(2))andβ-[Al_(0.8)Si_(0.2)-Ti_(13.2)Zr_(0.8)](V_(1)Mo_(0.4)Nb_(1.6)),both containing Zr elements.The fitted composition via the α andβphase cluster formulas has little difference with the actual alloy composition,suggesting that the validity of cluster-plus-glue-atom model in the alloy composition design.After hot isostatic pressing(HIP),both the Ti-6Al-4V and the novel alloy by LMD are characterized by prior-βcolumnar grains,while the typical<100>texture disappears.Compared with Ti-6Al-4V,Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy exhibits a combination of higher strength(1,056 MPa)and higher ductility(14%)at room temperature and higher strength(580 MPa)at 550℃ after HIP,and can potentially serves as LMD materials.

Preparation of Al-Si-Ti Master Alloys by Electrolysis of Silica and Titania in Cryolite-Alumina Melts

Aluminum silicon titanium master alloys were prepared in the laboratory by electrolysis of silica and titania dissolved in cryolite alumina melts. Alloys containing up to 12 mass% Si and 2.6 mass% Ti were formed after about 90 min of electrolysis at 950℃. The current efficiency for the preparation of the Al Si Ti alloys varied with time, temperature and cathodic current density. It is concluded that this electrolytic method may be an interesting alternative to the direct metal mixing process for formation of Al Si Ti master alloys.

激光选区熔化成形工艺对TA15钛合金内部缺陷与力学性能的影响

利用激光选区熔化(Selective laser melting,SLM)成形技术制备TA15钛合金,通过光学显微镜(Optical microscope,OM)、扫描电镜(Scanning electron microscope,SEM)和室温拉伸等研究了激光功率和扫描速度对SLM成形TA15钛合金内部缺陷与力学性能的影响规律。结果表明:在低激光功率(100~125 W)、高扫描速率(1200~1600 mm/s)区域,激光能量密度较低,合金内部缺陷主要为不规则形状的缺陷;在高激光功率(150~200 W)、低扫描速度(800~1000 mm/s)区域,激光能量密度过高,合金内部缺陷主要为规则球形缺陷。规则球形缺陷的存在会导致合金塑性显著降低、对强度影响较弱;而不规则未熔合缺陷的存在会显著降低合金强度和伸长率。TA15钛合金的最佳工艺参数:激光功率为200 W、激光扫描速度为1600 mm/s时,成形合金拉伸强度为(1291±4.2)MPa,断裂伸长率为(8.5±0.5)%。

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。

Influence of Electroshocking Treatment on Microstructure and Mechanical Properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Thin-Wall Specimen Manufactured by Laser Melting Deposition

In order to improve the properties of titanium alloys manufactured by laser melting deposition(LMD),the electroshocking treatment(EST)was proposed in this work.The effects of EST on microstructure and mechanical properties of LMD Ti-6.5Al-3.5Mo-1.5Zr-0.3Si were investigated.The results showed that the width of the heat affected band decreased and disappeared under the thermal and athermal effects of EST,resulting in the uniform microstructure.In the microstructure,theαlaths became coarser gradually,and the quantity ofα/βinterface was reduced.The reduction of the quantity ofα/βinterface leads to make less resistant to dislocation,resulting in the reduction in hardness and strength.The discontinuous grain boundaryαphase and nucleationαcolony near grain boundary inhibited the crack propagation and improved the ductility.Summary,EST can manipulate the microstructure and improve the mechanical properties of LMD titanium alloys.

粉末床熔融钛合金的表面抛光技术研究进展

粉末床熔融钛合金作为一种重要的金属材料,在航空航天、医疗器械以及汽车等领域得到广泛应用。然而,由于特殊的材料性质和加工方法,其表面质量与性能仍然是制约其应用的关键问题之一。对粉末床熔融钛合金的表面抛光技术研究进展进行了综述,介绍了化学抛光、电化学抛光、等离子电解抛光、激光抛光和机械抛光等技术的研究进展。这些技术为粉末床熔融钛合金的表面质量和性能满足不同应用需求提供了选择,同时还对复合抛光技术及相关技术发展进行了展望。

退火温度对激光熔化沉积TC31高温钛合金组织与性能的影响

为改善激光熔化沉积TC31高温钛合金力学性能,本文通过光学显微镜、SEM、TEM和力学性能测试的方法研究了退火温度对合金中组织演化行为的影响,及其与合金室温和650℃高温力学性能的关系。结果表明:组织中初生α相含量随着退火温度升高而降低,其溶解主要发生在950℃以上,980℃退火后含量仅为29%。当退火温度超过930℃时,初生α相片层宽度明显增加。随着退火温度升高,α/β界面处析出的(Ti,Zr)6Si3相尺寸增加,且进入α相片层内部。合金在800~1000℃退火时,合金室温拉伸屈服强度随退火温度升高趋于降低。受相界面析出的硅化物聚合长大及α相片层尺寸增加等因素影响,合金高温屈服强度随退火温度升高先降低后增加。合金经过1000℃退火后,呈现良好的高温性能,其650℃下抗拉强度达657 MPa、屈服强度约为466 MPa、延伸率27%。

SLM成形表面织构对TC4钛合金干摩擦磨损性能的影响

基于一步法思路,采用金属3D打印机基于激光选区熔化(SLM)技术制备表面带有凹坑织构的TC4钛合金试样,采用光学相机、超景深显微镜和扫描电镜观察织构成形情况,利用激光共聚焦位移测试仪和显微维氏硬度计分别测试表面粗糙度和表面硬度,在干摩擦条件下采用摩擦磨损试验仪考察不同载荷下织构密度对TC4钛合金试样摩擦学性能的影响,并使用扫描电镜对摩擦实验前后的表面形貌进行分析。研究结果表明:一步法SLM成形能够在TC4钛合金表面获得成形良好的直径500μm的织构;随着织构密度的提高,钛合金试样表面粗糙度增大,表面硬度有所降低;干摩擦条件下,提高TC4钛合金试样织构密度有利于磨屑的收集从而减少试样的三体磨损,提高载荷有利于改善摩擦副接触状态;5 N载荷下40%织构密度试样的平均摩擦因数和磨痕宽度均最小,与无织构试样相比,平均摩擦因数和磨痕宽度分别降低12%和16%;40%织构密度下,载荷提高会引起摩擦因数的降低和磨损量增大,磨损表面犁沟和片状剥落增多。在干摩擦条件下,3D打印一步法制备的表面织构可以显著改善TC4钛合金的磨粒磨损和黏着磨损。

增材制造钛合金的微铣削加工试验

增材制造(Additive manufacturing,AM)技术制备的钛合金部件在航空航天领域具有广泛的用途,对增材制造钛合金精密零部件而言,铣削、抛光等后处理加工是必不可少的工序。本文选用聚晶金刚石(Polycrystalline diamond,PCD)微铣刀对锻造钛合金、激光选区熔化(Selective laser melting,SLM)技术制备的未经过热处理和经过热处理的钛合金进行微铣削试验,研究了3种不同制造工艺的钛合金材料的微铣削加工性能。结果表明:SLM-热处理钛合金的铣削力最大,这与其材料硬度最高有关。微铣削过程中,所有钛合金材料的逆铣侧顶端毛刺尺寸均要大于顺铣侧顶端毛刺尺寸。在不同制造工艺的钛合金材料中,SLM-钛合金生成的顶端毛刺宽度最小,这与其塑性最差有关。SLM-热处理钛合金获得的表面质量最好,这不仅与材料的硬度和塑性有关,同时还受到孔隙度的影响。

钛合金激光选区熔化成形研究现状与展望

随着钛合金在各个领域的应用日益广泛,其成形工艺和组织性能的研究也成为国内外学者的关注焦点。与传统加工方式相比,激光选区熔化技术(Selective laser melting,SLM)具有成形率高、复杂零件易加工等优点,在航空航天和医疗领域有着广泛应用。目前,SLM技术在钛合金领域的应用尚处于初级阶段,对SLM成形钛合金组织性能的研究主要集中于熔池内孔隙缺陷和激光热源对钛合金显微组织及力学性能的影响等方面。随着SLM技术的不断推广应用,SLM技术在钛合金成形方面的研究将会有更广阔的发展空间,本文总结了国内外有关SLM成形钛合金的数值模拟、微观组织、性能和后处理方面的研究成果,为SLM成形钛合金的进一步发展提供借鉴和参考。

激光熔化沉积TiC/TC4复合材料热-流行为及陶瓷颗粒分布状态

颗粒增强钛基复合材料在航空航天等领域具有广阔的应用前景,采用仿真与试验相结合的方法,对激光熔化沉积TiC/TC4复合材料过程中的热-流行为和沉积层中陶瓷颗粒的分布状态进行了研究.结果表明,工艺参数对熔池的热-流行为及沉积层形貌具有显著的影响,熔池表面的流体流动呈波纹状,熔融金属从熔池中心向四周流动;熔池底部等温面上熔融金属从四周流向熔池底部,并出现漩涡现象.在激光熔化沉积过程中,TiC颗粒穿透熔池表面的Marangoni对流区,在熔池中与流体交互作用,最终在沉积层中出现沉积层中上方部位团聚、沉积层中下方部位团聚、沉积层中均匀分布等分布状态.

大型钛合金构件激光熔化沉积制造过程残余应力诱发开裂机理研究

残余应力诱发开裂问题仍是限制大型构件激光熔化沉积工业化应用的一大瓶颈。因此,探究激光熔化沉积大型复杂构件残余应力的演化规律,以及残余应力诱发裂纹萌生和扩展的微观组织相关性具有重要意义。通过对大型钛合金构件开裂断口形貌分析及宏观热-力耦合有限元计算,首次发现激光熔化沉积过程独特的热应力三阶段非对称循环加载模式,即稳定循环-突增加载阶段、非线性循环加载阶段及线性循环加载阶段。以热-力耦合计算得到的残余应力为输入,采用耦合损伤的晶体塑性计算研究了3种热应力加载模式对激光熔化沉积特有的网篮组织的破坏程度,发现线性循环加载模式对网篮组织破坏性最大,稳定循环-突增加载模式破坏性次之,非线性循环加载模式破坏性最小。这种热应力加载模式、断口形貌及微观组织分析进一步表明,残余应力诱发开裂现象是由过大的热应力累积、零件的几何特征、热应力加载模式及成形缺陷等多因素协同控制的,而非单一因素影响,这也为从适时消除应力、优化零件结构及工艺参数、减少和抑制缺陷产生等方面系统化控制开裂问题提供了方向。

等激光能量密度下选区激光熔化TC4钛合金的表面形貌和硬度

以TC4钛合金粉末为原料,通过选区激光熔化工艺(selective laser melting,SLM)成形实验并结合数值模拟,探讨了相等激光能量密度下,工艺参数对成形件性能的影响。结果表明:在等激光能量密度下,激光功率和扫描速度对熔池尺寸有着显著的影响;铺粉层厚是影响试样表面粗糙度的最主要因素,最佳铺粉层厚为0.03 mm;虽然激光能量密度相同,但是不同工艺参数组合依然会影响试样的表面形貌和微观组织;等激光能量密度下不同的工艺参数组合对SLM沉积态的表面硬度没有显著影响。

CeO_(2)添加量对激光选区熔化TC4合金摩擦磨损性能的影响

钛合金具有广阔的应用前景,为提高钛合金的成形质量和耐磨性能,采用激光选区熔化(Selective Laser Melting,SLM)技术制备TC4合金,通过添加不同含量(0、0.10%、0.15%、0.20%、0.25%)的CeO_(2)对TC4合金进行改性。使用XRD、SEM、电子万能试验机、摩擦磨损试验机和三维光学轮廓仪探究了CeO_(2)含量对TC4合金的显微组织、相组成、力学性能及摩擦磨损性能的影响。结果表明:采用激光选区熔化技术制备添加适量CeO_(2)的TC4合金,相比TC4合金原样,其组织得到细化,力学性能提升,摩擦系数和磨损量明显下降,黏着磨损和磨粒磨损的作用效果减弱。当CeO_(2)的含量为0.15%时,试样的硬度达到356.8 HV,屈服强度和抗拉强度分别达到1027 MPa和1293 MPa,远超锻件水平,平均摩擦系数和磨损量达到最低值,分别为0.412和3.729×10^(-2)mm^(3),其磨损机制为轻微的黏着磨损和磨粒磨损。