Microstructure and mechanical properties of as-built and heat-treated electron beam melted Ti–6Al–4V

This paper investigates the effect of post-deposition heat treatment on porosity, microstructure, and mechanical properties of Ti–6Al–4V produced via an Electron Beam Melting process. Samples were studied in the conditions of as-built and heat treated at 920°C and 1030°C. The as-built samples were characterised by columnar β grains consists of α+β microstructure with Widmanstätten and colony morphologies were found. Heat treatment resulted in increased α lath width. The yield strength and ultimate tensile strength was greater in the as-built condition than wrought material. Porosity re-growth occurred after heat treatment but it did not affect the tensile properties. Greater ductility after heat treatment was attributed to the larger α lath width which increases effective slip length.     

Effect of heat treatment on the corrosion resistance and mechanical properties of selective laser melting Ti6Al4V alloy

The present work shows that the effect of several heat treatments on the corrosion resistance and mechanical properties of Ti6Al4V processed by selective laser melting (SLM). The microstructure of Ti6Al4V alloy produced by selective laser melting exhibited bulky prior β columnar grains, and a large amount of fine acicular martensites α′ were observed inside the prior β columnar grains. The acicular martensitic α′ were transformed to a mixture of α and β after heat treatment, and the grain size increases with the increase of heat-treated temperature. The results of 3.5 wt% NaCl solution electrochemical corrosion test showed that the heat-treated samples possess a higher corrosion resistance than the as-received sample. Among of them, the sample after heat-treated at 730 °C exhibited best corrosion resistance and excellent fracture strain. The sample heat treated at 1015 °C showed worst mechanical properties due to the formation of Widmanstätten structure.     

Mechanical properties of Ti-6Al-4V specimens produced by shaped metal deposition

Abstract

Shaped metal deposition is a novel technique to build near net-shape components layer by layer by tungsten inert gas welding. Especially for complex shapes and small quantities, this technique can significantly lower the production cost of components by reducing the buy-to-fly ratio and lead time for production, diminishing final machining and preventing scrap. Tensile testing of Ti-6Al-4V components fabricated by shaped metal deposition shows that the mechanical properties are competitive to material fabricated by conventional techniques. The ultimate tensile strength is between 936 and 1014 MPa, depending on the orientation and location. Tensile testing vertical to the deposition layers reveals ductility between 14 and 21%, whereas testing parallel to the layers gives a ductility between 6 and 11%. Ultimate tensile strength and ductility are inversely related. Heat treatment within the α+β phase field does not change the mechanical properties, but heat treatment within the β phase field increases the ultimate tensile strength and decreases the ductility. The differences in ultimate tensile strength and ductility can be related to the α lath size and orientation of the elongated, prior β grains. The micro-hardness and Young’s modulus are similar to conventional Ti-6Al-4V with low oxygen content.     

基于α'组织设计适于激光立体成形的新型高塑性Ti-4.13Al-9.36V合金

为了提高Ti-6Al-4V合金的加工硬化率和塑性,基于其团簇成分式12[Al-Ti₁₂](AlTi₂)+5[Al-Ti₁₄](V₂Ti)设计成分式为4[Al-Ti₁₂](AlTi₂)+12[Al-Ti₁₄](V₂Ti)的(Ti-4.13Al-9.36V, %)合金,采用激光立体成形工艺制备Ti-4.13Al-9.36V和Ti-6.05Al-3.94V(对比合金),研究了沉积态和固溶温度对其显微组织和力学性能的影响。结果表明,沉积态Ti-4.13Al-9.36V和Ti-6.05Al-3.94V合金的显微组织均由基体外延生长的初生β柱状晶和晶内细小的网篮α板条组成。Ti-6.05Al-3.94V合金的初生β柱状晶的宽度约为770 μm,α板条的宽度约为0.71 μm;而Ti-4.13Al-9.36V合金的初生β柱状晶的宽度显著减小到606 μm,α板条的宽度约为0.48 μm。经920℃固溶-淬火处理后Ti-6.05Al-3.94V样品的显微组织为α'+α相,其室温拉伸屈服强度约为893 MPa,抗拉强度约为1071 MPa,延伸率约为3%。经750℃固溶-淬火处理后Ti-4.13Al-9.36V样品的显微组织为α'+α相,与α'马氏体相比,应力诱发的α'马氏体能显著地提高合金的加工硬化能力,其室温拉伸屈服强度约为383 MPa,抗拉强度约为 989 MPa,延伸率达到了17%。这表明,根据团簇理论模型调控α'+α的显微组织能有效提高激光立体成形Ti合金的加工硬化能力和塑性。     

Microstructures and mechanical properties of dual phase steel produced by laboratory simulated strip casting

Conventional dual phase (DP) steel (0.08C–0.81Si–1.47Mn–0.03Al wt.%) was manufactured using simulated strip casting schedule in laboratory. The average grain size of prior austenite was 117 ± 44 μm. The continuous cooling transformation diagram was obtained. The microstructures having polygonal ferrite in the range of 40–90%, martensite with small amount of bainite and Widmanstätten ferrite were observed, leading to an ultimate tensile strength in the range of 461–623 MPa and a corresponding total elongation in the range of 0.31–0.10. All samples exhibited three strain hardening stages. The predominant fracture mode of the studied steel was ductile, with the presence of some isolated cleavage facets, the number of which increased with an increase in martensite fraction. Compared to those of hot rolled DP steels, yield strength and ultimate tensile strength are lower due to large ferrite grain size, coarse martensite area and Widmanstätten ferrite.     

Evolution of inhomogeneous reinforced structure in TiBw/Ti-6AL-4V composite prepared by pre-sintering and canned β extrusion

2.5 vol.% TiBw/Ti-6Al-4V composite with a discontinuous columnar reinforced structure was successfully fabricated by pre-sintering and subsequent canned β extrusion process. Detail investigation on microstructural evolution revealed that intermediate Ti₃B₄ rather than TiB was substantially synthesized on the surface of coarse Ti64 powders due to insufficient reaction during pre-sintering, but the growth of TiB whiskers particularly along c-axis was significantly accelerated by subsequent canned β extrusion, mainly resulting from the introduced high pressure and severe plastic deformation, while highly preferred orientation of TiB whiskers along extrusion direction was gradually developed. As a result, a discontinuous columnar reinforced structure in TiBw/Ti64 composite was achieved and led to superior mechanical properties of ~ 1450 MPa in ultimate tensile strength and ~ 8.2% in fracture elongation at ambient temperature for the as-extruded composite.     

Microtwin formation in the α phase of duplex titanium alloys affected by strain rate

The effect of tensile strain rate on deformation microstructure was investigated in Ti-6-4 (Ti-6Al-4V) and SP700 (Ti-4.5Al-3V-2Mo-2Fe) of the duplex titanium alloys. Below a strain rate of 10⁻² s⁻¹, Ti-6-4 alloy had a higher ultimate tensile strength than SP700 alloy. However, the yield strength of SP700 was consistently greater than Ti-6-4 at different strain rates. The ductility of SP700 alloy associated with twin formation (especially at the slow strain rate of 10⁻⁴ s⁻¹), always exceeded that of Ti-6-4 alloy at different strain rates. It is caused by a large quantity of deformation twins took place in the α phase of SP700 due to the lower stacking fault energy by the β stabilizer of molybdenum alloying. In addition, the local deformation more was imposed on the α grains from the surrounding β-rich grains by redistributing strain as the strain rate decreased in SP700 duplex alloy.     

氢对Ti-6Al-4V合金室温压缩性能的影响

为了研究氢对Ti-6Al-4V合金室温压缩性能的影响,采用Zwick/Z100型材料试验机对置氢Ti-6Al-4V合金进行了压缩试验,并利用OM、XRD和TEM等材料分析方法对合金的微观组织进行了观察.研究表明:置氢前,Ti-6Al-4V合金由等轴的α相和β相组成,置氢后,出现马氏体组织和氢化物;随氢含量增加,马氏体和剩余β相数量增多;氢提高了Ti-6Al-4V合金的抗压强度和塑性等室温压缩性能,最大增幅分别为33.9%和56.3%;置氢Ti-6Al-4V合金抗压强度的提高主要归因于氢的固溶强化、马氏体相变强化和氢化物强化;塑性指标的提高主要是置氢合金中塑性β相数量的增多所致.     

EBSD imaging of orientation relationships and variant groupings in different martensitic alloys and Widmanstätten iron meteorites

An automatic method to colorize and quantify the classical Pitsch, Kurdjumov–Sachs, Greninger–Troiano and Nishiyama–Wasserman orientation relationships in the electron backscatter diffraction maps of martensitic/bainitic steels is detailed. Automatic analysis of variant grouping is also presented. The method was applied to low and high carbon steels, and to iron–nickel Widmanstätten meteorites. Many results of recent literature are confirmed. In low carbon steels the individual laths exhibit continuous orientation gradients between the classical orientation relationships, and the laths tend to be grouped by close-packed plane (morphological) packets. A crystallographic scenario describing the formation of the packets is proposed on the base of the one-step model. When the carbon content increases, the orientation spreading is reduced; and martensite tends to form plate groups and burst configurations. In iron–nickel meteorites, the centimeter long Widmanstätten laths do not exhibit continuous orientation gradients but are constituted of subgrains with uniform orientation relationship; the kamacite grains in the plessite regions are grouped into Bain zones, probably due to a recrystallization during the slow cooling of the meteorites.     

船用TA5钛合金激光焊接接头组织和性能研究

采用IPG光纤激光器对8 mm厚的TA5钛合金进行激光自熔焊接,并对焊接接头的微观组织和力学性能进行分析。结果表明,激光焊接接头表面成形连续、均匀、无飞溅,内部无气孔和裂纹等缺陷。母材组织为细小均匀的等轴α相;焊缝区组织主要由粗大的β柱状晶粒、大量的针状马氏体α'以及少量的板条马氏体组成;热影响区组织主要由等轴α相、少量的针状马氏体α'和少量的残余β组成;在熔合线的边界,柱状晶粒与等轴晶粒联生结晶、外延生长,保证了焊接接头的稳定连接。焊接接头各区域的显微硬度差异较大,最高硬度出现在熔合线附近,焊缝区和热影响区的显微硬度明显高于母材的。对拉伸断裂部位进行观察,拉伸断裂发生在远离焊缝的母材处,这说明激光焊接接头的抗拉强度与母材等强或者略高于母材的,这与大量针状马氏体形成的网篮组织有直接的关系。      

Micromechanism of improvement in crack initiation and propagation toughness of a Ti–Al–Sn–Zr–Mo alloy by coarsening prior β-grains

Abstract

Instrumented Charpy V impact tests and static and dynamic fracture toughness tests were carried out on Ti–6Al–2Sn–4Zr–6Mo alloys in which the prior β-grain size was varied by heat treatment. The effect of microstructure on the toughness was then examined. With increasing prior β-grain size, the elongation, crack initiation, and particularly propagation toughness increased and the strength decreased slightly. The increase in crack initiation toughness was caused mainly by the increase in Widmanstätten α-lath size or spacing, while the increase in crack propagation toughness was caused by the deflection of the crack propagation path, which was brought about by the decrease in intersubcolony spacing. The intersubcolony spacing decreased with increasing number of ‘diffusion controlled’ Widmanstätten α nucleating sites, which were introduced by the deformation strain.

MST/786     

Microstructure Dependent Fatigue Cracking Resistance of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy

Fatigue cracking behavior from a notch was investigated at room temperature for Ti-6.5Al-3.5Mo-1.5Zr-0.3Si(TC11) alloys with four different microstructures obtained at different cooling rates from the β transus temperature.It was found that the alloy with lamellar structures consisting of α/β lamellae or acicular α’ martensite laths had a higher fatigue crack initiation threshold from the notch,while the bimodal structure with coarse α grain had a lower fatigue cracking resistance.The alloy with α/β lamellar structure showed a higher fatigue crack growth resistance.The length scales of the microstructures were characterized to correlate with fatigue cracking behavior.Fatigue cracking mechanism related to microstructures was discussed.     

Mechanical properties of Ti-6Al-4V specimens produced by shaped metal deposition

Shaped metal deposition is a novel technique to build near net-shape components layer by layer by tungsten inert gas welding. Especially for complex shapes and small quantities, this technique can significantly lower the production cost of components by reducing the buy-to-fly ratio and lead time for production, diminishing final machining and preventing scrap. Tensile testing of Ti-6Al-4V components fabricated by shaped metal deposition shows that the mechanical properties are competitive to material fabricated by conventional techniques. The ultimate tensile strength is between 936 and 1014 MPa, depending on the orientation and location. Tensile testing vertical to the deposition layers reveals ductility between 14 and 21%, whereas testing parallel to the layers gives a ductility between 6 and 11%. Ultimate tensile strength and ductility are inversely related. Heat treatment within the α+β phase field does not change the mechanical properties, but heat treatment within the β phase field increases the ultimate tensile strength and decreases the ductility. The differences in ultimate tensile strength and ductility can be related to the α lath size and orientation of the elongated, prior β grains. The micro-hardness and Young’s modulus are similar to conventional Ti-6Al-4V with low oxygen content.     

电子束快速成形TC4合金的组织与断裂性能

利用超景深显微镜和扫描电镜对电子束选区熔化快速成形的沉积态TC4试样组织与断口形貌进行观察和分析,研究不同几何成形和加载方向对断裂性能的影响。结果表明,断裂性能在垂直试样中受到柱状晶组织的影响,具有各向异性,在沉积方向上的断裂韧度为94.94MPa·m^1/2,大于电子束扫描方向的断裂韧度85.33MPa·m^1/2,而伸长率很小,仅为3%;α相形态对断裂性能有影响:水平试样片层状的α集束组织伸长率及断裂韧度优于垂直试样相互交错的针状α组织,最大值为14.5%和101.45MPa·m^1/2,而抗拉强度和屈服强度较小;电子束选区熔化制备的TC4试样断口由许多不同尺寸的韧窝和弯曲的撕裂棱组成,断裂方式以延性韧窝状沿晶断裂为主,水平试样的断口撕裂棱曲折程度、韧窝尺寸和深度大于垂直试样。     

Dependence of mechanical properties on the microstructure characteristics of a near β titanium alloy Ti-7333

In this work, the microstructure and the corresponding tensile properties of the rolled Ti-7Mo-3Nb-3Cr-3Al(Ti-7333) alloy before and after the thermal treatments were investigated. The results show that a strong α-fiber texture is developed in the rolled Ti-7333 alloy. The deformed matrix and the texture significantly induce the variant selection of β phase. The high strength of the rolled Ti-7333 alloy is attributed to the 110 texture parallel to the tensile direction and the dispersed α phase within the matrix. After the solution treatment followed by the aging treatment, the texture decreases and the microstructure consists of the equiaxed β grains, the spheroidal α_p phase and various needle-like α variants. Eventually, the alloy could achieve an optimal combination with the strength of about 1450 MPa,the ductility of about 10.5% and a considerable shear strength of about 775 MPa. This balance can be ascribed to the performance of the spheroidal α_p phase and various needle-like α_s variants. The results indicate that the Ti-7333 alloy could be a promising candidate material for the high-strength fastener.     

抗Zr“中毒”Al-Ti-B-C中间合金对7050铝合金力学性能的影响

通过场发射扫描电子显微镜(FESEM),X射线衍射仪(XRD),能量色谱仪(EDS)分析Al-5Ti-1B,Al-4Ti-1C和Al-5Ti-0.8B-0.2C中间合金的微观组织与物相组成,比较研究3种中间合金对7050铝合金晶粒尺寸与力学性能的影响。结果表明:Zr的存在削弱了Al-5Ti-1B和Al-4Ti-1C中间合金的细化效果,而对Al-5Ti-0.8B-0.2C中间合金细化效果影响较小。含掺杂型TiC粒子的Al-5Ti-0.8B-0.2C中间合金具有较好的抗Zr"中毒"能力,加入量为0.2%(质量分数,下同)时,含Zr7050铝合金平均晶粒尺寸由200μm细化至(60±5)μm,室温极限抗拉强度由405MPa提高到515MPa,提高了27.2%,伸长率由2.1%提高到4.1%。而加入0.2%的Al-5Ti-1B或Al-4Ti-1C中间合金时晶粒尺寸较粗大且分布不均匀,表现出明显的细化"中毒"。     

挤压变形Al—0．8％Mg—0．6％Si—xSc合金的显微组织与力学性能

本文针对挤压变形Al—0．8％Mg—O．6％Si-xSc合金的显微组织和拉伸性能进行了研究,以确定稀土元素Sc和T6处理对该系合金性能的影响规律。结果表明,加入适量的元素Sc可以有效地细化挤压变形Al0．8％Mg-0．6％Si—xSc合金的组织,提高其室温抗拉强度、屈服强度和断裂伸长率;经过T6处理后,Al—08％Si-0．6％Si—xSc舍金的抗拉强度和屈服强度可得到显著提高;挤压变形Al—0．8％Mg～O．6％Si～xSc合金在拉伸加载条件下主要呈现韧性断裂特征。     

电子束选区熔化成形Ti_(2)AlNb合金微观组织与性能EI北大核心CSCD

Ti_(2)AlNb基合金由于具有优异的高温比强度、高温抗蠕变性能和较高的断裂韧度,因而被认为是替代传统镍基高温合金最具潜力的材料。采用电子束选区熔化(selective electron beam melting,SEBM)技术成形Ti-22Al-25Nb合金,通过工艺优化获得高致密度(5.42-5.43 g/cm^(3))的成形试样。研究了沉积态和热等静压(hot isostatic pressing,HIP)态试样的显微组织演变、物相演变及其对力学性能的影响。结果表明:沉积态和HIP态组织呈现出沿成形方向的柱状晶结构,且均由B2,O和α_(2)相组成,沉积态试样中的O/α_(2)相自上而下逐渐增加,HIP后组织趋于均匀化,且相对沉积态,析出相的宽度缩小、数量减少。沉积态试样中析出相较多的下部区域具有更高的显微硬度((345.87±5.09)HV),HIP后试样硬度值增加至388.91-390.48HV。沉积态试样室温抗拉强度和伸长率分别为(1061±23.71)MPa和(3.67±1.15)%,HIP后抗拉强度增加至(1101±23.07)MPa,伸长率降低至3.5%。     

选区激光熔化Ti6Al4V合金的各向异性

采用金相分析和拉伸测试等方法,分析了激光熔化成形Ti6Al4V试样在不同沉积高度、不同方向截面的组织和性能。结果表明,平行于沉积方向的截面其组织类似柱状晶,具有较弱的织构特征;垂直于沉积方向的截面其组织为块状结构,具有较强的织构特征。选区激光熔化成形Ti6Al4V合金在沉积高度方向上的力学性能受柱状晶尺寸的影响,随着沉积高度的增大其抗拉强度和屈服强度先降低后升高而延伸率先提高后降低。织构和熔合不良等缺陷,使试样垂直于沉积方向上的强度和塑性都比平行于沉积方向的试样高。     

Ti700sr高温钛合金TIG焊接接头组织及性能研究

采用TIG焊接方法对Ti700sr高温钛合金板材进行了焊接,研究了接头的组织形貌、硬度分布及力学性能。结果表明,Ti700sr高温钛合金板材焊接后的接头成形良好,焊缝区组织由粗大的柱状晶及细长的针状α相构成,热影响区组织由细针状α和残余β相构成,热影响区析出相得到有效控制,相边界上无明显硅化物析出;焊接热影响区的硬度相对较高,焊缝的硬度相对较低;接头室温抗拉强度约为903 MPa, 700℃高温抗拉强度为397 MPa,焊缝强度低于母材的。