混合元素法激光立体成形Ti-6Al-4V的组织及性能研究

以Ti、Al、V混合元素粉末为原料激光沉积Ti-6Al-4V,并对沉积态试样的组织演化及力学性能进行研究.结果表明,与采用预合金Ti-6Al-4V粉末为原料所获得的沉积试样的凝固组织特征有所不同,采用混合元素粉末为原料获得的沉积试样的凝固组织随激光功率的提高逐渐由等轴晶转化为柱状晶,熔池内合金化过程所产生的混合热的扰动作用是导致低功率条件下等轴晶形成的原因.原始β晶粒内的微观组织由大量的魏氏α板条和一定体积分数的板条间β相组成.这与采用预合金粉末基本相同.混合元素法激光立体成形Ti-6Al-4V的氧含量仅约0.1wt.%,沉积态Ti-6Al-4V的室温拉伸性能超过锻件标准要求.     

激光多层沉积Ti-6Al-3Mo合金的微观组织与性能

以纯Ti,Al,Mo元素粉末为原料,采用激光多层沉积技术制备Ti-6Al-3Mo合金,研究了激光多层沉积Ti-6Al-3Mo合金的微观组织特征及硬度分布.首先针对合金沉积层的凝固组织展开研究,分析激光多层沉积Ti-6Al-3Mo合金的凝固组织的形态特征及形成规律,并结合多元合金凝固柱状晶/等轴晶转变模型分析其形成机理.结果表明,激光多层沉积Ti-6Al-3Mo合金的凝固组织由外延生长的粗大柱状晶组成,仅在沉积试样的最顶部,形成一层薄薄的细小等轴晶;其次研究了β晶内α相的形成和分布.结果表明,原始β晶内的微观组织主要由大量的α束域,初生魏氏α板条以及板条间β相组成.在组织研究的基础上,对沉积层不同区域的硬度分布进行测试,为激光多层沉积Ti-6Al-3Mo合金的进一步深入研究及应用奠定科学基础.     

激光功率对激光熔化沉积Ti-6Al-4V-0.25C合金组织和性能的影响

采用含0.25%C(质量分数)的Ti-6Al-4V预合金粉末进行激光熔化沉积试验,研究了激光功率对Ti-6Al-4V-0.25C合金组织和性能的影响。结果表明,Ti-6Al-4V-0.25C合金微观结构为等轴β晶粒,晶粒内部形成了层状α+β结构,并且平均晶粒尺寸和α板条尺寸均随着激光功率的增加而逐渐增加。此外,随着激光功率的增加,合金拉伸性能得到明显提升,特别是在激光功率为1500 W时制备的合金样品,抗拉强度、屈服强度及伸长率分别为1191 MPa、1129 MPa和8.3%。一方面,这是由于激光功率增加使得合金孔隙率显著降低;另一方面,Ti-6Al-4V合金中含有微量的C元素,在冷却/凝固过程中,大多数的C原子固溶在Ti基体中,造成固溶强化。     

高功率激光立体成形Ti-6Al-4V合金组织研究

针对高功率条件下激光立体成形Ti-6Al-4V合金组织特征展开研究,揭示高功率条件下组织形成机理,并对比分析了高功率与中/低功率条件下组织形成的差异及原因。结果表明:由于高功率条件下具有更低的温度梯度和更高的凝固速度,激光立体成形Ti-6Al-4V合金的宏观组织由粗大的柱状晶、竹节状的小柱状晶和等轴晶三部分组成,并且沉积层之间存在层带;而中/低功率条件下只有贯穿多个沉积层呈外延生长的粗大的柱状晶。高功率条件下层带内典型微观组织是由大量的魏氏α集束组成,而层带间为α板条编织成的网篮状组织,并且部分α相球化成等轴状。与中低功率条件下典型组织相比,高功率条件下α板条长宽比明显减小,不存在针状α。     

元素添加方式对激光熔覆沉积Ti-25V-15Cr成形性的影响

目的以阻燃钛合金Ti-25V-15Cr为研究对象,主要研究V、Cr元素粉末的添加方式对激光熔覆沉积Ti-25V-15Cr合金的显微组织及成形性的影响。方法分别以经过粘结包覆Ti(150mm)+V(15mm)+Cr(15mm)、直接混合Ti(150mm)+V(15mm)+Cr(15mm)以及直接混合Ti(150mm)+V(100mm)+Cr(150mm)的元素混合粉末为原料,进行激光熔覆沉积实验,对沉积试样的高度、宽度以及显微组织特征进行研究。结果以粘结包覆Ti(150mm)+V(15mm)+Cr(15mm)和直接混合Ti(150mm)+V(100mm)+Cr(150mm)为原料获得的沉积试样,其沉积效率显著高于直接混合Ti(150mm)+V(15mm)+Cr(15mm)为原料的沉积试样,且沉积试样组织由相对细小的等轴晶和类等轴晶组成,而直接混合Ti(150mm)+V(15mm)+Cr(15mm)为原料的试样组织主要由外延生长的柱状晶组成。结论以粘结包覆Ti(150mm)+V(15mm)+Cr(15mm)为原材料时,在提高沉积效率的同时能够一定程度上细化晶粒。该方法对激光熔覆沉积材料的成形性、成分均匀性及显微组织具有显著影响。     

不同类型激光器对激光多层沉积Ti-35V-15Cr合金显微组织及性能的影响

目的 探讨半导体激光器与CO2激光器对激光多层沉积合金显微组织及性能的影响机理。方法 以充分混合的Ti、V、Cr粉末为原料,于预先打磨后的Ti-6Al-4V基板上使用CO2和半导体两种激光器进行激光多层沉积Ti-35V-15Cr,通过光学显微镜和扫描电镜、激光点火法、显微硬度测试和Jmat-Pro软件计算分别评价不同激光器下沉积试样的显微组织特点、抗阻燃性能对比和组织形成机理分析。结果 半导体激光器与CO2激光器沉积的试样显微组织存在很大差别,前者为全等轴组织,等轴晶平均尺寸为100 μm,晶粒大小与形状基本一致,沉积区与基材之间的过渡区域存在平均宽度为200 µm、长度为526 µm、长宽比为2.6的类等轴晶,通过扫描电镜观察发现在部分等轴晶内部存在亚晶结构;后者主要为平均尺寸120~200 µm的柱状晶组织,沉积试样顶部为平均直径为52 µm的细小等轴晶,通过扫描电镜观察发现枝晶偏析组织,枝晶间的距离为5~10 µm。抗阻燃性方面,半导体激光器制备的Ti-35V-15Cr试样的抗阻燃性能略优于CO2激光器制备的Ti-35V-15Cr试样,平均显微硬度前者为375HV,后者为363HV。结论 由于激光多层沉积Ti-35V-15Cr对半导体激光器与CO2激光器产生的激光吸收率不同而使二者形成完全不同的显微组织,由半导体激光器制备的Ti-35V-15Cr试样显微硬度更高、抗阻燃性能更好。     

基于不同Mo添加的激光立体成形Ti-6Al-xMo合金的显微组织演化和力学性能研究

本文采用激光立体成形技术(Laser Solid Forming,LSF),基于Mo当量混合Ti、Al、Mo粉末沉积新型Ti-6Al-xMo(x＝2、3、4)钛合金,研究了其显微组织形成与室温拉伸性能。结果表明：三种合金的凝固组织均呈现沿<100>方向生长的粗大柱状晶,顶部为细小等轴晶,且随着Mo含量的增加,柱状晶宽度逐渐减小,等轴晶层厚度逐渐增大;初生β晶粒中的微观结构是由初生α板条和残余β相组成的,还存在晶界α和α束域,通过电子背散射衍射(Electron Backscatter Diffraction, EBSD)分析发现三种成分均出现12种α变体且出现变体占优现象;随着Mo含量的增加,Ti-6Al-xMo强度硬度增加,延伸率减小,初生α板条宽度和面积比减小,增加到Ti-6Al-4Mo时,晶内出现次生α相。相比之下激光立体成形Ti-6Al-2Mo、Ti-6Al-3Mo分别具有抗拉强度962MPa、延伸率11.5%和抗拉强度982 MPa、延伸率9.2%的优异室温拉伸性能。     

利用选区激光熔化技术制备梯度结构的Ti-6Al-4V合金

采用选区激光熔化技术（SLM）制备了梯度Ti-6Al-4V合金。随着样品沉积厚度的逐渐增加,控制激光功率或扫描速率逐步升高或降低,以此研究了梯度结构Ti-6Al-4V合金的相变及结构演变。结果表明：由于选取激光熔化过程中的高冷却速率,SLM制备的Ti-6Al-4V合金的主要组织结构为初始β柱状晶里的针状马氏体。β柱状晶会随着激光功率的增加或扫描速率的降低而增宽。激光功率和扫描速率的变化会引起马氏体择优取向的变动。最后,由于局部不同的能量变化,随样品沉积厚度增加而逐步升高或降低的扫描速率会引发2种不同的空洞缺陷。     

微观组织特征对模拟海水中搅拌摩擦加工Ti-6Al-4V合金腐蚀磨损性能的影响

目的研究搅拌摩擦加工细晶Ti-6Al-4V合金在模拟海水中微观组织特征与腐蚀磨损性能的关系。方法通过控制搅拌摩擦加工工艺(200 r/min-25 mm/min和200 r/min-50 mm/min)获得具有等轴细晶组织和片层状α相组织的Ti-6Al-4V合金。使用往复磨损试验机和电化学工作站,在模拟海水中对Ti-6Al-4V合金进行腐蚀磨损实验,获得摩擦系数-时间曲线、动电位极化曲线等一系列摩擦磨损和电化学曲线。使用激光共聚焦显微镜和扫描电子显微镜对磨痕进行观察,计算磨损率,并分析磨损机制。通过计算腐蚀磨损分量研究材料损耗的主要影响因素。结果在腐蚀磨损中,因表面氧化膜被破坏,具有细晶结构的Ti-6Al-4V合金晶界面积大,腐蚀电位降低,但腐蚀电流密度小于原始试样。搅拌摩擦加工试样在腐蚀磨损实验中的摩擦系数更稳定,OCP条件下,具有细小等轴晶组织的搅拌摩擦加工Ti-6Al-4V合金的摩擦系数最低,磨损率较原始试样低20%。片层组织特征Ti-6Al-4V合金因微观力学性能各向异性而影响对磨球的行进路线,犁沟较混乱。原始样品的磨损机制主要为磨粒磨损和腐蚀磨损,搅拌摩擦加工后,样品在模拟海水中的磨损机制为磨粒磨损、分层磨损和腐蚀磨损。结论等轴细晶组织Ti-6Al-4V合金在模拟海水中表现出低的磨损率和低的摩擦系数,该组织特征具有最优的耐腐蚀磨损性能。     

电脉冲处理对激光沉积Ti-6Al-4V合金强度各向异性的影响（英文）

为消除激光沉积Ti-6Al-4V合金的强度各向异性,利用拉伸试验、光学显微组织观察、扫描电子显微观察、电子背散射衍射分析和透射电子显微观察研究电脉冲对激光沉积Ti-6Al-4V合金显微组织与强度的影响。结果显示,随着施加电压从0增加到130 V,β柱状晶内的显微组织按如下顺序演化：α′马氏体→集束α组织→网篮α组织。130 V电脉冲处理会弱化β柱状晶内马氏体织构。沉积态Ti-6Al-4V合金表现出约6.2%的屈服强度各向异性;经130 V的电脉冲处理后,屈服强度各向异性减小到0.6%。这主要是由于沿不同方向变形时,130 V电脉冲处理样品表现出近似相同的施密特因子分布。     

直接能量沉积Ti-XV-15Cr(X=20,25,30,35)合金的组织和阻燃性能

使用直接能量沉积技术,以纯Ti、纯V和纯Cr粉末为原料制备一系列Ti-YV-15Cr(X=20,25,30,35)合金.研究了V含量对Ti-XV-15Cr合金的晶粒形貌、显微硬度、弹性模量及阻燃性能的影响.结果表明,Ti-20V-15Cr、Ti-25V-15Cr和Ti-30V-15Cr合金的显微组织由外延生长的柱状晶和...     

Energy Density Dependence of Bonding Characteristics of Selective Laser-Melted Nb–Si-Based Alloy on Titanium Substrate

Spherical Nb–20Si–24Ti–2Cr–2Al pre-alloyed powders were processed by selective laser melting(SLM) on Ti6Al4V substrates with different energy densities. A series of single tracks and single layers were produced using different processing parameters, including powder size, laser power, scanning speed and hatch distance. Results showed that the pre-alloyed powders ranging from 45 to 75 lm were more applicable to SLM with less balling tendency, in comparison with those between 75 and 180 lm. The increase in linear energy density(LED) resulted in the decrease in contact angle and the increase in the width of single track as well as its penetration depth into the substrate. Smaller hatch distance leaded to a larger remelted part of the former track and a higher volumetric laser energy density. With a thickness of 75.6 lm, an interfacial intermediate layer, enriched in Ti and depleted in Nb, Si, Cr and Al, was formed between the SLM part and the Ti6Al4V substrate. The mechanisms of the elimination of balling phenomenon by employing a higher LED and the interfacial bonding characteristics between Nb–Si-based alloys via SLM and the Ti6Al4V substrate were discussed.     

Effect of Laser Oscillation on the Microstructure and Mechanical Properties of Laser Melting Deposition Titanium AlloysEI北大核心CSCD

针对激光熔化沉积冶金组织与缺陷,借鉴激光摆动焊接技术,提出一种激光摆动送粉增材制造TC4钛合金工艺,借助激光原位摆动改变熔池运动轨迹进而影响温度梯度和凝固速率,改善增材制造钛合金的微观组织。利用OM、SEM、EBSD和Vickers硬度计研究了激光摆动送粉增材制造工艺对TC4钛合金微观组织演变及力学性能的影响。结果表明,无摆动激光熔化沉积实验的最佳工艺参数为:激光功率1000 W,扫描速率8 mm/s,送粉速率6.92 g/min;直线型激光摆动的最佳工艺参数为:摆动频率200 Hz,摆动幅度1.5 mm。直线型激光摆动对熔池形貌改善显著,气孔和裂纹等缺陷较少,柱状晶数量和尺寸均有所减小,并且晶粒出现了等轴化的现象。相比无摆动样品,激光摆动后Ti-6Al-4V合金单道区域平均晶粒尺寸从5.20μm减小到4.37μm;硬度从418.00 HV提升到428.75 HV。     

HIP diffusion bonding of P/M titanium alloy Ti-6Al-4V and stainless steel 1Cr18Ni9Ti

The HIP diffusion bonding of P/M titanium alloy Ti-6A1-4V and stainless steel 1Cr18Ni9Ti using pure Ni as intermediate layer was studied. Bonding joint with complex bonding interface was obtained by HIPing pre-alloyed Ti-6Al-4V powders and stainless steel 1Crl 8Ni9Ti in a vacuum canning. The joint strengths were examined and the characteristics of bonding joint were observed. The result shows that the maximized strength of HIP diffusion bonding between P/M titanium alloy Ti-6Al-4V and stainless steel 1Cr18Ni9Ti can be up to 388 MPa and the microstructure of bonding joint is acceptable.     

Densification,microstructural evolutions of 90W-7Ni-3Fe tungsten heavy alloys during laser melting deposition process

Thin walled 90W-7Ni-3Fe tungsten heavy alloys (WHAs) have been prepared by a laser melting deposition (LMD) additive manufacturing technique using different input laser volume energy densities. Detailed investigations on densification and microstructural evolutions of the LMD process have been carried out. The result shows that the sample density increases with increasing input energy density by elimination of “lack of fusion” defects. However, some gas delivered with powders gets trapped in the molten pool due to the fast cooling rate and complex shapes of W particles, resulting in a prevalence of small round pore defects even under high input energy densities. Near full density can be obtained when the energy density reaches 74 J/mm³. The LMD WHAs have two phase microstructures consisting of polygonal or dendritic W particles embedded in a nickel‑iron matrix, which has large sized columnar grains due to epitaxial growth. The polygonal particles are partially dissolved/melted W powder particles. The dendritic particles are newly formed grains due to the reprecipitation of supersaturated W in the nickel‑iron matrix during solidification. The proportion of dendritic particles increases with the increasing input energy density. A microstructure evolution process adapted from traditional liquid phase sintering process containing three stages of rearrangement, solution-reprecipitation, and solid state is proposed for the LMD process.     

Influence of temperature conditions on grain refinement of pure Cu solidified with low-voltage pulsed magnetic field

The influence of temperature conditions on the grain refinement of pure Cu solidified with low-voltage pulsed magnetic field (LVPMF) was investigated. With the pouring temperature (T_p) and mould temperature (T_m) increasing, the solidified microstructure of pure Cu was gradually changed from fine equiaxed grains to coarse columnar grains and then to the mixed structure of coarse equiaxed grains and columnar grains. Little change was observed from the microstructure of pure Cu solidified with and without LVPMF for the low T_p and T_m. But for the high T_p and T_m, applying LVPFM remarkably reduced the coarse columnar grains and obtained fine equiaxed grains. The grain refinement by LVPFM is considered to be caused by the electromagnetic flow. The smaller cooling rate resulted by higher T_p and T_m offers much acting time for LVPMF and thus better grain refinement can be achieved.     

Research on Laser Direct Deposition Process of Ti-6Al-4V Alloy

Laser direct deposition （LDD） of metallic components is an advanced technology of combining CAD/CAM （computer aided design/computer aided manufacturing）, high power laser, and rapid prototyping. This technology uses laser beam to melt the powders fed coaxiaUy into the molten pool by the laser beam to fabricate fuUy dense metallic components. The present article mainly studies the LDD of Ti-6Al-4V alloy, which can be used to fabricate aircraft components. The mechanical properties of the Ti-6Al-4V alloy, fabricated by LDD, are obtained using the tension test, and the oxygen content of used powders and deposited specimens are measured. In the present article, it can be seen that the mechanical properties obtained using this method are higher than the ones obtained by casting, and equal to those got by wrought anneal. One aircraft part has been made using the LDD process. Because of this aircraft part, with sophisticated shape, the effect of the laser scanning track on the internal soundness of the deposited part was discussed.     

MICROSTRUCTURE IN LASER FUSED HIGH SPEED STEEL W6Mo5Cr4V2(M2)

Microstructure of the deepest zone of high speed steel W6Mo5Cr4V2(M2)melt after laser fu-sion was found to be so fine as the ehill zone of a solidified ingot.When narrower chill zoneformed,the long columnar dendrites grow into the melt and then the fine equiaxed cellularstructure appears in upper melt region nearly surface.The substructure of cellular grains anddendrites was observed to consist of martensite and retained austenile,while the carbides asM_6C_■ Cr_7C_3 and MC distributed at their boundaries.It is believed that the highermicrohardness up to HV_(0.1)=865—960 of the laser fused structure of the alloy is due to the oc-currence of martensite.     

Microstructural evolution of a PM TiAl alloy during heat treatment in α+γ phase field

In this study,the effect of temperatures and cooling rates of heat treatment on the microstructure of a powder metallurgy (PM) Ti-46Al-2Cr-2Nb-(B,W) (at.％) alloy was studied.Depending on the cooling rate and temperature,the different structures were obtained from the initial near-γ (NG) microstructures by heat treatment in the α+γ field.The results show that the microstructures of samples after furnace cooling (FC) consist primarily of equiaxed γ and α2 grains,with a few grains containing lamellae.Duplex microstructures consist mainly of γ grains and lamellar colonies were obtained in the quenching into another furnace at 900℃ (QFC) samples.However,further increasing of the cooling rate to air cooling (AC) induces the transformation of α→α2 and results in a microstructure with equiaxed γ and α2 grains,and no lamellar colonies are found.