Heat-treated microstructure and mechanical properties of laser solid forming Ti-6Al-4V alloy

The effects of heat treatment on the microstructure and mechanical properties of laser solid forming （LSF） Ti-6Al-4V alloy were investigated The influences of the temperature and time of solution treatment and aging treatment were analyzed. The results show that the microstructure of LSFed samples consists of Widmanstatten α laths and a little acicular in columnar prior β grains with an average grain width of 300 μm, which grow epitaxiaUy from the substrate along the deposition direction （27）. Solution treatment had an important effect on the width, aspect ratio, and volmne fraction of primary and secondary a laths, and aging treatment mainly affects the aspect ratio and volume fraction of primary α laths and the width and volume fraction of secondary a laths. Globular a phase was first observed in LSFed samples when the samples were heat treated with solution treatment （950℃, 8 h/air cooling （AC）） or with solution treatment （950℃, 1 h/AC） and aging treatment （550℃, above 8 h/AC）, respectively. The coarsening and globularization mechanisms of a phase in LSFed Ti-6Al-4V alloy during heat treatment were presented. To obtain good integrated mechanical properties for LSFed Ti-6Al-4V alloys, an optimized heat treatment regimen was suggested.

Effect of Intermediate Heat Treatment Temperature on Microstructure and Notch Sensitivity of Laser Solid Formed Inconel 718 Superalloy

Inconel 718 superalloys deposited by laser solid forming （LSF） were heat treated with solution treatment,intermediate heat treatment （IHT） and two-stage aging treatment in sequence （SITA heat treatment）.The effect of IHT temperature on microstructure,tensile property and notch sensitivity of LSFed Inconel 718 superalloy at 500 ℃ were investigated.As-deposited columnar grains have transformed to equiaxed grains and the grains were refined due to the recrystallization during the SITA heat treatment.It is found that the size and amount of δ phase dispersed at grain boundaries decreased with the increasing of IHT temperature,and δ phase disappeared when the IHT temperature reached 1 020 ℃.The ultimate tensile strength （UTS） and yield strength （YS） of smooth samples increased to a maximum when the IHT temperature reached 980 ℃ and then decreased slightly to a minimum when the IHT temperature was 1 000 ℃,and followed by slight increasing again till the IHT temperature reached 1 020 ℃,resulted from the competition of precipitation strengthening effect of γ″ and γ＇ phase and the grain boundary weakening effect caused by the gradual disappearance of δ phase with increasing the IHT temperature.The notch sensitivity factor （qe） decreased but still greater than 1 as the IHT temperature increased,which is attributed to the decrease of the size and amount of δ precipitation.

Influence of processing parameters on deposition characteristics of Inconel 625 superalloy fabricated by laser solid forming

A series of single track clads of Inconel 625 alloy were fabricated by laser solid forming.To achieve the high dimensional accuracy and excellent mechanical properties,the effect of processing parameters on the geometry,the formation of Laves phase and the residual stress was investigated.The results show that laser power and scanning speed had a dramatical influence on the width and height of single-track clads.According to the columnar to equiaxed transition curve of Inconel 625,the grain morphology can be predicted during the LSF process.With the increasing laser power and the decreasing scanning speed,the segregation degree of Si,Nb,Mo,the volume fraction and size of Laves phase increased.Vickers indentation was used to demonstrate that optimizing processing parameter can achieve the minimum residual tensile stress.

Hot deformation behavior and microstructure evolution of the laser solid formed TC4 titanium alloy

Hot compressive experiments of the laser solid formed(LSFed)TC4 titanium alloy were conducted at a wide temperature range of 650-950℃and strain rate of 0.01-10 s^(-1).The Arrheniustype constitutive models of the LSFed TC4 alloy were established at the temperature range of 800-950℃and of 650-800℃,respectively.The average relative error between the predicted stresses and experimental values in those two temperature ranges are 10.4%and 8.3%,respectively,indicating that the prediction models constructed in this paper are in a good agreement with experimental data.Processing maps were established by the principle of dynamic materials modeling on the basis of the data achieved from the hot compression experiments.The processing parameters corresponding to the stable and unstable regions of material deformation can be determined from the processing maps.The microstructure evolution of the stable and unstable regions of the samples after tests were observed.Finally,the effect of hot compressive parameters on the microstructure were investigated to research the dynamic recrystallization and the texture of the deformed LSFed TC4 alloy.

Microstructure evolution of laser solid forming of Ti-Al-V ternary system alloys from blended elemental powders

Morphology evolution of prior β grains of laser solid forming （LSF） Ti-xAl-yV （x 11,y 20） alloys from blended elemental powders is investigated. The formation mechanism of grain morphology is revealed by incorporating columnar to equiaxed transition （CET） mechanism during solidification. The morphology of prior β grains of LSF Ti-6Al-yV changes from columnar to equiaxed grains with increasing element V content from 4 to 20 wt.-%. This agrees well with CET theoretical prediction. Likewise, the grain morphology of LSF Ti-xAl-2V from blended elemental powders changes from large columnar to small equiaxed with increasing Al content from 2 to 11 wt.-%. The macro-morphologies of LSF Ti-8Al-2V and Ti-11Al-2V from blended elemental powders do not agree with CET predictions. This is caused by the increased disturbance effects of mixing enthalpy with increasing Al content, generated in the alloying process of Ti, Al, and V in the molten pool.

Effect of dimensionless heat input during laser solid forming of high-strength steel

Laser solid forming(LSF)technology can be used to rapidly manufacture and repair high-strength steel parts with superior performance,but the value of the heat input during operation is difficult to quantify,which has a substantial impact on the microstructure and mechanical properties of the parts.A promising method to improve the forming efficiency and quality of LSFed parts is to accurately control the heat input and explore its relationship with the microstructure and mechanical properties.To remove the interference of other variables from the experiment,the dimensionless heat input Q;^(∗)was introduced.The Q^(∗)values were designed in advance to calculate the experimental parameters used to perform the LSF experiment.The microstructure was observed at different regions of the sample,and its mechanical properties were analyzed.From the results,the following conclusions were drawn.The Q;^(∗)value was directly related to the cooling rate and heat accumulation in the top structure,leading to the formation of different microstructures;it also modified the original structure at the bottom,affecting the subsequent thermal cycle and indirectly changing the tempered martensite morphology.The heat input also affected the mechanical properties of the sample.The hardness of the stable zone decreased with increasing Q;^(∗)value,and the lowest value was 190 HV.Similarly,the tensile strength and yield strength of the LSFed samples decreased considerably with increasing Q;^(∗)value,and the lowest values were 735 and 604 MPa,respectively.Only the elongation and reduction in the area increased after a slight decrease.The Q;^(∗)value had a significant effect on heat treatment.When Q;^(∗)=2.9,the increase in tensile strength and yield strength after heat treatment was the largest(29%and 44%,respectively).

High strength and ductility of 34CrNiMo6 steel produced by laser solid forming

Because of the excellent mechanical properties of 34 CrNiMo6 steel, it is widely used in high-value components. Many conventional approaches to strengthening-steels typically involve the loss of useful ductility.In this study, 34 CrNiMo6 Steel having high strength and ductility is produced by laser solid forming(LSF)with a quenching-tempering(QT) treatment. Tempering of bainite is mainly by solid phase transformation in the previous LSF layers during the LSF process. The stable microstructure of LSF consists of ferrite and fine carbides. The microstructure transfers to tempered sorbite after heat-treatment. The tensile properties of the LSF steel meet those of the wrought standard. The UTS and elongation of LSF sample at 858 MPa, 19.2%, respectively, are greater than those of the wrought. The QT treatment enhanced the ultimate tensile strength and yield strength of the LSF sample. The ultimate tensile strength, yield strength, reduction in area, and elongation of the LSF+QT sample at 980 MPa, 916 MPa, 58.9%, and 13.9%,respectively, are greater than those of the wrought standard. The yield strength of the LSF+QT sample is approximately 1.27 times that of the wrought. The LSF samples failed in a ductile fracture mode, while the LSF+QT samples showed mixed-mode failure. The defects have only a small effect on the tensile properties owing to the excellent ductility of the LSF sample.

Microstructure and compressive/tensile characteristic of large size Zr-based bulk metallic glass prepared by laser solid forming

The large size, crack-free Zr_(55)Cu_(30)Al_(10)Ni_(5) bulk metallic glass(BMGs) with the diameter of 54 mm and the height of 15 mm was built by laser solid forming additive manufacturing technology, whose size is larger than the critical diameter by casting. The microstructure, tensile and compressive deformation behaviors and fracture morphology of laser solid formed Zr_(55)Cu_(30)Al_(10)Ni_5 BMGs were investigated. It is found that the crystallization mainly occurs in the heat-affected zones of deposition layers, which consist of Al_5Ni_3Zr_2, NiZr_2, ZrCu, CuZr_2 phases. The content of amorphous phase in the deposit is about 63%.Under the compressive loading, the deposit presents no plasticity before fracture occurs. The fracture process is mainly controlled by the shear stress and the compressive shear fracture angles of about39?. The compressive strength reaches 1452 MPa, which is equivalent to that of as-Cast Zr_(55)Cu_(30)Al_(10)Ni_5 BMGs, and there exist vein-like patterns, river-like patterns and smooth regions at the compressive fractography. Under the tensile loading, the deposit presents the brittle fracture pattern without plastic deformation. The fracture process exhibits normal fracture model, and the tensile shear fracture angle of about 90?. The tensile strength is only about 609 MPa, and the tensile fractography mainly consists of micro-scaled cores and vein-like patterns, dimple-like patterns, chocolate-like patterns and smooth regions. The results further verified the feasibility and large potential of laser additive manufacturing on fabrication and industrial application of large-scale BMGs parts.

Laser Solid Forming Repairing and Remanufacturing of High Strength Steel

Laser solid forming (LSF) is an advanced manufacture technology developed from early 1990s, which can realize the rapid manufacturing high performance near-net-shaping complicated metallic components with full-dense directly. Currently this technology has been widely used for rapid manufacturing of metal parts, repairing and remanufacturing service of large parts with defects in aerospace, energy, transportation industry etc. In present paper, the main progresses on the research and application of LSF are reviewed, and the emphasis has been focused on manufacturing high performance high strength steel metal parts. The results of LSFed high strength steel samples show that the comprehensive mechanical properties are usually in the classes of forging parts, which the dense, fine and homogeneous microstructure in LSFed parts, especially, high strength steel parts with metallurgical-defects-free can be obtained by careful optimizing the forming and heat treatment parameter. To realize the high performance repairing and remanufacturing of the high strength steel component is one of the most remarkable progress for LSF recently. The mechanical properties of the repaired and remanufacturing parts by LSF can reach the wrought standards only with annealing treatment. It is believed that the repair and remanufacturing of high performance metallic components by LSF should be one of the most promising applications for LSF in the coming future.

自由曲面镜补偿大功率激光波前畸变技术研究

对于一台性能稳定的激光器,在出光阶段整个系统处于热交换的稳定状态,即激光波前分布可以保持稳定不变。基于此特点,提出制造自由曲面镜,以校正激光器的波前畸变,提高光束质量。本文首先介绍了自由曲面镜的波前补偿原理、设计及加工过程,然后通过数学建模,从理论上对其波前补偿能力进行了仿真计算,最后在板条固体激光器中进行了波前补偿实验:在激光器输出功率为12.5 kW时,自由曲面镜对激光光束相位及远场光束质量都有明显的改善和提高。自由曲面镜不像变形镜那样受到致动器间距的限制,因此对于高阶像差的校正也更为有效,且成本低廉,再者也不会增加系统的复杂度,与自适应光学系统相比各有所长。

金属材料激光立体成形技术

对激光立体成形技术的基本原理、发展状况以及成形特性、凝固组织形成规律进行了系统深入的研究 ,发现要获得理想的成形效果 ,就必须对单层涂覆厚度、单道涂覆宽度、搭接率等主要参数进行精确控制。在工艺研究的同时 ,对成形件微观组织形成规律进行了研究 ,发现其内部组织主要由外延生长的细长枝晶构成 ,其枝晶一次间距在 10～30 μm之间。在进一步严格控制工艺条件的基础上 ,获得了具有定向乃至单晶组织的试样。结合成形特性方面的研究结果 ,通过总结优化工艺 ,获得了不同合金的激光立体成形件 ,成形件内部致密 ,表面质量良好 。

激光立体成形AlSi10Mg合金的微观组织及力学性能

激光立体成形已逐渐成为大型高性能复杂铝合金构件制造的一条重要途径。采用具有不同波长的CO_2和YAG激光器在铸态基材上进行了AlSi10Mg合金的激光立体成形,研究了不同激光器对AlSi10Mg合金沉积态和T6热处理态下的微观组织和力学性能的影响。利用XRD、OM和SEM研究了AlSi10Mg合金成形件的微观组织;利用电子拉力试验机测试了AlSi10Mg合金成形件的力学性能。结果表明:相比铸态基材,AlSi10Mg合金沉积态组织主要由<100>取向沿沉积方向外延生长的柱状α-Al枝晶和枝晶间呈纤维或颗粒状生长的Al-Si共晶组成,组织显著细化;且在530℃,3~5 min固溶处理后可实现共晶Si的球化。与CO_2激光相比,采用更短波长的YAG激光进行成形时组织更为细化。经T6热处理后,采用YAG激光成形的AlSi10Mg合金力学性能明显优于压铸铝合金。

激光立体成形Ti60-Ti_2AlNb梯度材料的组织与相演变

采用激光立体成形技术制备了沿沉积方向成分渐变的立墙式Ti60-Ti_2AlNb梯度材料,研究了沉积态Ti60-Ti_2AlNb梯度材料的相与显微组织的演变规律。随Al和Nb含量的增加,梯度材料中呈现α+β→α+α′→α′→α+β→α+β/B2+α_2→β/B2+α_2→β/B2+α_2+O→B2+O→B2的相演变趋势,α相在Ti60到Ti60-60%Ti_2AlNb (质量分数)的成分范围内一直存在。梯度材料的硬度同样随着Al和Nb含量的增加而增加,并随着B2+O相的形成达到极大值,不过随着在Ti_2AlNb端部全B2相的获得,硬度急剧降低。基于钛合金富Ti区非平衡相图,结合Al和Nb元素对α,α_2,β/B2和O相稳定性的影响分析,及考虑激光立体成形所具有的反复回火/退火和热积累效应,对梯度材料在激光立体成形过程中呈现的相演化规律进行了解释。

Ti-Ti_2AlNb功能梯度材料的激光立体成形研究

采用激光立体成形技术制备了从Ti到Ti2AlNb成分连续渐变、外形规则、高度为17 mm的梯度材料.分析了梯度材料的组织及相结构演变规律和硬度变化规律.随着Al和Nb成分的提高,Ti—Ti_2AlNb功能梯度材料的相呈现α′→α+β→α+α′→α′→α+β→α+β/B2+α_2→β/B2+α_2→β/B2→B2+α_2+O→B2的演变过程,实现了由α型钛合金经过α+β型及β型钛合金向Ti_2AlNb基合金的转变.硬度值HV从底部纯Ti的170连续渐变到顶端Ti_2AlNb的470.基于钛合金富Ti区非平衡相图,并结合Al和Nb元素在钛合金中对α,β和α_2稳定性的影响分析,对梯度材料在激光立体成形过程中的相演化过程进行了解释.

热处理对激光立体成形TC11钛合金组织的影响

通过对TC11钛合金激光立体成形件沉积态和热处理态组织进行对比研究,探索改善TC11钛合金激光立体成形组织,提高材料高温综合性能的途径。结果表明,TC11钛合金的沉积态组织由贯穿多个熔覆层粗大柱状晶和粗大等轴晶组成,原始柱状β-Ti晶内的微观组织是由条状α和残留β组成。沉积态试样在950℃热处理后组织为等轴α、条状α和β转变基体组成的近似三态组织,晶界α大部分破碎球化消失,部分未破碎的晶界上镶嵌有α集束。粗大β晶内等轴α的产生与亚晶有关。在970℃热处理后为网篮组织,等轴α较少,α板条有粗化趋势;在1030℃再结晶后再经950℃热处理的组织是由粗大α板条组成的魏氏组织,在α边界和α内部残留有大量细小β,晶界α基本没有破碎消失。

热处理对激光立体成形TC4残余应力的影响

采用小孔释放法对激光立体成形TC4钛合金沉积态和热处理后的残余应力进行了测试。结果表明,激光立体成形TC4合金的残余应力属于低应力水平,沿激光扫描方向的残余应力σY和垂直于激光扫描方向的残余应力σZ具有类似地分布规律。激光扫描起始位置的残余应力值较小,到中间位置达到最大的压应力,而到熔覆结束位置转变为最大的拉应力;靠近基材处熔覆层的残余应力为较大的压应力,随着熔覆高度的增加,到顶部转变为较小的拉应力。相比沉积态试样,去应力退火后σY和σZ分别平均降低59.8%和72.3%,固溶时效处理后分别平均降低64.7%和67.8%。热处理后残余应力分布趋于平缓,可有效地消除和调整激光成形过程产生的残余应力。

金属增材制造技术及其专用材料研究进展

金属增材制造已成为先进制造技术的一个重要发展方向,是制造领域的国际制高点,有着广阔的发展前景,也存在着巨大的挑战。介绍了激光选区熔化、电子束选区熔化、激光立体成形、电子束熔丝沉积等金属增材制造技术在成形装备、工艺技术和应用方面的研究进展,总结了增材制造用金属粉末和丝材的研制情况,指出了现阶段该技术存在的问题和未来研究方向。

激光立体成形Ti60合金组织性能

研究激光立体成形(Laser Solid Formed,LSF)Ti60合金热处理(双重退火980℃,2hAC+650℃,3hAC)前后的组织形成规律,分析其在室温和高温(600℃)下的拉伸性能。研究发现:Ti60合金在激光立体成形过程中由于熔池顶部形成的等轴晶层占有一定的比例,在熔覆新层时未被完全覆盖,在整个熔覆层中呈现出等轴晶的宏观形貌,并出现了层带组织。Ti60合金激光沉积态显微组织为魏氏组织,由大量沿原始等轴β晶界向晶内生长的α板条束和少量板条间β相组成,成形件室温和高温强度分别高于锻造件,室温塑性比锻造件低,而高温塑性超过锻态;经过双重退火后,成形件中的层带组织消失,晶界α相被打断,不连续分布在原始的β晶界处,晶内α板条粗化,并部分球化,这使得室温和高温强度略有下降,但塑性增高,综合力学性能提高。

激光成形制备生物医用材料研究现状与发展趋势

激光成形技术能够实现生物医用材料、人造肢体及医用植入体的个性化设计和生产,并且具有很少的工序环节和很短的加工周期,因此在生物医用材料的制备领域具有重大应用价值。目前适合于生物医用材料制备的激光成形技术主要有立体光刻(SL),分层实体制造(LOM),选择性激光烧结/熔化(SLS/SLM)和激光立体成形(LSF)技术。基于各种激光成形制备技术的原理和特点,综述了激光成形制备生物医用材料的研究进展和应用现状,认为中国在激光成形的各个单项技术领域同发达国家的差别并不大,但综合集成和产业化的差距却非常大。因此,形成包含完整产业链的产学研创新联盟是激光成形技术在中国生物医用材料领域科技发展和产业振兴的重要途径。先进的装备技术是任何一种技术充分发展和应用的必要基础,也是我国生物医用材料产业落后于发达国家的关键环节之一。因此,迫切需要建立适用于医用植入体制造的专用激光立体成形制备系统,形成具有市场化前景、自主知识产权的产品工程化技术和工艺流程,并建立相应的技术标准体系,以显著提升我国生物医用材料及医用植入体的技术水平,促进我国医用植入及组织工程领域的整体发展。

激光立体成形Ti-20%Ni合金枝晶的组织演化

Ti-20%Ni(质量分数)合金激光立体成形组织由β-Ti枝晶和枝晶间(β-Ti+Ti_2Ni)层片共晶及棒状共晶组成.随着激光能量密度D_e减小,枝晶特征尺寸F减小.枝晶特征尺寸及共晶间距的变化规律分别与枝品生长KGT经典模型和共晶生长TMK经典模型吻合较好.